Exam 4 Ch 19 Flashcards
What controls the cell cycle?
Cyclin-dependent kinases (CDKs)
What is the accessory protein that binds to CDKs and control their activity?
cyclins
How are CDKs activated?
Activated when bound to a cyclin
What are the cell levels for CDKs like?
They do not change
What kind of cyclins do G1 cyclins have?
Cyclin D
G1 cyclin is linked to signals by what?
growth factors
G1 cyclins induce production of what?
Cyclin D, G1/S cyclins and proteins for DNA replication
What kind of cyclin do G1/S cyclins have?
Cyclin E
What cyclin gets the cell past the restriction point?
G1/S cyclins
What is the s phase?
DNA synthesis phase, Replication machinery assembled, centrosome is duplicated
What happens to the centrosome during S phase?
Centrosome is duplicated and becomes the spindle poles
What are the S phase cyclins?
Cyclin A and cyclin E
What are the S phase cyclins responsible for?
Inducing DNA synthesis: activate enzymes for DNA synthesis and loading polymerases on the DNA
DNA of homologous chromosomes is replicated in what phase?
S phase
During the S phase, there are an _n set of chromosomes
4
What are chromatids?
Identical chromosomes of replicated chromosomes
What are sister chromatids?
The two identical chromatids
Sister chromatids are held together by the ______ and ______
Centromere and cohesions
During G1 phase, how are cohesions?
Cohesins associate with the chromosomes
During S phase, how are cohesions?
As DNA is replicated, replication fork passes through the cohesion loops
After replication passes, cohesins “glue” the sister chromatids together
During the G2 phase, cell must verify:
All the DNA has been correctly duplicated
DNA is sufficient to produce two cells
Errors made during DNA replication are repaired
Any breaks in the DNA are repaired
The cell has to verify all the DNA has been correctly duplicated, DNA is sufficient to produce two cells. Errors made during DNA replication are repaired and any breaks in the DNA are repaired because
2 reasons. What are causing the errors?
Cell stress and damage due to radiation, chemicals or drugs that interfere with microtubules
At G2-M checkpoint what are the major detectors of DNA damage?
ATM (ataxia telangiectasia mutated)
ATR (ataxia telangiectasia Rad3- related protein)
DNA-PK(DNA-dependent protein kinase)
What do the major detectors of DNA damage do?
These all detect lesions in DNA
Recruit DNA repair mechanisms
If a DNA cannot be repaired– apoptosis (cell death)
What are the mitotic cyclins that induce mitosis?
Cyclin A and Cyclin B
Mitotic cylin causes entry into mitosis, what happens?
Chromosome condensation
Nuclear envelope breakdown
Mitotic spindle formation
Etc.
When does Cyclin B start producing?
Starts at S phase. Present BUT no enzyme activity until G2 phase
Cyclin B/CDK1 is present but is NOT active because _____ _____ phosphorylates CDK1 to keep it inactivated
Wee1 kinase
Once DNA replication is finished, how is mitosis induced?
Cdc25 phosphatase removes inhibitory phosphates from CDK1
How do you rapidly remove cyclin to inactivate the CDKs to induce mitosis?
By rapid destruction of the cyclins using the proteasome
APC/C is an E-3 ligase
Binds to cyclins and ubiquitinates them
But not the CDKs
This target the cyclin for destruction by the proteasome
CDK becomes inactive without the cyclin
6 stages of mitosis
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
Interphase
Chromosomes duplicated during S-phase
Centrosome duplicated
Prophase
Chromosomes condense( Chromatids attached at the centromere)
Cohesion proteins broken down so sister chromatids connected only by the centromere
(Some cohesion remind at the centromere which holds the sister chromatids together)
Nucleoli disappear
Duplicated centrosomes– now spindle poles move to opposite poles of the cell
Spindle fibers begin to form
Kinetochore assembles at the centromere of each chromosome
The kinetochore
structure forms at the centromere of the chromosomes
Kinetochore creation happens during prophase
The spindle fiber microtubules then attach to the kinetochore during the next phase prometaphase
Prometaphase
Chromosomes continue to condense
Mitotic spindle microtubules attach to the kinetochores
Nuclear envelope breaks down
How do the spindle fiber microtubules attach to the kinetochore?
Use “search and capture” mechanism
Spindle fiber microtubules use “search and capture” mechanism to attach to the kinetochore. What happens if there are inccorect attachments?
Forms unstable interactions
What is the dissolution of the nuclear envelope during interphase and in prophase
In interphase, the chromosomes are tethered to the ring of nuclear lamins just under the nuclear envelope
In prophase, nuclear lamins dissolve into the cytosol and trigger the nuclear membrane to fragment
Metaphase
Chromosomes line up at the metaphase plate
Each sister chromatid is attached to a spindle fiber via the kinetochores
Spindle fibers radiate out from the spindle poles at opposite sides of the cell
Chromosomes move to be equidistant between the two spindle poles
How does movement of chromosomes occur
Involves kinesin and dynein motor protein walking on the microtubules to position the chromosomes
Along with microtubule assembly and disassembly
Anaphase
Remaining cohesins at the centromere are destroyed
Sister chromatids are pulled apart toward opposite poles by:
Microtubule depolymerization at the kinetochore and motor proteins pulling the spindle fibers at the kinetochore and the spindle pole
Telophase
Chromosomes reach the opposite poles
Chromosomes decondense
Nuclear envelope reforms around the chromosomes
Mitotic spindle breaks down
Contractile ring forms under the membrane
Cytokinesis
Contractile ring from telophase contracts due to actin and myosin
Contraction of the ring forms a cleavage furrow
Pinches the cell into two
