Cell Division Flashcards
What is contact inhibition of cell growth?
Cells grow normally by detecting neighbouring cells
What happens during the three stages of interphase?
G1 – the cell makes sure that it has everything that is necessary for duplication
S – DNA replication, protein synthesis and replication of organelles
G2 – the cell checks that everything is ready to enter mitosis
What are centrosomes and what do they consist of?
Centrosomes are organelles near the nucleus of a cell, which contain centrioles (mother and daughter), and from which spindle fibres develop in cell division
What happens to the centrosomes during G1 and S?
The mother and daughter centrioles separate in G1
Then the mother produces another daughter and the daughter produces another mother, resulting in the formation of 2 centrosomes (the duplication takes place during S phase)
What are the points around the centrosome from which microtubules arise?
Nucleating sites
NOTE: nucleation is the assembly of microtubules
Describe the condensation of chromatin that takes place duringprophase.
Chromatin condenses around nucleosomes to form chromosomes
What is a kinetochore?
Protein complexes that are attached to each sister chromatid – they are important in detecting the attachment of microtubules
Describe the arrangement of centrosomes at the end of prophase.
They are on opposite sides of the nucleus
What happens in initial spindle formation
Radial microtubule arrays form around the centrosomes which begin to grow towards other centrosomes
What is formed when radial microtubule arrays from the two centrosomes meet in the middle?
Polar microtubules
What happens to the sister chromatids as soon as they are captured by microtubule arrays from both centrosomes?
They slide towards the middle of the cell
What keeps the sister chromatids stuck together?
Cohesin (protein complex)
What happens in anaphase A?
Cohesive broken down and microtubules become shorter so daughter chromosome pulled towards opposite pole
What happens in anaphase B?
Daughter chromatids continue to migrate towards the poles
The centrosomes migrate apart
Describe what happens in telophase.
Daughter chromatids arrive at the pole and the nuclear envelope reassembles
Assembly of a contractile ring of actin and myosin filaments where the cells are going to split
The contractile ring squeezes the cell so it divides into two daughter cells
NOTE: cleavage furrow = where the cell is going to be cleaved
What is the midbody?
The point where the actin-myosin contractile ring is formed
What can cause aneuploidy?
Mitotic checkpoint defect Mis-attachment of the spindles (so chromatids end up at different poles to the ones that they should be at) Aberrant mitosis (production of an abnormal number of centrosomes leads to abnormal division of the chromatids, and abnormal cytokinesis)
Name four different types of spindle attachment.
Amphitelic – normal spindle attachment
Syntelic – both kinetochores of the sister chromatids are attached to spindles from one centrosome
Merotelic – one kinetochore of one of the sister chromatids is attached to spindles from both centrosomes
Monotelic – one kinetochore of one of the sister chromatids is attached to a spindle, the other is unattached
Broadly speaking, explain how cell cycle checkpoints can be a target for anti-cancer therapy.
By targeting the cell cycle checkpoints, the cancer cells can be arrested in mitosis
Cells are very vulnerable when they are in mitosis and are more easily killed
Give an example of anti-cancer drugs that target cell cycle checkpoints for breast and ovarian
Taxanes and Vinca alkaloids
These alter microtubule dynamics and produce unattached kinetochores, which leads to long-term microtubule arrest
What can happen to cells that are held up at a checkpoint?
They can undergo DNA repair and then proceed through the cell cycle
If the damage is irreparable, they can undergo apoptosis
Where are the main checkpoints within the cell cycle?
During G1
Just before mitosis to check for DNA damage
Metaphase-anaphase checkpoint (spindle assembly checkpoint)
What happens during prophase
Chromatin condenses to form chromosomes of sister Chromatids
Centrosomes migrate to opposite sides of the nucleus and organise assembly of spindle microtubules
Mitotic spindles form between 2 centrosomes
What happens in early prometaphase
Nuclear membrane breakdowns
Spindle formation complete
Microtubules attach to chromosomes at kinetochore
What happens in late prometaphase
Microtubules from opposite pole is attached to sister kinetochore and congresses to middle of cell down microtubule
Proteins involved in spindle assembly checkpoint
CENP-E
BUB kinase
Why is mitosis the most vulnerable period of cell cycle
DNA damage can’t be repaired
Transcription silenced
Cells more easily killed
Describe how the spindle assembly checkpoint works.
The kinetochore has proteins that emit a signal when the kinetochore is
NOT attached to microtubules
When a microtubule attaches to the kinetochore, it stops emitting the signal
At the end of metaphase, you want all the kinetochores to stop sending signals before you can proceed to anaphase