I. The key roles of cell division

A. Reproduction, Growth, and Repair

B. Distributes identical sets of chromosomes to daughter cells.

1. GenomeGenome = all the genes in a cell; an organism’s genetic material

C. Terms you should know

1. Somatic cells =

2. Gametes =

3. Gene =

4. Chromatin =

5. Chromosome =

6. Sister Chromatids =

7. Centromere =

8. Mitosis =

9. Cytokinesis =

10. Meiosis =

11. Parent cell = 12. Daughter cells = 13. Centrosome = 14. Mitotic spindle = 15. Kinetochore =

16. Centriole =

II. The Mitotic Cell Cycle

A. An overview

1. Mitosis or the “Mitotic (M) Phase” includes mitosis and cytokinesis -- this is the shortest part of the cell cycle.

2. Interphase -- 90% of the cycle. Divided into 3 subphases:

a. G1 phase (“first gap”) -- Cell grows (makes proteins and organelles)

b. S phase (synthesis) -- chromosomes are copied (DNA replication)

c. G2 phase (“second gap”) -- Cell grows (makes proteins and organelles)

G1, S, G2 Prophase Prometaphase

B. Mitosis : the phases

1. Prophase, Prometaphase, Metaphase, Anaphase, Telophase

C. Mitosis: a closer look…refer to book for details

D. The mitotic spindle distributes chromosomes to daughter cells

1. Made of microtubules and associated proteins (while assembling, microtubules of cytoskeleton disassemble providing material)

a. assembly takes place in the centrosome which also contains the centrioles.

3. At the end of prophase some spindle microtubules attach to kinetochores while others interact with microtubules from opposite pole.

a. protein and specific sections of chromosomal DNA at the centromere of a duplicated chromosome

4. During metaphase, the Metaphase plate is formed

a. plane midway between poles where chromosomes are aligned.

5. During anaphase kinetochore microtubules shorten by depolymerizing (hydrolysis)…see picture on next slide, while nonkinetochore microtubules elongate the cell.

E. Cytokinesis: A closer look

1. In animal cell, it occurs by a process known as cleavage

a. cleavage furrow begins as a shallow groove in the cell surface near the old metaphase plate.

b. on cytoplasmic side, there is a contractile ring of actin microfilaments associated with myosin proteins

b. contraction of this ring is like pulling a drawstring until parent cell is pinched in two.

Read about the experiment that was done to show that the shortening of the microtubule occurs at the kinetochore, not that pole. Pg. 235

2. Plant cells are different due to the cell wall a. No cleavage furrow…produce a cell plate instead. b. Vesicles, made in the golgi apparatus and containing cell wall material, move along microtubules to middle of cell

where they grow together . This produces the cell plate.c. The cell plate enlarges until the vesicle walls fuse with the plasma membrane along the perimeter of the cell.d. Two daughter cells result, each with own plasma membrane and cell wall material between them.

1. Given that prokaryotes preceded eukaryotes on Earth, it is hypothesized that mitosis evolved from binary fission “division in half”

a. bacteria reproduces this way

E. Evolution of Mitosis

Bacterial chromosome is attached to plasma membrane

Copies remain attached

III. Regulation of the cell cycle

A. Sequential events of the cell cycle are directed by a distinct “cell cycle control system”

1. proceeds on its own, driven by a built-in clock

2. HOWEVER, it is regulated at certain checkpoints by internal and external controls.

3. In an animal cell, there are built in stop signals that stop the cell cycle at certain checkpoints until they are overidden by “go-ahead” signals.

4. Signals at checkpoints come from cellular surveillance (is a process completed or not?) or from outside the cell

5. Three major checkpoints – found in G1, G2, and M phases.

6. There is a G0 phase

B. Checkpoints – a closer look 1. G1 – “go ahead signal” a. if it gets signal – cell continues to S phase b. if no signal – cell goes into nondividing state (Go) 2. G2 – go ahead signal initiates M phase 3. M phase – all chromosomes lined up at the metaphase plate initiates separation of sister chromatids

C. Process of giving signals is Signal Transduction 1. Cell receiving signal has specific receptor protein in is plasma membrane

a. the binding of a messenger (molecule) to the receptor protein triggers a chain reaction involving other proteins, which relay the message to a molecule that performs a specific activity inside the cell.

D. Type of molecules that make up the cell cycle control system1. Cyclins and Cyclin-Dependent Kinases a. Cyclin-Dependent Kinases (Cdks) – proteins that activate or inactivate other proteins by phosphorylating them. b. They are “cyclin-dependent” because they are only active when attached to a cyclin. They are present in the cell at a constant concentration and usually in the inactive form. c. Cyclin – a protein that cyclically fluctuates its concentration within the cell.2. MPF – “maturation promoting factor” a. an example of cyclin-cdk complex b. triggers the cell’s passage past the G2 checkpoint into the M phase. c. Cyclins associated with Cdk molecules accumulate during interphase d. MPF initiates mitosis by phosphorylating nuclear envelope, fragmenting it. e. MPF initiates a sequence of events leading to the breakdown of its own cyclin.

E. Internal Signals 1. Anaphase does not begin until all the chromosomes are

at the metaphase plate. How does the cell know when this happens? a. Kinetochores that are not attached to spindle microtubules give off a signal that inhibits the anaphase-promoting complex (APC) to become active b. Once the APC is active it breaks down proteins holding sister chromatids together.

F. External signals

1. Presence of growth factor – protein that stimulates cells to divide

a. each cell type responds specifically to a certain growth factor or combination of different growth factors

2. Density-dependent inhibition – crowded cells stop dividing

a. when a cell population reaches a certain density, the amount of required growth factors and nutrients available to each cell becomes insufficient to allow continued cell growth

3. Anchorage Dependence – to divide, cells must be attached to a substrate

a. most cells in your body are attached to an extracellular matrix.

[Cancer cells do not exhibit density dependent inhibition nor anchorage dependence]

This is similar to cutting yourself

Anchorage Dependence