1. Aim: How is the cell cycle regulated?
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3. A Cell’s Life Cycle
Figure 3–23 The Cell Life Cycle.

4. 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 cells

5. A Cell’s Life Cycle
Figure 3–23 The Cell Life Cycle.

6. 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

7. 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

8. 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

9. 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.
A defective cell will divide an not undergo apoptosis.

10. Pericentriolar material1
Early
Late
(d) ANAPHASE
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
(a) INTERPHASE
Centrioles
Centrosome:
(f) IDENTICAL CELLS IN INTERPHASE
Cleavage furrow
(e) TELOPHASE
(c) METAPHASE
Cleavage
furrow 2 3 4 5 6
(b) PROPHASE
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
Metaphase plate
Chromosome
all at 700x LM
Centromere
(two chromatids
joined at
centromere 1
Early
Late
(d) ANAPHASE
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
(a) INTERPHASE
Centrioles
Centrosome:
Cleavage furrow
(e) TELOPHASE
(c) METAPHASE 2 3 4 5
Cleavage
furrow
(b) PROPHASE
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
Metaphase plate
Chromosome
all at 700x LM
(two chromatids
joined at
centromere
Centromere 1
Early
Late
(d) ANAPHASE
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
Chromosome
(a) INTERPHASE
Centrioles
Centrosome:
(c) METAPHASE 2 3 4
Cleavage
furrow
(b) PROPHASE
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
Metaphase plate
all at 700x LM
(two chromatids
joined at
centromere
Centromere 1
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
Metaphase plate
(a) INTERPHASE
Centrioles
Centrosome:
(c) METAPHASE 2 3
Late
Early
(b) PROPHASE
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
all at 700x LM
Chromosome
(two chromatids
joined at
centromere
Centromere 1
Late
Early
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
Chromosome
(two chromatids
joined at
centromere
(a) INTERPHASE
(b) PROPHASE
Centrioles
Centrosome:
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore 2
all at 700x LM
Centromere 1
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
(a) INTERPHASE
Centrioles
Centrosome:
all at 700x LM

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

12. 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)

13. Slower mitotic rate means longer cell life
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.
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

14. Tumors and Cancer Cancer develops in steps Abnormal cell Primary tumor
Metastasis
Secondary tumor
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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

16. Regulating the Cell Life Cycle
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings