Lecture 18? - Cell Division Flashcards
What are 3 reasons cells divide?
- embryogenesis
- growth and reproduction
- wound healing and tissue repair
Prokaryotes divide by _____? What are the reproductive signals, replication of DNA, segregation of DNA molecules, and cytokinesis like?
Prokaryotes divide by binary fission
- Reproductive signal: enviroment is in optimal conditions, enough nutrients
- Replication of DNA: circular DNA, replication starts at ORI, moves bidirectionally and ends at TER sit
- Segregation of DNA molecules: replication at the center, ORI leads movement to opposite poles
- Cytokinesis: begins immediately after chromosome replication
Eukaryotes divide by ____ & ____? What are the reproductive signals, replication of DNA, segregation of DNA molcules, and cytokinesis like?
Eukaryotes divide by nmitosis & cytokinesis
- Reproductive signal: unicellular (sim to bacteria), multicellular are signals that come from internal and external enviroments
- Replication of DNA: many linear DNA. replication starts at multiple ORI sites (faster rate of division)
- Segregation of DNA molecules: complex process for seperation of sister chromatids
- Cytokinesis: different mechanisms in plants and animals
How does cytokinesis differ in plant and animal cells?
In animal cells, since there is no cell wall, the two cells form a cleavage furror prior to seperating.
In plant cells, since there is a cell wall, a cell plate forms between the two cells. The cell plate turns into a cell wall.
What phases are in the cell cycle and what happens in them?
Interphase:
- G1 (most cell growth will occur here)
- S (DNA synthesis/replication)
- G2 (spindle synthesis occurs, prep for mitosis, cell growth continues)
Mitosis:
- M (where division occurs, followed by cytokinesis)
What is cyclin?
Cyclin is a regulatory protein required for MPF. Cyclin varies in concetration.
What is MPF? Explain the complex.
MPF controls the passage from G2 to M phase, it is a M-phase promoting factor. It consists of cyclin and CDK (cyclin-dependent kinase). CDK catalyzes phosphorylation of other proteints to start mitosis. CDK needs two phosphates in order to work, both sites are phosphorylated after cyclin binds to CDK. In order for CDK to activate MPF, one phosphate is removed by phosphatase.
How many checkpoints are in the cell cycle? What is the most important one?
There are 3 checkpoints in the cell cycle. The most important is the restrictive checkpoint which is between G1 and S phase. It makes sure the cell size is adequate, there is enough nutrients, and that DNA is undamaged.
what are p21 and p53?
Theyre tumor suppressors that are used in the restrictive checkpoint. Tumor suppresors are regulatory proteins that halt cell cycle or intitate apoptosis.
What’s a chromosome? What is it made of? What does the replicated chromosome have?
A chromosome is made of chromatin which is a combination of DNA and proteins. When replicated it will have its iconic “X” shape. It will also have cohesins which will hold the sister chromatids together, and condensins which make the chromosome compact at then end of G2.
Explain how the human karyotype is made out
The human karyotype has 46 chromosomes, 23 pairs. There are always 1 pair of chromosomes at the end that are sex-linked. XY is male, XX is female. Other than those 2, there are 22 autosomes, which are non sex-linked. Each pair will have 2 chromosomes, one from dad and one from mom, this allows for genetic variation since the alleles are not the same.
How do the spindle apparatus work?
The spindle apparatus is what moves sister chromatids to opposite poles of the cells. On each pole of the cell you have a centrisome, an organelle in the cell. Each centrosome has a pair of centrioles.
What occurs in prophase? (mitosis)
- Condensation of chromosomes
- Spindle assembly
What occurs in pro metaphase? (mitosis)
- Nuclear envelope dissappears
- Chromsome attachment to spindle
What occurs in metaphase?(mitosis)
- Alignment of chromosomes to the center
