1. Chapter The Cell Cycle

2. Essential Knowledge
3.a.2 – In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis, or meiosis plus fertilization ( ).

3. Roles of Cell Division Reproduction (uni vs. multi) Growth
Repair/replace old or damaged cells
To distribute identical genetic material to two new daughter cells
Goal: To split the sister chromatids and give one to each new cell – to make two new cells with the correct amount of genetic info

4. Two cell types Somatic Sex Non-sex cells (all body cells EXCEPT sex)
Ex: red blood, skin, muscle
Sex
Otherwise known as gametes
Ex: sperm, egg

5. Genome The cell's hereditary endowment of DNA
Usually packaged into chromosomes (easier to manage during the cell cycle)
Prokaryotes:
Single stranded, in cytoplasm, circular in shape
Eukaryotes:
Double stranded, in nucleus, helix/spiral in shape

6. Chromosomes Made of a DNA and protein complex called chromatin
During cell division, the chromatin becomes highly condensed into the chromosomes
# of chromosomes:
Sex cell (haploid cell)
23 (no pairs)—only contains one set of chromosomes
Somatic cell (diploid cell)
46 (in 23 pairs)—contain two sets of chromosomes

7. Chromosomes vs. Chromatin
Long, thin fiber
Uncondensed
Before/after cell division
Genetic material usually in this form
Chromosome
Characteristic “X” shape
Condensed into this shape
Only during cell division

8. Chromosomes - Structure
At cell division, each chromosome has been duplicated
The duplicated chromosome consists of two sister chromatids
Centromere – the point where two sister chromatids are connected

10. Cell Cycle – 2 parts
1. Interphase - (90% of cycle) - when the cell grows and duplicates the chromosomes 2. Mitotic Phase (M) - when the chromosomes are split into separate cells

12. Interphase - parts In order: G1 - first gap S - synthesis
G2 - second gap

13. G1, S, G2
G1:
Cell grows and carries out regular biochemical functions S:
DNA is replicated or synthesized - chromosomes are replicated
G2:
Cell completes preparations
Comment: A cell can complete S, but fail to enter G2.

14. Mitotic Phase - parts
1. Mitosis - division of replicated chromosomes 2. Cytokinesis - division of the cell’s cytoplasm

15. Mitosis - Purpose To divide the 2 copies of the DNA equally
To separate the sister chromatids into separate cells

16. Mitosis Steps Prophase Prometaphase Metaphase Anaphase Telophase
Mitosis Video #1
Mitosis Video #2

17. Prophase

18. Prophase Nucleoli disappear Chromatin condenses into chromosomes
Centrioles separate to opposite ends of the cell
Mitotic spindle begins to form

19. Prometaphase

20. Prometaphase Nuclear envelope dissolves
Spindle fibers join with the kinetochore of the centromeres

21. Metaphase

22. Metaphase Centrioles now at opposite ends of the cell
Chromosomes line up on the metaphase plate
Spindle apparatus fully developed

23. Anaphase

24. Anaphase
Centromeres break and the duplicate chromosomes are pulled away from each other toward opposite ends of the cell
Cell elongates; poles move slightly further apart

25. Kinetochores
Specialized regions of the centromeres where spindle microtubules attach
Appear to “ratchet” the chromosome down the spindle fiber microtubule using a motor protein
Microtubules dissolve behind the kinetochore

27. Telophase

28. Telophase Chromosomes uncoil back to chromatin
Nuclear envelope reforms
Nucleoli reappear
Spindle fibers disappear
Cytokinesis usually starts

29. Cytokinesis

30. Cytokinesis – Animal vs. Plant
Cleavage furrow forms
Microfilaments contracts and divides the cytoplasm into two parts
Plant
Cell plate develops in between the two new daughter cells (from Golgi vesicles)
New cell wall developed around the cell plate

31. Animal Cell - Mitosis

32. Plant Cell - Mitosis

33. Evolution of Mitosis

34. Evolution, cont. Hypothesis: Mitosis has origins in prokaryotic cells
How do we know this?
Proteins involved are identical
Ex: kinetochores, protein kinase checkpoints, etc.

35. Regulation of Cell Division
Must be controlled
Rate of cell division depends on the cell type
Ex - skin: frequently
liver - as needed
brain - rarely or never

36. Checkpoints A critical control point in the cell cycle
Several are known
Cells must receive a “go-ahead” signal before proceeding to the next phase

37. G1 Checkpoint Also called the “restriction point” in mammalian cells
Places cells in a non-dividing phase called the Go phase

38. GO

39. Go Phase Non-dividing state Most cells are in this state
Some cells can be reactivated back into M phase from the Go phase

40. Protein Kinase Checkpoint - G2
Uses protein kinases to signal “go-ahead” for the G2 phase
Activated by a protein complex whose concentration changes over the cell cycle

41. GO
Protein Kinase

42. MPF M-phase Promoting Factor
Protein complex required for a cell to progress from G2 to Mitosis
Role of MPF - to trigger a chain of protein kinase activations
Active MPF has: cdk and cyclin

43. GO
Protein Kinase
MPF

44. CDK and Cyclin CDK: Cyclin: Protein Kinase
Amount remains constant during cycle
Inactive unless bound with cyclin
Cyclin:
Protein whose concentration builds up over G1, S and G2
When enough cyclin is present, active MPF is formed

45. Active MPF Triggers Mitosis
Activates a cyclin-degrading enzyme, which lowers the amount of cyclin in the cell
Result - no active MPF to trigger another mitosis until the cycle is repeated

46. Growth Factors External signals that affect mitosis Examples: PDGF
Density-dependent inhibition
Anchorage dependence

47. PDGF Platelet-Derived Growth Factor
Stimulates cell division to heal injuries

48. Density-Dependent Inhibition
The number of cells in an area force competition for nutrients, space, and growth factors
When density is high -
no cell division
When density is low -
cells divide

50. Anchorage Dependence
Inhibition of cell division unless the cell is attached to a substratum
Prevents cells from dividing and floating off in the body

51. Cancer Cells Do not stop dividing.
The control mechanisms for cell division have failed

52. Cell division balance
Regulation of cell division is a balance between:
Mitosis - making new cells
Apoptosis - cell suicide
Cancer can result if either process doesn’t work

53. Summary Identify the roles of cell division
Identify the composition of a chromosome.
Recognize the phases of the cell cycle.
Identify the stages and characteristics of Interphase.
Identify the stages and characteristics of Mitosis.
Recognize the mechanisms of Cytokinesis.
Recognize factors that control cell division.
Recognize the results when the regulation of cell division goes wrong.