Cell Division Flashcards
relatively how much shorter are chromosomes than linear DNA itself?
About 10000X, so you need an F ton of packaging
T/F. Sister chromatids are genetically identical and share a centromere.
False, they are genetically identical but they do not share a centromere
what is a centrosome
organelle, microtubule protein organizing center
T/F. Physical position of centromere matters.
False, it can be near the end, or middle of chromosomes and configurations work just fine
how can we ID centromere DNA sequence?
budding yeast experiments, asymmetric division. ID’d 125bp centromere sequence necessary and sufficient to confer centrosome identity
neocentromeres
acquisition of a new centromere at a new chromosomal site. people with this issue typically asymptomatic, with the exception of fertility issues due to problems with meiosis
if DNA sequence is not sufficient for centrosome recognition, what is?
Histone marker CENP-A is the conserved epigenetic mark that specifies centromere identity. CENP-A has a divergent N-terminal tail from H3, and the DNA is slightly underwound at entry and exit point in the chromosome. This ID’s a unique epigenetic environment, stabling inherited over generations, that affects where centrosomes form.
what do kinetochores do?
- can drive chromosome movement through — mitotic assembly checkpoint
- assemble on centromeres and link chromosomes to microtubule plus ends
how many microtubules can each kinetochore bind?
about 20, called a kinetochore fiber
what are two varieties of microtubules
astral and polar
what does kinesin do?
kinesin walks along polar microtubules to conteract forces that would otherwise collapse the spindle
how is dynamic instability of microtubules maintained?
ends always GTP bound, but this GTP is rapidly hydrolyzed, causing the end to kink a little bit - makes protofilaments want to start to peel apart. You resist this conformational strain by having a GTP bound cap.
T/F. it’s much easier to extend an existing filament than to start a new one
True. Gamma tubulin ring complex nucleate microtubules, become a platform for the building of new microtubules.
explain the “search and capture” hypothesis of microtubule/kinetochore interaction
- centrosome is major microtubule organizing center in animal cells. centrosome can probe space around it by shooting out MTs that are rapidly growing a shrinking stochastically. When they grow and hit a kinetochore, they form a stable complex that initiates shit. “search and capture hypothesis”. if two cells enter into mitosis at the same time, they can complete division at diff times due to this stochastic MT capture process
how can a kinetochore remain bound to a microtubule while being actively depolymerized?
This is an ongoing area of research, but likely due to motor molecules at kinetochore capable of tracking depolymerization
