CHAPTER 14

Cellular Reproduction

1

Overview of the cell cycle

DNA replicationDNA Damage and repair

Nuclear and Cell Division

Regulation of the Cell cycleGrowth Factors and Cell Proliferation

WILL NOT BEIncluded in the exam

2

Introduction

• Cells reproduce by the process of cell division.

• Mitosis leads to cells that are genetically identical to their parent.

• Meiosis leads to production of cells with half of the genetic content of the parent.

3

14.1 The Cell Cycle (1)

• The cell cycle is the series of stages that a cell goes through. It consists of the M phase and the interphase.

– The M phase includes the process of mitosis and cytokinesis.

– Mitosis last about an hour or so.

– Interphase constitutes the majority of the cell cycle and lasts longer than the M phase (~23 hrs);

– it may extend for days, week, or longer.

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An overview of the eukaryotic cell cycle

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The Eukaryotic Cell Cycle

Cell growth === Cell division=== Cell proliferation

-Duplication of DNA-Replication of DNA-DNA synthesis

---Mitosis/ Cytokinesis---Regulation of Cell cycle

Cell cycleMitosis ~0.5 hrs1-Starts--condension the chromatin2a-sister chromatids2b-nuclear envelop disorganize2c-mitotic spindle3-cytokinesis

G1 8 to 10 hrs

S 6 to 8 hrs

G2 4 to 6 hrs

~23.5 hrs

Go: the cell is out the cell cycle

GoTerminal differentiation

-Protein synthesis ?

6

The Cell Cycle (3)

• Cell cycles in vivo

– Three cell types are distinguished based on their capacity to grow and divide.

• Nerve cells have lost the ability to divide, but not all of them.

• Liver cells divides in function of stimulus

• Stem cells will divide frequently.

– Stem cells have asymmetric cell division in which the daughter cells have different fates.

7

The Cell Cycle (4)

• Control of the Cell Cycle

– Cell cycle is focused on initiation of DNA replication and initiation of mitosis.

– The cytoplasm contains factors that regulate the state of the nucleus.

• The cytoplasm of a replicating cell contains factors that stimulate initiation of DNA synthesis.

• The cytoplasm of a cell undergoing mitosis contains factors that trigger chromosomal condensation.

8

The stages of mitosis in animal and plants cells

9

Microtubule Polarity in the Mitotic Spindle

Polarity of MT

10

Microtubule Polarity in the Mitotic Spindle

Chromosome alignment and separation

Separated by microtubules, also requires additional proteins like Topoisomerase II, changes in adhesive proteins, (anaphase)and motor proteins (three different roles--mitotic motors-)

11

Mitotic Motors

1. Kinetochore microtubulesPlus & minus ends

Depolymerases binds MT and induces depolymerization(chromokinesin, C-terminal and bipolar kinesin)

2. Polar microtubules

ATP hydrolysis is require for MT sliding (C-terminal and bipolar kinesin)

3. Astral microtubules

MT associated (cytoplasmic dynein) with cell cortex at plasma membrane (actin microfilaments)Taxol: it blocks MT

depolymerization12

Cytokinesis and Cell Plate Formation in a Plant Cell

Youtube====50-year cell division puzzle solved

Vesicles from Golgi and ER

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Typical eukaryotic cell cycle --- G1, S, G2, M

---Control / Regulation Systems:

1--Appropriate time and sequence of events2--Each event must be completed3--Respond to external conditions (nutrients and growth factors)

Cell cycle control: Key Transition Points in the Cell Cycle

1

2 3

Chromosome segregation

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Cell Fusion Evidence for the Role of Cytoplasmic Chemical Signals in Cell Cycle Regulation

Specific moleculespresent in the cytoplasmthat induce the transformation

from S to G1(DNA replication genes=proteins)

from M to G1(cell cycle regulation genes=proteins)

Gene: cdc2=cell division cycle--regulate the transition from G2 to M--cdc2: protein kinase

Regulation by phosphorylation?

15

Experimental demonstration that cells contain factors that stimulate entry into mitosis

16

Cell Cycle Regulation

Mitotic M-cyclinsMitotic M-cdks

S cyclins

G1 cyclinsG1 cdks

http://www-rcf.usc.edu/~forsburg/cclecture.html

How is the cell cycle regulated?

Cdc2 (Cell Division Cycle ) =kinase

Kinase

PhosphataseSubstrate(P1)

Substrate(P2)

(Cyclins)=substrate

(Cyclin-dependent kinase)-CDK-

Cdc=cdk 17

Evidence for the Existence of MPF

Maturation promoting factor=MPF=mitotic cdk-cyclin complex

----control the G2 to M transition

18

Fluctuating Levels of Mitotic Cyclin and MPF During the Cell Cycle

Maximal Enzymatic Activity during the G2-M transition

Substrate: degradation or synthesis?

Regulation: phosphorylation or de-phosphorylation?

CDK Rel

ativ

e ac

tivity

19

Phosphorylation and Dephosphorylation in the Activation of a Cdk-Cyclin Complex

Ser= variableThr= 161Tyr=15

MPF-i

mitotic cdk-cyclin complex=MPF

MPF-a

20

Fluctuating Levels of Mitotic Cyclin and MPF During the Cell Cycle

Maximal Enzymatic Activity during the G2-M transition

Substrate: degradation or synthesis?

Regulation:?

Rel

ativ

e ac

tivity

CDK

21

The Mitotic Cdk Cycle

1-Phosphorylation of lamin in the nuclear lamina induces depolarization

2-Phosphorylation of condensin induces chromosome condensation

3-Phosphorylation of MT induces polymerization

4-Phosphorylation of Anaphase promoting degradation complex.-APC-(ubiquitin ligase)

Cell Cycle Control-I

22

The Anaphase-Promoting Complex and the Spindle Checkpoint

Mitotic CDK-cyclin

Anaphase promoting complex(ubiquitin ligase)

23

The Anaphase-Promoting Complex and the Spindle Checkpoint

Regulation of the anaphase promoting complex:Binding with cdc20

APC cdc20

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APC cdh1

-degradate mitotic cyclins

SCF controls G1/S through G2/M transitionsUbiquitin ligase-degradation.

SCF

complex

complex

p27 and p21 (cyclin-dependent-kinase inhibitors (CKIs) G1/S cyclin, Cyclin E

25

Role of the Rb (Retinoblastoma) Protein in Cell Cycle Control

Cell Cycle Control-II

G1 cdk cyclin

26

Cell Cycle Regulation

Mitotic M-cyclinsMitotic M-cdks

S cyclins

G1 cyclinsG1 cdks

How is the cell cycle regulated?

, 6

/A

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DNA Damage: p53-dependent and independent pathways

---DNA damage: ?? can not be repaired--

Cell Cycle Control-III

ATM kinase=ataxia telangiectasia mutated/mutation

ATM=Ionizing radiation

28

ATR= UV radiation

ATR kinase: Inactivation of cyclin

DNA Damage: p53-dependent and independent pathways

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http://www.epa.gov

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1. Spindle checkpoint

Kinetochore attachmentMad, Bub, Cdc20

2. DNA replication checkpoint

Completion of DNA synthesisG2/M transitionPhosphorylation of mitotic cyclin

3. DNA damage checkpoint

Cell cycle halted at various stagesp53 – guardian of the genome

Checkpoints=Cell Cycle Control

TimerCdkCyclins

A. DNA integrity (DNA damage)

B. Processes(complete)

31

General Model for Cell Cycle Regulation

RegulationNutrients

MitogensEGFPDGF

APC complex

Growth factorsExtra-cellular signals

APC / SCF complex

32

Growth Factor Signaling via the Ras Pathway

-bacteria and yeast cell proliferation/division

-mammalian cells cell proliferation/division

Nutrients

Glucose

Growth factor = mitogens

33

Growth Factor Signaling via the Ras Pathway

34

Growth Factor Signaling via the Ras Pathway

Raf=MAPkkk

MEK=MAPkk

ERK=MAPk

Mitogenic Activated Protein

Serine/Threonine

PM or endosomes

Tyrosine

35

The PI3K-Akt Signaling Pathway

Insulin (I) and Insulin-like growth factor (IGF)

36

EGF/ PDGF TGF-

(+) (-)

Cell Growth / Proliferation

Mothers Against Decapentaplegic (MAD)Small Mothers Against paralysis (SMA)

Phosphorylation of Smad

Activation of p27, p21 and p15 (Cdk inhibitors)

MAPK

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