Exam 4 Lecture 2: Cell Cycle II Flashcards
Draw the mitotic spindle to explain what the following structures do:
Astral Microtubules
Kinetochore Microtubules
Interpolar Microtubules
ALL microtubule minus ends originate within the centrosomes
Astral microtubules: grow away from pole and spindle itself, anchoring spindle to cell membrane
Kinetochore microtubules: bind to sister chromatid DNA
Interpolar microtubules: overlap with each other in the middle, allowing for attachment points for motors
What is the focus of the spindle pole?
AKA what structure is at the poles?
The centrosome is the focus of the spindle pores
ALL microtubule minus ends emenate emenate from this structure
Within a centrosome, you have two centrioles
Centriole Replication:
Centriole Replication occurs during ____ phase
The two centrioles seperate, and then duplicate during ___ phase
At the beginning of ___ phase the complex splits in two and the two pairs seperate
The microtubules nucleate on the mother’s only to form an ____
Centriole Replication occurs during G1 phase
They then seperate.
Each mother centriole replicates to form a daughter during S phase (now you have four)
Then at the beginning of M phase, the complex splits in two and the two pairs seperate
The microtubules nucleate on the mother’s only to form an aster.
Microtubule Motors Organize the Spindle:
Explain the role of dyenin and kinesin
Motor proteins kinesin and dynein organize tubules into a bipolar array, and centrosomes form spindle poles.
The kinesins walk towards plus end, pull apart stuff overlapping in the middle
Dynenin walk towards minus end, help pull the entrie thing apart… dynenin also bound to cell membrane
Explain how the chromosomes segregate in Anaphase A and Anaphase B
Anaphase A: where the sister chromatids seperate, drivien by microtubule depolymerization and flux
Anaphase B: drags spindle pulls further away to make adequate room for cleavage furrow, this is driven by motors (dynenin specifically)
Motor proteins ____ and ____ organize the spindle by cross-linking microtubules and generating force that focuses the poles:
_______ do antiparallel cross-linking
________ do outward push
Motor proteins kinesin and dyenin organize the spindle by cross-linking microtubules and generating force that focuses the poles.
Antiparallel cross-linking by kinesin-5
Outward push by kinesin-4,10
The ____ is the structural attachment point for the microtubules
The kinetochore is a structural attachment point for the microtubules
The kinetochore microtubules connect to the kinetochore that is on the centromere region of the chromosome
Explain centrosome vs centromere
Centrosome: two centrioles, anchors microtubules at the poles to form the spindle
Centromere: heterochromatin region on sister chromatids that serves as the anchor site for kinetochore MTs
Explain how the chromosomes even become attached to the microtubules
In late prophase, the nuclear envelope starts to dissapear, and then in early prometaphase the kinetochore MTs laterally attach to the chromosomes
The lateral attachment and movement is rapidly converted to an end-on attachment so that by metaphase they are all lined up appropriately.
The microtubules attach to the correct side of the kinetochore by ______
Increased _____ solidifies the attachment, while decreased _____ destabilizes it.
The most stable attachment is when ____
Microtubules attach to the correct side of the kinetochore by trial and error.
Increased tension solidifies the attachment, while decreased tension destabilizes it.
The most stable attachment is when they are being pulled in opposite directions.
What force stabilizes microtubule attachment to the sister chromatids?
TENSION stabilizes MT attachment into the chromosomes.
What best describes a centromere?
Centromere: heterochromatin that holds sister chromatids together, anchor site for kinetochore MTs
What are the three major forces driving chromosome positioning?
Three Major Forces driving Chromosome Positioning:
- Depolymerization of tubulin at the plus and and ratcheting of the kinetochore attachment
- Microtubule flux (treadmilling)
- Polar ejection force
Explain the depolymerizaton of microtubules near the kinetochore
Depolymerization of microtubules at the kinetochore tends to move the chromosomes towards the spindle (away from the middle)
LOOK at the picture
Explain “microtubule flux”
Depolymerization near the ____ is balanced by polymerization near the ____, resulting in treadmilling.
Microtubule Flux:
Depolymerization near the spindle is balanced by polymerization near the kinetochore, resulting in treadmilling of the microtubule
Explain “polar ejection force”:
______ motors attached to the arms of the chromatids push the chromosomes away from the poles
Kinesin motors attached to the arms of sister chromatids push the chromosomes away from the poles
The Kinesins walk down an interpolar microtubule to bring the chromosome toward the middle plate
This force pushes chromosomes AWAY from the spindle pole
Cytokinesis:
_____ & _____ make up the contractile ring
ACTIN AND MYOSIN make up the contractile ring
Myosin sits directly ontop of the actin
What is the midbody?
Midbody is the bridge between the two cells pulling apart during cytokinesis
_____ double ring forms at the midbody during abcission
Septin double ring forms at the midbody during abcission
The contractile ring is regulated by ______
The active form of it (_______) binds to ____, which promote the assembly of actin filaments.
It also binds to _____, which phosphorylate the myosin light chain, thereby activating myosin.
The contractile ring is regulated by GTPase RhoA
The active GTP bound form of RhoA binds to formins, and promotes the assembly of the actin filaments.
It also binds to Rho-activated kinases, which result in the phosphorylation of the myosin light chains, thereby activating myosin.
Explain the RhoA activation cascade:
In order to get the contractile ring to happen, which thing is most important to localize?
Localize the Rho GEF at the metaphase plate
How does the cleavage furrow know where to form?
Name the three possible models of contractile ring positioning
Three models for how the cell knows where to position contractile ring:
- Astral stimulation model (astral MTs carry furrow inducing signals to cortex)
- Central Spindle Stimulation Model (the spindle midzone generates cleavage inducing signals)
- Astral Relaxation (signal is strong at poles, weak at equator)
Mitosis vs Meiosis:
Mitosis occurs all the time in _____ cells, replacing cells that die and allowing growing and remodeling of tissues. Daughter cells are identical, and are ____ (full chromosomal complement, 2 copies of each chromosome)
Meiosis only occurs in ___ cells, and produces ____ These only have one copy of each chromosome
Mitosis: occurs in somatic cells all the time, daughter cells are identical to parent and are diploid (full chromosomal complement - 2 copies of each chromosome)
Meiosis: only occurs in germ cells, and produces haploid gamates
When does recombination occur?
What are the two advantageous things about recombination?
Recombination occyrs during Meiosis 1 (metaphase)
Two advantageous things about recomb:
- ability to get genetic variability
- acts as a crosslink to keep the chromosome pair together so that the cell can divide correctly
For asymmetric cell division, the cell components have to be _______
For asymmetric cell division, the cell components have to be segregated.
What is the term for when multiple nuclei share the same cytoplasm, aka it is “mitosis without cytokenesis”?
Syncytium: when multiple nuclei share the same cytoplasm
What proteins stimulate the start of the cell cycle?
Mitogens bind to receptors that activate a signal transduction cascade, ending in expression of genes for growth and division.
These division stimulating signals are balanced by inhibitory regulators so that cell division doesn’t get out of control.
DNA Damage Arrests the Cell Cycle:
Activation of kinases results in activation of ___, a regulatory protein that promotes the expression of ____ (which promites inhibits Cdk’s).
If ____ doesn’t work cells will continue to divide despite DNA damage.
Activation of kinases results in activation of p53, a regulatory protein that regulates the expression of p21, which inhibits Cdk’s.
If p53 doesn’t work, cells will divide anyway despite DNA damage.
What is the name for the gene that inhibits muscle cell growth?
Myostatin is the gene that inhibits muscle cell growh
That giant muscular bull had a mutation in his myostatin gene
The crossover point of recombination is called ____
Crossover point of recombination: chiasma
Which meiosis looks more like mitosis?
Meiosis II looks like mitosis
