1. Cell Cycle,
Mitosis, and Meiosis
Biology is the only subject in which multiplication is the same thing as division… 1

2. The Cell cycle “Life cycle” of a cell
cell is formed from a mitotic division
cell grows & matures
to divide again
cell grows & matures to never divide again
G1, S, G2, M
liver cells
G1G0
epithelial cells, blood cells,
stem cells
brain / nerve cells
muscle cells 2

3. Cell Cycle Interphase: Divided into 3 phases: G0 Mitosis Phase
G1 = 1st Gap
cell doing its “everyday job”
cell grows
S = DNA Synthesis
copies DNA (chromosomes)
G2 = 2nd Gap
prepares for division
cell grows (more)
Mitosis Phase
cell division occurs G0
signal to divide 3

4. Replicated Chromosome
2 sister chromatids
narrow at centromeres
contain identical copies of original DNA
Centromeres are segments of DNA which have long series of tandem repeats = 100,000s of bases long. The sequence of the repeated bases is quite variable. It has proven difficult to sequence.
Why copy the DNA?

5. What if it gets out of control?
How is this process regulated/controlled?
What if it gets out of control?

6. Overview of Cell Cycle Control
There’s no turning back,
now!
Overview of Cell Cycle Control
Two irreversible points in cell cycle
replication of genetic material
separation of sister chromatids
Checkpoints regulate cycle
process is assessed & possibly halted
centromere
sister chromatids
single-stranded
chromosomes
double-stranded  

7. Checkpoint control system
3 major checkpoints: G1
can DNA synthesis begin? G2
has DNA synthesis been completed correctly?
commitment to mitosis M
are all chromosomes attached to spindle?
can sister chromatids separate correctly?
Which checkpoint will start prep for cell division?

8. Checkpoint Consequences:
If checkpoint is not met:
Exits cycle to G0 phase (only if at G1)
otherwise…
Apoptosis – cell death

9. How Do Cells Know When to Divide?
Chemical signals in cytosol
CYCLINS: Proteins that buildup in cytosol
CDK’s – “Cyclin Dependent KINASE” enzymes
always present in cytosol
bind with cyclins to phosphorylate other proteins

10. CDK’s and Cyclins More cyclins = more bonding with CDK
More CDK/cyclin complexes = cell division more likely to happen or passing checkpoints
Genes for CDK and cyclins are highly conserved through evolution.

11. Checkpoint Failure: CANCER!
Uncontrolled cell division
Loss of checkpoint control
Oncogenes turned on (growth promoter genes)
Tumor suppressor genes off
p53 major protein in checkpoint G1
Escapes apoptosis (no cell suicide)
Touch-sensor genes off
no density-dependent inhib
Blood vessel growth on
What are carcinogens?

12. Draw and label stages in notebook!
What about Mitosis?
Evolved from Binary Fission of prokaryotes
Cells start and end diploid (2N)
Two sets of chromosomes; somatic cells
Starts with 1 cell and ends with 2 cells
Stages: Prophase, Metaphase, Anaphase, Telophase with Cytokinesis
Draw and label stages in notebook!

13. Comparing Cytokinesis

14. What about Meiosis? Only when making sex cells (gametes)
Cells start 2N, but finish haploid (N)
Start with 1 cell, end with 4 cells
Increases variability by:
genetic recombination (sperm/egg)
crossing over by chromosomes
Goes through 2 cycles:
Meiosis 1 and Meiosis 2
P1M1A1T1 and P2M2A2T2

15. Meiosis 1 and Meiosis 2 How many chromosomes in the cell?
At what point are the cells haploid?
(Having 1/2 the number of chromosomes?)

16. Human male karyotype
46 chromosomes
23 pairs
2 sets

17. Homologous chromosomes
Paired chromosomes
both chromosomes of a pair carry “matching” genes
homologous = same information
single stranded homologous chromosomes
diploid 2n
2n = 4
TETRAD :
4 chromatids
double stranded homologous chromosomes

18. Crossing Over A.K.A Synapsis During Prophase 1
homologous pairs (tetrads) swap genetic material
Increases genetic variations

19. Meiosis 1 1st division crossing over occurs
single
stranded
Meiosis 1
1st division
crossing over occurs
separation of homologous pairs
2N to N (diploid to haploid)
2n = 4
double
stranded
prophase 1
2n = 4
double
stranded
metaphase 1
reduction
1n = 2
double
stranded
telophase 1

20. 4 Meiosis 2 separates sister chromatids stays haploid 4 cells at end
double
stranded
prophase 2
1n = 2
double
stranded
metaphase 2
1n = 2
single
stranded
telophase 2 4

21. Putting it all together…
meiosis  fertilization  mitosis + development
gametes 46 23 46 23 46 46 46 46 46 23
meiosis 46 46
egg 46 46 23
zygote
fertilization
mitosis
sperm
development