Aim: How is the cell cycle regulated? Do Now: 1.Worksheet HW: Study for test tomorrow

Aim: How is the cell cycle regulated?

Do Now:1.Worksheet

HW: Study for test tomorrow

The Cell Cycle

• Most of a cell’s life is spent in a

nondividing state (interphase)

• Body (somatic) cells divide in three stages

–DNA replication duplicates genetic

material exactly

–Mitosis divides genetic material equally

– Cytokinesis divides cytoplasm and

organelles into two daughter cellsCopyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

A Cell’s Life Cycle

Figure 3–23 The Cell Life Cycle.

A Cell’s Life Cycle• Interphase

– The non-dividing period

• G-zero (G0) phase—specialized cell functions only

• G1 phase—cell growth, organelle duplication,

protein synthesis

• S phase—DNA replication and histone synthesis

• G2 phase—finishes protein synthesis and centriole

replication

• Mitosis Duplicated DNA divides into two sets of

chromosomes

Regulating the Cell Life Cycle

• Normally, cell division balances cell loss• Increased cell division– Internal factors (M-phase promoting factor,

MPF) – Extracellular chemical factors (growth

factors)• Decreased cell division– Repressor genes (faulty repressors cause

cancers)–Worn out telomeres (terminal DNA segments)

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Control of Cell Destiny•MPF- Maturation promoting factor (MPF)–Signal that induces cell division.–Consists of group of enzymes called cdc2 proteins (and proteins called cyclins.

•Cyclins build up during interphase and then activates cdc2 proteins which activates MPF which results in cell division.

•Apoptosis –Programmed cell death

Tumor Suppressor Genes• Produce proteins that normally inhibit

cell division.– Loss or alternation of p53 gene

leads to breast cancer, colon cancer, and other tumors.

–Normal p53 gene protein arrests a cell in G1 which prevents cell division.• Repair of damaged DNA and induces apoptosis in the cells where repair was not successful

Oncogenes

• Most oncogenes are mutations of certain normal genes called proto-oncogenes.

• When a proto-oncogene mutates (changes) into an oncogene, it becomes a "bad" gene that can become permanently turned on or activated when it is not supposed to be.

1

Pericentriolar material

NucleolusNuclear envelopeChromatinPlasma membraneCytosol

(a) INTERPHASE

CentriolesCentrosome:

all at 700xLM

1

LateEarly



Chromosome(two chromatidsjoined atcentromere

(a) INTERPHASE

(b) PROPHASE


Fragments ofnuclear envelope

Mitotic spindle(microtubules)

Kinetochore

2

all at 700xLM

Centromere

1



Metaphase plate

(a) INTERPHASE


(c) METAPHASE

2

3

LateEarly (b) PROPHASE



Kinetochore

all at 700xLM


Centromere

1

EarlyLate(d) ANAPHASE



Chromosome

(a) INTERPHASE


(c) METAPHASE

2

3

4

Cleavage furrow




Kinetochore

Metaphase plate

all at 700xLM


Centromere

1




(a) INTERPHASE


Cleavage furrow

(e) TELOPHASE

(c) METAPHASE

2

3

4

5

Cleavage furrow




Kinetochore

Metaphase plate

Chromosome

all at 700xLM


Centromere

1



NucleolusNuclear envelopeChromatinPlasma membrane

Cytosol(a) INTERPHASE


(f) IDENTICAL CELLS IN INTERPHASE

Cleavage furrow

(e) TELOPHASE

(c) METAPHASE

Cleavage furrow

2

3

4

5

6




Kinetochore

Metaphase plate

Chromosome

all at 700xLM

Centromere


–Rate of cell division

• Slower mitotic rate means longer

cell life

–Muscle cells, neurons rarely divide

–Exposed cells (skin and digestive

tract) live only days or hours.


Mitotic Rate

Tumors and Cancer

• Cancer develops in steps

– Abnormal cell

– Primary tumor

–Metastasis

– Secondary tumor


Tumors and Cancer

Figure 3–26 The Development of Cancer.Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Summary

• Why is interphase important to a cell?• Distinguish mitosis and meiosis.• Define apoptosis• Why are tumor suppressor genes important?

Regulating the Cell Life Cycle


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Aim: How is the cell cycle regulated? Do Now: 1.Worksheet HW: Study for test tomorrow