1. Where the magic happens!
Cell Division
Where the magic happens!

4. Remember Cell Theory? Q: What was cell theory?
A: All living things are made of cells AND that all cells come from other cells.
This part of the unit is going to be about HOW cells come from other cells.

5. Basic idea: get bigger and split
The cell’s overall goal is to divide into two cells. To do this it needs to give each new ‘daughter’ cell:
- all the necessary organelles
- a copy of the entire genome
Q: What is the ‘genome?’
A: The entire set of genetic information in an organism

6. The Eukaryotic Genome
In each of our bodies’ cells (with some exceptions) there are 46 chromosomes.
Each chromosome can have tens of thousands of genes.
Each gene can be composed of more than a hundred thousand base pairs.

7. Difference between Mitosis and Meiosis?
Eukaryotic cell division (mitosis) consists of:
Mitosis, the division of the nucleus
Cytokinesis, the division of the cytoplasm
In meiosis
Sex cells are produced after a reduction in chromosome number

8. Separation of sister chromatids
Each duplicated chromosome
Has two sister chromatids, which separate during cell division
0.5 µm
Chromosome duplication (including DNA synthesis)
Centromere
Separation of sister chromatids
Sister chromatids
Centromeres
A eukaryotic cell has multiple chromosomes, one of which is represented here. Before duplication, each chromosome has a single DNA molecule.
Once duplicated, a chromosome consists of two sister chromatids connected at the centromere. Each chromatid contains a copy of the DNA molecule.
Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells.

10. Chromosomes Our genome is composed of Chromosomes (‘colored bodies’)
Each chromosome can range from 25 million to 250 million base pairs.

11. Some chromosomal vocabulary
Chromosome
Chromatid
Centromere
Centriole
Spindel Fibers

12. The Cell Cycle Two main phases:
Interphase: replicating chromosomes and growth
Mitotic Phase: separating chromosomes and splitting the cell

13. BAM!!! What's going on in the cell in respect to time.
INTERPHASE G1
S (DNA synthesis) G2
Cytokinesis Mitosis
MITOTIC (M) PHASE

14. Interphase is broken up into 3 phases.
G1: Growth
S: ‘synthesis’ (replication of chromosomes)
G2: more growth, making the molecules needed for cell division

15. Kinetochore microtubule
Mitosis consists of five distinct phases
Prophase
Prometaphase
G2 OF INTERPHASE
PROPHASE
PROMETAPHASE
Centrosomes (with centriole pairs)
Chromatin (duplicated)
Early mitotic spindle
Aster
Centromere
Fragments of nuclear envelope
Kinetochore
Nucleolus
Nuclear envelope
Plasma membrane
Chromosome, consisting of two sister chromatids
Kinetochore microtubule
Nonkinetochore microtubules

16. TELOPHASE AND CYTOKINESIS
3. Metaphase
4. Anaphase
5. Telophase
Centrosome at one spindle pole
Daughter chromosomes
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Spindle
Metaphase plate
Nucleolus forming
Cleavage furrow
Nuclear envelope forming
Figure 12.6

17. Mitotic Phase
The process of a single cell splitting into two daughter cells.

18. Prophase Chromatin condenses into identifiable chromosomes
Mitotic spindle begins to form (yay for microtubules)
Centrosomes move apart
Q: What are the structures in the centrosomes that form microtubules?
A: Centrioles! Remember- they are not found in plants!
Prophase

19. Prometaphase Nuclear envelope fragments
Kinetochore microtubules attach to centromere region
Centrosomes are at or near poles of cell

20. Metaphase
Mitotic spindle has lined the chromosomes up at the metaphase plate.
Centrosomes are at poles and begin to elongate cell

21. Anaphase
Kinetochore microtubules begin to pull apart sister chromatids
Spindle apparatus continues to elongate cell
Q: How are sister chromatids different?
A: they aren’t! Barring mutation, they should be identical!

22. Telophase Kinetochore microtubules detach Nuclear envelopes reappear
Chromosomes begin to unpack
Cleavage furrow begin to form
Q: What is actin?
A: a globular protein monomer

23. Cytokinesis
Cleavage furrow (made of actin – microfilaments) contracts to pinch cell in half. Results in two daughter cells.
Q: How is cytokinesis different in plant cells?
A: they need to form a new cell wall – they do this by forming a ‘cell plate’

24. (b) Cell plate formation in a plant cell (SEM)
In plant cells, during cytokinesis
a cell plate forms
Daughter cells
1 µm
Vesicles forming cell plate
Wall of patent cell
Cell plate
New cell wall
(b) Cell plate formation in a plant cell (SEM)

25. Summary Interphase: grow and replicate Prophase: condense
Prometaphase: nucleus bye bye
Metaphase: line up on the plate
Anaphase: pull ‘em apart
Telophase: nucleus hello and decondense
Cytokinesis: cleavage

26. Got it!?!?! You ok? Or feel like this?

27. Question
Your homework will ask you about prokaryotic cell division. How is eukaryotic cell division similar to prokaryotic and how is it different?
Discuss with people on your table.

28. Binary Fission Prokaryotes (bacteria)
Reproduce by a type of cell division called binary fission

29. In binary fission: The bacterial chromosome replicates
The two daughter chromosomes actively move apart
Origin of
replication
E. coli cell
Bacterial
Chromosome
Cell wall
Plasma
Membrane
Two copies
of origin
Origin
Chromosome replication begins.
Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. 1
Replication continues. One copy of the origin is now at each end of the cell. 2
Replication finishes. The plasma membrane grows inward, and
new cell wall is deposited. 3
Two daughter cells result. 4

30. Coming attractions…
We will next discuss HOW the cell cycle is REGULATED and what kinds of things happen when that regulation is not working properly. (HINT: cancer)