1. CATALYST
“Energy cannot be created or destroyed but can be converted from one form to another.”
What are some ways energy is transformed/transferred in cellular respiration? In photosynthesis?

2. CELL DIVISION
The continuity of life is based on the reproduction of cells, or cell division!
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3. CELL DIVISION
Most cell division results in daughter cells with identical genetic information, DNA
A special type of division produces nonidentical daughter cells
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4. Why divide? Unicellular Organisms: Multicellular Organisms:
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5. The Cell Cycle S G1 (DNA synthesis) Cytokinesis Mitosis G2 INTERPHASE
Fig. 12-5
INTERPHASE S
(DNA synthesis) G1
Cytokinesis G2
Mitosis
Interphase consists of three phases: growth, synthesis of DNA, preparation for mitosis
MITOTIC
(M) PHASE
The Cell Cycle

6. VISUALIZING CELL DIVISION
DNA molecules in a cell are packaged into chromosomes
In 1882, the German anatomist Walther Flemming developed dyes to observe chromosomes during mitosis and cytokinesis
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7. CHROMOSOME NUMBER Is it associated with complexity?
2n / n ; haploid / diploid
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8. 0.5 µm Chromosomes DNA molecules Chromo- some arm Chromosome
Fig. 12-4
0.5 µm
Chromosomes
DNA molecules
Chromo-
some arm
Chromosome
duplication
(including DNA
synthesis)
Centromere
Sister
chromatids
Figure 12.4 Chromosome duplication and distribution during cell division
Separation of
sister chromatids
Centromere
Sister chromatids

9. THE STAGES OF MITOSIS

10. THE STAGES OF MITOSIS

11. THE STAGES OF MITOSIS

12. THE STAGES OF MITOSIS

13. Fig. 12-9
CYTOKINESIS
Vesicles
forming
cell plate
Wall of
parent cell
1 µm
100 µm
Cleavage furrow
Cell plate
New cell wall
Figure 12.9 Cytokinesis in animal and plant cells
Contractile ring of
microfilaments
Daughter cells
Daughter cells
(a) Cleavage of an animal cell (SEM)
(b) Cell plate formation in a plant cell (TEM)

14. Regulation of the Cell Cycle:
WHY IS IT IMPORTANT?

15. Internal Regulation of the Cell Cycle
Use of checkpoints, that give a stop or go-ahead signal at different points; G1; G2; Mitosis check point
2 purposes: 1) if there are errors  can abort the cell cycle (don’t want to reproduce and pass on errors) 2) rates of the cell cycle vary greatly from organisma and from cell to cell
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16. G0 G1 G1 G1 checkpoint (b) Cell does not receive a go-ahead signal
Fig G0
G1 checkpoint
For many cells, the G1 checkpoint seems to be the most important one
If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide
If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0 phase G1 G1
Cell receives a go-ahead
signal
(b) Cell does not receive a
go-ahead signal

17. Internal Regulation of the Cell Cycle
Kinases:
Cyclin-dependent kinases:
Cyclin:
MPF:
Protein kinases are enzymes that activate or inactivate other proteins by phosphorlating them (transferring a P from ATP to do work). In mitosis  kinases depend on cyclins so are called “cyclin-dependent kinases” Cyclins are proteins whose concentration varies cyclically in the cell
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18. (b) Molecular mechanisms that help regulate the cell cycle
Fig b G1 S
Cdk
Cyclin accumulation M
Degraded
cyclin G2 G2
checkpoint
Cdk
Figure Molecular control of the cell cycle at the G2 checkpoint
Cyclin is
degraded
Cyclin
MPF
(b) Molecular mechanisms that help regulate the cell cycle

19. (a) Fluctuation of MPF activity and cyclin concentration during
Fig a M G1 S G2 M G1 S G2 M G1
MPF activity
Cyclin
concentration
Figure Molecular control of the cell cycle at the G2 checkpoint
Time
(a) Fluctuation of MPF activity and cyclin concentration during
the cell cycle

20. External Regulation of the Cell Cycle
Growth factors -
Density dependence -
Anchorage dependence -
Another example of external signals is density-dependent inhibition, in which crowded cells stop dividing
Most animal cells also exhibit anchorage dependence, in which they must be attached to a substratum in order to divide
Example: platelet-derived growth factor (PDGF) is one of the numerous growth factors or proteins that regulate cell growth and division. In particular, it plays a significant role in blood vessel formation (angiogenesis).
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21. Density-dependent inhibition
Fig
Anchorage dependence
Density-dependent inhibition
Density-dependent inhibition
Figure Density-dependent inhibition and anchorage dependence of cell division
25 µm
25 µm
(a) Normal mammalian cells
(b) Cancer cells