1. Notes: Cell Division & the Cell Cycle (Ch. 12)

2. One of the major characteristics of a living thing is the ability to GROW.
What does growth mean in terms of the cell? Bigger cells or more cells?

3. cell size is limited by its surface area to volume ratio (SA:V)
Why more cells?
cell size is limited by its surface area to volume ratio (SA:V)
if a cell gets too large, it wouldn’t be possible for it to get oxygen/nutrients in and wastes out by diffusion

5. Cell Division
In simple terms: 1 cell divides into 2 new cells

6. 3 main stages of the Cell Cycle
Interphase
longest stage (90%); preparation for cell division
Mitosis (10%)
nucleus divides into 2 nuclei, each with the same # and kind of chromosomes (DNA) as the parent cell
Cytokinesis
cytoplasm divides forming 2 distinct cells

7. Cell Cycle G1 = growth (producing proteins & organelles)
S = DNA Synthesis (duplicated) & more growth
G2 = growth & completes preparation for division

8. MITOSIS = the division of the nucleus
Why is it important that the nucleus divides?
it stores the DNA (information of life)
all new cells need this information

9. Chromosomes = tightly coiled chromatin (DNA); consist of 2 identical chromatids (sister chromatids); which are connected in the center by a CENTROMERE
**a human cell entering mitosis contains 46 chromosomes (=DIPLOID number)

10. chromosome
centromere
chromatin
DNA

11. How Does Chromatin Coil so Tightly?
Chromatin wraps around 8 histone proteins
A second type of histone (H1) holds the nucleosome “beads” together to increase compaction further

13. Next: the stages of MITOSIS!

14. Prophase Prometaphase Metaphase Anaphase Telophase
Mitosis is one, continuous event, but it can be described as happening in 5 phases:
Prophase
Prometaphase
Metaphase
Anaphase
Telophase

15. **Remember, the cell is coming out of Interphase…

16. PROPHASE chromatin condenses & chromosomes become visible
Centrosomes/ centrioles separate and start to move to the opposite sides of the nucleus;

17. PROMETAPHASE nuclear envelope breaks down and the nucleolus disappears
spindle fibers (from centrioles) connect to chromosomes at their centromeres (kinetochore);

18. METAPHASE
**chromosomes line up in the center of the cell (metaphase plate);
**fibers connect from the poles (end) of the spindle to the centromere/kinetochore of each chromosome

19. ANAPHASE
centromeres split, causing the sister chromatids to separate, becoming individual chromosomes
chromosomes are pulled apart to opposite ends of the cell

20. TELOPHASE chromosomes uncoil into chromatin;
new nuclear envelope forms around the chromatin
spindle breaks apart
nucleolus reappears in each new nucleus

22. Finally… CYTOKINESIS
in animal cells: cell membrane pinches in & divides (cleavage furrow)
in plant cells: a cell plate (new cell wall) forms

24. Then the cell returns to Interphase… and the process continues
One More Time!

26. Which of the following processes take place during interphase?SL
Cell division
Cell division & Active Transport
Active Transport & Protein Synthesis
Active Transport, Protein Synthesis, Replication of DNA

27. How are all cells formed?
By cell division
By mitosis
By fragmentation
By cytokinesis

28. Chromatids are Made of microtubules Bacterial chromosomes
Strands of duplicate genetic material
Supercoils of protein

29. What is the correct order for Mitosis?
Interphase, Prophase, Prometaphase, Metaphase, Anaphase, Telophase
Prophase, Prometaphase, Metaphase, Anaphase, Telophase
Telophase, Anaphase, Metaphase, Prometaphase, Prophase
Interphase, Prophase, Prometaphase, Metaphase, Anaphase, Telophase, Cytokinesis

30. This cell is in which phase of Mitosis?
Prophase
Prometaphase
Anaphase
telophase