1. Cell Cycle

2. describes the life cycle of a cell differs fundamentally between prokaryotes & eukaryotes shares four features among all cell types –reproductive signal –DNA replication –genome segregation –cytokinesis produces a new individual or new parts

3. Prokaryotic Cell Cycle one circular chromosome –packed on a protein frame in the nucleoid –anchored to the plasma membrane chromosome replication yields two anchored circles cell growth separates anchored circles annular pinching separates daughter cells Binary Fission

4. binary fission in a bacterium Figure 9.2

5. chromosome numbers vary widely Table 9.1

6. Eukaryotic Cell Cycle multiple linear chromosomes –wrapped on a protein frame –contained within the nucleus replication yields two complete sets of chromosomes mitosis segregates one set of chromosomes to each end of the cell cytokinesis divides the cytoplasm to form two new cells

7. Eukaryotic Cell Cycle mitosis, cytokinesis (M phase) and interphase interphase represents most of the cell cycle

8. eukaryotic cell cycle Figure 9.3 growth & biosynthesis growth & biosynthesis

9. Cell Cycle Decision Making G1 => S transition & G2 => M transitions require signals CDKs signal cell cycle transitions –Cyclin-Dependent Kinases kinases phosphorylate target proteins phosphorylation activates (some) proteins –Cyclins activate CDKs by allosteric binding Cyclins cycle

10. eukaryotic cell cycle regulation Figure 9.4 “Go!” “Don’t go!” “Radiation damage! Don’t go!” “Go!” “Okay, go!” “Go!” Replicate!

11. external signals stimulate cell division growth factors stimulate cell division –platelet-derived growth factor wound healing –interleukins immune system function –erythropoietin red blood cell production each provides information to the cell regarding the needs of the body

12. Eukaryotic Chromosomes chromsomes consist of chromatin –double stranded DNA –protein “spools” chromatin is ~1/2 DNA & 1/2 protein chromatin is highly organized –DNA wraps around histone proteins to form nucleosomes –during cell division, nucleosomes coil tightly to form highly-condensed chromatin

13. organization of chromatin Figure 9.5

14. organization of chromatin Figure 9.6

15. Replication during S phase –partially wound DNA is replicated to form two identical copies of each chromosome –two sister chromatids remain attached at the centromere each chromosome enters M phase as two linked sister chromatids mitosis separates the chromatids and distributes one to each daughter cell

16. mitosis: chromatin & cytoskeleton Figure 9.8

17. events of mitotic phases Prophase –chromosomes condense –nucleolus disorganizes –spindle apparatus begins to organize –kinetochores forms

18. mitosis: cartoon version Figure 9.8

19. Mitotic spindle apparatus Figure 9.7

20. events of mitotic phases Prometaphase –nuclear envelope is fragmented –spindle fibers bind kinetochores –chromosomes begin to migrate to equatorial plate

21. events of mitotic phases Metaphase –chromosomes are aligned at equatorial plate Anaphase –sister chromatids separate –daughter chromosomes migrate to poles Telophase –prophase is reversed

22. Animal Cytokinesis Plant Figure 9.10

23. Cytokinesis: Division of Cytoplasm Animals –annular pinching by actin & myosin ring Plants –deposition of cell plate by Golgi vesicles Organelles are distributed to daughter cells ~randomly

24. Modes of Reproduction asexual reproduction –production of genetic clones through mitotic cell divisions –common among plants (vegetative propagation) and unicellular eukaryotes –eliminates costs & risks associated with sexual reproduction –offspring lack genetic variability

25. Modes of Reproduction sexual reproduction –offspring exhibit genetic variability each bears a unique combination of parental genetic contributions –requires meiosis - reduction of chromosome number from 2n (diploid) to 1n (haploid) fertilization - combination of 1n parental contributions to produce 2n offspring

26. Fungal/animal life cycles Figure 9.12

27. Modes of Reproduction meiosis produces –gametes - animals, some protists –spores - fungi, plants, some protists produce 1n adults produce gametes fertilization (gamete fusion) produces –zygotes produce 2n adults and/or undergo meiosis

28. Modes of Reproduction meiosis –two divisions –reduces 2n parent cell to 1n products –always produces 4 haploid products begins with 4 homologous chromatids –recombination produces novel chromatids –phases resemble mitotic phases, except meiosis I - homologs pair at prophase meiosis I - homologs separate at anaphase

29. Meiosis I: cartoon version Figure 9.14

30. Modes of Reproduction meiosis I –prophase I chromosomes condense, spindle forms nuclear envelope fragments homologs pair (synapsis) crossing over

31. crossing- over occurs during prophase I Figure 9.15 Figure 9.16

32. Modes of Reproduction meiosis I –metaphase I homolog pairs align at equatorial plate –anaphase I homologs separate to poles –telophase I may or may not happen

33. Modes of Reproduction interkinesis –period between telophase I and prophase II –no replication occurs

34. Modes of Reproduction meiosis II –prophase II reverses telophase I –metaphase II chromosomes align at equatorial plate –anaphase II sister chromatids separate to poles –telophase II reverses prophase

35. mitosis => identical daughters meiosis => variable daughters Figure 9.17

36. nondisjunction at anaphase I of meiosis Figure 9.18

37. Errors of Reproduction meiotic errors may result in chromosomal disorders –aneuploidy - incorrect genetic complement nondisjuction translocation

38. Errors of Reproduction meiotic errors may result in chromosomal disorders –polyploidy 3, 4, or more sets of chromosomes can perform mitosis (reproduce asexually) 1, 3,5, etc. cannot perform meiosis

39. Cell Death death by necrosis –damage, poison, starvation death by apoptosis (programmed cell death) –discards un-needed or old cells –signals are common in many organisms –many cancers result from failed apoptosis

40. apoptosis: programmed cell death Figure 9.18

41. cell death mechanisms Table 9.2