Cellular Reproduction: Mitosis & Cytokinesis (4) Flashcards
prophase
nuclear envelop disappears & c’somes condense (lamins)
prometaphase
mitotic spindle forms: c’somes attach to spindle
metaphase
c’somes aligned along equator
anaphase
chromatids separate; c’somes migrate to poles
telophase
c’somes decondense; nuclear envelope forrms
mitosis
process of partitioning newly replicated chromosomes into separate parts of the cell
astral microtubules
radiate from centrosome, form aster (centrosome is essentially a microtubule organizing center)
Help mitotic apparatus, determine cleavage
kinetochore microtubules
attach to chromosomes at kinetochore; pull chromosomes to diff poles
polar microtubules
connect to opposing pair, support framework & help push centrosomes apart
Help push centrosomes apart
minus end. Lose or gain microtubules?
point toward centrosome & away from kinetochore
lose microtubules
plus end. Lose or gain microtubules?
point away from centrosome
gain
how do the + & - ends differ?
differ in rates of assembly
higher at + & low at -
what are the 2 events in spindle assembly?
Formation of Poles: spindle microtubules must “attach” or anchor to poles
Get longer & attach to microtubules
Capture of chromosomes: spindle microtubules must attach to chromosomes
when are centrosomes made?
S phase
how do centrosomes move to poles?
motor PROs
microtubule organizing center
duplication of centrosomes
what do motor PROs ensure in prophase?
microtubules are properly aligned
kinesins
walk toward + end of MT
dyneins
- end directed motor PROs, move towards _ end
how do motor PROs help align microtubules? & when does this occur?
identify plane of cell division & align accordingly
form an array during the beginning of mitosis
prophase
what determines the plane of cell division?
distance b/w 2 centrosomes
What are the 3 movements of centrosomes during late Prophase?
motor PROs help align microtubules
centrosome alignment
centrosome separation
what causes microtubules to shorten?
Dynein PRO is anchored into the membrane, when it moves towards the minus end it causes the astral microtubules to shorten & pulls
what pushes microtubules?
kinesin
what pulls microtubules?
dyneins
Centromeric heterochromatin
highly condensed DNA
non-coding, provides structure to c’some to hold in correct shape
has binding factors mediating MT
fibrous corona
outermost layer of the kinetochore
where is the region of growth in microtubules? & how is it done? & where?
plus end
tubulin subunits added to continue growth
kinetochore
where do the microtubules attach?
outermost layer –> fibrous corona
what mediates MT in lengthening?
centromeric heterochromatin has binding factors mediating MT
when does c’some capture occur?
prometaphase once the nuckear envelope is broken down
when are there rapid fluctuations in MT lenghth?
prometaphase during c’some capture
what generates c’some movement
MT dynamics & motors
rapid depolymerization & polymerization occurring at the + end (at kinetochore)
MT motors assist in:
maintaining flow of tubulin
tethering the kinetochore
treadmilling
no net elongation/shrinking of the MT
how was tubulin movement determined?
red labeled tubulin subunits were added to a cell
red dye is seen only at the kinetochores at first –> site of addition
red labeled subunits began to be pushed to the minus end
depolymerization in MTs
met loss at the + end & c’some moves to the right
polymerization
net gain at the + end & c’some moves away from centrosome
how is there enough room for tubulin subunits to be added?
MT PROs hold the MT far enough away from the kinetochore
spindle checkpoint
cell monitors status of events before going on to anaphase, important for the c’somes to be evenly lined up
if one of the c’somes isn’t at the metaphase plate it waits to give it a chance to get there
Mechanism of the Spindle Checkpoint
Securin holds sister chromatids
APC causes ubiquitination of securin enabling chromatids to split apart
Cdc20 activates APC (positive regulator)
MAD2PRO attaches to the kinetochore of improperly aligned c’somes inhibiting cdc20 prevents chromosomes from separating
What causes the inhibition of cdc20?
MAD2PRO
what PROprevents improper separation of c’somes?
MAD2PRO
cleavage furrow
method of cytokinesis in animals
constriction occurs with a contractile ring
contractile PRO (actin & myosin II) slide past each other shortening their lengths
Actin
• cytoskeleton PRO of the cleavage furrow
Pulled by myosin II causing it to shorten
Myosin II
head PRO of the cleavage furrow
Pulls actin filaments causing the actin to become smaller
What is the evidence for myosin II in cytokinesis? & what were the results?
Myosin II Knock-outs gene for myosin II is deleted
Antisense inhibition of myosin II mRNA
Antimyosin II antibodies
Bind to myosin & disrupts structure (function) resulting in an abnormal cell
results: cell that can replicate their c’somes but are unable to divide –> results in large, multinucleated cells
Why is binding an antibody useful in PRO inhibition?
high specificity
binding an antibody to a PRO may disrupt the normal function of the PRO due to steric hindrance
what is an ex of mitosis without cell division? & how can we study nuclei?
early insect embryos –> syncytial blastoderm
nuclear divisions occur without cell division creating a big, nucleated cell to enhance PRO production. Once there is enough PRO, membranes will form around the nuclei
GFP labeling of c’somes
what is the benefit of multinucleated cells?
rapid gene expression –> lots of PRO & RNA
what is an ex of cell division wtihout DNA rep?
meiosis
2 sequential cell divisions without an intervening phase of replication
