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Thwin_Grace_Block5_MM8_Cell Division (Mitosis (Anaphase (sister chromatids…
Thwin_Grace_Block5_MM8_Cell Division
Meiosis
Meiosis I
separates homologous chromosomes
makes cell go from diploid to haploid daughter cells
Prophase I
occupies >90% of meiosis time
crossing over may occur while homologues are held together in synapsis
crossing over is when nonsister chromatids of a homologous pair cut off a random piece of chromosome and exchange the DNA
synapsis is a protein structure that physically connects homologues across their length
synapsis holds together until late prophase
chiasmata are the X-shaped regions formed by crossing over
tetrads are the four sister chromatids of a homologous pair
Metaphase I
both chromatids of a homologous pair attach to a microtubule from opposite centrosomes
Anaphase i
sister chromatids remain attasched at the centromere and move toward the same pole
Telophase I and Cytokinesis
both daughter cells have a complete haploid set of chromosomes
each chromosome still has two sister chromatids
Meiosis II
very similar to mitosis in processes
the difference between mitosis and meiosis II is that meiosis II acts on a haploid cell, not a diploid cell
Metaphase II
sister chromatids of a chromosome may not be identical because of crossing over
Anaphase II
sister chromatids split, moving toawrd opposite poles as individual chromosomes
Telophase II & Cytokinesis
each of four daughter cells may be genetically distinct due to crossing over
Interphase
G1
first gap (growing stagge)
cell grows, produces proteins and gets nutrients
checkpoint: P53 checks for DNA damage, cyclins and cdks are also involved
G0
rest state the cell enters when it is not ready to continue on with mitosis
G2
second gap (growing stage)
centrosome has replicated, now there are 2 (each has 2 centrioles)
DNA is still a jumbled mess
checkpoint: MPF pushes cell along in cell division by phosphorylating
S (synthesis)
DNA replication occurs
cell continues to grow
Mitosis
Prophase
chromatin fibers condense into chromosomes with 2 chromatids
nucleoli disappear
mitotic spindle begins to form
centrosomes move away from each other, push apart by growing microtubules
Metaphase
longest stage of mitosis at about 20 min
centrosomes now at oposite ends of cell
chromosomes line up at metaphase plate w/ centrosomes right on the plate
Prometaphase
nucelar envelope fragments/dissolves
spindle's microtubules can invade nuclear area
microtubules attach to kinetochores of chromosomes
nonkinetochore microtubules interact with microtubules from the opposite pole of the spindle
Anaphase
sister chromatids suddenly part, becoming their own chromosome
chromosomes move toward ends of cells as microtubules shorten
cell elongates
checkpoint: APC is a positive regulator that checks that each kinetochore is connected to a microtubule
APC also destroys cohesin in kinetochores by activating separase enzyme
Telophase
2 daughter nuclei form in cell
nuclear envelopes arise
chromosomes become less dense
Cytokinesis
a cleavage furrow pinches the cell in 2
cleavage furrow is a shallow groove in the cell surface near the old metaphase plate
actin and myosin in a contractile ring deepen furrow
plants: cell plate forms between daughter cells, enlarging until fusing with the existing plasma membrane
Prokaryotic Reproduction
asexual reproduction
binary fission
parent cell equally divides into two daughter cells
budding
a single daughter cell forms as a bud off of the parent cell
sexual reproduction
conjugation
2 bacteria cells connect to each other with a conjugation pillus
if genetic material is replicated and moved into the recipient cell, it may form a different progeny
for example, if a donor cell has an HFr and tried to replicate and give the plasmid to the recipient but cannot finish it, the recipient cell may receive an incomplete F factor, becoming an F' cell
transformation
may occur when a bacteria strain that is missing a gene ad is placed in the same area as bacteria that does have that gene
when the good bacteria die, their DNA is released and the bacteria without the gene may pick the gene up
transduction
a page is a bacterial virus
a phage may enter a bacterium and incorporate into the plasmid, forming a prophage