Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

BIO 2B03 > Module 10 > Flashcards

Module 10 Flashcards

(109 cards)

Start Studying
1
Q

What molecular event initiates mitotic changes during prophase?

A

The activation of MPF (Cyclin B-CDK) to phosphorylate target proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

When MPF phosphorylates target proteins, what events occur?

A

1) Chromosome Condensation
2) Spindle Assembly
3) Nuclear Envelope Breakdown
4) Endomembrane Fragmentation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What reverses the mitotic changes at the end of mitosis?

A

The inactivation of MPF (via Cyclin B degradation), leading to phosphatases dephosphorylating target proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What prophase events are triggered by activation of MPF?

A

1) Mitotic Spindle Formation
2) Chromosome Condensation
3) Chromatid Cohesion Regulation
4) Nuclear Envelope Breakdown (NEB)
5) Endomembrane Fragmentation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What processes occur during telophase to reverse mitosis?

A

1) Disassembly of the mitotic spindle
2) Chromosome decondensation
3) Reassembly of the nuclear envelope
4) Reformation of endomembrane system

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What allows telophase changes to occur as the cell exits mitosis?

A

1) Cyclin B degradation → MPF inactivation
2) Phosphatases dephosphorylate MPF targets

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What proteins are phosphorylated to initiate chromosome condensation?

A

1) Histones H1 & H3
2) Condensins
3) Cohesins
4) Topoisomerase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

T or F: When chromosomes condense due to phosphorylation events, chromatin becomes highly compacted and typical mitotic X-shaped chromosomes form

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Which histones are phosphorylated during mitosis, and by what kinase?

A

Histone H1 & H3 - phosphorylated by Aurora B

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the role of cohesins in chromosome structure?

A

They hold sister chromatids together

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How is cohesin release regulated during mitosis?

A

a) Phosphorylated by MPF and Aurora B
b) Arm cohesins dissociate in prophase
c) Centromeric cohesins stay intact until anaphase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the function of condensins during mitosis?

A

They help condense DNA for proper mitotic chromosome structure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How are condensins activated?

A

Phosphorylation by Cyclin B-CDK (MPF)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Multiple MPF phosphorylation sites were found in a condensin protein identified in Xenopus, what was the name?

A

XCAP-D2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is NEB and when does it occur?

A

[NEB] nuclear envelope breakdown

It happens during prophase to prometaphase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

T or F: The nuclear membrane is only composed of one lipid bilayer, the outer nuclear membrane (ONM)

A

False - it is composed of two lipid bilayers, the outer nuclear membrane (continuous with the rough ER) and inner nuclear membrane (associated with nuclear lamina)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the nuclear lamina made of?

A

[intermediate filament proteins] lamin A, B, and C

the lamin network supports nuclear envelope integrity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What happens to lamins during NEB?

A

a) Lamin A/C are phosphorylated → dissociate into cytosol
b) Lamin B remains bound to the nuclear membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

In prophase, what happens to the three lamin proteins and what does that lead to?

A

The three lamin proteins are phosphorylated at specific serine residues by MPF, which initiates disassembly of the nuclear lamina and breakdown of the nuclear envelope

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What experimental approach was used to test lamin phosphorylation?

A

a) Human lamin A with serine-to-alanine mutations were introduced into hamster cells
b) Since alanine cannot be phosphorylated, NEB failed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What did the lamin A mutant experiment demonstrate?

A

Phosphorylation of lamin A is necessary for nuclear envelope breakdown

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What triggers nuclear envelope reassembly during telophase?

A

Inactivation of MPF → Cdc14 phosphatases dephosphorylate lamins A and C so the nuclear lamina can reform

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How does the nuclear envelope physically reform around chromatin?

A

Membrane vesicles with lamin B fuse around decondensing chromosomes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

In NEB, what are other proteins that are phosphorylated in addition to the lamin proteins?

A

1) Chromosomal proteins (that anchor chromosomes to nuclear lamina)
2) Nuclear pore complex proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What are karyomeres, and when do they form?
Small, membrane-bound sac that form around individual chromosomes during telophase, they represent partial nuclear envelopes before later fusing with one another to form the complete nuclear envelope
26
How do karyomeres fuse together to form the nuclear envelope?
Mediated by Rab-like proteins
27
What causes fragmentation of the endomembrane system during mitosis?
Phosphorylation of GM130 (Serine 25 - PS25) by Cyclin B-CDK
28
T or F: Dictyokinesis is the process of Golgi apparatus division, where vesicles and tubules of the fragmented Golgi accumulate in two clusters, one at each pole
True
29
T or F: Not all organelles are reorganized
False - they all are
30
What is the fate of most mammalian cells in the body regarding the cell cycle?
Most enter G0 and will never re-enter the cell cycle; they are terminally differentiated and undergo apoptosis
31
What types of cells are examples of post-mitotic cells?
Red blood cells, nerve cells, and muscle cells
32
How are lost post-mitotic cells replaced?
Through cell division of adult stem cells, followed by differentiation
33
Can some cells re-enter the cell cycle from G0?
Yes, some cells withdraw temporarily and can re-enter G1 when stimulated by appropriate signals
34
How does cell cycle regulation in fission yeast compare to vertebrates?
[fission yeast] requires a single Cyclin and a single CDK [vertebrates] use multiple Cyclin/CDK variants
35
Which Cyclin/CDK complexes are associated with different phases in vertebrates?
[early G1] Cyclin D/CDK4 or CDK6 [S-phase] Cyclin E/CDK2 [Completion of S-phase] Cyclin A/CDK2 & Cyclin A/CDK1 [Mitosis] Cyclin B/CDK1
36
Is there Cyclin/CDK regulation in G0?
No, there is no Cyclin or CDK expression in G0
37
What is required for a cell to re-enter the cycle from G0?
Expression of D-type cyclins and CDK4/6, induced by mitogens or growth factors
38
What are mitogens?
Signalling molecules that induce cell division by causing expression of G1 Cyclin/CDKs
39
What is the Restriction Point (RP)?
A point late in G1 when passage through the cell cycle becomes independent of the mitogen
40
What happens after a cell passes the Restriction Point?
It will continue into S phase even if the mitogen is removed
41
What are the two categories of gene expression after mitogen addition?
Early response genes and delayed response genes
42
How are early response genes regulated?
By transcription factors already present in the cell, activated by phosphorylation (e.g., SRF and TCF via MAP-kinase)
43
What do early response genes encode?
Transcription factors like c-Fos and c-Jun
44
What do delayed response genes encode? Of these encoded proteins, which are encoded first?
Transcription factors like E2F, and proteins like Cyclin D, Cyclin E, CDK2, CDK4, and CDK6 [first] CDK4, CDK6, Cyclin D [second] CDK2, Cyclin E
45
Why must expression of some delayed response genes be maintained until the cell passes through the restriction point?
To ensure the cell passes through the restriction point
46
Why is early gene expression not blocked by inhibitors of protein synthesis?
Because their transcription factors (SRF and TCF) are already present and require only phosphorylation
47
What is an example of an early response gene?
c-Fos, which activates transcription of delayed response genes
48
What role do SRF and TCF play in early response gene expression?
They are transcription factors activated by MAP-kinase that initiate transcription of early response genes, like c-Fos & c-Jun
49
T or F: TCF and SRF do not need to be translated, only phosphorylated to activate early response genes such as c-Fos, which does need to be translated
True
50
What happens when protein synthesis is inhibited while mitogens are added?
Early response gene transcription occurs, but delayed response gene expression does not
51
Why do early response gene mRNA levels remain high in the presence of translation inhibitors?
Because early gene transcription continues, but inhibitory proteins (encoded by early genes) can't be produced to turn it off
52
Why are delayed response genes not transcribed when translation is blocked?
Because transcription factors needed to activate delayed response genes are encoded by early genes and must be translated first
53
How is the passage through the Restriction Point reflected in Cyclin/CDK activity?
It correlates with the end of Cyclin D/CDK4-6 activity and the start of Cyclin E/CDK2 expression
54
What is the relationship between different Cyclin/CDK complexes during the cell cycle?
Each Cyclin/CDK induces the expression of the next one in the cycle
55
When does the Restriction Point occur in the context of Cyclin expression?
Between Cyclin D/CDK4-6 and Cyclin E/CDK2 activity, towards the end of G1
56
T or F: A mitogen that was introduced was EGF (epidermal growth factor)
True
57
What happens if a mitogen is removed before the Restriction Point is passed?
Cyclin D/CDK4-6 levels drop, and the cell retreats back into G0
58
What happens if a mitogen is removed after the Restriction Point is passed?
Cyclin E/CDK2 levels are high enough to allow progression into S-phase
59
What does the Restriction Point signify functionally?
It is the growth-factor dependent point after which the cell is committed to completing the cell cycle
60
What transcription factor is inhibited by Rb (retinoblastoma) protein?
E2F (delayed response transcription factor)
61
What is the function of E2F in the cell cycle?
Regulates the expression of genes required for S-phase (e.g., DNA replication and repair proteins, CDK1, CDC25)
62
How is E2F activated?
Through phosphorylation of Rb by Cyclin D/CDK4-6, which causes Rb to release E2F
63
What happens to Rb if the mitogen is removed before the Restriction Point?
Cyclin D levels fall, and Rb is dephosphorylated by phosphatases, inactivating E2F and pushing the cell back to G0
64
What complex maintains Rb phosphorylation and promotes continued cell cycle progression after the RP?
Cyclin E/CDK2
65
How does E2F maintain its own activity after activation?
By inducing expression of both Cyclin E/CDK2 and the E2F gene itself (positive feedback loop)
66
Is Cyclin E/CDK2 expression dependent on mitogen levels after the Restriction Point?
No, it is maintained independently once enough E2F is active
67
What is the purpose of cell cycle checkpoints?
To monitor cell integrity and delay progression until errors are corrected
68
What happens if an error cannot be corrected during the cell cycle?
The cell undergoes apoptosis
69
What processes are monitored by cell cycle checkpoints?
DNA damage, unreplicated DNA, mitotic spindle assembly, chromosome attachment at metaphase, and completion of anaphase
70
What are the two common types of DNA damage and their causes? Which proteins recognize damaged DNA in the cell cycle?
1) Double-stranded breaks: caused by ionizing radiation (ATM) 2) Thymine dimers: caused by UV radiation (ATR)
71
What activates Chk1 kinase in response to thymine dimers?
ATR Kinase
72
What is the role of Chk1 in the DNA damage checkpoint?
It phosphorylates and inactivates Cdc25, blocking MPF activation and arresting the cell in G2
73
What happens to Cdc25 after phosphorylation by Chk1 in the long-term?
It is sequestered in the cytosol via the 14-3-3 adaptor protein
74
What is the benefit of G2 arrest in response to DNA damage?
It gives the cell time to deploy repair mechanisms
75
How does ATR function in the DNA replication checkpoint?
ATR binds to incomplete replication forks and activates a pathway that delays mitosis by inactivating MPF.
76
Why is MPF inactivation important during the DNA replication checkpoint?
It prevents the cell from entering mitosis until DNA replication is complete
77
What kinase is activated by ATM in response to double-stranded breaks?
Chk2 kinase
78
What is the role of Chk2 in the DNA damage checkpoint?
It phosphorylates and stabilizes p53.
79
What does p53 activate after stabilization?
Transcription of p21 (CIP) and other DNA repair genes
80
What is the function of p21 (CIP)?
It is a general Cyclin/CDK inhibitor that causes cell cycle arrest, particularly in G1, allowing for time to repair cell damage
81
T or F: Other target genes of p53 include cell cycle repair genes
True
82
Why is p53 usually inactive in cells? What makes p53 stable and active?
a) It is rapidly polyubiquitinylated and degraded b) Phosphorylation, typically by Chk2
83
What are two key outcomes of sustained p53 activity?
a) Activation of p21 for cell cycle arrest b) Expression of pro-apoptotic genes if damage cannot be repaired
84
What are the two main mechanisms used by DNA damage checkpoints?
1) ATM Pathway - Activation of p53 → p21 synthesis 2) ATR Pathway - Inactivation of Cdc25 → sustained inhibition of Cyclin/CDK activity
85
What is the purpose of the Spindle Assembly Checkpoint (SAC)?
To prevent anaphase until all chromosomes are properly attached to the spindle
86
What will a single unattached chromosome cause in the SAC?
A delay in metaphase and inhibition of anaphase onset
87
Where are kinetochore proteins located, and why are they important in the SAC?
At the centromeres of chromosomes; they must attach to spindle microtubules to satisfy the SAC
88
What is benomyl, and how is it used in SAC studies?
Benomyl is a chemical that destabilizes microtubules, causing checkpoint arrest due to unattached chromosomes
89
What happens to wild-type cells after benomyl is removed?
They reassemble spindles and proceed through metaphase and into anaphase after successful checkpoint arrest
90
What is the result of nondisjunction?
One daughter cell has an extra chromosome, and the other is missing a homologous chromosome
91
T or F: Some SAC mutants can pass through into anaphase without proper spindle attachment, leading to nondisjunction and aneuploidy
True
92
What does Mad2 do in the Spindle Assembly Checkpoint?
It inactivates APC-Cdc20 to prevent premature anaphase
93
How does inactivation of APC-Cdc20 prevent anaphase?
It keeps securin intact, which inhibits separase, thereby blocking sister chromatid separation
94
What are the two conformations of Mad2, and where are they found?
1) Open Mad2 (O): inactive, associates with unattached kinetochores 2) Closed Mad2 (C): active, binds Cdc20 and inhibits APC
95
How is Mad2 converted from open to closed conformation?
Through interaction with Mad1 at unattached kinetochores
96
What happens when closed Mad2 binds Cdc20?
It prevents Cdc20 from activating APC, halting cell cycle progression
97
What signals the passing of the SAC?
All kinetochores are attached to microtubules; Mad1 and Mad2 are released
98
What role does p31 play in checkpoint inactivation?
It binds closed Mad2 and promotes its return to the open state, reducing its affinity for Cdc20
99
What happens once Cdc20 is released from Mad2?
Cdc20 activates APC, which degrades securin and activates separase, triggering anaphase
100
What is the goal of the Mitotic Exit Network (MEN)?
To ensure proper chromosome segregation before exit from mitosis
101
What is required for mitotic exit? What activates APC-Cdh1 in the first place? [MEN]
a) Inactivation of MPF by APC-Cdh1, which degrades Cyclin B b) Dephosphorylation of Cdh1 by Cdc14 phosphatase
102
Where is Cdc14 located during interphase and early mitosis? When is Cdc14 released and activated? Why must Cdc14 be inactive before anaphase?
a) In the nucleolus, where it is inactive b) After anaphase has occurred c) To prevent premature exit from mitosis
103
What form is Tem1 in before anaphase, and why?
Tem1-GDP (inactive), due to the action of Tem1-GAP
104
Why is Tem1-GEF unable to activate Tem1 before anaphase?
It is located on the daughter bud membrane, spatially separated from Tem1
105
What does inactive Tem1 prevent?
Activation of Cdc14 and initiation of the Mitotic Exit Network
106
What happens if the mitotic spindle is misaligned during anaphase? [rotated 90 degrees]
Tem1 doesn’t interact with Tem1-GEF, remains inactive, and MEN is not activated
107
What is the consequence of failed MEN activation?
Cdc14 remains sequestered, Cdh1 stays inactive, MPF remains active, and mitotic exit does not occur
108
In addition to dephosphorylation of Cdc14, How does Cdc14 prevent premature S-phase entry?
By keeping Sic1 unphosphorylated, which inhibits S-phase Cyclin/CDKs
109
What happens to Cdc14 in the next cell cycle? What leads to Sic1 degradation, allowing S-phase to begin?
a) It is inactivated by phosphorylation from G1 Cyclin/CDKs b) Phosphorylation of Sic1 targets it for degradation by SCF E3 ligase, which leads to S-phase

BIO 2B03 (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions