question

How do cells replicate?

answer

1) copying DNA 2) separating copies 3) dividing cytoplasm to create two complete cells

question

chromosome

answer

("colored-body") gene-carrying structure containing DNA and associated proteins (threadlike structures)

question

histones

answer

single long DNA double helix that is wrapped around proteins

question

gene

answer

region of DNA that codes for a particular protein or RNA

question

chromatid

answer

each of the double-stranded DNA copies in a replicated chromosome (before mitosis, they are joined along their length by proteins called cohesins)

question

centromere

answer

region of a replicated chromosome where the two sister chromatids are joined most tightly and the kinetochore is formed during M phase

question

sister chromatids

answer

chromatid copies that remain attached at their centromere

question

M phase (mitotic)

answer

phase of the cell cycle during which cell division occurs

question

interphase ("between-phase")

answer

- portion of the cell cycle between one M phase and the next - no dramatic changes - cells spend most of its time here - includes G1, S, and G2

question

S (synthesis) phase

answer

DNA is synthesized for the replication of chromosomes

question

cell cycle

answer

orderly sequence of events that leads a eukaryotic cell through the duplication of its chromosomes to the time it divides

question

when are "gap" phases?

answer

before and after S phase

question

G1 phase

answer

- gap between end of M phase and start of S phase - first part of interphase before DNA synthesis

question

G2 phase

answer

- gap between end of S phase and start of M phase - last part of interphase

question

order of cell cycle

answer

M phase, G1, S, G2

question

why do gap phases exist?

answer

- cells perform their functional roles mostly during G1 phase (multicellular organisms) - cell uses G2 to prepare for M phase

question

two events of M phase

answer

- division of nucleus - division of cytoplasm

question

cytokinesis

answer

- follows mitosis - divides cytoplasm of parent cell to form two daughter cells

question

how chromosomes change during: G1 phase

answer

4 unreplicated chromosomes

question

how chromosomes change during: G2 phase

answer

4 unreplicated chromosomes, each consisting of two sister chromatids

question

how chromosomes change during: M phase (parent cell)

answer

replicated chromosomes condense

question

how chromosomes change during: M phase (daughter cells)

answer

sister chromatids separate & two daughter cells are formed by cytokinesis

question

chromatin

answer

complex of DNA and proteins (mainly histones) that compose eukaryotic organisms

question

types of chromatin

answer

- heterochromatin (highly compact) - euchromatin (loosely coiled)

question

state of chromatin during interphase

answer

relaxed or less condensed, forming long & thin strands

question

chromosomes during mitosis

answer

- two sister chromatids separate to form independent daughter chromosomes - one copy of each chromosome goes to each of the two daughter cells - each cell receives the same complement of chromosomes as the parent cell had

question

5 subphases within M phase

answer

- prophase - prometaphase - metaphase - anaphase - telophase

question

prophase

answer

- "before-phase" - chromosomes condense into compact structures - individual chromosomes first become visible in light microscope

question

spindle apparatus

answer

- formed during prophase - structure that produces mechanical forces that (1) move replicated chromosomes during early mitosis and (2) pull chromatids apart in late mitosis

question

microtubules

answer

- spindle apparatus consists of this - composed of a-tubulin and b-tubulin - asymmetric (plus and minus end) - plus end is where growth occurs - minus end is where disassembly occurs

question

polar microtubules

answer

some microtubules extend from each spindle pole and overlap with one another

question

centrosome

answer

structure that contains a pair of centrioles

question

centrioles

answer

small cylindrical structures contained within the centrosome near the nucleus of a eukaryotic cell

question

prometaphase

answer

- "before the middle-phase" - nuclear envelope disintegrates - allows cytoplasmic microtubules to attach to chromosomes at kinetochores - these events define the start of this phase

question

kinetochores

answer

protein complex that forms on chromosome during metaphase and serves as a site for microtubule attachment

question

kinesin and dynein

answer

motors that "walk" chromosomes up and down microtubules

question

metaphase

answer

- "middle-phase" - chromosomes migrate to the middle - lined up on imaginary plate between two spindle poles called "metaphase plate"

question

astral microtubules

answer

hold spindle poles in place partly because of this

question

anaphase

answer

- "against-phase" - cohesins that hold sister chromatids together at the centromeres split - each replicated chromosome is pulled apart and creates two independent daughter chromosomes - doubles number of chromosomes in cell

question

movement during anaphase

answer

- daughter chromosomes move to opposite poles via attachment of kinetochore proteins to the shrinking kinetochore microtubules - two poles of the spindle are pushed and pulled farther apart

question

telophase

answer

- "end-phase" - nuclear envelope reforms around each set of chromosomes - chromosomes begin to de-condense - when two nuclei form, mitosis is complete - cytoplasm must divide via cytokinesis

question

result of cytokinesis

answer

two daughter cells

question

what happens to cytoplasmic contents?

answer

when cell was in interphase, the contents (including organelles) increased in number or volume so that the two daughter cells each has its own nucleus and organelles

question

cell plate

answer

flattened, sac-like structure formed in the middle of a dividing plant cell which divides the cytoplasm into two separate cells

question

cleavage furrow

answer

- animal and eukaryotic cells - ring of overlapping actin filaments starts to contract - ring shrinks and tightens which pulls membrane with it

question

binary fission

answer

- bacteria - genetic material is replicated and pushed into opposite sides of cell - cell divides in half - does not include mitosis

question

steps of binary fission

answer

1. DNA is copied and protein filaments attach 2. DNA copies are separated; ring of protein forms 3. Ring of protein draws in membrane 4. Fission complete

question

Is M phase controlled by regulatory molecules in the cytoplasm?

answer

M-phase cytoplasm contains a regulatory molecule that induces M phase in interphase cells

question

M phase-promoting factor (MPF)

answer

- initiates M phase in oocytes - phosphorylates a number of specific proteins that initiate mitosis or meiosis - dimer

question

what is MPF made out of?

answer

- protein kinase - cyclins

question

protein kinase

answer

enzyme that catalyzes the transfer of a phosphate group from ATP to a target protein

question

cyclins

answer

- concentration fluctuates throughout cycle - regulatory proteins - control of cell cycle via cyclin-dependent kinases

question

cyclin-dependent kinase (cdk)

answer

- protein kinase subunit of MPF - functional only when bound to a cyclin - involved in control of cell cycle

question

how is MPF turned on?

answer

MPF's cdk subunit is further regulated by two phosphorylation sites on the subunit

question

how is MPF turned off?

answer

an enzyme complex begins degrading MPF's cyclin subunit, triggering a chain of events that deactivates it

question

MPF deactivation illustrates two key concepts about regulatory systems in cells

answer

- negative feedback: process is slowed or shut down by one of its products - destroying specific proteins (proteasome)

question

cell-cycle checkpoints

answer

several points in the cell cycle at which progression of a cell through the cell cycle can be regulated

question

tumor

answer

mass of cells formed by uncontrolled cell division

question

M-phase checkpoints

answer

pass if: - chromosomes have attached to spindle apparatus - chromosomes have properly segregated and MPF is absent

question

G1 checkpoint

answer

pass if: - cell size is adequate - nutrients are sufficient - social signals are present - DNA is undamaged

question

p53

answer

if DNA is physically damaged, this protein activates genes that either stop the cell cycle until the damage can be repaired or cause the cell's programmed, controlled destruction (acts as a brake on cell cycle)

question

apoptosis

answer

self-destruction of a cell (programmed)

question

tumor suppressors

answer

protein that prevents cell division when conditions are unfavorable

question

cancer

answer

- disease caused by cells that divide in an uncontrolled fashion - causes disease because they use nutrients and space needed by normal cells and disrupt function of normal tissue

question

cancerous cells have two types of defects related to cell division

answer

1) defects that activate proteins required for cell growth when they shouldn't be active 2) defects that prevent tumor suppressor genes from shutting down the cell cycle

question

malignant tumor

answer

cancerous

question

benign tumor

answer

noncancerous

question

metastasis

answer

spread of cancerous cells from their site of origin to distant sites in the body

question

cancer involves defects in which checkpoint?

answer

G1

question

social control

answer

- cells divide in response to signals from other cells - cells are allowed to divide only when it is in the best interest of the organism as a whole

question

growth factors

answer

- social control is based on this - polypeptides or small proteins that stimulate cell division

question

Rb protein

answer

- key molecule that enforces G1 checkpoint - when E2F is first produced, its activity is blocked by this tumor suppressor gene

question

E2F

answer

- key regulatory protein - when activated, it triggers the expression of genes required for S phase

question

steps of G1 checkpoint

answer

1. growth factors arrive from other cells 2. growth factors cause increase in cyclin and E2F concentrations 3. cyclin binds to Cdk; Cdk is phosphorylated; Rb inactivates E2F by binding to it 4. Inactivating phosphate is removed, and active Cdk phosphorylates Rb 5. Phosphorylated Rb E2F 6. E2F triggers production of S-phase proteins

question

cells can become cancerous when

answer

checkpoints and social controls fail (G1 cyclin can be overproduced or Rb is defective)

question

what happens when G1 cyclins are overproduced?

answer

they bind to Cdk and help activate it so that Rb is continuously phosphorylated and unable to bind to E2F

question

what happens if Rb is defective?

answer

it does not bind normally to E2F and that E2F will activate the genes that push the cell into S phase which ultimately leads to uncontrolled cell division

question

Which statement about daughter cells following mitosis and cytokinesis is correct? a. They are genetically different from each other and from the parent cell. b. They are genetically identical to each other and to the parent cell. c. They are genetically identical to each other but different from the parent cell. d. Only one of the two daughter cells is genetically identical to the parent cell.

answer

b

question

After S phase, what comprises a single chromosome? a. two daughter chromosomes b. a double stranded DNA molecule c. two single-stranded DNA molecules d. two sister chromatids

answer

d

question

Progression through the cell cycle is regulated by oscillations in the concentration of which type of molecule? a. p53, Rb, and other tumor suppressors b. receptor tyrosine kinases c. cyclins d. cyclin-dependent kinases

answer

c

question

Evaluate each of the following defects. Which could lead to uncontrolled growth in cancer? 1. T/F: the overexpression of MPF activity 2. T/F: a nonfunctional Rb protein 3. T/F: the overexpression of G1 cyclin 4. T/F: a nonfunctional E2F protein

answer

1. F 2. T 3. T 4. F

question

A particular cell type spends 4 hours in G1 phase, 2 hours in S phase, 2 hours in G2 phase, and 30 minutes in M phase. If a pulse-chase experiment were performed with radioactive thymidine on an asynchronous culture of such cells, what percentage of mitotic cells would be radiolabeled 9 hours after the pulse? a. 0% b. 50% c. 75% d. 100%

answer

a

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