1. VIII. CELL REPRODUCTION

2. VIII. CELL REPRODUCTION
Overview: Why Reproduce?

3. VIII. CELL REPRODUCTION Overview: Why Reproduce?
Reproduction is selected for, by definition. X X X X

4. - WHY??
Bigger is better….
As cells increase in size, they decrease in efficiency.

5. - WHY??
Bigger is better….
So selection favors growth…
But as cells increase in size, they decrease in efficiency.

6. SA/V = 6
SA/V = 3
SA/V = 1.5
The “surface area to volume ratio” decreases as something increases in size….

7. SA/V = 6
SA/V = 3
SA/V = 1.5
The “surface area to volume ratio” decreases as something increases in size….
The surface area – the membrane – limits the rate of supply of nutrients to the cell.
The volume – where all the enzymes are – represents potential production and ‘demand’ for nutrients.

8. SA/V = 6
SA/V = 3
SA/V = 1.5
So, as something gets larger, the volume increases more than the surface area… and the demand for nutrients (to meet peak productivity) grows faster than the rate at which the more slowly increasing SA can supply them. So, supply fails to meet demand, and the cell cannot meet peak productivity… it becomes less efficient.

9. - WHY??
Bigger is better….
So selection favors growth…
But as cells increase in size, they decrease in efficiency.
So, to get bigger, most organisms increase cell number, not cell size….

10. - WHY??
And with many cells, cell specialization can increase efficiency at the organismal level.

11. VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell CycleG1 G2 S
(DNA synthesis)
INTERPHASE
Cytokinesis
MITOTIC
(M) PHASE
Mitosis

12. VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle
    1.  Interphase:       a.  G1: high metabolic activity (protein synthesis) chromosomes diffuse; one DNA double helix per chromosome
               

13. VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
    1.  Interphase:
Some cell types are "stuck" in this stage when they mature... it is only "stem cells" that keep dividing.  In some tissues, all stem cells  eventually mature, so the tissue can't regenerate (neurons)

14. LE 12-15 G0
G1 checkpoint G1 G1
If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle.
If a cell does not receive a go-ahead signal at the G1 checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state.

17. VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle
    1.  Interphase
a. G1
b. S
Chromosome
duplication
(including DNA
synthesis)
Centromere
Sister chromatids

18. VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
    1.  Interphase
a. G1
b. S
c. G2

19. VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
    1.  Interphase
2. Mitosis

20. VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
1. Initiation
- Replisomes land at "origin"
- They have a variety of enzymes that work together, including:
HELICASE that unzips the double helix.
PRIMASE, an RNA POLYMERASE, that starts replication DNA POLYMERASES that make DNA.

21. - HELICASE separates strands5' 3' 3' 5'

22. 5' 3' - HELICASE separates strands
- PRIMASE lays down RNA from 5' 3' (like transcription) 5' 3'

23. 5' 3' 3' 5' - HELICASE separates strands
- PRIMASE lays down RNA from 5' 3' (like transcription)
- DNA POLYMERASE - 'knocks' primase off and adds DNA bases to the free 3' OH group.... 5' 3' 3' 5'

24. VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
So, into each 'replication fork',there is "continuous synthesis" on one strand 5'
"FORK"
"FORK" 3' 3' 5'

25. What about the other strands?
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
What about the other strands? 5' 3' 3' 5'

26. 5' 5' What about the other strands? PROBLEM!!!
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
What about the other strands? PROBLEM!!!
Only 5' phosphates available.....so they can't be extended 5' 5' 3' 3' 5' 5'

27. 5' 5' The process must start again.... 5' 3' 3' 3' 3' 5'
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
The process must start again.... 5'
Primase makes RNA 5' 3' 3' 3' 3' 5'
Primase makes RNA 5'

28. The process must start again....
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
The process must start again....
DNA POLY adds DNA 5' 3'
DNA POLY adds DNA

29. 5' 5' 5' And what happens when more DNA is opened up???? 5' 3' 3' 5'
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
And what happens when more DNA is opened up???? 5' 5' 3' 3' 5' 5' 5' 3'

30. 5' 5' 5' Continuous synthesis can continue from 3' end of DNA 5' 3' 3'
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
Continuous synthesis can continue from 3' end of DNA 5' 5' 3' 3' 5' 5' 5' 3'

31. 5' 5' 5' 5' But Primase must begin the process on "lagging" strand 5'
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
But Primase must begin the process on "lagging" strand 5' 5' 3' 3' 5' 5' 5' 5' 3'

32. 5' 5' 5' 5' ...then DNA POLY can add DNA bases to "primer" 5' 3' 3' 5'
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
...then DNA POLY can add DNA bases to "primer" 5' 5' 3' 3' 5' 5' 5' 5' 3'

33. 5' 5' 5' 5' And this happens at the other fork...... DNA is opened...
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
And this happens at the other fork DNA is opened... 3' 5' 5' 3' 5' 3' 5' 5' 5' 3'

34. 5' 5' 5' 5' Continuous synthesis occurs from the free 3' end 3' 5' 3'
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
Continuous synthesis occurs from the free 3' end 3' 5' 5' 3' 5' 5' 5' 3' 3' 3' 5'

35. VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
Discontinuous synthesis on "lagging strand" (Primase, etc) 3' 5' 5' 5' 3' 5' 5' 5' 3' 3' 3' 5'

36. 5' 5' 5' 5' 5' 5' So, BOTH STRAND HAVE "OKAZAKI FRAGMENTS...." 3' 5'
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
So, BOTH STRAND HAVE "OKAZAKI FRAGMENTS...." 3' 5' 5' 5' 5' 3' 5' 5' 5' 3' 3' 5'

37. 5' 5' 5' 5' 5' 5' NOW WHAT??? We have RNA in the DNA double helix 3'
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
NOW WHAT??? We have RNA in the DNA double helix 3' 5' 5' 5' 5' 3' 5' 5' 5' 3' 3' 5'

38. Repair DNA Polymerases cut RNA out and add DNA to 3'
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
Repair DNA Polymerases cut RNA out and add DNA to 3' 3' 5' 3' 3' 3' 3' 3' 3' 5'

39. Repair DNA Polymerases cut RNA out and add DNA to 3' 3' 5'
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
DNA Repair
Repair DNA Polymerases cut RNA out and add DNA to 3' 3' 5' 3' 3' 3' 3' 3' 3' 5'

40. Final linkage between DNA frag's made by LIGASE 3' 5'
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
DNA Repair
Final linkage between DNA frag's made by LIGASE 3' 5' 3' 3' 5' 3' 5' 3' 5' 3' 5' 3'
H2O

41. Final linkage between DNA frag's made by LIGASE 3' 5'
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
DNA Repair
Final linkage between DNA frag's made by LIGASE 3' 5' 3' 3' 5' 3' 5' 3' 5' 3'
REPLICATION COMPLETE
H2O

42. VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
Initiation
Replication at the fork
DNA Repair
Semi-conservative replication

43. VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
C. Mitosis

44. INTERPHASE PROPHASE PROMETAPHASE LE 12-6aa Centrosomes
(with centriole pairs
Chromatin
(duplicated)
Early mitotic
spindle
Aster
Fragments
of nuclear
envelope
Kinetochore
Nonkinetochore
microtubules
Centromere
Nucleus
Nuclear
envelope
Plasma
membrane
Chromosome, consisting
of two sister chromatids
Kinetochore
microtubule

45. METAPHASE ANAPHASE TELOPHASE LE 12-6ba Metaphase plate Cleavage furrow
Nucleolus
forming
Nuclear
envelope
forming
Centrosome at
one spindle pole
Daughter
chromosomes
Spindle

46. VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle
B. DNA Replication
C. Mitosis
G2 OF INTERPHASE
PROPHASE
PROMETAPHASE

47. VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle
LE 12-6da
VIII. CELL REPRODUCTION
Overview: Why Reproduce?
A. The Cell Cycle
B. DNA Replication
C. Mitosis  
TELOPHASE AND CYTOKINESIS
METAPHASE
ANAPHASE

48. VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle
B. DNA Replication
C. Mitosis  
10 µm
Nucleus
Chromatin
condensing
Chromosomes
Nucleolus
Cell plate
Prometaphase. We
now see discrete chromosomes; each
consists of two identical sister chromatids. Later
in prometaphase, the
nuclear envelope will fragment.
Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at
the metaphase plate.
Anaphase. The
chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of the cell as their kinetochore micro-
tubules shorten.
Prophase. The
chromatin is condensing.
The nucleolus is beginning to disappear.
Although not yet visible in the micrograph, the mitotic spindle is starting to form.
Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divide the cytoplasm in two, is growing toward the perimeter of the parent cell.

49. Cleavage of an animal cell (SEM)
Cleavage furrow
Contractile ring of
microfilaments
Daughter cells
Cleavage of an animal cell (SEM)

50. Cell plate formation in a plant cell (TEM)
LE 12-9b
Vesicles
forming
cell plate
Wall of
parent cell
1 µm
Cell plate
New cell wall
Daughter cells
Cell plate formation in a plant cell (TEM)