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Cell Bio 1-4 > Cell Bio 4 > Flashcards

Cell Bio 4 Flashcards

(47 cards)

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1
Q

Functions of the cell cycle

A

Reproduction and Inheritance

DNA replication

Segregation of chromosomes

Coordination of growth with division (increase in cell mass)

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2
Q

Cell cycle

A

ordered sequence of events in which a cell:

  • Duplicates DNA and Chromosomes
  • Divides into two genetically identical cells
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3
Q

Cell cycle phases

A
  • G1
  • S
  • G2
  • Metaphase

Interphase: G1-G2, cell increases in size

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4
Q

When is the most physical change observed in the cell during the cell cycle?

A

Most dramatic events observed microscopically occur during M phase.

Interphase cells look morphologically similar.

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4
Q

When is the most physical change observed in the cell during the cell cycle?

A

Most dramatic events observed microscopically occur during M phase.

Interphase cells look morphologically similar.

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5
Q

Events during the Cell Cycle (1)

A

G1:

  • Cell growth and metabolism
  • where most cells arrest when not dividing (G0)
  • variable length (11 hours)
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6
Q

Events during the Cell Cycle (2)

A

S:

-DNA replication (6-8 hours)

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7
Q

Events during the Cell Cycle (3)

A

G2:

preperation for chromosome segregation and cell division (4 hours)

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8
Q

Events during the Cell Cycle (4)

A 
M:
-Chromatin condense
-Nuclear envelope breakdown
-Sister chromatids attach to mitotic spindle
-segregation of chromatids
-decondense and reformation of intact nuclei
-cytokinesis
(1 hour)
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9
Q

M phase

A

Prophase:

  • nuclear envoloppe breaks down
  • spindle apparatus forms
  • chromosomes condense

Metaphase
-chromosomes line up at the metaphase plate a the center of the cell

Anaphase:
-sister chromatids seperate pulled towards spindle poles

Telophase:
-chromosomes decondense reassembly of nuclear membranes

High accuracy and fidelity are required to assure that the chromsosome will be segregated properly.

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10
Q

S. cerevisiae

A

Budding Yeast

Discovery of cell cycle was made through yeast.

Budding yeast have a bud that forms during cell division

Much longer G1 phase

Cell cycle stage can be inferred by the size of the bud.

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11
Q

S. pombe

A

The fission yeast

Grows by elongation of the ends (as they go through the various phases of the cell cyclethe cell gets progressively longer and longer)

cytokinesis occurs by the formation of septum

Have longer G2 and M phases

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12
Q

Temperature Sensitive Mutants

A

Mutants of yeast cells allow the ability to identify genes that regulate cell cycle, these mutants were called cdc mutants.

At a certain temperature the mutant form of the protein that is defective will become active.

at a lower temperatures the protein is active and functioning.

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13
Q

Control of G2 to M transition in S. pombe

A

Loss of cdc2 activity (recessive) prevents S. pombe from entering M phase.

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14
Q

Cdc2 expression/S. cervisae equivalent

A

Cdc2 is transcribed and translated throughout the cell cycke and is also cyclin dependent kinase (CDK)

Cdc28

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15
Q

Proteins controlling cell cycle are highly ________ between all ________ organism.

A

Conserved

Eukaryotic

Human cdc2 can rescue yeast mutants without cdc2

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16
Q

S. pombe with cdc2 knocked out

A

Mutant form will be stuck in G2 and grow indefinetly

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17
Q

Three protein families involved in cell cycle

A

Kinases: add phosphates (enzyme)

Phosphotases: remove phosphotases (enzyme)

Cyclins: control kinase actvity

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18
Q

CDK and Cyclin

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A

Heterodimer of CDK and mitotic cyclin Cdc2 makes MPF (mitosis promoting factor)

19
Q

Activity and synthesis of Cdc2

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A

Cdc2 is constituively expressed (always present in the cell)

Cdc2 is not always active in the cell, the kinase activty peaks in late G2 phase.

20
Q

Cyclin Expression and Control of cdc2

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A

Cyclin is synthesized in greater amounts during the late G2 phase. At late G2 Cdc2 kinase binds cyclin to form and activate MPF.

the activity of kinase is regulated by the amount of cyclin present, in order to have a fullu active kinase there needs to be a cyclin present.

21
Q

Cyclins bind to and activate ____

22
Q

Cyclins are only ______ during the _____ _____ ____ that they trigger and are _______ in other ___ ____ _____.

Study These Flashcards
A

present
cell cycle stage
absent
cell cycle stages

23
Q

Cyclins are divided into four classes based on their ______ and ______ during the cell cycle

Study These Flashcards
A

presence
activity

G1 cyclin
G1/S cyclin
S cyclin
mitotic cyclin

24
Regulation of cyclins occurs at the
Transcriptional level | by ubiquitin-mediated proteasome-dependent degredation
25
Ubiquitin (Ub)
76 AA protein | Found in all eukaryotic cells
26
Ubiquitin ligases + conjugating enzyme
Ubiquitin ligase contains two bindging sites: - ubiquitin comjugating enzyme binding sites - Target protein binding site Target protein and enzyme bind to binding sites. ubiquitin conjugating enzyme adds ubiquitin (polyubiquination) onto the target proteins. ubiquitin is recognized by protease and the target protein is degraded.
27
Cyclins and Degredation by Ubiquitin Ligase
The cyclins are targeted for destruction one of the ligases that helps facilitate this is SCF
28
Wee1
Wee1 is a kinase that phosphorylates CDK leading to its inactivation. Phosphorylates tyrosine aa at position 15
29
Cdc25
a phosphotase that removes the inhibtory phosphate group from CDK and promotes its activation
30
Regulation of CDK (not cyclin)
Kinases can be regulated by being phosphorylated themselves.
31
Deficit of Cdc25/Excess of wee1
The cell will be arrested in the G2 phase leading to a very long shape (MPFs are inactive)
32
Deficit of Wee1/Excess of cdc25
premature activation of MPF, leading to small cells (short G2)
33
Regulation of MPF activity in S. pombe (Activation of CDK only during mitosis)
Depends on phosphorylation of two residues (Tyr15 and Thr161) in the catalytic CDK subunit. Wee1 inhibitory kinase CAK (CDK-activating kinase) Cdc25 activating phosphotase CAK sets up CDK to active, activation does not occur yet due to the presence of inhibitory phosphate group at Tyr15. regulation prevents premature activation of MPF MPF is active in the later stages of G2
34
What will the cell do with active MPF
``` Phosphorylation Chromosome condensation (H1, condensin complexes) ``` Dissasembly of the nuclear envelope Interphase microtubule disassembly and the mitotic spindle formation remodeling Golgi, ER which blocks vesicular traffic.
35
Exit from mitosis which phase?
MPF should be inactivated at Anaphase
36
Mechanism of exit from mitosis
Rapid mitotic cyclin degredation following polyubiquitination. APC/C recognizes the destruction box of 9 amino acids located in cyclin
37
Key enzyme in exit from mitosis
Anaphase-promoting complex/cyclosome (APC/C) a ubiquitin ligase
38
Regulation of mitotic cyclin levels
Maximal activity during metaphase Active APC/C recognizes the destruction box and induces polyubiquitination. Ubiquitin marks M-phase cyclins for proteolytic degredation in proteasomes MPF activity drops down and the cell returns to interphase.
38
Regulation of mitotic cyclin levels
Maximal activity during metaphase Active APC/C recognizes the destruction box and induces polyubiquitination. Ubiquitin marks M-phase cyclins for proteolytic degredation in proteasomes MPF activity drops down and the cell returns to interphase.
39
Cyclin levels during the cell cycle
- at late G2 cdc2 kinase binds cyclin to form and activate MPF - Later in M-phase APC/C promotes degredation of cyclin
40
S-phase entry is regulated by degredation of a CDK inhibitor by SCF ubiquitin ligase
CDK is associated with S phase cyclin during G1 but we don't want S-phase cyclin and the CDK complex to be active during G1. Activity is restrained by and s-phase inhibitor that binds to the s-phase CDK/cyclin complex. To enter S-phase G1/S cyclin will associate with CDK and phosphorylate the inhibitor on the s-phase cyclin comples. and the phosphorylated inhibitor can be recognized by SCF UL promoting its ubiquination and degredation.
40
S-phase entry is regulated by degredation of a CDK inhibitor by SCF ubiquitin ligase
CDK is associated with S phase cyclin during G1 but we don't want S-phase cyclin and the CDK complex to be active during G1. Activity is restrained by and s-phase inhibitor that binds to the s-phase CDK/cyclin complex. To enter S-phase G1/S cyclin will associate with CDK and phosphorylate the inhibitor on the s-phase cyclin comples. and the phosphorylated inhibitor can be recognized by SCF UL promoting its ubiquination and degredation.
41
Overview of Cell Cycle (G1-S phase)
G1 to S-phase: - G1/S-phase CDKs activate expression of S phase cyclin CDKs components by phosphorylating the S phase inhibitor - SCF proteasome degrades phosphorylated S-PHASE cdk inhibitor in late G1 - SCF/proteasome degrades G1 phase cyclins
42
Overview of cell cycle (S-G2)
- Active Sphase cyclines promote DNA replication - SCF degrades S-phase cyclins - The progressive accumulation of mitotic cyclin associating with CDK - wee1 Kinase is active - cak is active
43
Overview of cell cycle (G2-M)
- cdc2525 phosphotase occurs which removes the phosphate from Tyr 15 - Optimal activation of the MPF leading to full activation of mitosis
44
Mitosis
- As we progress to anaphase we get activation of APC/C complex - the APC/C will recognize cyclin and promote its degredation through ubiquination dropping off MPS activity

Cell Bio 1-4 (4 decks)

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