Cell Cycle Flashcards
What are 4 stages for cell cycle?
Prophase, prometaphase, metaphase, anaphase + telophase
What happens in prophase?
Chromosomes condense
Centromere move to opposite poles
Mitotic spindle forms
What happens in prometaphase?
Breakdown of nuclear envelope
Chromosomes attach to mitotic spindle
What happens in metaphase ?
Centrosome are at opposite poles
Chromosomes are at their most condensed + line up at equator of mitotic spindle
What happens in anaphase?
Sister chromatids separate synchronously
Each new daughter chromosomes moving to opposite spindle poles
What happens in telophase?
Chromosome arrives at spindle poles
Chromosomes decondense
Nuclear envelope reforms
What are 3 types of spindle microtubules?
Astral
Kinetochore
Interpolar
What is definition of kinetochore?
Protein structure formed on chromatid where spindle fibres attach to pull
What is centromere?
Part of chromosome connected to spindle fibre
What is definition of chromatids?
2 chromosomes that have been replicated + linked through centromere
What is definition of cytokinesis?
Divides cytoplasm into 2 daughter cells
At position of metaphase plane
What is mitotic spindle?
Bipolar array of microtubules=> + end=growing end, - end= shrinking end
Start to assemble during prophase from centrosomes at each pole
Attach to chromosomes via kinetochore
Pull apart sister chromatids
What is composed of contractile ring?
Is composed of actin + myosin II outside the cell into 2 daughter cells
Accumulates between poles of mitotic spindle beneath plasma membrane
Ring contracts + forms cleavage furrow => dividing cell in two
What is centrosome?
Is where microtubules assemble
What is meiosis?
Specialised cell division that starts with one diploid cells + ends with 4 haploid cells
What occurs in meiosis I?
Homologous chromosomes line up on spindle + separate to opposite poles
What occurs in meiosis II?
Sister chromatids line up on spindle + separate to opposite spindle pole
When meiosis goes wrong, it is called
Non disjunction
Regulation of cell cycle
Entry into cell cycle must be strictly controlled
Each phase must occur only once per cell cycle
Phases must be in correct order: G1-S-G2-M
Phases must be non-overlapping
What are 3 checkpoints?
G1 checkpoint=> check extracellular environment, check DNA for damage
G2 checkpoint=> check DNA replicated properly, check DNA for damage
Metaphase checkpoint=> are all chromosomes aligned on mitotic spindle
What are cell cycle regulators?
Cyclin dependent kinases (Cdk)=> enzymes that phosphorylate target proteins. Become active when bound to corresponding cyclin
Cyclins=> regulators of Cdks. Different cyclins are produced at each phase of cell cycle
Cell cycle control in Yeast
Single Cdk binds successively to different cyclins
Cdk binding to S cyclin triggers S phase
Cell cycle control in humans
Different classes of Cdk + cyclins act at each stage of cell cycle
Cyclin 1=> ensures DNA replication occurs properly
What are 2 families of cyclin dependent kinase inhibitors?
Inhibitor of kinase 4 family (INK4)=> inhibit G1 CDKs
CDK inhibitory protein/ kinase inhibitor protein (CIP/KIP)=> inhibit all other CDK-cyclin complexes gradually sequestered by G1 CDKs thus allowing activation of later CDKs
Cell cycle + cancer
Neoplasia
Mis regulation of cell cycle causes cancer
Cells escape normal cell cycle checkpoint=> uncontrolled progression through cell cycle
Many genes that regulate cell cycle (p53,pRB) are often mutated in human cancers
