Lecture 42: Cell Cycle and Mitosis Flashcards
Describe Cell Theory
- cells arise only by replication and division of a pre-existing cell
- cells are the smallest unit of life
- all organisms are composed of 1 or more cells
What is cancer?
disease of uncontrolled proliferation/cell division
Describe G1 stage
- only variable time frame in cycle with 10+ hours
- RNA and protein synthesis occurs
Describe S phase
- 7.5 hours
- DNA replication phase
Describe G2 phase
- 3.5-4 hours
- RNA and protein synthesis occurs, alongside growth of cell cytoplasm and replication of organelles
Describe M phase
- 1 hour
- division of cell to provide two genetically identical daughter cells
Describe G0 phase
- cell quiescence
- cells exit cell cycle and either go on to differentiate OR go dormant
Define Post-mitotic
after a cell has differentiated and specialised, cell loses replicative potential and doesn’t respond to proliferation cues
Why do cells enter G0?
- when there is limited space/nutrients
- to differentiate
What are the pre-requisites of mitosis?
- completion of S phase DNA replication
- sufficient cell growth
- intact genome (no DNA damage)
Describe Prophase
- chromosomes condense to become visible sister chromatids cohesed at the centromere (cohesion down arms is lost)
- nuclear envelope disintegrates
- centrosomes separate to opposite poles of the cell and nucleate microtubules
Describe the action of Eg5
- a dimeric kinesin
- slides microtubules past one another to perform search and capture of chromosomes
What does inhibition of Eg5 do?
- creates syntelic (monopolar) attachment of microtubules
- synchronises cells to same stage in lab
Describe Prometaphase
- chromosomes congress to equator of cell
- microtubules nucleated from centrosome form bipolar spindle (amphitelic attachment)
- kinetochores captured by microtubules
Describe Metaphase
- chromosomes align along the equator
- microtubules maintain a symmetrical bipolar attachment
- SAC occurs here
What is the mitotic exit?
metaphase-anaphase transition
Describe Anaphase (A)
- cohesion lost from sister chromatids
- chromosomes move to opposite spindle poles
- centrosomes remain same distance apart
- CDK 1 is inactivated
Describe Anaphase (B)
- chromosomes continue to move to opposite poles
- distance between centrosomes begins to increase
- midzone microtubules slide past one-another
- cleavage plane is determined
Describe telophase
- chromosomes begin to decondense
- nuclear envelope reforms
- cleavage furrow forms and ingresses
- thick bundles of microtubules between chromatin mass (intercellular bridge)
Describe Cytokinesis
- chromosomes decondense and packaged into nuclei
- cell constricts into two genetically identical daughter cells
What causes the cleavage of the cells?
- ring of Actin and Myosin II filaments perpendicular to midzone microtubules
- in same mechanism as muscle contraction
What stages are defined as early mitosis?
prophase
prometaphase
metaphase
What stages are defined as late mitosis?
anaphase
telophase
cytokinesis
