The cell cycle Flashcards
Two things must happen for the cell cycle
- Duplication of the cell contents e.g. DNA, organelles, cytoplasm…
- Division into new progeny cells
How many cycles does it take for unicellular organisms to replicate
Each cell cycle gives 2 new organisms
How many cycles does it take for multicellular organisms to replicate
Zygote must undergo many rounds of the cell cycle to make a fully grown human
Phases of the cell cycle
M, S, G0/G1/G2 phases
Why and which cells are in the G0 phase
- Cell cycle isnt possible e.g. nerve cells since they are fully differentiated
- Maintained in G0 unless stimulated to divide e.g. hepatocytes
- Constantly in the cell cycle e.g. epithelial cells of the gut or haematopoietic cells in the bone marrow
How can you visually see the DNA content changing during the cell cycle
Fluorescence activated cell sorter (FACS) analysis
Gap 1 phase function
Growth and preparation for s phase
S phase function
Chromosome duplication
Gap 2 phase function
Growth and preparation for M phase
Prophase
Chromosomes condense, centrosomes move to opposite poles, mitotic spindles start to form
Prometaphase
Nuclear envelope breaks down and chromosomes attach to mitotic spindle
Metaphase
Centrosomes are at the opposite poles, chromosomes are at the most condensed state and line up at the equator of the spindle
Anaphase
Sister chromatids separate, each new daughter chromatid moving to the opposite pole
Telophase
Chromosomes arrive at the spindle poles, chromosomes de-condense and nuclear envelope reforms
Cytokinesis
Cytoplasmic division at the position of the metaphase plane. Contractile ring of actin and myosin II constrict the cell into 2 new daughter cells
What makes up the mitotic spindle
Bipolar array of microtubules
How does the mitotic spindle connect to chromosomes and what is it
Via the kinetochore; A large protein structure assembled on the centrosome
What are the different types of mitotic spindle
- Astral
- Kinetochore
- Interpolar
What occurs in meiosis I
Homologous chromosomes line up on the spindle fibre and separate to opposite spindle poles
What occurs in meiosis II
Sister chromatids line up on the spindle and separate to opposite spindle poles
What is non-disjunction
Failure of homologous chromosomes to separate from one another at either meiotic division I or II
what are some non fatal autosome mutations
Edwards syndrome - trisomy 18
Patau syndrome - trisomy 13
Downs syndrome - Trisomy 21
what are some sex chromosome mutations
Turners syndrome - XO
Triple X syndrome - XXX
Klinefelters - XXY
summarise the G1 checkpoint
Extracellular environment?
Growth factors?
Mitogenic signals?
Check DNA for damage?
summarise G2 checkpoint
DNA replicated properly?
Check DNA for damage?
summarise M checkpoint
All chromosomes aligned on the mitotic spindle?
what are cyclin dependant-kinases - CDKs
Enzymes that phosphorylate target proteins used in the regulation of the cell cycle
Becomes active when bound to a corresponding cyclin
What are cyclins
Regulators of CDKs, different cyclins are produced at each phase of the cycle
What is involved in the cell cycle of yeast
S-cyclin binds with CDK to trigger S phase
M-cyclin binds with CDK to trigger M phase
Cyclin D pathway
- Binds to CDK4, activating it
- CDK4 partially phosphorylates pRB
- E2F is released from pRB
- E2F regulated genes can be made allowing the cell to progress from the G1 to S phase
How does the cell cycle arrest in the G1 phase so damaged DNA can be repaired
- P53 will be phosphorylated and activated when the DNA is damaged
- P53 will bind to the promoter region of the P21 gene, stimulating its expression
- P21 will bind and inhibit G1 CDKs therefore the cell cycle is stopped
Cyclin dependant kinase inhibitors
- INK4 - inhibits cycle progression after G1 point as it inhibits CDK4
- CIP/KIP - inhibits all other CDK-cyclin complexes
Neoplasia
mutated P53 and pRB genes lead to uncontrolled progression through the cell cycle
What regulates the early G1 phase
Cyclin D and CDK4
What triggers the S phase
Cyclin E and CDK2
What regulates the completion of the S phase
Cyclin A and CDK1 and 2
What triggers the M phase
Cyclin B and CDK1
