D2.1 Cell Division Flashcards
What is the dividing cell referred to?
Mother cell
What are the new cells referred to?
Daughter cells
Cytokinesis
The division of a cell’s cytoplasm to form two cells.
How is cytokinesis carried out in plant cells?
1) Vesicles containing pectin line up in the middle of the cell.
2) Vesicles fuse together form a middle lamella.
2) Cellulose is added on either side to form a wall for each daughter cell.
Cytokinesis in animal cells
1) Actin and myosin proteins adjacent to the cell membrane run parallel in a ring around the equator of the cell.
2) A and M exert tension to form a cleavage furrow.
3) The membrane is pulled inwards so it eventually splits the cell.
What is an example of equal cytokinesis?
A human zygote dividing to form a two-cell embryo.
What is are examples of unequal cytokinesis?
1) Oogenesis, where the small cell is a polar cell that soon dies.
2) Budding in yeast: The mother cell develops an outgrowth with little cytoplasm that then receives its own nucleus and separates.
What happens to small cells produced by unequal cytokinesis?
They can grow and survive if they receive a nucleus and another organelle that cannot be assembled from cell components.
What do u call cells without a nucleus?
Anucleate, like red blood cells (survive for approx 120 days).
Why is nuclear division important?
- So each daughter cell can receive a nucleus and genetic information.
- Growth
- Reproduction
- Repair
Why is DNA replication important before the start of meiosis and mitosis?
- The two daughter cells produced by mitosis will have the entire genome.
- Provides enough DNA for a mother cell to divide twice in meiosis.
- Provides enough DNA for recombination by the process of crossing over.
How is DNA prepared for cell division?
1) DNA is elongated to chromatin.
2) DNA is replicated.
3) The 2 DNA molecules are condensed into structures called sister chromatins.
How does DNA condensation to chromos take place?
- DNA double helix is wrapped around histone proteins.
- Resulting structures are added together.
- Supercoiling: 10,000um of DNA packed into 1ums of chromosome.
Microtubules
Narrow tubular structures assembled by tubulin proteins.
How are sister chromatids separated?
- More tubulins are added so that microtubules extend towards the cell’s equator.
- Kinetochores at the centromere remove tubulins to make microtubules pull the chromatids to the poles.
Prophase
- Chromosomes are condensing.
- Microtubules grow from centrioles to form spindle shapes.
- Spindle microtubules extend from each pole to the equator.
Metaphase
- Nuclear membrane has disintegrates.
- Chromosomes line up at the equator,
- Spindle microtubules attach to kinetochores, sister chromatids attached to separate poles.
Anaphase
- Kinetochores shorten spindle microtubules, and the identical chromosomes are pulled to opposite poles.
- Each separated sister chromatid is now a chromosome.
Telophase
- Chromosomes have reached the pole, spindle microtubules break down.
- Chromos uncoil and the cell goes through cytokinesis.
Diplois Cell
A set of 23 homologous pairs of chromosomes.
Haploid
23 chromosomes
Prophase I
Homologous chromosomes pair up, spindle microtubules form, nuclear membrane breaks down.
Metaphase I
- Chromosomes line up randomly at the equator.
- Spindle microtubules attach to a chromosome of the pair.
Anaphase I
- Each chromosome is pulled to opposite poles of the cell.
Prophase II
- New spindle microtubules form.
Anaphase II
- Kinetochores pull chromatids to the poles.
- Sister chromatids are non-identical because of exchange of alleles in crossing.
Telophase II
- Chromosomes decondense inside, and the nuclear membrane forms.
- 4 haploid cells are produced.
Non-disjunction
When a pair of homologous chromosomes fails to separate in anaphase I.
What causes Down syndrome?
Non-disjunction in pair 21 causes a zygote with a trisomy in chromosome 21.
Bivariate
Pair of homologous chromosomes, one from each parent.
What are the ways that meiosis produces genetic variation?
1) The random orientation of bivariates in metaphase I can produce many combinations when homologous pairs separate in anaphase I.
2) Chromosomes cross over in meiosis at random chiasma, which produces various combinations of alleles.
Why is cell proliferation (repeated division of cells) needed in plants and animals?
1) Growth
2) Cell replacement for repair.
What are the two main cycles the cell goes through?
Interphase and Mitosis
What are the 3 phases of interphase?
G1: Cell synthesizes proteins and carries out its functions.
S Phase: DNA is replicated
G2: Cell grows, duplicates organelles, produces enzymes needed for division, etc..
Cylins
Proteins are used to control progression through the checkpoints that separate, and their concentration rises and falls during the cell cycle.
How do cyclins regulate teh cell cycle?
- They reach a threshold concentration.
- Bind to kinase enzymes to activate them, kinases phosphorylate proteins.
- Phosphorylated proteins perform tasks specific to the cell cycle.
Mutations in what type of genes can cause tumour cells?
1) Proto-oncogenes
2) Suppressor genes that prevent uncontrolled cell division.
Tumour
A mass of proliferating cells in which normal control of the cell cycle is lost.
Primary tumours
Tumours that vary in their rate of growth.
Benign Tumour
Ts that grow slowly and are not life-threatening.
Malignant Tumour
Grow aggressively and may spread to other parts of the body.
Metastasis
The spreading of cells to form secondary cells.
Mitotic Index formula
(number of cells in mitosis)/Total number of cells
