question

Once received at the yeast cell's surface, how is the mating signal changed or transducer into a form that begins about the cellular response of mating?

answer

the recived signal is converted into a specific cellular response i na series of steps called the transduction pathway

question

T/F the molecular details of the signal transduction pathways in yeast and in mammals are very different.

answer

F- strikingly similar these similarities and others more recently uncovered between signaling systems in bacteria and plants suggest that early versions of toad's cell-signaling mechanisms evolved well before the first multicellular creatures appeared on Earth -think that signaling molecules evolved first from prokaryotes and single cells eukaryotes then were adopted for new uses by their multicellular descendants

question

Explain direct contact (a kind of local signaling)

answer

1. direct contact -communication in which cell junctions where the cytoplasm directly connects adjacent cells in these cases, signaling substances dissolved in the cytosol can pass freely between adjacent cells animal and plant cells have this

question

Explain cell-cell recognition what kind of signaling is it?

answer

animal cells may communicate via direct contact between membrane bound cell-surface molecules in a process called cell-cell recognition immunity and embryonic development interact via molecules protruding from the surface it is local signaling

question

In many other cases of local signaling, what happens?

answer

messenger molecules are secreted by the signaling cell some of these travel only short distances (local regulators)

question

What is a local regulator and what kind of signaling is it involved in?

answer

they influence ells in the vicinity a kind of local signaling molecule that are secreted by the singaling cell one class of local regulators in animals are GROWTH FACTORS

question

Explain growth factors mechanisms of signaling.

answer

consists of compounds that stimulate nearby target cells to grow and divide

question

T/F numerous cells can simultaneously reviece and respond to the molecules of growth factor produced by a single cell in their vicinity

answer

T: this is called paracrine signaling

question

What is paracrine signaling?

answer

when numerous cells in a vacninity can simultaneously receive and respond to the molecules ex. growth factor the secreting cell acts on nearby target cells by discharging molecules of a local regulator (growth factor) into the extracellular fluid

question

What is synaptic signaling?

answer

a more specific kind of LOCAL signaling than the paracrine signaling -a nerve cell releases neurotransmitters into a synapse and stimulates the target cell occurs in the ANIMAL nervous system the molecules diffuse through the synapse and thus trigger a response in the target cell

question

Why do plants use mechanisms somewhat different from those operating locally in animals?

answer

cell walls

question

What is similar in plants and animals?

answer

they both use chemicals called hormones for LONG DISTANCE SIGNALING

question

Explain hormonal signaling in animals (long distance)

answer

endocrine signaling -specialized cells release hormones-> travels to the other parts of the bodies to reach target cells via the BLOOD these cells can recognize and respond to the hormones

question

What are plant hormones called?

answer

plant growth factors they sometimes travel through vessels but more often they move through cells or diffuse through the air to reach their target cells

question

T/F only local regulators vary in size in shape, not hormones

answer

F: hormones do too ex plant hormone ethylene promoting fruit ripening and regulating growth is a hydrocarbon of only 6 atoms small enough to pass through cell walls in contrast, mammalian hormone insulin which regulates sugar levels in the blood is a HUGE PRO

question

Explain how the transmutation of a signal through the nervous system is an example of long-distance signaling.

answer

an electrical signal travels the distance of the nerve and is then converted back to a chemical signal when a signaling molecule is released and crosses the synapse to another nerve cell here it is converted back into an electrical signal in this way, a nerve signal can travel along a series of nerve cells because some nerve cells are quite long, the nerve signal can quickly move great distances

question

What happens when a cell encounters a secreted signaling molecule?

answer

the ability of a cell to respond is determined by whether it has a specific receptor molecule that can bind to the signaling molecule the information conveyed ny this binding signal must then be changed into another form-> transducer - inside the cell before the cell can response

question

Explain the mechanisms of epinephrine or adrenaline

answer

glycogen break down releases the sugar glucose 1 phosphate which the cell converts to glycogen 6 phosphate the cell can then use this compound, an early intermediate in glycolysis for ENERGY PRODUCTION alternatively, the compound can be stripped of a phosphate and released from the liver cell into the blood as glucose which can fuel cells throughout the body THUS, one effect of epinephrine is the mobilization of furl reserves which can be used by animal to either defend itself or escape

question

Explain Sutherlands pioneering work in understanding how chemical messengers act via signal transduction pathways

answer

1971 nobel prize investigating how the animal hormone epinephrine stimulates the breakdown of glycogen within the liver cells and skeletal muscle cells discovered that epinephrine stimulates glycogen breakdown by somehow activating a cytosolic enzyme, glycogen phosphorylase however, when EP was added to a test-tube mixture containing the enzyme and its substrate, glycogen, no breakdown occurred. EP could activate glycogen phosphorylase only when the hormone was added to a solution containing INTACT cells

question

What is the substrate in the EP pathway What is the enzyme What is the signal

answer

glycogen glycogen phophorylase EP

question

What did the results of Sutherland's experiment tell him?

answer

1. EP does NOT interact DIRECTLY with the enzyme responsible for glycogen breakdown -> an intermediate step or series of steps must be occurring inside the cell 2. The plasma membrane is somehow involved in transmitting the signal (since the EP doesn't enter the cell) his early work suggested that the process of going on at the RECEIVING end of a cellular conversation can be dissected in to 3 stages 1. reception 2. transduction 3. Response

question

Explain reception.

answer

the target cell's detection of a signaling molecule coming from outside the cell a chemical signal is detected when the signaling molecule binds to a receptor protein located at the cell's surface or inside the cell NOTE can be either on surface or inside

question

Explain transduction

answer

the binding of the signaling molecule changes the receptor protein in some way initiating the precess of transduction the transduction stage converts the signal to a form that can bring about a specific cellular response the Sutherland's system, the binding of EP to a receptor protein in a liver cell's plasma membrane leads to the activation of glycogen phosphorylase signal transdction pathway= sequenceo f changes in a series of different molecules the molecules in the pathway are called RELAY molecules

question

T/F: transduction always has the same number of steps

answer

F: can be single step but more often it is a sequence of changes in a series of different molecules

question

Explain the response stage.

answer

the transduced signal finally triggers a SPECIFIC cellular response the response may b almost any imaginable cellular activity: catalysis (by an enzyme aka glucose phosphorylase), rearrangement of the cytosekelon, or activation of specific genes in the nucleus the cell0 signaling process helps ensure that the crucial activities like these occur in the right cells, at the right time, and in proper coordination with the activities of other cells of the organic

question

Explain how signaling is involved in ensuring that yeast cels fuse only with cells of the opposite mating type

answer

The two cells of opposite type alpha and a each secrete a certain signaling molecules which can only be bound by receptors carried on cells f o the opposite mating type. Thus the a mating factor CANNOT bind to another A cel and cause it to grout toward the first a cell. Only an alpha cell can receive the signaling molecules and respond by directed growth

question

Explain how nerve cells provide an example of BOTH local and long distance signaling

answer

the secretion of neurotransmitter molecules at a synapse is an example of local signaling. The electrical signal that travels along a very long nerve cell and is passed to the next nerve cell can be considered an example of long-distance signaling. NOTE: the local signaling at the synapse between the 2 cells is necessary for the signal to pass from one cell to the next (BOTH NEEDED) local is needed for the long distance

question

When epinephrine is mixed with glycogen phosphorylase and glycogen in a test type, is glucose 1 phosphate generate? Why or why not?

answer

glucose 1 phosphate is not generated because the activation of the enzyme requires an intact cell with the intact receptor being on the plasma membrane and an intact signal transduction pathway (all three****) The enzyme cannot be activated directly by interaction with the signaling molecule in the test tube

question

In liver cells glycogen phosphorylase acts in which of the 3 stages of the signaling pathway associated with epinephrine initiated signal?

answer

The third stage, the response to the epinephrine signaling the effect in the cell

question

What is reception?

answer

A signaling molecule binds to a receptor protein causing it to change shape DEPENDS ON THE RECEPTOR

question

Explain the specificity of the reception part of cell communication.

answer

seen in EP: the hormone in the blood encounters many types of cells as it circulates in the blood but only certain target cells DETECT and REACT to the hormone molecule a receptor PRO on or in the target cell allows the cell to HEAR the signal and RESPOND to it the signaling molecule complementarity of shape to a specific site on the receptor and attaches there

question

Explain how the singling molecule acts in the reception process

answer

ligand - the term for a molecule that SPECIFICALLY binds to another molecule, often a larger one generally causes a receptor protein to undergo a change in shape

question

Explan the role of shape change in reception

answer

ligand binds and causes a change in shape of the receptor, the change in shape of the receptor, allows it to interact with other cellular molecules for other kinds of receptors, the immediate effect of the ligand bindingg is to cause the affregation of two or more receptor molecules (tyrosine kinase) which leads to further molecular events inside the cell

question

What are most signal receptors?

answer

plasma membrane proteins their ligands re water-soluble and generally too large too freely pass through the hydrophobic membrane other signal receptors are located inside the cell and their ligands are hydrophobic (steroid hormones)

question

What do most water-soluble signaling molecules bind to?

answer

receptor PRO that span the cell's plasma membrane (TRANSMEMBRANE) transmits the information from the extracellular environment to the inside of the cell by changing the shape or aggregating when a specific ligand binds to it

question

What are the 3 major type of receptors in the plasma membrane (transmembrane)?

answer

1. G protein 2. receptor tyrosine kinases 3. ion channel receptors

question

Explain how cell surface receptor molecules play crucial roles in their biological system in animals and how their malfunctions are bad.

answer

cancer, heart disease, asthma working out the structure and function of these receptors ail allow us to better understand and treat these conditions

question

What % of PRO do cell surface receptors make up?

answer

30% of all human PRO

question

What is the largest family of human cell-surface receptors?

answer

G protein coupled receptors consists of nearly 1000 G protein coupled receptors elucidating these structures:

question

What would abnormal functioning of tyrosine kinases receptors cause?

answer

many types of cancers breast cancer- excessive levels of a receptor tyrosine kinase HER2 Herceptin is a protein that binds to HER2 on cells and inhibits their growth thus preventing further tumor development

question

Where are intracellular receptors found?

answer

in either the cytoplasm or nucleus of target cels

question

What has to be the case of the signaling molecule to reach an intracellular receptor?

answer

passes through the target cell's plasma membrane hydrophobic or small enough

question

What are some example of intracellular signaling molecules?

answer

steroid hormones of animals (testosterone, estrogen, cortisol) nitric oxide (NO) (a gas- very small molecules readily pass between the membrane phospholipids)

question

Explain the activity of testosterone.

answer

secreted by cells of the testes in males it then travels through the blood and ENTERS cells all over the body HOWEVER only cells that contain the receptor molecule for it respond... in these cells that respond, the hormone binds to the receptor protein- >activates it-> the active form of the receptor protein then enters the nuleus and turns on specific genes that control male sex characteristics

question

How does the activated hormone receptor complex turn on genes?

answer

the genes in a cell's DNA function by being transcribed and processed into messenger RNA which leaves the nucleus and is translated into specific proteins by ribosomes in the cytoplasm special proteins called transcription factors control which genres are turned on that is which genes are transcribed into mRNA in a particular cell at a [articular time the testosterone receptor, when activated ACTS AS A TRANSCRIPTION FACTOR that turns on specific genes By acting as a transcription factor, the testosterone receptor ITSELF carries out the complete transduction of the signal most other intracellular receptors function in the SAME WAY although, many of them like thyroid hormone receptor, are already in the nucleus BEFORE the signaling molecule reaches them

question

T/F most intracellular receptors are structurally similar

answer

T: suggesting an evolutionary kinship

question

Nerve growth factor (NGF) is a water soluble signaling molecule. Would you expect that the receptor for NGF is intracellular or in the plasma membrane, why?

answer

NGF is water soluble hydrophilic so it cannot pass through the lipid membrane to reach intracellular receptors such as sterior hormones can therefore you would expect the NGF receptor to be in the plasma membrane

question

What would the effect be if a cell made defective receptor tyrosine kinase proteins that were unable to DIMERIZE?

answer

The cell with the faulty receptor would not be able to respond appropriately to the signaling molecule when it was present This would most likely have dire consequences for the cell, since regulation of the cell's activities by this receptor would not occur right

question

How is ligand binding similar to the process of allosteric resolution of enzymes?

answer

Binding of a ligand to a receptor changes the shape of the receptor altering the ability of the receptor to transmit a signal. Binding of an allosteric regulator to an enzyme changes the shape of the enzyme, either promoting or inhibiting enzyme activity

question

What is protein kinase and what is its role is its role in signal transduction pathway?

answer

A protein kinase is an enzyme that transfers a phosphate group from ATP to a protein, usually activating that protein (often a second type of protein kinase) Many signal tansduction pathways include a series of such interactions in which each phosphorylated protein kinase in turn phosphorylates the next protein kinase in the series. Such phosphorylation cascades cary a signal from outside the cell to the cellular proteins that will carry out the response (target proteins)

question

When a signal transduction pathways involves a phosphorylation cascade, how does the cell's response get turned off?

answer

protein phosphatases reverse the effects of kinases (GTPase) also it is specific to the pathway: can use an inhibition of the enzyme or you can also break down the second messenger

question

What is the actual SIGNAL that is being transduced in any signal transduction pathway? In what way is this information being passed from the exterior to the interior of the cell?

answer

THe signal that is being transducer is the information that a signaling molecule is bound to the cell surface receptor Information is transduced by ways of sequential protein-protein interactions that change protein shapes, causing them to function in a way that passes the signal along THE INFORMATION IS TRANSDUCED VIA CONFORMATIONAL CHANGE

question

Upon activation of phospholipase C by the binding of a ligand to a receptor, what effect does the IP3 gated calcium channel have on Ca2+ concentration in the cytosol?

answer

The IP3 gated channel opens, allowing calcium ions to flow out of the ER which raises the cytosolic Ca2+ concentration

question

When receptors for signaling molecules are plasma membrane aka transmembrane PRO, what is the characteristics of the transduction?

answer

the transduction stage of the cell signaling is usually a multistep pathway steps often include activation of proteins by addition or removal of phosphate groups or release of other small molecules or ions that act as messengers

question

What is a benefits of multiple steps of the transduction pathways?

answer

1. amplification 2. Fine tuning

question

Explain amplification

answer

if some of the molecules in a pathway transmit the signal to numerous molecules at the next step in a series, the result can be a large number of activated molecules at the end of the pathway

question

Explain fine tuning

answer

multiple step pathways provide more opportunities for coordination and regulation than do simpler systems this allows fine tuning of the response in both unicellular and multicellular organisms

question

What is step 1 of a transduction pathway?

answer

the binding of a specific signaling molecule to a receptor in the plasma membrane triggers the first step in a chain of molecular interactions

question

DEfine signaling transduction pathway

answer

chain of molecular interactions that leads to a particular response within the cell

question

What happens after the signal binds?

answer

the signal activated receptor activates another molecule which activates another and so on until the protein that produces the final cellular response is activated

question

What is responsible for repaying a signal from a receptor to response?

answer

relay proteins

question

What is a major theme of regulation at cellular level?

answer

unifying theme is the interaction of proteins

question

T/F: the original signaling molecule is being physically passed along a signaling pathway

answer

F: in most cases it never even enters the cell instead, we mean that certain information is passed on

question

What does the following statement mean: the signal is relayed along a pathway

answer

certain information is passed on at each step, the signal is transduced into a different form, commonly in the shape change of a PROTEIN CONFORMATIONAL CHANGE very often, the shape change is brought about by phosphorylation

question

What is a protein kinase?

answer

an ENZYME that transfers phosphate groups from ATP to a protein

question

Compare a receptor tyrosine kinase to a kinase that is cytoplasmic

answer

receptor tyrosine kinase: -phosphorylates tyrosines on the other receptor tyrosine kinase in a dimer whereas most cytoplasmic protein kinases act on proteins different from themselves - most cytoplasmic protein kinases phosphorylate the AA tyrosine where as cytosplamic protein kinases phosphorylate either of 2 other amino acids: serene or threonine NOTE that they both are phosphorylating amino acids

question

What are many of the relay molecules in signal transduction pathways?

answer

protein kinases and they often act on other protein kinases in the pathway

question

What do many of the protein kinases in signal transduction pathways work on?

answer

other protein kinases this creates a phosphorylation cascade

question

Explain phosphorylation cascade

answer

signal is transmitted by a cascade of protein phosphorylations each bringing with it a shape change each shape change results from the interaction of the newly added phosphate groups with charged or polar amino acids the addition of phosphate groups often changes a protein from an inactive form to an active form NOTE that in other cases, phosphorylation decreases the activity of a protein

question

T/F: phosphorylation always activates a protein

answer

FFFFF: also results in the decrease in the activity of a protein

question

Explain the specificity seen in Protein kinases

answer

a single cell may have hundreds of different kinds, each specific for a different substrate protein together, they probably regulate a large proportion of the thousands of proteins in a cell

question

What usually happens with defective protein kinases?

answer

most protein kinases regulate cell reproduction abnormal activity of such a kinase can cause abnormal cell growth and thus contribute to cancer development

question

T/F: the turning off of protein kinases doesn't matter

answer

F: equally as important in the phosphorylation cascade are the protein phosphorytase

question

What is the antagonist to a kinase?

answer

a protein phosphatase - dephosphorylates a protein enzymes that can rapidly remove phosphate groups from proteins, a process called dephosphorylation remove a phosphate group from KINASES

question

Explain the mechanism and importance of dephospho relation.

answer

by dephospho rylation and thus inactivating protein kinases, pho sphatases provide the mechanism for turning off he signal transduction pathways when the initial signal is no longer present NOTE THE KEY: when the initial signal is no longer present also make the protein kinases available for reuse, enabling the cell to respond again to an extracellular signal the phosphorylation-dephosphorylation system acts as a molecular switch in the cell, turning activities on or off, or up or down as required at any given moment, the activity of a protein is regulated by phosphorylation depends on the balance in the cell between active kinase molecules and active phosphatase molecules example: insulin is released in the blood when there is too much blood glucose which activates phosphatase- the enzyme then acts to dephosphorylate other enzymes such as phosphrylase kinase, glycogen phosphroylase, and glycogen SYNTHASE

question

T/F: Not all components of signal transduction pathways are proteins

answer

T: seen with the second messengers

question

Explain the structure of a second messenger and why this would allow an external signal to ve brought into the

answer

small, non protein, water-soluble molecules or ions because they are small and water soluble, they can readily spread throughout the cell by diffusion

question

What is a second messenger and why is that its name?

answer

small, water soluble molecules that are not proteins, they participate in pathways that are initiated by both G protein coupled receptors and receptor kinases term is used because the pathway's first messenger is considered to be the extracellular signaling molecules- the LIGAND that binds to the membrane receptor

question

What are the transduction pathways that use second messengers? What are common second messengers in them?

answer

G protein initiated and protein kinase initiated -cyclic AMP and calcium ions -also another example of one is PI3 and DAG

question

What is the relationship with relay proteins and second messengers?

answer

a large variety of relay proteins are sensitive to the cytosolic concentrations of one or the other of second messengers

question

Explain Sutherland's reasoning when he discovered second messengers.

answer

established that epinephrine somehow causes glycogen breakdown without passing through the plasma membrane this discovery prompted him to search for a second messenger that transmits the signal from the plasma membrane to the metabolic machined because he found that epinephrine does not cross the membrane found that binding of epinephrine to the plasma membrane of a liver cell elevates the cytosolic concentration of a compounds called cAMP

question

Explain how epinephrine binding to a G protein channel receptor causes the production of CAMP is this indirect or direct and how

answer

an enzyme in the membrane: adenylyl cyclase converts ATP to cAMP in response to an extracellular signal, in this case, provided by epinephrine BUT epinephrine doesn't stimulate adenylyl cyclase directly, when epinephrine outside the cell binds to a specific receptor protein -> this is a G protein-> the protein activates adenylyl cyclase which in turn can catalyze the synthesis of many molecules of cAMP in this way the normal cellular concentration of CAMP can be boosted 20-fold in a matter of seconds the CAMP broadcasts the signal to the cytoplasm

question

What makes it so the cAMP does not last long?

answer

in the absence of the hormone it doesn't last long because another enzyme called phosphodiesterase converts cAMP to AMP another surge of epinephrine is needed to boost the cytosolic concentration of cAMP again

question

What would be needed to boost the amount of cAMP after phosphodiesterase converts CAMP to ATP?

answer

another surge of epinephrine

question

T/F: epinephrine is the only hormone that triggers CAMP to rise in [] in the cell

answer

F: subsequent research has revealed that epinephrine is only one of the many hormones and other signaling molecules that trigger this research has also brought to light the other components of CAMP pathways ...

question

What are the other components of cAMP pathways?

answer

G protein coupled receptors, ligands, G proteins, and protein kinases

question

What is the immediate effect of cAMP?

answer

usually the activation os a serene/threosnin kinsase called protein kinase A (the activated protein kinaes A then phosphorylates various other proteins depending on the cell type) look in figure 11.16 fir the complete pathway

question

What is protein kinase a?

answer

A relay protein while CAMP is the second messenger that relays information to it

question

What is further regulation of cell metabolism provided by?

answer

inhibition of adenylyl cyclase by other G protein systems break down cAMP GTPase

question

Explain a G protein system that inhibits adenylyl cyclase.

answer

a different signaling molecule acticates a different receptor, which in turn activates an INHIBITORY G Protein This shows us that not all pathways are causing excitation

question

ASK: would this be considered part of the regulation that he is talking about in his slides?

answer

...

question

Explain in molecular detail how v. cholerae causes disease.

answer

bacteria forms a biofilm on the lining of the SI and produces a toxin this toxin is an enzyme that chemically modifies a G protein involved in regulating salt and water secretion because the modified G protein is unable to hydrolyze GTP to GDP (to turn off) it remains stuck in its active form, continuously stimulating adenylyl cyclase to make cAMP the resulting high [] of cAMP causes the intestinal cells to secrete large amounts of salts into the intestine with water following BY OSMOSIS diarrhea

question

Explain how GMP (which is also a second messenger that is formed by the guanosine cyclase enzyme that turns linear GTP to cyclic cGMP) is a singaling molecule.

answer

treatments: in one pathways, cGMP acts as a signaling molecule whose effect include relaxation of smooth muscle cells in the artery walls a compound that inhibits the hydrolysis of cGMP to GMP thus prolonging the signal was originally used for chest pains and is now used for viagra

question

Explain why inhibiting the hydrolysis of cGMP to GMP or even GTP to GDP would be bad.

answer

you prevent it from being turned off, you therefore prolong the effect of the signal in the cause of cGMP this was seen as a treatment to vasodilate but when talking about cell division, this could lead to cancer

question

What are the signaling molecules in animals that induce responses from their target cells via signal transduction pathway that increase the cytosolic concentration of calcium ions

answer

neurotransmitters, growth factors (used by protein kinase receptors), and some hormones aka these are the ligands that make the second messenger CALCIUM be used

question

What would calcium do in animal cells? Plant cells?

answer

muscle contraction, secretion of substances, and cell division greening in response to light

question

What pathways do cells use Ca as a second messenger in?

answer

G protein and tyrosine kinase pathways

question

T/F cells always contain Ca

answer

T: although this is the case, this ion is a sec ond messenger

question

Why is Ca a second messenger if it is always in the cell?

answer

because its [] in the cytosol is normally much lower that the [] outside the cell [] gradient

question

How is the [] gradient of Ca molecules maintained and thus how is this a regulatory mechanism?

answer

Ca ions are actively transmpoted into the ER by various protein pumps as a result, the calcium [] in the ER is usually much higher than that in the cytosol because the cytosolic calcium is low, a small change in absolute numbers of ions represents a relatively larger percentage change in the calcium []

question

Explain the signal transduction pathway that uses Ca as a second messenger (it is not the only second messenger)

answer

cytosolic Ca level may rise usually by a mechanism that releases Ca from the cell's ER the pathways leading to calcium release involve another second messengers: DAG and IP2 these 2 second messengers are produced by CLEAVAGE of PIP2 (a phospholipid in the plasma membrane) via phospholipase C (the enzyme that is activated by the G protein) Effector? the phospholipase C Second messengers? DAG, PI3, and Calcium PI3 stimulates the release of Ca from the ER by binding to a IP3 gated ligand ion channel in the plasma membrane Because IP3 acts BEFORE calcium, Ca could theoretically be called the third messenger but it isn't because second messenger is used for all small, nonprotein components of signal transduction pathways.

question

ASK: is the PI3 gated calcium channel an effector PRO or is it considered a relay molecule?

answer

...

question

How can a target cell's response to a signal hormone molecule result in a response that affects a million other molecules?

answer

at each step in a cascade of sequential activations, on molecule or ion may activate numerous molecules functioning in the next step

question

If 2 cells have different scaffolding proteins, explain how they might behave differently in response to the same signaling molecule

answer

Scaffolding proteins hold together molecular components of signaling pathways in a complex with each other. Different scaffolding proteins would assemble different collections of proteins, leading to different cellular responses in the 2 cells

question

Review the discussion of protein phosphates (pg216) some human diseases are associated with malfunctioning protein pho sphatases. How would such proteins affect signaling pathways?

answer

A malfunctioning protein phosphatase would not be able to dephosphorylate a particular receptor or relay protein. As a result, the signaling pathway, once activated would not be able to be terminated. in fact, one study found this to happen a lot in colorectal cancers

question

Give an example of apoptosis during embryonic development and explain its function in the developing embryo

answer

in formation of the hand or paw in mammals, cells in the regions between the digits are programmed to undergo apoptosis. THis serves to shape the digits of the hand or paw so that they are not webbed

question

What types of protein defects could result in apoptosis occurring when it should not? what types could result in apoptosis not occurring when it should?

answer

if a receptor protein for a death-signaling molecules were defective such that it was activated even in the absence of the death signal, this would lead to apoptosis when it wouldn't normally occur. Similar defects in any of the proteins in the signaling pathway, which would activate these relay or response proteins in the absence of interaction with the previous protein or second messenger in the pathway, would have the same effect. Conversely, if any protein in the pathway were defective in its ability to respond to an interaction with an early protein or other molecule or ion, apoptosis would not occur when it normally should. For example, a receptor protein for a death signaling ligand might not be able to be activated, even when ligand was bound -> this would stop the signal from being transduced into the cell

question

____: Cell signaling leads to regulation of transcription or cytoplasmic activities

answer

response

question

What is the nature of the final step in a signaling pathway?

answer

leads to the regulation of one or more cellular activities the response at the end o the pathway may occur in the nucleus or in the cytoplasm

question

Where would the response occur?

answer

either the nucleus or the cytoplasm

question

What would the response be if it is in the nucleus?

answer

regulate protein synthesis, usually by turning specific genes on or off in the nucleus of the cell ex. an activated steroid receptor: the final activated molecule in a signaling pathway functioning as a transcription factor

question

What is an example of the target protein being a transcription factor?

answer

the response to the growth factor signal is transcription, the synthesis of mRNA which will be translated in the cytoplasm into a specific protein in other cases, the transcription factor may regulate a gene by turning it off

question

T/F: transcription factors always turn genes ON

answer

F: can regulate a gene by turning it off often a transcription factor regulates several different genes

question

What would be the location if the signaling pathways is regulating the activity of protons rather then their synthesis directly affecting proteins that function outside the nucleus

answer

cytoplasm

question

What is an example of a direct affect of protein function via a signaling pathway that has the response in the cytoplasm?

answer

a signal may cause the opening or closing of an ion channel in the plasma membrane or a change in cell metabolism seen in the seponse of liver cells to the hormone epinephrine: helps regulate cellular energy metabolism by affecting the activity of and enzyme tje final step in the signaling pathways that begins with epinephrine binging activates the enzyme that catalyses the breakdown of glycogen the response is the release of glucose 1-phosphte molecules from glycogen NOTE: as each molecule is activated, the response is amplified

question

What is an example of signaling events having a response that regulates other cellular attributes, even the activity of the cell as a whole?

answer

the mating with yeast and directional growth

question

What are some of the molecular messengers that initiate cell division pathways?

answer

growth factors and certain plant hormones malfunctioning of them would lead to dvelopemtn of cancer

question

T/F: Regardless of whether the response occurs in the nucleus or the cytoplasm, it is fine-tuned at multiple points rather than simply being turned on or off

answer

T

question

What are the 4 aspects of fine tuning?.

answer

1. a signlaing pathway with numerous steps between the initial signaling event at the cell surface and the cell's response results in amplification of the signal and thus the response 2. Such a multistep pathway has many different poitns at which the cell's response can be regulated, contributing to the specifcity of the response and allowing coordination with other signaling pathways 3. The overall efficiency of the response is enhanced by the presence of proteins known as scaffolding proteins 4. A crucial point in fine-tuning the response is the termination of the signal

question

How do elaborate enzyme cascaes amplify the cell's response to a signal?

answer

At each catalytic step in the cascade, the number of activated products is much greater than in the preceding step -example: in the epinephrine triggered pathway, each adenylyl cyclase molecules catalyses the formation of many cAMP molecules, each molecule of protein kinase A phosphorylates many molecules of the next kinase in the pathway and so on.

question

What does the amplification effect stem from?

answer

the fact that these proteins persist in the active form long enough to process numerous molecules of substrate before they become inactive again

question

What is the result of the amplification of the signal?

answer

a small number of epinephrine or any signal molecule binding to receptors on the surface of a liver cell or muscle cell can lead to the release of hundreds of millions of glucose molecules from glycogen THIS IS GOOD

question

Explain the specificity of cell signaling and coordination of the response as seen in liver and heart cells.

answer

both are in contact with your blood and are therefore constantly exposed to many different hormone molecules, as well as to local regulators secreted by nearby cells yet the liver cells response to some signals but ignores others and the same is true for the heart cell and some kinds go signals trigger responses for both but the responses are DIFFERENT example: epinephrine stimulates the liver cell to break down glycogen while it makes the heart contract and increase heart rate

question

How do we account for the difference in the actions of the heart and liver cell?

answer

explanation for the specificity exhibited in cellular responses to signals is the same as the basic explanation for the differences between cells: BEcause different kinds of cells turn on different sets of genes, different kinds of cells have different collections of proteins The response of a particular cell to a signal depends on its particular collection os signal receptor proteins, reay proteins and proteins needed to carry out the response a liver cell, for example, is poised to respond to ep. by having the proteins of the membrane as well as those needed to manufacture glycogen thus, the 2 cells that response differently to the same signal differ in one or more of the proteins that handle AND response to the signal

question

What are the kinds of proteins that a response of a particular cell to a signal depend on?

answer

receptor, relay, and proteins needed to carry out the response

question

What do 2 cells that respond differently to the same signal differ in?

answer

1 or more of the proteins that handle and response to the signal different pathways may have some molecules in common: same receptor but differing other molecules different receptor for the same signaling molecule single king of signal diverges into 2 responses: such a branched pathway is seen with tyrosine kinases which can activate multiple relay proteins AND second messengers which can regulate numerous proteins two pathways triggered by separate signals converge to modulate a single response

question

cross talk= converge and branching what are they involved in?/ why are they important?

answer

regulating and coordinating a cell's responses to information coming in from different sources in the body

question

Explain how the use of some of the same proteins in more than one signaling pathway beneficial.

answer

economize the number of different proteins it must make

question

Explain why it would be inefficient to have not many relay proteins and how scaffolding proteins come in to play

answer

because most relay molecules are proteins and proteins are too large to diffuse quickly through the viscous cytosol of the cell so the scaffolding protein comes into play ...

question

How does a particular protein kinase find its substrate?

answer

the efficiency of signal transduction is increased by the presence of scaffolding proteins

question

T/F: scaffolding proteins are relay molecules

answer

T -they are large relay proteins to which several other relay proteins are simultaneously attached

question

What is an example of an action of a scaffolding protein

answer

one scaffolding protein isolated from mouse bran cells holds 3 protein kinases and a carries these kinases with it when it binds to an appropriately activated membrane receptor; it his facilitates a specific phosphorlation cascade also, researchers have found them in brain cells that permanently hold together networks of signaling pathway proteins at synapses -this hardwiring enhances the speed and accuracy of signal transfer between cells, because the rate of protein-protein interactions is not limited by DIFFUSION THESE are INDIRECT role of activation of proteins

question

T/F scaffolding proteins are only an indirect way to activate relay proteins.

answer

False: they may also play a more direct role in activating some of the other relay proteins

question

What is the importance of the relay proteins that serve as points of branching or intersection in signaling pathways?

answer

highlighted by the problems associated when these proteins are defective or missing WAS: the absence of single relay protein leads to diverse effects these symptoms are because of the absence of the protein in cells of the immune system - this protein is usually located just under the cell surface and it interacts with both microfilaments of the cytoskeleton and several different components of signaling pathways that really information from the cell surface, including pathways regulation immune cell proliferation this multifunctional relay protein is thus both a branch point and an impotent intersection point in a complex signal transduction network that controls immune cell behavior when WAS is absent, the cytoskeleton is not properly organized and signaling pathways are disrupted leading to the WAS symptoms

question

What cells undergo apoptosis?

answer

cells that are infected, damaged or have reached the end of their functional life span often undergo programmed cell death

question

What is apoptosis?

answer

programmed cell suicide during this process, cellular agents chop up the DNA and fragment the organelles and other cytoplasmic components the cell shrinks and becomes lobed (blabbing) and the cell's parts are packed up in vesicles that are engulfed and digested by specialized scavenger cells leaving no trace NO LYSIS

question

How is apoptosis protective?

answer

protects neighboring cells from damage that they would otherwise suffer if a dying cell merely leaked out all its contents, including many of the digestive juices

question

What are the 2 key apoptosis genes? What is the "brake" in nematodes in the outer mitochondrial membrane that serves as a master regulator of apoptosis- acts as a brake in the absence of a signal promoting apoptosis

answer

Ced-3 and Ced-4 and Ced-9

question

What triggers apoptosis in worms and other species?

answer

signals that activate a cascade of suicide proteins in the cells destined to die C elegant research revealed 2 key apoptotic genes: Ced 3 and Ced 4 which code for proteins Ced 3 and Ced 4

question

Explain how apoptosis is an example lot regulation/ response happening at the level of protein activity rather than development and gene synthesis.

answer

The Ced 3 and Ced 4 proteins involved in apoptosis are continually present in cells, but in inactive form (not being transcribed) thus, regulation occurs at the level of protein activity rather than through gene activity and protein synthesis In C elegans, Ced 9 is the master regulator and apoptosis happens when a signal overrides the break that prevents apoptosis from happening

question

What are the main proteases of aopotosis?

answer

caspases

question

What does the pathways of apoptosis in animal cells depend on?

answer

several different pathways involving 15 different caspases can carry out apoptosis Depends on 1. the type of cell and 2. the particular signal that initiates apoptosis

question

Explain one major pathway of apoptosis

answer

involves certain mitochondrial proteins that are triggered to for molecular pores in the mitochondrial outer membrane causing it to leak and release other proeints that promote aptoptosis cytochrome C- a protein promotin apoptosis which functions in mitochondrial electron transport in normal healthy cells acts as a death facto when it is released from the mitochondria the process uses similar proteins to those used in nematodes Ced 3, 4, and 9

question

In apoptoic pathways, what are Ced 3, 4, and 9 considered?

answer

The relay proteins capable of transducing apoptic signals

question

What happens at key gateways of apoptosis?

answer

relay proteins integrate signals from several different sources and can send a cell down an apoptotic pathway

question

Where does the signal often originate?

answer

outside the cell , like the death signaling molecule, which presumably was released by a neighboring cell

question

What happens when a death signaling ligand occupies a cell surface receptor?

answer

this binding leads to activation of caspases and other enzymes that carry out apoptosis without involving the mitochondria pathway This process of signal reception, transduction, and response is similar to the normal transduction pathways

question

What is an example of apoptotic signaling coming from inside?

answer

2 other alarm signals that can lead to apoptosis originate from inside the cell rather than from a cell surface receptor 1. comes from the nucleus generated when DNA has suffered irreparable damage 2. comes from the endoplasmic reticulum when excieeive protein misfiling occurs

question

How do mammals make life or death decisions?

answer

by somehow integrating the death signals and life signals they receive from these external and internal sources

question

Why is a built in cell suicide mechanism important?

answer

essential to development and maintenance in all animals

question

What do the similarities between apoptosis genes in nematodes and mammals as well as the apoptosis that occurs in multicellular fungi and unicellular heart indicate?

answer

the basic mechanism evolved early in evolution of eukaryotes

question

What is apoptosis important for in vertebrates?

answer

normal development of the nervous system, normal operation of the immune system, and normal morphogenesis of hands and feet in humans and paws ion there mammals the level of apoptosis between developing digits is lower in the webbed feet of ducks and other water birds than in the non webbed feet and hands of humans and land birds

question

What degenerative diseases happened because of the involvement of apoptosis?

answer

Alzeihemrs and Parkinsons also, cancer can result in a failure of cell suicide: melanoma has been linked to faulty forms of human version of Ced 4 proteins

question

What is a characteristic of apoptotic pathways?

answer

quite elaborate, after all, the life or death question is the most fundamental one imaginable for a cell

question

What produces the flight or fight response?

answer

adrenal glands releasing epinephrine (a hormone) at times of stress

question

What do hormonal signaling and the subsequent response by cells and tissues throughout the gazelle's body illustrate?

answer

how cell-to cell communication allows the trillions of cells in a multicellular organism to talk to each other -> coordinating activities

question

T/F only multicellular organisms use cell communication

answer

F

question

What is the universal mechanisms of cellular communication evidence for?

answer

evolutionary relatedness of all life - the same small set of cell-signaling mechanisms shows up again and again in diverse species, biological processes ranging from hormone action to embryonic development to cancer

question

How do cells most often communicate with each other?

answer

chemical signals can also use changes in the environment (light and touch)

question

Explain how yeast communicate during mating

answer

identify their mates by chemical signaling 2 mating types or sexes are alpha and a mating type a secrete molecule called a factor which can bind to specific receptor proteins on nearby alpha cells at the same time the alpha cells secrete alpha factor which binds to receptors on a cells WITHOUT actually entering the cells, the 2 mating factors cause the cells to grow toward each other and also bring about other cellular changes-> fusion of the 2 cells of opposite type received signal is then converted to a specific cellular response in a series of steps called signal transduction pathway SIMILAIR To that in mammals suggest evolved before the first multicellular creatures appeared on earth

question

describe biofilms and how do they communicate?

answer

use quorum sensing in which it allows bacterial propulsions to coordinate their behaviors so they can carry out activities that are only productive when performed by a given number of cells in synchrony aggregation of bacterial cells that are adhered on to a surface and derive nutrition from that cur face myaxobacteria use this chemical signaling to shair information about nutrient availability

question

What happens when a cell encounters a secreted signaling molecule?

answer

he information conveyed by this binding is the SIGNAL -> must then be changed to another form (transduced) inside the cell before the cell can respond

question

What does the ability of a cell to respond determined by?

answer

whether it has a specific receptor molecule that can bind to the signaling molecule the information conveyed by this binding is the SIGNAL -> must then be changed to another form (transduced) inside the cell before the cell can respond

question

Explain Sutherland and origin of understanding how chemical messengers act via signal transduction

answer

1971 Nobel Prize -were investigating how the animal hormone epinephrine (adrenaline) stimulates the breakdown of the storage polysacchride glycogen within the liver cells and skeletal muscle cells glycogen breakdown releases the sugar glucose 1-phosphate which the cell converts to glucose 6- phosphate the cell (liver cell) can then use this compound (an early intermediate in glycolysis) for ENERGY production alternatively, the compound (glucose 6 phosphate) can be stripped of phosphate and released from the liver cell into the blood as glucose which can fuel cells throughout the body THUS: effect 1 of epinephrine: the mobilization of fuel reserves which can then be used by the animal to either defend itself (fight) or escape (flight) Research team discovered: -epinephrine stimulates glycogen breakdown by somehow activating a cytosolic enzyme, GLYCOGEN PHOSPHORYLASE (inside the cell) -HOWEVER, when epinephrine was added to a testube mixture, (substrate and enzyme) NO breakdown occurred ...

question

What did the test tube mixture contain that epinephrine was added to in Sutherland's experiment?

answer

glycogen (the substrate) + glycogen phosphorylase the point was to make it more efficient because they thought that the cel membrane was preventing more epinephrine from getting in... BUT nothing happened

question

What did sutherland learn form the experiment and why?

answer

Epinephrine could activate glycogen phosphorylase only when the hormone was added to a solution containing INTACT cells

question

What did the result of sutherland's experiment tell him?

answer

1. epinephrine does not interact directly with the enzyme responsible for glycogen breakdown - an intermediate step or series of steps must be occurring inside the cell 2. the plasma membrane is somehow involved in transmitting the signal suggested that the process going on at the receiving end of a cellular conversation can be dissected into 3 stages: reception, transduction (intermediate) and response

question

What variances do you see in a G-Protein channel receptor?

answer

vary in binding sites for their signaling molecules (ligands) and also for different types of G proteins inside the cell BUT they are nevertheless remarkably similar

question

What similarity does a G-protein channel receptor share with many other receptors?

answer

transmembrane

question

What is the structural similarity among G-Protein channel receptors?

answer

pass through the membrane many times and are classified by how many times they do make up a large family of eukaryotic receptor proteins with a SECONDARY structure in which the single polypeptide has 7-trnsmembrane alpha helices Specific loops between the helices form binding sites for signaling and G protein molecules

question

What is a G protein channel receptor?

answer

a cell-surface, transmembrane receptor that works with the help of a G ptrotin (a protein that bings the energy-rich molecule GTP) Many different signaling molecules use this: epinephrine and many other hormones (non steroid), neurotransmitters

question

What are some of the functions of G protein receptor systems?

answer

very widespread and diverse -roles in embryonic development, sensory reception (visual, smell, taste depend on)

question

What do similarities in G protein coupled receptors in diverse organisms suggest?

answer

that G proteins and associated receptors evolved very early

question

What are some diseases that G protein channel receptors are part of?

answer

bacterial infections : -cholera, pertussis, botulism, amon others make their victims ill by producing toxins that interfere with G protein function Pharmocologists now realize that up to 60% of all medicines used today exert their effects by influencing G protein pathways

question

What is the first step in the GPCR?

answer

loosely attached to the cytoplasmic side of the membrane, the G protein functions as a molecular switch that is either honor off depending on which of the 2 guanine nucleotides is attached. WHen GDp is bound to the G protein-> inactive The receptor and the G protein work together with another protein, (an enzyme)

question

What is the role of the G protein in the GPCR?????? What does its activity depend on? When is it active and when is it inactive?

answer

molecular switch depends on which of the 2 guanine nucleotides that is attached (GDP or GTP) active: when bound to GTP inactive: when bound to GDP

question

What are the 3 protein subunits involved that work together in a G protein channel receptor?

answer

receptor, G protein, and an enzyme

question

What is the second step in the G protein channel receptor?

answer

When the appropriate signaling molecule binds to the extracellular side of the receptor, the receptor is activated and undergoes conformational change Its cytoplasmic side then binds to an inactive G protein causing a GTP to displace the GDP THIS ACTIVATES THE G PROTEIN

question

What is the third step in the GPCR?

answer

The activated G protein dissociated from the receptor, diffuses along the membrane, and then binds to an enzyme, altering the enzymes shape and activity (conformational change of the enzyme caused by the binding of a active G protein) Once activated, the enzyme can trigger the next step leading to a cellular response. NOTE: this binding of a signaling molecule is reversible: like other ligands, they bond and dissociate many times. The ligand [] outside the cell determines how often a ligand is bound and causes signaling)

question

What mode of transportation does the G protein take once it is activated?

answer

diffusion (inactive) to the enzyme NOTE this is a cell so not a very far distance

question

What determines how often a ligand is bound and causes signaling?

answer

the extracellular [] of the ligand

question

What is the 4th step in the GPCR?

answer

The changes in the enzyme and G protein are only TEMPORARY... because... 1. The G proton also functions as a GTPase enzyme- it then hydrolyzes its bound GTP to GDP-> no inactive, the G protein leaves the enzyme (enzyme now returns to its normal state) The G proton is now available for reuse The GTPase function of the G proton allows the pathway to shut down rapidly when the signaling molecule is no longer present

question

What is the GTPase function importance?

answer

allows the pathway to shut down rapidly when the signaling molecule is no longer present.

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