Lecture 21 Cell Cycle and Cell Division I

8/13/2019 Lecture 21 Cell Cycle and Cell Division I

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Cell Biology

Spring 2013Dr. Melloy

Lecture 21: Cytoskeleton Research Movie,

Cell Cycle and Cell Division I

Assigned Reading: Chapter 18 (3rdedition)

Lab Report 3 due in lab this week


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Rho protein family = monomeric GTP-binding proteins affecting actin organization

lamellopodia filopodia


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Outline:

1. Cell cycle phases

2. Cyclins and CDKs

3. Cell cycle checkpoints

4. Anaphase promoting complex

5. S-Cdk and control of DNA replication6. DNA damage checkpoint

7. M phase


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Cell cycle= cycle of duplication of a cells contents followed by cell division


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Examples of essential processes of cell cycle occurring during these phases


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Cell cycle checkpoint= point in the cell cycle where progress in the cycle

can be halted until conditions are suitable for the cell to move to

the next stage; molecular brakes


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Cell cycle control and protein kinases:

Cyclin-dependent kinases (CDKs)=kinases of the cell cycle control

system; serine/threonine protein kinases

Cyclins=

proteins binding cyclin-dependent kinases (cdks)

proteins necessary for cdk function

proteins whose levels rise and fall during the cell cycle

Cyclin expressed during M phase = M-cyclin

Cdk during M phase = M-cdk


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Changing M-cdk activity during the cell cycle


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Cyclin-Cdk complex activity controlled by

cyclin association AND phosphorylation state


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Activated

M-Cdk can activate

more M-cdk through

a positive

feedback loop


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Different cyclins associate with different Cdks to trigger certain events

of the cell cycle


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APC

Cyclins are degraded by ubiquitin-mediated proteolysis

Ubiquitin ligase(E3) = Anaphase-promoting complex (APC)

( specific to M-cyclin)

Phosphorylation state of Cdks and cyclin association are not

the only forms of Cyclin-cdk complex regulation!


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Ubiquitination of proteins:

quick and specific

targeting for degradation

ubiquitin added to target protein

through an enzymatic pathway

containing three enzymes:an E1, E2, and E3 enzyme

Ubiquitination and degradation

of certain proteins is required

for chromosome segregation

E1 + ATP+Ub

E1

Ub

E2

Ub

E3

Ub

Protein X

Ub

Protein X

UbUb

Ub

Degradation by

26S Proteasome

APC


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23S-Cdk pulls the trigger on DNA replication phosphorylation of Cdc6

Cell cycle checkpoint system: control of DNA replication

Cdc6ORC

S-cdk


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Mitosis= nuclear division

Cytokinesis= cytoplasmic division


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Stages of mitosis in

newt lung cells

1

1

2

3

4

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Followed by cytokinesis

Blue= chromosomes

Green= spindleRed= actin

Also review

Panel 18-1

Lecture 21 Cell Cycle and Cell Division I

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Transcript of Lecture 21 Cell Cycle and Cell Division I