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 and house the microtubule organising centre (MTOC)
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.
The double helices wrap around histones to form beads-on-a-string This is then further compacted to form 30 nm fibres It is then compacted to form a chromosome scaffold and then further wrapped until you get a chromosome (1400 nm)
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
Describe spindle formation
Radial microtubule arrays (ASTERS) form around each controsome Radial arrays meet Polar microtubules form
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 are the three main types of half-spindle?
Kinetochore microtubule – attached to kinetochores Polar microtubule – attached to a microtubule array from the other centrosome Astral microtubule – microtubule originating from a centrosome that does not connect to a kinetochore
What keeps the sister chromatids stuck together?
Cohesin (protein complex)
What happens in anaphase A?
Cohesin is broken down and the microtubules get shorter so the chromatids start moving towards their respective poles
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 during cytokinesis
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
Name two proteins that allow the kinetochores to detect spindle attachment.
CENP-E BUB-protein kinase (this dissociates from the kinetochores when the chromatids are properly attached to the spindle – then they go on to signal progression to anaphase)
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.
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?
Cell cycle arrest 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)
