What are the two phases of cell division, and how are they different?
nuclear division (mitosis or meiosis), deal with the nucleus and nuclear envelope; and cytokinesis, which deals with the cytoplasm
Stages of mitosis
condensation, alignment, seperation, restoration.
Condensation (mitosis)
the nucleoli disappear, chromatic condenses into chromosomes. The nuclear envelope breaks down. The mitotic spindle is assembled (microtubules develop from the microtubule organizing centers(MTOC), and attach to a specialized region in the centromere called a kinetochore, which they then use to pull the chromosomes)
Alignment (mitosis)
Chromosomes align on the metaphase plate, and are then pulled apart into two separate sister chromatids each. One separated, the chromatids are called chromosomes.
Seperation (mitosis)
The two sets of (chromosomes, once sister chromatids) are pulled to opposite poles as tubulin units are uncoupled from microtubules, making them shorter
Restoration (mitosis)
A nuclear envelope is restored around each pole
Describe cytokinesis in plant and animal cells
In plant cells, vesicles from the golgi body migrate to the center of the cell, and fuse to form a cell plate in between the two developing nuclei. This cuts the cell in half (vesicles eventually become part of the membrane). In animals, actin(micro) filaments form a ring inside the plasma membrane between the two forming nuclei. They act like purse strings to draw the cell in half, creating a cleavage furrow.
Condensation (meiosis)
Same as mitosis, but one the chromosomes are condensed, homologous chromosomes (one of each from mum and dad) pair with each other (synapsis). Then, they form close associations called chiasmata, where geneti material is crossed over
Alignment (meiosis)
Homologous chromosomes are spread across the metaphase plate. Each pair of chromatids is pulled to a different side.
Condensation and alignment and all the other stuff part 2 (meiosis)
The two chromatids of each pair of used-to-be-sister chromatids are pulled away from each other again, forming four haploid cells.
somatic cells
body cells (diploid): anything except for gametes (haploid), sex cells
Where does genetic variation come from?
- Crossing over
- Independent assortment of homologues. The homologous chromosome from mum may go with a different homologous chromosome from dad. Yay.
- Joining of gametes from two individuals
Two functional limitations for cell size are…
- Surface area to Volume ratio. Agar cubes. The surface area becomes too small for the cell to get nutrients effectively
- Genome to volume ratio. It gets harder for the cell to produce enough to maintain its homeostasis.
Internal regulation of the cell cycle:
- Checkpoints. Multiple checkpoints throughout the cell cycle to ensure that everything is going well. If not, apoptosis (programmed cell death)
- Cyclin-dependant kinases. Kinases phosphorylate proteins to activate them. When cycling attaches to a cdk, it activates it, which then leads to a pass/fail of a checkpoint.
External factors that influence the cell cycle
- Growth factors, such as platelet derived growth factors (PDGFs), which stimulate division when they encounter damaged tissue
- Density-dependant inhibition. Cells stop dividing when their area is dense w other cells
- Anchorage dependance. Most cells only divide when attached to an external surface, like a different cell or a culture dish
Cancer?
When cells just don’t care about checkpoints and multiply a ton.
