1. The cell cycle consists of interphase and mitosis. Interphase includes the G1, S, and G2 phases where the cell grows and duplicates its DNA. 2. Mitosis is divided into prophase, metaphase, anaphase, and telophase where the duplicated chromosomes separate and the cell divides. Cytokinesis then divides the cytoplasm. 3. Cell division is regulated by both internal and external factors like maturation promoting factors and growth factors that increase division or repressor genes that decrease division. Abnormal cell regulation can lead to tumor formation.

1. Cell Life Cycle
Figure 3–3
How do cells reproduce?
• Most of a cell’s life is spent in a nondividing
state (interphase)
• Body (somatic) cells divide in 3 stages:
– DNA replication duplicates genetic material exactly
– Mitosis divides genetic material equally
– Cytokinesis divides cytoplasm and organelles into 2
daughter cells

2. Interphase
• The nondividing period:
– G-zero 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

3. DNA Replication
Figure 3–24
• DNA strands unwind
• DNA polymerase attaches complementary
nucleotides

4. Somatic Cell Nuclear Division
Two important processes to
maintain constant number of
chromosomes.
• Duplication of chromosomes
• Distribution of duplicated
chromosomes into two daughter cells

5. 1
2 3
4
5
6 7 8
9
1
0
1
1
1
2
1
3
1
4
1
5 1
6
1
7
1
8
1
9 2
0 2
1 2
2
Y
X
X Y
The Human
Karyotype

6. 46
46
46
2N or Diploid Number
in Humans
Mother Cell
Daughter Cells
Importance of Mitosis

7. Importance of Mitosis (cont.)
• a. Cellular replacement
• b. Tissue Repair
• c. Development
• d. Tumor growth

8. Cell cycle prior to mitosis:
• Interphase: nondividing state but cell is
metabolically active.
• nucleus clearly visible
• one or more nucleoli-nucleolar organizer
regions of chromosomes.
• chromosomes long and thin
• centriole (animal cells only) located along
margin of nucleus

9. Replication of DNA and duplication
of chromosomes occurs in the cell
cycle.
Centromere
Chromatids

10. Prophase:
• prepares the cell for division
• chromosomes shorten and thicken
• centriole divides into two entities
which migrate down sides of
nuclear envelope, spindle fibers
stretch between centrioles

11. Prophase: The cell is prepared for
nuclear division
Nuclear envelope has disappeared
Spindle has formed
Chromosomes short and thick

12. Metaphase: final preparation for
nuclear division
• chromosomes line up on equatorial plate
of division
• centromeres of chromosomes attached
by kinetocores (protein) to spindle fibers,
microtubules made up of tubulin

13. A single chromosome
attached to spindle fibers

14. Anaphase: chromosome
halves migrate to poles
• centromeres divide
• chromosome halves migrate to opposite
poles of cell
• chromosomes migrate by sliding of
microtubules

15. Telophase:
• reverse of activities of prophase
• chromosomes reach poles of
cell
• spindle fibers degraded
• nuclear membrane reassembled
• chromosomes elongate
• nucleoli reassembled

16. Cytokinesis - division of the cell
• Cytokinesis occurs by constriction of actin
fibers forming a belt around cell in animal
cells
• Plant cells form a cell plate from nuclear
membrane and then cellulose is added to
the plate.

17. Animal cell - cytokinesis occurs by
constriction of actin fibers
Plant cell - cytokinesis
occurs by synthesis of
cell plate.

18. Typical Timing of Mitosis

34. What regulates cell division?
Mitotic Rate and Energy
• Rate of cell division:
– slower mitotic rate means longer cell life
– cell division requires energy (ATP)
Long Life, Short Life
• Muscle cells, neurons rarely divide
• Exposed cells (skin and digestive tract)
live only days or hours

35. Chemicals Controlling Cell Division
Table 3–4

36. Regulating Cell Life
• Normally, cell division balances cell loss
Factors Increase Cell Division
• Increases cell division:
– internal factors (Maturation Promoting Factor)
– extracellular chemical factors (growth factors)
Factors Decrease Cell Division
• Decreases cell division:
– repressor genes (faulty repressors cause cancers)
– worn out telomeres (terminal DNA segments)

37. Cancer
Figure 3–26
• Cancer illness that disrupts cellular controls and
• Oncogenes: mutated genes that cause cancer
produces malignant cells
• Cancer Stages - develops in steps:
– abnormal cell
– primary tumor
– metastasis
– secondary tumor

38. Cell Division and Tumors
• Tumor (neoplasm):
– enlarged mass of cells
– abnormal cell growth and division
Benign Tumors
• Benign tumor:
– contained
– not life threatening
Malignant Tumors
• Malignant tumor:
– spread into surrounding tissues (invasion)
– start new tumors (metastasis)

39. KEY CONCEPT
• Mutations disrupt normal controls over cell
growth and division
• Cancers often begin where stem cells are
dividing rapidly
• More chromosome copies mean greater
chance of error

40. Cell Diversity
• All cells carry complete DNA instructions for all
body functions
What makes cells different?
• Cells specialize or differentiate:
– to form tissues (liver cells, fat cells, and neurons)
– by turning off all genes not needed by that cell
• All body cells, except sex cells, contain the
same 46 chromosomes
• Differentiation depends on which genes are
active and which are inactive