The Cell Cycle and Cell Division

1. 7 The Cell Cycle and Cell Division AP Biology Radjewski 2012

2. Chapter 7 The Cell Cycle and Cell Division • Key Concepts • 7.2 Binary Fission and Mitosis • 7.3 Cell Reproduction Control

3. Two types of Reproduction Asexual Reproduction Sexual Reproduction Creates gametes (sex cells – sperm and egg cells) Product has genetic diversity 2 parents are involved Examples - meiosis • Faster • Creates genetically identical cells (clones) • Common in nature • Only 1 parent is involved • Examples: binary fission in prokaryotes and mitosis in eukaryotes

4. Asexual Reproduction on a Large Scale

5. Sexual Reproduction on a big scale

6. Basic Term - Chromosome • Consist of DNA and protein • 3 forms • Chromatin – 1 long strand, wrapped around histones • Chromatid – half of a chromosome • Chromosome – full X, 2 sister chromatids held together by a centromere • Contain specialized proteins called kinetochores • Homologous Chromosomes – in pairs, similar in shape, size and information (1 from Mom and 1 from Dad) - TETRAD

7. Basic Term - Chromosome

8. Figure 7.5 The Phases of the Eukaryotic Cell Cycle (Part 1)

9. Two kinds of Cells Diploid Cells Haploid Cells Chromosomes are not in pairs Abbreviated 1n Example – Gametes/Sex Cells/Sperm/Egg/Spores Human haploid # = 23 • Chromosomes are in pairs • Abbreviated 2n • Example – Somatic (body) cells, zygote • Humans diploid # = 46

10. Karyotype of Homo sapiens • Mitotic (doubled) chromosomes taken from a white blood cell at metaphase • 23 chromosome pairs, 46 total • Stained with Giemsa stain to reveal differences in the DNA/protein associations. • Banding distinctive to each chromosome • What was the sex of this individual?

11. For any cell to divide Four events must occur for cell division: Reproductive signal—to initiate cell division Replication of DNA Segregation—distribution of the DNA into the two new cells Cytokinesis—division of the cytoplasm and separation of the two new cells

12. Concept 7.2 Both Binary Fission and Mitosis Produce Genetically Identical Cells In prokaryotes, cell division results in reproduction of the entire organism. The cell: Grows in size Replicates its DNA Separates the DNA and cytoplasm into two cells through binary fission

13. Cell Cycle Interphase • 5 parts • G1 - growth • S – DNA Synthesis • G2 – prepare for mitosis • M – mitosis (PMAT) • C – Cytokinesis – division of the cytoplasm

14. Interphase 3 parts – G1,S,G2 Nucleolus and Nuclear Membrane is Visible Longest phase of the cell cycle Chromatin is visible

15. Figure 7.5 The Phases of the Eukaryotic Cell Cycle (Part 2)

16. Prophase 1st stage of mitosis Chromatin  chromosomes Centrosome and spindle fibers are visible and start to organize and move to opposite poles Pair of centrioles Nuclear Membrane and Nucleolus disappear

17. Metaphase 2nd stage of mitosis Chromosomes are lined up at the equator of the cell, connected to the spindle fibers by their centromere

18. Anaphase 3rd phase in mitosis Chromosomes  chromatids Spindle fibers pull the chromosomes apart and move them towards opposite poles

19. Telophase Last phase of mitosis Chromatids  chromatin (less compact) Nuclear membrane and nucleolus return Overlaps with Cytokinesis Animal vs. Plant

20. Cytokinesis After Interphase Division of the cytoplasm (cleavage furrow vs. cell plate) Each daughter cell contains an exact copy of DNA and are identical in every way

21. Figure 7.6 The Phases of Mitosis (1)

22. Figure 7.6 The Phases of Mitosis (2)

23. Concept 7.3 Cell Reproduction Is Under Precise Control The reproductive rates of most prokaryotes respond to environmental conditions. In eukaryotes, cell division is related to the needs of the entire organism. Cells divide in response to extracellular signals, like growth factors.

24. Concept 7.3 Cell Reproduction Is Under Precise Control Progression is tightly regulated—the G1-S transition is called R, the restriction point. Passing this point usually means the cell will proceed with the cell cycle and divide.

25. Concept 7.3 Cell Reproduction Is Under Precise Control Specific signals trigger the transition from one phase to another. Transitions also depend on activation of cyclin-dependent kinases (Cdk’s). A protein kinase is an enzyme that catalyzes phosphorylation from ATP to a protein. Phosphorylation changes the shape and function of a protein by changing its charges.

26. Concept 7.3 Cell Reproduction Is Under Precise Control Cdk is activated by binding to cyclin (by allosteric regulation); this alters its shape and exposes its active site. The G1-S cyclin-Cdk complex acts as a protein kinase and triggers transition from G1 to S. Other cyclin-Cdk’s act at different stages of the cell cycle, called cell cycle checkpoints.

27. Figure 7.10 Cyclins Are Transient in the Cell Cycle

28. Concept 7.3 Cell Reproduction Is Under Precise Control Example of G1-S cyclin-Cdk regulation: Progress past the restriction point in G1 depends on retinoblastoma protein(RB). RB normally inhibits the cell cycle, but when phosphorylated by G1-S cyclin-Cdk, RB becomes inactive and no longer blocks the cell cycle. RB + ATP  RB-P + ADP Active – blocks cell cycle Inactive – allows cell cycle to go forward