Microbiology Lecture Notes 5&6 – Flashcards

Ribosomes 

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The positioning of the amino acid over the sequence that is exposed. 

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The mRNA will fail to advance and the remaining code on the mRNA will go unread. 

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• The prokaroytic ribosome is less dense and slightly smaller. It's density, as measured in Svedburg units (70s), is less than that of a eukaroytic cells ribosome (80s) . 
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• Targetting of the bacterial ribosome with antimicrobial preperation/anitbiotic. 
• For example the antibiotic streptomycin targets the ribsomes of prokaryotic cells. 

• Interferring with ribosomes allows for the disruption of protein synthesis. 
• Without protein synthesis the bacteria can not produce enzymes necessary for biochemical reactions and essential functioning. 

• Intermediate selective toxicity, because there are similiarities between prokaroytic and eurkaryotic ribosomes, but there are also differences. The differences make it a reasonably good target. 

• NO selective toxicity would result from targetting DNA in bacterial cells because their DNA is made of the same chemical components (deoxyribose and the same four nueclotide bases) as ours is. It is a BAD idea. 
• The more selective, the higher the selective toxicity.

• YES! Both are double helix. However bacterial DNA is composed of a single strand (haploid) folded at one end.
• Our DNA is double stranded (diploid)

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• Sugar backbone- deoxyribose
• 4 nucleotide bases: (A)denine, (G)uanine, (C)ytosine, (T)hymine

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• Bacterial DNA is always HAPLOID.
• Haploid is the term used when a cell has only one set of chromosomes.

The single strand of DNA given to each daughter cell is folded and twisted.

(note: the DNA can be linear as well as the circular pattern pictured here) 

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• It makes bacteria the ideal subject for genetic engineering and testing because dominance, codominance, incomplete dominance, blending and recessive genes do not need to be considered as they would in the diploid cell

• Because haploid DNA results in dominance, codominance, incomplete dominance, blending and recessive relationtions between genes whereas diploid DNA is simply a copy of the single parent's DNAs

Haploid DNA contains only one complete set of chromosomes. 

Diploid DNA contains two complete sets of chromosomes.

• Bacteria mutate in response to enviroment leading to variation.
• Bacteria are also able to add genetic information (via plasmids) which leads to variation. 
• On occassion random selection or crossover between organisms.

In the nucleoid region 

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Nope.

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Plasmids are also known as extra-chromosomal DNA. 

They are located in the cytoplasm. 

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• Plasmids are variant structures. 
• Not all bacterial cells have plasmids, but many do. 

On plasmids, at least it can be stored there. 

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• Never. Only information not essential to the basic functions of the organism would be stored on a plasmid. Shape is pretty essential. 

• No, information about the basic structure of the cell wall is essential to the basic functioning of the cell and therefore would never be stored on a plasmid. Only non-essential functions, such as antibiotic resistance are stored there.

• NEVER, because glycolysis is a basic function of bacterial cells. This information would be on the main chromosome. 

• Yes. 
• Antibiotic resistance, in the form of an enzyme or inhibitor that targets the active site or helps to denature the antibiotic is not necessary for the basic functioning of the bacteria therfore it would be stored on a plasmid. 

• Plasmids contain transponal information, information that can be moved about, integrated and removed from the main chromosome. 

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Verticle transmission

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In verticle transmission, genes are passed from parent to offspring

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• Both.
• The plasmid is sometimes copied and passed to both daughter cells. It is sometimes not copied and only one daughter cell gets it. In either case, this is verticle gene transmission.
• The plasmid is also active in conjugation, a type of horizontal gene transmission.

A pilus. 

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Conjugation

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The docking device is called a pilus. It must be present on one of the cells only.

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• We call the cell that lends its plasmid the donor cell. 
• We call the cell that copies all or part of the plasmid the recipient cell. 

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• The plasmid enters the recipient bacterium which begins to copies the plasmid base information. 

• When the donor plasmid "says" we're finished, the plasmid leaves the recipient bacterium and returns to the donor plasmid. 

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• No. In conjugation the entirety of the plasmids information is not usually transferred. 
• There is not usually time to copy all of the information before the donor bacteria wants the plasmid back. 

• Horizontal Transmission

• VRE is Vancomycin-Resistant Enterococci. 
• It is an antibiotic resistant infection that is housed in the intestines, we know this because "entero" refers to the gut. 

• It may have gotten the antibiotic resistant from VRE (Vancomycin resistant enterococcus) via horizontal transmission via conjugation. 

• Because enterococcus lives in the intestinal tract, where prior round of antibiotics will likely have killed off a lot of the healthy flora making it easier for the VRE to take hold and utilize their nutrient source. 

1. Overuse of prescription antibiotics
• Inappropriatly prescribed
• Wrongly prescriped 
• Ineffective for bacteria 
• Use for minor illness
2. Failure to complete a course of antibiotics
3. Prophylatic use of antibiotics in animals that are then consumed

• Air vacuoles maintain bouyancy so that cells can remain at the depth in the water appropriate for them to receive sufficient amounths of oxygen, light and nutrients. 

• Metachromatic granules
• Polysaccharide graules
• Lipid Inclusions 
• Sulfur Granules 
• Carboxysomes
• Magnetosomes

• The pilus is used for conjugation in the horizontal transfer of genetic material
• It is also used in some instances for motility, as kind of grappling hook device. 

Pilus

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• A twitching motion used to retract the pilus and thereby pull the bacteria closer to the target the pilus has attached to .

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A-Monotrichous (one flagellum)

B-Lophotrichous (tuft of flagella on one end)

C-Amphitrichous (flagella on each end)

D-Peritrichous (flagella all over surface)

Atrichous (without projections)

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Peritrichous (E)

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Amphitrichous (C)

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Lophotrichous

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Peritrichous

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• Peritrichous, which have flagella all over their surface, swarm in cultures.

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Runs and tumbles

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A "Run"

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A "TUMBLE"

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• Chemotaxis is a response to chemical stimuli. 
• If an organism shows positive chemotaxis, it moves towards or shows affinity to the chemical stimuli. 
• If an organism shows negative chemotaxis, it moves away from a chemical stimuli. 

• Phototaxis is a response to light stimuli. 
• If an organism shows positive phototaxis, it moves towards or shows affinity to the light.
• If an organism shows negative phototaxis, it moves away from light.

• thermotaxis is a response to heat stimuli. 
• If an organism shows positive thermotaxis, it moves towards or shows affinity to the heat 
• If an organism shows negative chemotaxis, it moves away from heat.

Axial filaments are found only in spirochetes. They allow motility. 

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Fimbriae

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Fimbriae are associated with gram negative organisms.

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• NO. Only gram negative bacteria possess fimbriae but not all gram negative bacteria possess fimbriae. 

• Fimbriae increase virulence, which increases the likelihood that a pathogenic organism will cause disease. 

• Pathogenicity:  This is a qualitative trait, referring to the inherent, genetic capacity of a microorganism to cause disease.
• If a disease is pathogenic, its likelihood of causing disease is measured in virulence. 

No. An organism may have one, none or more than one.

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Circular

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No. It must be  integrated into the bacterial DNA to be expressed. 

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a plasmid

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• A flagella allows the propulsion of a bacteria forward. Flagellum also allow a tumbling motion which enables a tumbling movement in order to change direction. 

Glycocalyx or Sugar Coat

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• The glycocalyx is a polysaccharide configuration. It is a variant structure. It is not always present. 

• No. A glycocalyx is not necessary to the basic functioning of the cell, therefore it may be stored on a plasmid and not utilized unless needed. 

The glycocalyx is external to the cell wall. 

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The glycocalyx may manifest as either a capsule or a slime layer. 

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• When an organsim that produces a slime layer is moved, the slime layer is left behind and reproduced in the new location, assuming the location is conducive to it.

• Capsules are substantially thicker and more chemically complex than slime layers.

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• Which is used for attachment purposes?
• A capsule
• A slime layer
• Both

• A capsule can be used for:
• Attachment
• Metabolic Support
• Protection against host's immunue system.

• The capsule acts a kind of invisibility cloak helping the bacteria who have it to evade the macrophages or scavenger cells of the immune system. 
• Another way of thinking about it is that the capsule makes the bacteria unpalatable to the macrophage.
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Macrophages 

• a large white blood cell, occurring principally in connective tissue and in the bloodstream that ingests foreign particles, serves as an antigen-presenting cell, and functions in the destruction of foreign antigens (as bacteria and viruses) by phagocytosis.

• Virulence enhances pathogencity. If an organism is not pathogenic, that is, not disease causing, adding a capsule will not make it pathogenic. 

• A capsule makes the organism more likely to evade the immune system long enough to multiply to its ID₅₀.

• The organism with the capsule, though there are less of them, are more likely to evade the immune system for longer and therefore to replicate to their ID₅₀  before detection and cause symptoms of infection. 

• Quorum sensing is a system of stimulus and response correlated to population density. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population.

Bacterial Sporulation or formation of an endospore

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• The capsule is a variant structure even among those populations that can produce them.

• In order for a process to qualify as a means of reproduction, an increase in population must result. This is why endospores do not qualify. One bacteria makes one endospore. 

1! To make an endospore, the bacterial cell copies its DNA one time. When it dies it releases an endospore. 

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1! Only one. 

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Gram Positive Bacillus!

There is only one exception to this, the gram negative bacillis, Coxilla burnetti

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All clostridial organisms are spore formers. 

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• 1. Lack of groceries (lack of nutrients in current enviroment)
• 2. Inapporiate temperature. 
• 3. Lack of water
• 4. Inapprotiate pH

• Absolute. Although endospore formation is stimulated by less than optimal conditions, in a population of endospore producing bacteria, there will always be some bacteria forming endospores. 

Sporulating or sporogensis

(Prof. McCleary used the first term)

• DNA, a ribsomes, an enzyme or two, all surrounded by a spore coat and calcium as a desiccant, or drying agent. 

• The addition of calcium, which acts to remove the water from the endospore, allows it to withstand high temperatures for relatively long periods of time.  

• Dipicolinic acid helps stabilize protein content in endospores. It is essential in endospore formation. This is the only place it is seen. 

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• Endospores are present. Dipicolinic acid is only in endospore. It acts as a protein stabilizer. 

• In order for endospores to be released, the cell containing them must die.
• Endospores can survive for thousands of years. 

Normal bacteria: Boil water at 80?C for 10 minutes

Endospores: 100°C for a couple hours. 

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Destruction of endospores

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500 RADS

(50 is lethal to a human)

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• The pH of an adult stomach, which is between 4-2, is inhospitable to the endospore. It's too acidic. In babies the pH is higher, or less acidic. The organism can become botulism there. It produces a toxin which creates illness. 

• Reserve deposits of inorganic phosphate are called Metachromatic Granules. 
• They are called meta-chormatic because they sometimes stain red with certain blue dies. 
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• Metachormatic granules sometimes stain red with blue dies.
• They contain inorganic phosphate that can be used in the synthesis of ATP
• Note: ATP- Adenosine Triphosphate requires phosphate

• Metachromatic granules contain inclusions of inorganic phosphate. This inorganic phosphate is used in the production of ATP.

Polysaccharide granules typically consist of glycogen and starch. 

These inclusion serve as a nutrient reserve. 

Lipid Inclusions

The most common storage form is poly ?-hydroxybutric acid. 

• Carboxysomes are inclusions that contain ribulose 1,5 - diphosphate carboxylase
• The organism that have this inclusion are photosynthetic, and use carbon dioxide as their sole source of carbon. 
• These use the ribulose 1,5 diphosphate to fix carbon dioxide

• Photosynthesizing bacteria use carbon dioxide as their sole source of carbon. The inclusion they need to fix the carbon dixiode are carboxysomes, which consists of the enzyme ribulose 1,5 diphosphate caroxylase. 

• Metachormatic granules consist of inorganic phosphate molecules and are used to produce ATP in certain bacteria, algae, fungi and bacteria. .

Both contain chemicals (inorganic phosphate & sulfur respectively) that are used to produce energy by the cell.

• An organism with an ID₅₀ of 25 is more virulant than an organism with an ID₅₀ of 200 because one need only take in 25 of the ID₂₅ organism to produce clinical symptoms of that organism where one must take in 200 of the other organism. 

• The physical and chemical requirments dovetail or join and overlap with one another. 

• Acidophiles. These are the only type that could survive the acidic environment of yogurt (pH ~4).

Isotonic and hypotonic environments make water available to organisms.

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A hypotonic environment

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In an isotonic solution water moves both into and out of the cell.

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In a hypotonic solution, the water moves into the cell. 

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In a hypertonic solution water moves out of the cell. This reults in plasmolysis. 

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• For most bacteria there is 30 degree range at which they will grow, for example, psychophiles, (extreme cold loving bacteria) grow between -10 and 20 degrees celcius.  
• Prof. McCleary later noted that there was between 20-30 degrees variability. Clearly Mesopholes and Hyperthermophiles have larger ranges than this. (image below is same as text book p.154)
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The lowest temperature at which an organism will grow?

• Note: Bacteria do not necessarily die in environments below this temperature, they simply can not grow below this temperature. 

• The optimal growth temperature of bacteria is always closer to the maximal growth temperature because heat speeds up metabolic reactions. 

• Their proteins are denatured and they can not longer engage in metabolic processes.

• A fever may bring the body temperature above the maximum growth temperature for a pathogenic bacteria, and in effect kill the bacteria. 

• 1. Because the fever is an effective immune response that may well kill bacteria by increase the body's temperature above their maximal growth temp. 
• 2. Because if one continually dampens the immune system, it becomes much less effective. 

Lyophilized

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• YES! They are freeze dried with liquid nitrogen so they do not grow but they are alive. 

• Psychotrophs are extreme cold loving bacteria. They grow between -10 and 20 degrees C. 

• Cold loving bacteria are called psychotrophs. They grow between 0 and 30 degrees Celcius. 

• Mesophiles sometimes lead to fevers as an immune response to kill lower temp range mesophiles. 
• Mesophiles sometimes induce fever to make conditions more favorable for their replication

• A mesophile is a moderate temperate loving organism.
• It can grow between 10 and 50 degrees Celcius.  
• It grows best between 20-40 degrees.