1. How Cells Divide

2. Bacterial Cell Division
Bacteria divide by binary fission.
the single, circular bacterial chromosome is replicated
Occurs in the NUCLEOID region
Clonal- offspring cell is identical to parent cell

4. Eukaryotic Chromosomes
-linear chromsomes
-every species has a different number of chromosomes
-composed of chromatin – a complex of DNA (40%) and proteins (histones) (60%)

6. Eukaryotic Chromosomes
Karyotype: the particular array of chromosomes of an organism
Chromosomes vary in
Size
Staining properties
Location of centromere
Length of arms

7. Eukaryotic Cell Cycle The eukaryotic cell cycle has 5 main phases:
1. G1 (gap phase 1)
2. S (synthesis)
3. G2 (gap phase 2)
4. M (mitosis)
5. C (cytokinesis)
G0 (resting phase)
The length of a complete cell cycle varies greatly among cell types.
Interphase

8. Time proportions for each cycle

9. Interphase Interphase is composed of: G1 (gap phase 1) S phase
time of cell growth
Usually longest phase
S phase
synthesis of DNA (DNA replication)
2 sister chromatids are produced
G2 (gap phase 2)
chromosomes condense, growth, organelles replicate, spindle assembles

11. Mitosis Mitosis is divided into 5 phases: 1. Prophase 2. Prometaphase
4. Anaphase
5. Telophase

12. Mitosis
Prophase:
Chromosomes continue to condense and first become visible
Centrioles move to each pole of the cell
Spindle apparatus is assembled
Spindles form between centrioles
Nuclear envelope dissolves
ER re-absorbs its components

14. Mitosis Prometaphase: Nondisjunction can occur
Chromosomes become attached to the spindle apparatus
Sister chromatids are connected to opposite poles of the spindle
Microtubules begin to pull each chromosome toward the center of the cell
Nondisjunction can occur

16. Mitosis Metaphase: Karyotyping
Microtubules pull the chromosomes to align them at the center of the cell, equidistant from both poles
Metaphase plate: imaginary plane through the center of the cell where the chromosomes align
Chromosomes are most condensed here
Karyotyping

19. Mitosis Anaphase: Microtubules pull sister chromatids toward the poles
In anaphase A, sister chromatids are pulled apart towards poles
In anaphase B the poles move apart
Cell becomes visibly elongated
Shortest phase

21. Mitosis Telophase: Spindle apparatus disassembles
Tubules broken down which will be used to create cytoskeleton of daughter cells
Nuclear envelope forms around each set of sister chromatids
Chromosomes begin to uncoil
Uncoiling permits gene expression
Nucleolus reappears in each new nucleus

23. Cytokinesis Cytokinesis – cleavage of the cell into equal halves
In animal cells –cleavage furrow
In plant cells –cell plate
Organelles go with whatever side of the cell they happen to be on
As long as there are a few organelles on either side, the cell can make more