Cell cycle and its control Flashcards
Semester 1 year 1
Almost all normal cells won’t proliferate unless stimulated by what, and what can overrule them?
-extrinsic factors
-other signalling factors can overrule them
What 4 phases make up the cell cycle and what happens in each?
-M phase - replicated DNA is separated + cytokinesis
-S phase - DNA replication
-G1 phase - gap between M phase + S phase
-G2 phase - gap between S phase + M phase
Which phases make up interphase?
All but M phase
What occurs in M phase?
-prophase
-prometaphase
-metaphase
-anaphase
-telophase
-cytokinesis
What happens in prophase?
Movement of centrioles to polar ends of nucleus + chromosome condensation
What happens during prometaphase and metaphase?
-pro = components of mitotic spindle elongate away from spindle poles
-met = chromosome pair alignment is completed
What happens in anaphase and telophase?
-ana = pairs of sister chromatids separate
-tel = chromosomes decondense + nuclear membrane is re-established
What happens during G1 phase in interphase?
-preparation for DNA synthesis
-cells increase in size
-ribosomes RNA produced
What happens during S phase in interphase?
-DNA synthesised
-chromosomes are duplicated
What happens during G2 phase in interphase?
-preparation for nuclear division
-cells check fidelity of DNA
What do cells enter if they exit the G1 phase?
-enter G0 phase
-won’t divide or grow in this phase
-can re-enter the cell cycle
What allows cells to exit the G1 phase and enter the G0 phase?
-they consult the extracellular environment
-if environment not right, they can exit the cell cycle
At what points can growth factors be removed in G1 phase to determine what phase the cell enters next?
-removed before R point - don’t proceed + go to phase G0
-removed after R point - proceed to S, G2 + M phase
What can dysregulation of R point decision making lead to?
Formation of most types of cancer
Describe the genetic approach to investigating the genes responsible for cell cycle transitions
-requires cells that have a mutation in an already accepted cell cycle transition gene
-if mutation stops cell cycle, then stops cells from proliferating
Why is yeast used as a genetic model?
-rapid division rate
-cell cycle control genes are highly conserved
-yeast can grow as haploids or diploids
-easy to grow
-can tell which phase of cell cycle the cell is in just by looking at it
Describe the biochemical approach to investigating the genes responsible for cell cycle transitions
-use toads
-oocytes grow without dividing + become arrested in G2
-eventually divide + transition into M phase, where they become arrested again
-when fertilised, released from M phase + division occurs without cells changing size until tadpole produced
-something in egg cytoplasm can catalyse transition from G2 to M phase - maturation promoting factor (MPF)
What controls the G2 phase to M phase transition?
Mutations in certain genes that control the phases lead to identification of CDK genes + cyclins
When active, what do cyclins and CDKs exist as?
Complexes
How do you quantify kinase activity?
-selective extraction of kinase
-incubation with a protein substrate + ATP
-electrophoresis of substrate + imaging
What is the difference in CKS and cyclins between yeast and mammals?
-in yeast, only 1 CDK gene (CDK1) + multiple cyclins
-in humans, multiple CDKs + multiple cyclins
Describe the levels of cyclins E, A and B throughout the cell cycle
-E = low levels through most of G1, rapid increase after R point
-A = levels increase with entrance to S phase
-B = levels increase in anticipation of mitosis
What does the levels of cyclin decreasing as the cell progresses through the cycle ensure?
The cell cycle can only progress in 1 direction
