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Molecular Test III > Lecture 22 Cell Cycle I > Flashcards

Lecture 22 Cell Cycle I Flashcards

1
Q

What are the two steps of cell reproduction?

A

Duplicate contents of cell

Cytokinesis

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2
Q

What are the three major functional aspects of the cell cycle?

A

Cell growth and chromosome replication
Segregation of chromosomes
Cell division

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3
Q

How many mistakes are made in one cell division?

A

6
mistake rate 1 x 10 ^-9
6.4 X 10^9 base pairs in diploid genome

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4
Q

How many cells in the body

A

3x10^13

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5
Q

How many cell divisions in one lifetime?

A

10^16

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6
Q

Liver cell cycle =

A

1 year

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7
Q

How many RBC?

A

25 trillion

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8
Q

How many RBC produced per second?

A

2.4 million

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9
Q

What is a disease of excess cell proliferation?

A

cancer

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10
Q

What is the cell-cycle control system?

A

Complex network of regulatory proteins

Ordered series of biochemical switches

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11
Q

What initiates main events of cell cycle?

A

Reg proteins

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12
Q

What coordinates events in the cell cycle so that they occur at the appropriate time?

A

proteins

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13
Q

When are chromosomes duplicated in the cell cycle?

A

S phase

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14
Q

Chromosome segregation and cell division occurs during what phase of the cell cycle?

A

M

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15
Q

Prophase:

A

Chromosomes condense into rigid rods called sister chromatids

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16
Q

Metaphase:

A

Line up at equator; attach to spindles

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17
Q

Anaphase:

A

Sister chromatids become daughter chromosomes; pulled apart

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18
Q

Telophase:

A

Spindle disassembles, separate nuclei, cytokinesis

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19
Q

GAP phases:

A

cells have extra gap pahses to allow more time for growth
G1 phase between M and S
G2 phase between S and M

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20
Q

How many phases to the cell cycle?

A

4

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21
Q

What makes up interphase cycle?

A

G1, S G2

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22
Q

M phase last how long?

A

1 hour

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23
Q

What is an important switch point?

A

G1 - decide to go into cell cycle or stay resting

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24
Q

Checkpoint I:

A

START-cell commits to cell cycle entry and chromosome duplication (also called restriction point)

Going from G1 to S
Qs: is the environment favorable

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25
Q

Checkpoint II:

A

G2/M - chromosome alignment on spindle in metaphase

Q?: is all DNA replicated, is the environment favorable

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26
Q

Checkpoint III:

A

metaphase - to - anaphase transition - trigger sister chromatid separation and cytokinesis
Qs: are all chromosomes attached to the spindle

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27
Q

What is the model organism to study cell cycle?

A

Yeast

Animal embryos

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28
Q

Fission yeast

A

Grows by elongation at ends; division occurs when septum or cell plate forms midway along rod-shaped cell

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29
Q

Budding yeast

A

Oval yeast that divides by forming a bud; the bud first appears at G1 and grows until mitosis phase

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30
Q

Genes identified in yeast encode components of what?

A

cell-cycle control system = Cdc genes: cell-division cycle genes

31
Q

What are mamalian cell lines that can be used to study cell-cycle?

A

fibroblasts

However, these cells stop dividing in culture after a # of cell cycles

32
Q

Immortalized cell lines:

A

Cell lines grow forever
Murine erythroleukemia cells
Useful for studying erythroid cell development and the generation of RBC
Also HEL cells

33
Q

If conditions are unfavorable for cell division, the cell cycle control system will do what?

A

Signal to block progression through START

34
Q

What does the cell cycle control system use to turn on various steps of the cell cycle?

A

Series of biochemical switches made of cyclin dependent kinases (Cdks) - phosphorylate proteins to activate them

35
Q

What is the heart of the cell-cycle control system?

A

Cdks

Activities of Cdks rise and fall during cell cycle

36
Q

What do Cdks cause?

A

cyclical changes in phosphorylation of substrates that regulate cell cycle events

37
Q

What are proteins that regulate Cdks?

A

cyclins

The level of cyclins vary and cycles during the cell cycle - therefor their name

38
Q

What are Cdks dependent on?

A

Cyclins - must be bound to cyclin to have activity

39
Q

Cyclin levels or Cdks levels are constant?

A

Cdks

40
Q

G1/S cyclins:

A

Activates Cdks in late G1
Helps trigger progression through START
commitment made to cell cycle entry
Levels drop in S phase

41
Q

S cyclins

A

Bind Cdks after progression through START
Helps stimulate chromosome duplication
S-cyclin levels remain high until mitosis

42
Q

M-cyclins

A

Activate Cdks that stimulate entry into mitosis at G2/M checkpoint
M-cyclins removed mid-mitosis

43
Q

G1 cyclins

A

Govern activity of G1/S cyclins (control progression through START checkpoint)

44
Q

What are the 4 Cdks in vertebrates?

A

Two interact with G1 cyclins: G1-Cdk
One with G1/S and S cyclins: G1/S-Cdk and S-Cdk
One with M-cyclins: M-Cdk

45
Q

Without cyclin bound (inactive state), the active site of Cdk is blocked by what?

A

a region of the protein called the T loop

46
Q

PHosphorylation of Cdk caused by CAK causes what?

A

phosphorylation of Cdk at T-loop fully activates enzyme
(cave site)

For Cdk to be completely activated it needs cyclin and CAK

47
Q

Cdk activity determined primarily by rise and fall of cyclin levels, however a different phosporylation of Cdk inhibits activity of cyclin-Cdk complex. Describe what occurs in the roof site of Cdk

A

Wee1: inhibits Cdk activity by phosphorylating the roof site
Cdc25: phosphatase that dephosphorylates roof site to increase Cdk activity

48
Q

CKI proteins:

A

Causes Cdk-cyclin to be inhibited
A CKI (p27) binds to both Cdk and cyclin to inactivate
This is primarily used for control of G1/S-Cdks + S-Cdks early in cell cycle

49
Q

INK4A gene causes what?

A

inhibitory effects on Cdk
It is a CKI involved in the G1 phase of cell cycle
Mutation occurs in this gene in hereditary melanoma
Cannot control cell cycle and cells grwo uncontrollably and you get cancer

50
Q

What is a major tumor suppressor?

A

p53

p53 influences the expression of many genes

51
Q

How is p21 created and what is its function?

A

It is a gene that is up-regulated by p53.
p53 is a major tumor suppressor
p21 is a CKI to stop division
Without it the cells will divide uncontrollably

52
Q

G1/S-Cdk makes what cyclin?

A

Makes S cyclin

G1/S-Cdk is important for movement through START

53
Q

S-Cdk is important to start what?

A

DNA replication

54
Q

How are CKI’s destroyed so that Cdks like s-Cdks can be activated?

A

p27 is a CKI that binds to both cyclin and Cdk (CKI)
Proteolysis of CKI’s can turn on the Cdk.
Ubiquitin system stimulates destruction of regulatory proteins
Use protein called SCF-ubiquitin ligase to add ubiquitin
Target for proteasomes

*SCR activity depends on F-Box proteins (help SCF recognize target)

55
Q

Why is there lots of primed M-Cdk around by the end of G2?

A

It is formed in its inactive formed
Phosphorylated by CAK to activate it but Wee1 holds M-Cdk in inactive state
When ready to be activated it is dephosphorylated by Cdc25

note when M-Cdk is finally acitvated, it can cause positive feedback on Cdc25 or Wee1, so promotes and suppresses. Good to regulate and prevent cancer

56
Q

Progression from metaphase to anaphase is triggered not by protein phosphorylation but by what instead?

A

Protein destruction

Key regulator is APC/C: anaphase-promoting complex (or cyclosome)

57
Q

What is APC/C?

A

A member of ubiquitin ligase family of enzymes
Catalyzes addition of ubiquitin to proteins to cause destruction
2 major proteins it affects are cohesin and securin in that order

Levels rise mid-mitosis

58
Q

What is Cohesin?

A

Sister chromatids are glued together along their length by this protein
Members of SMC proteins
Forms rings around sister chromatids
Protected by securin

59
Q

What is Secruin?

A

Protects cohesin protein linages that holds sister chromatid pairs together in early mitosis
Does so by inhibiting a protein called separase that cleaves cohesin

60
Q

Describe how APC/C allows sister-chromatids to separate and have anaphase begin

A

APC/C levels rise mid-mitosis
Add ubiquitin on securin
activates separase
Separase breaks down cohesin

61
Q

What does increased levels of APC/C do to Cdk-cyclin complexes?

A

Adds ubiquitin on cyclins and Cdks are inactivated

62
Q

What cyclins are the major target of APC/C?

A

S and M-cyclins

Dont want to duplicate chromosomes again

63
Q

How is APC/C activated?

A

By binding to Cdc20

64
Q

What stimulates genes making G1/S-cyclin and S-Cyclin?

A

G1-Cdk

65
Q

What triggers prophase, prometaphase and metaphase at G2/M stage?

A

Increase of M-Cdk activity

  • assembly of mitotic spindle
  • attachment to sister chromatids
66
Q

What complex is critical in order for chromosomes to be duplicated only once?

A

PRE-RC and for it to be only present during G1 phase
No new PRE-RC are made during S and M phases
Between G1-G1 NO MORE!!!!!

67
Q

What inhibits assembly of PRE-RC?

A

Cdk activity
MAJOR POINT!!!!
When S-Cdk and M-Cdk are high during S and M stage NO PRE-RC IS FORMED

68
Q

What is the assembly of PRE-RC stimulated by?

A

APC/C

!!!!! So PRE-RC assembly occurs in late mitosis and early G1 when Cdk activity is low and APC/C activity is high

69
Q

How is the PRE-RC complex created?

A 
In G1
Two proteins (Cdc6 and Cdt1) bind ORC and help load 6 proteins (Mcm proteins) - creates helicase to unwind DNA

The Cdc6, Cdt1 bound to ORC and the 6 proteins creates the PRE-RC

70
Q

What happens to the PRE-RC during the cell cycle

A

Once the cell cycle begins, S-Cdk triggers assembly of pre initiation protein complex.
S-Cdks triggers disassembly of the Cdc6 (part of PRE-RC complex) by phosphorylating it
Also phosphorylates ORC to inhibit function
Cdt1 inhibited by geminin

= preinitiation complex can bind to DNA, unwinds, and begins DNA replication

71
Q

What is a KEY STEP in the control of initiation of DNA replication?

A

S-Cdks blocks formation again of pre-RC by causing destruction of Cdc and inactivation of ORC by phosphorylation

72
Q

How are PRE-RC components reformed after M phase?

A

APC/C causes components to be dephosphorylated
In late mitosis and early G1, APC/C triggers destruction of geminin, which had inhibited Cdt1
Cdt1 activated now allows PRE-RC assembly for next cell cycle

73
Q

What is a key point about the components of PRE-RC?

A

Cdc6, Cdt1, Mcm helicase cannot form a new PRE-RC until M-Cdk is inactivated and APC/C is activated at the end of mitosis

Molecular Test III (7 decks)

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