1. Cell Division

2. Cell Division Reproduction of unicellular organisms
Growth and development from fertilized egg
Replacement of damaged cells
From emc.maricopa.edu

3. Prokaryotes (Bacteria)
Most genes are in a single circular chromosome
Reproduce by binary fission
Chromosome is replicated and equally distributed to two daughter cells

5. Vocab
Chromosomes: threadlike structures that are composed of DNA and protein
Chromatin: DNA-protein complex
Mitosis: nuclear division where duplicated chromosomes are evenly distributed to daughter nuclei
Cytokinesis: cytoplasmic division that forms two separate daughter cells

6. Cell Cycle
Sequence of events between the time a cell divides to form two daughter cells and the time those daughter cells divide
Duration varies with cell type
Nerve and muscle cells never or rarely divide once formed
Alternates between M phase and Interphase

7. Interphase The normal life activities of the cell
Consists of 3 stages:
1. G1: growth takes place
-- usually longest phase
-- increased activity of enzymes for DNA synthesis near the end of this stage

8. Cells that are not dividing usually become arrested just prior to the beginning of S phase (“G0”)
2. S: DNA synthesis
3. G2: increased protein synthesis
-- final preparations for cell division
Restriction Point: occurs late in G1, it’s the point where a cell becomes committed to divide

10. Stages of Mitosis Prophase: Nucleoli disappear
Chromatin fibers condense into observable chromosomes (sister chromatids joined at centromere)
Mitotic spindle (aggregate of a and b tubulin) forms
Centrosomes move apart

11. Prophase
From sparknotes.com

12. Prometaphase Nuclear envelope fragments
Spindle fibers extend from each pole toward cell’s equator
Kinetochores put chromosomes into motion

13. Metaphase
Centrosomes (“microtubule organizing centers”) are positioned at opposite poles of cell
Chromosomes move to metaphase plate
Centromeres of all chromosomes are aligned on metaphase plate

15. Anaphase Sister chromatids split apart into separate chromosomes
Chromatids move to opposite poles of the cell

16. Telophase and Cytokinesis
Daughter nuclei begin to form at the two poles
Nuclear envelopes form around the chromosomes from fragments of parent cell’s nuclear envelope
Nucleoli reappear
Chromatin fibers uncoil

18. Mitosis and Cytokinesis

19. Cell Cycle Controls
1. Cell density: crowding of cells inhibits cell division
2. Presence of growth factors and essential nutrients
3. Cell size (surface area to volume ratio)

20. Regulatory Proteins
Cell cycle events are regulated by changes in activity of regulatory proteins (protein kinases)
Protein kinases: enzymes that catalyze transfer of a phosphate group from ATP to target protein
Phosphate group creates conformational change to activate or inactivate protein

21. Cyclins
Regulatory proteins that control cyclical changes in kinase activity
Protein kinases that regulate cell cycles are cyclin-dependent kinases (Cdks)
Cdks are only active when attached to a particular cyclin
[Cdk] stays the same through cell cycle, but activity changes as [cyclin] changes

22. Example of a Cdk MPF (maturation promoting factor)
Active MPF phosphorylates chromatin proteins, so chromosomes condense in prophase
Cyclin accumulates during Interphase
Cyclin combines with Cdk to form active MPF, so as [cyclin] rises and falls, active MPF changes in the same way

23. Active MPF activates proteins that participate in mitosis and initiates prophase
Near the end of mitosis, cyclin is destroyed by an enzyme that is activated by MPF
Destruction of cyclin causes decline in active MPF at end of mitosis
Continuing cyclin synthesis raises the concentration again during Interphase

24. CDK and Cyclin