Cell replication Flashcards
What are the 3 major proteins within the cytoskeleton?
Actin filaments, intermediate filaments, microtubules
What is the function of microtubules?
Radiates from the microtubule organising centre (centrosome) and plays a key role in the formation of the mitotic spindle during mitosis
What are the 6 stages of cell cycle?
- M-phase – mitosis
- Interphase
- G0 – cell cycle machinery dismantled
- G1 – decision point
- S – Synthesis of DNA/proteins
- G2 – decision point
What occurs during the S phase?
During the S-phase, the initiation of translation and elongation is increased, and protein capacity is also increased. Organelles are also replicated such as centrosomes, mitochondria, Golgi body etc.
What is the centrosome?
The centrosome is the microtubule organising centre and consists of two centrioles which will form the mitotic spindle.
What are the 6 stges of mitosis?
- Prophase - condensation of chromosomes, centrosomes migrate to opposite sides of nucleus and begin to form the mitotic spindle
- Prometaphase – nuclear membrane breaks down, spindle formation completed, chromosomes attach to spindle via kinetochores
- Metaphase – Kinetochores bind to microtubules from opposite pole causing chromosomes attached to each pole slide towards the centre along microtubules
- Anaphase – Paired chromatids are held together by cohesin. This cohesin is broken down and the microtubules are shortened, separating the chromatids into daughter chromosomes which are pulled to opposite spindle poles.
- Telophase – Daughter chromosomes arrive at the spindle and a nuclear envelope reassembles around them at each pole. A contractile ring made of actin and myosin is also formed around the cleavage furrow.
- Cytokinesis – Acto-myosin ring contracts, forming two new daughter cells.
What occurs during the M checkpoint?
At the M checkpoint during metaphase, BUB protein kinases are associated to kinetochores until the chromosomes are properly attached to the spindle via the kinetochore. BUBs disassociated when the chromosomes are attached properly to the spindle. Once all disassociated, anaphase proceeds.
What occurs at the G1 checkpoint?
The cell commits to replication depending on external factors such as growth factors and signals.
What occurs at the G2 checkpoint?
The chromosomes are checked to see if all chromosome have been replicated and the replicated DNA has not been damaged.
What happens to cell in absence of stimulus?
- Cells in the absence of stimulus go to the G0 phase in which the cells are not dormant but are non-dividing. This occurs in most cells in the body that are differentiated to perform specific functions.
What are the 5 steps of the signalling cascade?
- Response to extracellular factors
- Signal amplification
- Signal integration
- Modulation by other pathways
- Regulation of divergent responses
What are protein kinase cascades?
Protein kinase cascades occur when kinases phosphorylate other kinases to switch them on and reverse the phosphorylation using phosphatases to switch kinases off.
What are the 4 cyclin dependent kinases?
Cdk1, Cdk2, Cdk4, Cdk6.
What are the 4 cyclins?
Cyclins – CyclinA, CyclinB, CyclinD, CyclinE. These are transiently expressed at specific points in the cell cycle. They are regulated at the level of expression by being synthesised only when necessary and degrading afterwards.
Cyclins increases in the order D, E, A and B from G1 phase to mitosis. They regulate the cell cycle only when tightly bound to cdks. To be fully active the cdk-cyclin complex must also be phosphorylated in specific locations. This is positive regulation where the active molecules cause the cell cycle to progress.
What are negative regulators?
The second group of cell cycle regulatory molecules are negative regulators. Negative regulators halt the cell cycle.
