Lecture 6: The cell Cycle Flashcards
What is the period of regular cell growth, metabolic activity and repair called?
Interphase, it includes G1, G2,S
In which phase does DNA replication take place?
S phase (synthesis phase)
What happens in M phase
The nucleus and cytoplasm divide
Mitosis: nuclear division
Cytokinesis: cytoplasmic division
What cells don’t divide in the body?
- Many mature cells do not divide: like terminally differentiated cells like nerve cells, muscle cells, red blood cells as they become differentiated they loose the ability to divide
- Some cells only divide when given an appropriate stimulus: like liver cells divide when damages
- Some divide normally on an ongoing basis : epithelial stem cells
Which phase does non-diving cells come under
G0, they don’t divide but are normal and are not dead. But some cells go from G0 to G1 then S-phase -G2 and then M phase
What is the cell-cycle control system?
This delays later events until the earlier events are complete and has 3 major check points:
START CHECPOINT or transition (G1-S):
G2-M transition
Metaphase -to-anaphase transition also called spindle assembly check point
What is the start transitions
Phase before S phase - G1
What do problems in checkpoints cause
Chromosome segregation defects
What is cell progression controlled by?
By molecular switches, and is triggered by cyclin-dependent protein kinases.
Cdks-complexes are activated for entry then inactivated
Entry into M-phase is regulated by M-Cdk and phosphorylates other regulatory proteins
What is the first phase after interphase and what happens in it ?
It is prophase, this occurs after interphase. During the G1 phase, centrosomes duplication initiated and completed by G2.
S-phase: chromosomes replicates (decondensed)
In prophase the replicates chromosomes condense and nito tic assembly starts
What are deposited on the chromatids in S-phase and what happens in end of G2 phase
Cohesins are deposited to hold the two sister chromatids together and at the end of G2, condensions makes the replicated chromosomes compact
What are the steps happening in prophase?
1) chromosome condensation and sister chromatid resolution takes place
Cohesins are removed from chromosomes arms, but not from the centromers
Condensing condenses DNA in each sister chromatid
And in order for mitotic spindle assembly to start, it requires disassembly and reassembly of microtubles and needs duplicated centrosomes
How many fibrils are required in a cebtriole?
It needs nine fibrils of 3 microtubles pairs
How many times are centrosomes duplicated ans when is it initiated and when is it completed by
It is duplicated once per cell cycle, and is initiated in G1, and completed by G2
How are centrioles duplicated?
They are semi-conservative
When does mitotic spindle assembly start?
In prophase (M phase) this need ms assembly and is assembly of microtubles dynamics
Next is nuclear envelope breakdown
When does nuclear envelope breakdown occur
Between prophase and prometaphase
How can you break down nuclear envelope?
Phosphorylation of lamins and nuclear pore proteins trigger the disassembly of nuclear envelope into small membrane vesicles
What are the steps in prometaphase?
Once the nuclear envelope is disassembled, mitotic spindle assembly can be completed, the KINETOCHORE microtubules in the mitotic spindle attach to the duplicated chromosomes and the chromosome movement begins
What does mitotic spindle assembly and function require?
Microtubule dynamics (disassembly and assembly)
Microtubule motor protein activity (kinesins and cytoplasmic dynein)
What do astral microtubules do!
They help to position the mitotic spindle
What do non-kinetochore microtubules do?
They cross linked microtubules throughout the mitotic spindle like kinesin-5 other microtubules-associated proteins
What do kinetochore microtubules do?
They attach duplicated chromosomes to the spindle poles
Where are kinetochore microtubles attached and located?
They are located at the centromere of chromosomes. One kinetochore for each sister chromatid in The duplicated chromosome. The kinetochore likes to bind at the plus end of the microtubules.