Cell Bio: Chapter 18 Flashcards
(110 cards)
1
Q
What are the two broad phases of the eukaryotic cell cycle?
A
M phase and Interphase.
2
Q
What does M phase consist of?
A
Mitosis and cytokinesis.
3
Q
What does interphase consist of?
A
G1, S and G2 phases.
4
Q
What is a CDK?
A
A cyclin dependent kinase (only active when a cyclin is bound).
5
Q
What do active CDKs phosphorylate?
A
Target proteins during the cell cycle.
6
Q
What happens when cyclin is synthesized?
A
CDKs are turned on.
7
Q
What happens when cyclins are degraded?
A
CDKs are turned off.
8
Q
True/False: All CDKs need to be phosphorylated to be activated.
A
True.
9
Q
Where does G1-CDK act?
A
Early in G1 and helps drive the cell through G1 to S phase.
10
Q
What is G1-CDK/cyclin activated by?
A
Growth factor signaling pathways.
11
Q
Where does G1/S-CDK and S-CDK drive the cell?
A
S phase.
12
Q
Where does M-CDK act?
A
Helping cells into M phase.
13
Q
What does progression through G1 phase require?
A
Signal transduction through mitogen/growth signaling pathways.
14
Q
What does the MAPK activate?
A
A transcription factor that activates gene expression of Myc.
15
Q
What does the Myc protein turn on?
A
G1 cyclin expression.
16
Q
What can happen if Myc is overexpressed?
A
Cancer can form.
17
Q
What does Rb do?
A
Keeps S phase switched off by binding to and inhibiting E2F.
18
Q
What does the G1-CDK initiate?
A
Rb phosphorylation.
19
Q
What happens when Rb is phosphorylated?
A
It becomes inactivated, and releases the E2F toxin factor.
20
Q
What does E2F activate?
A
S phase gene expression including G1/S cyclin and S cyclin.
21
Q
What happens when G1/S cyclin and S cyclin are activated?
A
They bind to the S-CDK and turn on DNA replication machinery.
22
Q
What does ORC bind to?
A
Origins of replication throughout the cell cycle.
23
Q
What happens in early G1 when Cdc6 regulatory proteins bind to ORC?
A
It promotes the binding of other components including DNA helicase to form a big complex.
24
Q
What happens when Cdc6 is phosphorylated by S-CDK?
A
It degrades, and ORC becomes activated (DNA replication now active).
25
Why can the cell not start replication again in the same phase?
Cdc6 is degraded and not synthesized until the next G1 phase.
26
When does DNA replication occur?
When one strand is used as a template for copying the new strand.
27
Which direction is DNA synthesized?
5'-3'; new nucleotides are added to the 3' free hydroxyl on the DNA.
28
Why does DNA replicate semiconservatively?
Each DNA contains an old "conserved" strand and a newly synthesized one.
29
What happens when DNA is unwound?
A replication fork is formed.
30
Is DNA synthesized on both the leading and the lagging strands?
Yes; on the lagging strand, synthesis is discontinuous with Okazaki fragments.
31
What is the function of primers?
Starting new strands of DNA (leaves a gap when removed).
32
Why do chromosomes not shrink every generation due to primers being removed?
Telomerase adds additional repeats to the template strand.
33
Which cells host an active telomerase?
Typically only gametes early in our development, or in stem cells.
34
What happens after S phase?
Cells spend 4-6 hours in G2 where they grow larger and check for DNA damage. Then they enter M phase.
35
What does M phase consist of?
Prophase, prometaphase, metaphase, anaphase, and cytokinesis.
36
What pulls sister chromatids apart?
Microtubules.
37
What forms the contractile ring during cytokinesis?
Actin and myosin.
38
What is the function of centrosomes?
Serving as nucleation sites for the growth of microtubules.
39
Where are centrosomes duplicated?
During interphase (2 are required to separate sister chromatids).
40
What happens in prophase?
Chromosomes condense, and the mitotic spindle forms.
41
What happens in prometaphase?
The nuclear envelope breaks down, allowing spindle microtubules to contact and bind to chromosomes at the kinetochore. The nuclear lamina is also phosphorylated and disassembled.
42
What happens in metaphase?
The mitotic spindle pulls and aligns all chromosomes at the metaphase plate.
43
What happens in anaphase?
Sister chromatids are separated and the spindle draws them to opposite poles of the cell.
44
What happens in telophase?
The nuclear envelop reforms around the chromosomes to form two nuclei.
45
What happens in cytokinesis?
The two cytoplasms are separated; each cell has its own plasma membrane.
46
What holds sister chromatids together?
Cohesin protein complexes.
47
What helps pull chromosomes together before M phase?
Condensin protein complexes.
48
What triggers the breakdown of the nuclear envelope in prometaphase?
Phosphorylation and consequent disassembly of the nuclear envelope.
49
What are kinetochore proteins?
Special proteins that assemble at the centromere region of the chromosomes.
50
What are the 3 different types of microtubules making up the mitotic spindle?
Aster, kinetochore, and interpolar microtubules.
51
What are aster microtubules?
Microtubules that stabilize the spindle by binding to the plasma membrane and searching for kinetochores.
52
What are kinetochore microtubules?
Microtubules that attach to sister chromatids at the kinetochore.
53
What are interpolar microtubules?
Microtubules that stabilize the spindle in bipolar form by binding to each other in the middle.
54
What is required for a cell to enter anaphase?
Microtubules must be attached to both kinetochores on each chromosomes to have proper tension.
55
What does anaphase activate?
The APC (Anaphase Promoting Complex).
56
What does APC trigger?
The degradation of securin, which activated separase.
57
What does separase do?
Cleaves and inactivates the cohesins.
58
What is Anaphase A?
Chromosomes are pulled poleward by shortening kinetochore microtubules.
59
What is Anaphase B?
Poles are pushed apart by interpolar microtubules and pulled apart by aster microtubules.
60
What happens when nuclear lamins are dephosphorylated in telophase?
They reassociated to reform the nuclear lamina. Nuclear pores come back and begin the transport of nuclear proteins.
61
How many times do mitochondria and chloroplasts divide during the cell cycle?
Roughly once per cycle.
62
What can organelle fragments bind to?
Motor protens that attach to spindle microtubules to be pulled to daughter cells.
63
What forms the cleavage furrow in animal cells during cytokinesis?
The actin/myosin contractile ring. It ensures that the cleavage furrow cuts between two groups of segregated daughter chromosomes so each cell gets an identical set of them.
64
What guides the assembly of a new cell wall in plant cells?
The phragmoblast.
65
What does the phragmoblast consist of?
The remains of the interpolar microtubules at the equator of the old mitotic spindle.
66
What happens when something is unfavorable in the cell cycle (DNA damage)?
The cell must stop and wait for conditions to improve, or fix the damage before continuing.
67
What drives movement throught a cell cycle checkpoint?
CDKs.
68
(Xenophus frog eggs) What happens when a cytoplasm from an M phase cell is injected into an immature cell?
The cell is driven into M phase.
69
What happens when interphase cytoplasm is injected into an immature cell?
Nothing.
70
What affects the concentrations of M-CDK in cells?
Activity is only high when levels of cyclin are. When interphase starts, more cyclins are gradually made.
71
When is the cyclin degraded?
At the end of M phase to turn off the CDK and exit from M phase.
72
What controls degradation?
The same APC that triggers sister chromatid separation.
73
True/False: The CDK needs appropriate phosphorylation for activation.
True; the cyclin is not the only important part.
74
What does the inhibitory kinase Wee1 phosphorylate?
Inhibitory sites on an M-CDK; this activates kinase CAK, which phosphorylates activating sites.
75
When is the M-CDK finally activated?
When Cdc25 phosphatase removes the inhibitory phosphate.
76
What can the active M-CDK cyclin activate?
Phosphorylation of the nuclear lamin proteins, the condensin complex, microtubule associated proteins, and APC.
77
What happens when DNA is damaged?
p53 is phosphorylated and activates p21 gene expression.
78
What is p21?
A CDK inhibitor which stops the cell cycle by binding to and inactivating CDK/cyclin pairs.
79
What if there is a mutation in p53?
It can cause cancer since the cell cycle is unable to be stopped to fix the DNA.
80
What happens at the G2-M phase checkpoint if DNA is not properly replicated?
Proteins associated with replicating DNA inhibit Cdc25 (M-CDK stays inactive).
81
What are mitogens?
Signaling molecules that can stimulat cell proliferation.
82
What is the function of growth factors?
Promote cell growth.
83
What is the function of survival factors?
Inhibiting cell death.
84
What if no mitogens are present?
Cells can withdraw from G1 and enter G0.
85
Can cells exist in G0 for the lifespan of an organism?
Yes; muscle cells and neurons continue to function, but never divide during G0.
86
What can growth factors signal?
Making more proteins and cellular components (helps cells grow).
87
When do many animal cells do most of their growing?
After they have permanently stopped dividing.
88
What can PDGF and EGF function as?
Growth factors and mitogens.
89
What is myostatin?
A signaling ligand inhibiting growth and proliferation of the myoblasts (fuse to form skeletal muscle cells).
90
What happens in the absence of survival signals?
Cells die by the process of apoptosis (programmed cell death).
91
What happens to cells that do not get enough survival signals?
They die so the number of cells matches the number of target cells.
92
What if there is no survival signal and no Bcl-2?
The cell undergoes apoptosis.
93
What can Bcl-2 bind to?
Mitochondria; this blocks the function of Bak and Bax.
94
True/False: More than half the nerve cells produced in a developing vertebrate nervous system die every hour.
False; they often die soon after they are formed.
95
What is necrosis?
When cell side due to acute injury; they typically swell and burst, spilling their contents all over their neighbors.
96
How is apoptosis different from necrosis?
Cells that die from apoptosis shrink and condense, and are often engulfed by phagocytic cells before the dead cell's contenst can spill over other cells.
97
What are caspases?
A family of proteases that clear other proteins. Kept in an inactive conformation as a procaspase molecule.
98
What happens when the procaspase is cleaved?
It creates an active caspase protease, which initiates apoptosis.
99
When the first caspase is cleaved, what does it do?
It cleaves and activates a second, which in turn cleaves and activates even more.
100
What do active caspases break down?
Cytosolic and nuclear proteins.
101
Where does the cleavage of nuclear lamins lead?
Nuclear membrane disruption.
102
Why is the caspase cascade irreversible?
Very important proteins are being cleaved.
103
What do Bax and Bak bind to if there is no survival signal?
Mitochondria; this forms a channel causing cytochrome C to release from the mitochondria.
104
Where does cytochrome C normally function?
The electron transport chain; used to make ATP.
105
What happens when cytochrome C is released?
It interacts with an adaptor and caspase 9 to form the apoptosome.
106
If transcription of Bcl-2 is activated by survival signals, is apopsosis blocked?
Yes; if there is no survival signal and no Bcl-2, the cell undergoes apoptosis.
107
What is apoptosis triggered by in the extrinsic pathway?
External cells.
108
What ligand is present in killer lymphocytes?
The Fas ligand.
109
What can the Fas ligand bind to on infected cells?
The Fas receptor; this triggers apoptosis.
110
What can the Fas receptor activate?
Caspase 8, which can trigger the caspase cascade, and the release of cytochrome C.
