Lecture 7 Flashcards
(28 cards)
During _____, centrosomes begin to move apart and migrate to the poles for the orientation of the
mitotic apparatus
prophase
_____ motor protein (walks towards the minus end) pulls the astral
microtubules to the cell cortex, during prophase
Dynein
_____ motor protein (walks
towards the plus end) cross-links non-kinetochore microtubules and pushes
the centrosomes apart, in prophase
Kinesin
Microtubules begin making contact with
chromosomes in _______ when the
nuclear envelope breaks down
prometaphase
true/false: microtubules are constantly extending from and drawing
back to the centrosome
true
true/false: microtubules don’t have initial unstable attachments
false
Eventually, the chromosomes become equidistant from the
poles – forming the _______
metaphase plate
The sister chromatins are held together by
protein complexes called
_______
cohesins
Cohesin linkage of chromatids is broken by the
enzyme ______
separase
Anaphase begins when the
inhibitor of separase, _______, is tagged and degraded by APC/C
securin
_______ triggers sister-chromatid separation at anaphase
Proteolysis
________: poleward
movement of the chromosomes
accompanied by shortening of
the kinetochore microtubules.
________: The separation of
the spindle poles themselves
Anaphase A
Anaphase B
What happens when all chromosomes are not properly attached?
polyploidy- some progeny have less or more chromosomes
The kinetochores of unattached chromosomes send a “stop” signal
to the cell-cycle control system at the ___________, this signal results in the blocking of the activation of APC/C, and as
a result, chromosomes remain glued together
Spindle assembly checkpoint
what are the two consequences of blocking APC/C?
It blocks the destruction of cyclins by APC/C
Cdks remain active— delays mitosis
how do we re-form the nuclear envelope in telophase?
Dephosphorylation of nuclear pore proteins and lamins at
telophase helps reverse the process
- the phosphorylation of these proteins DISASSEMBLE the nuclear envelope in prometaphase, so the de-phosphorylation reverses this!
true/false: Mitosis is complete with the formation
of nuclear envelope
true
when is the first visible sign of cytokinesis?
anaphase
__________: Requires the formation of a structure based on actin and myosin filaments (the contractile ring)
cytokinesis
Where is the plane of cleavage going to be? in cytokinesis
Perpendicular to the long axis of the mitotic
spindle, not neccesarily in the middle!
how does cytokinesis happen in plants?
cell walls! New cell wall starts to assemble inside the cell at the equator of the old spindle after the chromosome segregation- fuses to form new cell wall
what is the first level of DNA packing?
histones
what are nucleosomes made of?
DNA sequence wrapped around a core of
histone proteins
How is DNA held to histones?
DNA is held by the histones due to non-covalent bonds, especially ionic bonds between negatively charged phosphate
backbone of DNA and positive charge
of histones
