1. Cell Cycle & Mitosis Meiosis

2. Context
All living things (cells) come from other living things (cells)
Cell division is necessary for:
Reproduction
Growth and development
Tissue renewal
Cell cycle – describes the life cycle of a cell

3. Somatic Cells vs. Gametes
Somatic cells – body cells
Contain entire genome within nucleus (or two copies of every chromosome)
Gametes – sex cells (i.e. sperm or egg)
Contain only half (or one copy (from mom or dad) of every chromosome)

4. Phases of the Cell Cycle
M (mitotic) phase:
When mitosis (cell division) occurs
Interphase:
G1 (Gap 1)
Cell grows
S (Synthesis aka DNA replication)
Cell replicates DNA
G2 (Gap 2)
Cell grows and prepares for cell division

5. Chromatin  DNA + proteins (histones) in eukaryotic cells
Chromosome  structures consisting of chromatin
Sister chromatid  one half of a replicated chromosome

6. Centromere  point of connection between sister chromatids
Kinetochore  protein complex found at centromere

7. Centrosome  organelle that organizes microtubules
Centriole  animals cells only (function unknown)

8. Phases of Mitosis (literal cell division)
1st - G2 of interphase
Nuclear envelope forms
Centrosomes (& centrioles in animal cells) appear
2nd - Prophase
Chromatin condenses into chromosomes
Mitotic spindle appears
3rd - Prometaphase
Nuclear envelope breaks up (fragments)
Microtubules attach to centromeres at kinetochore

9. 4th – Metaphase 5th – Anaphase
Chromosomes middle (metaphase plate)
Spindle fibers attached to each chromatid at kinetochore
5th – Anaphase
Two sister chromatids pull apart at centromere and move towards opposite end of cell (towards centrosomes)

10. 6th – Telophase and Cytokinesis
Two daughter nuclei form from fragments of original nucleus
Chromatin becomes less condensed
Cytokinesis – division of cytoplasm and formation of two daughter cells
Animal cells  involves cleavage furrow
Plant cells  involves cell plate (formed by vesicles!)

12. Reminder: Binary Fission (prokaryotic cell division)

13. Cell Cycle Control Frequency of cell division varies with cell type
RBCs every 24hr
Mature nerve cells never divide
Cell cycle checkpoints:

14. Cyclin-dependent kinases (Cdk)
Kinase – an enzyme that activate or inactivate other proteins by phosphorylation
Cyclin – protein who’s concentration fluctuates cyclically

15. Cancer Cancer cells derive from normal cells gone wrong
Ex: Mutation in gene that regulates cell cycle checkpoint; now cell does not stop at that checkpoint but just keeps dividing.
Cancer cells also
Have no contact inhibition
Aren’t anchorage dependent (thus metastasize)
Express vascularization proteins (bring in blood vessels to feed tumor)
And so much more.

17. Meiosis
Process whereby gametes (sex cells) are produced for sexual reproduction purposes
Eggs in female; sperm in male
Sexual reproduction  egg meets sperm = fertilization
Offspring have genetic variation
Asexual reproduction  mitotic cell division in single-celled eukaryotes (e.g. amoeba)
Clones (parent and offspring are identical)

18. Diploid vs. Haploid
In humans, each somatic cell has 46 chromosomes (23 from mom & 23 from dad) or 23 homologous chromosomes (homologues)
Somatic cells are diploid (full set of chromosomes) or 2n
Gametes are haploid (half set) or n

19. Steps of Meiosis
2 rounds:
Meiosis I (4n to 2n)
Meiosis II (2n to n)

20. Meiosis I
Interphase:
Diploid cell’s chromosomes duplicate during interphase (2n  4n)
Centrosomes replicate

21. Prophase I Chromosomes condense
Homologous pairs match up and become physically connected at synaptonemal complex via process called synapsis
CROSSING OVER  Genetic exchange of information between non-sister chromatids

22. Telophase I & Cytokinesis
Metaphase I
Homologous pairs line up on metaphase plate in tetrads
Anaphase I
Homologous pairs split up BUT sister chromatids stay together!
Telophase I & Cytokinesis
2 daughter cells, both 2n, which go on to divide again

23. Meiosis II Prophase II Metaphase II Anaphase II
Chromosomes meet at metaphase plate; sister chromatids are NOT identical (due to crossing over)
Anaphase II
Centromeres of each chromosome separate (sister chromatids pull apart)
Telophase II and cytokinesis
4 haploid non-identical daughter cells are produced

24. End Result of Meiosis 2n  4n  2n  n
Production of four haploid daughter cells all of which are genetically distinct from each other and the parent cell

26. Genetic variation Mutations in DNA
Crossing over during prophase I of meiosis followed by (hopefully) random sexual reproduction
Independent assortment of homologous pairs during metaphase I

27. Independent Assortment