Week 5 - Cell Cycle Flashcards
What is mitosis?
process by which the chromosones in the cell are separated into two identical sets of chromosones each in its own nucleus
What is cytokinesis?
process in which the cytoplasm divides to form two idential daughter cells
What occurs during the M phase of the cell cycle?
mitosis and cytokinesis
What phases of the cell cycle make up interphase?
G1, S and G2
What occurs during the gap phases (G1 and G2) of interphase?
cell continues to grow and moniters both its external state and the external environment
ensures that conditions are stable to move onto to S phase and mitosis (checkpoints)
G1 - synthesises mRNA and proteins
What occurs during S phase?
DNA replication
What are the three main checkpoints of the cell cycle control system?
transition from G1 to S phase (G1 checkpoint)
transition from G2 to M phase (G2 checkpoint)
just before end of M phase (M checkpoint)
What is the cell checking for at the end of G1 before it can proceed into S phase?
Is the enrvironment favourable for proliferation before comitting to DNA replication?
What is G0?
a resting phase that cells can enter if contitions are not favourable to progress to S phase
What does the cell check for in the transition from G2 to M phase?
Has all the DNA replicated?
Is the environment favourable?
What does the cell check for during M phase?
Are the duplicated chromosones properly attached to the mitotic spindle?
What is the purpose of cyclin-dependent kinases (Cdk’s)?
they regulate DNA regulation, mitosis and cytokinesis
binds to cyclin to become enzymatically active
once activated a cyclin - Cdk complex phosphorylates key proteins in the cell that are required to initiate particular steps in the cell cycle
CDKs are continually expressed in cells while cyclins are synthesised at specific points of the cell cycle as a response to other signalling pathways
What state are most of the cells of your body in?
G0, because they are non-dividing
What cyclin triggers entry into M phase?
M cyclin
What cyclin-Cdk complexes help to launch S phase?
S-Cdk and G1/S-Cdk
What are the possible options for a cell at the G1 checkpoint?
proceed to S phase
withdraw to G0
pause temporarily in G1 until the conditions are right
permanently withdraw from the cycle in the case of terminally differentiated cells
What happens to Cdk’s during G1?
they are inactivated which creates a stable environment for the cell to grow
Cdk inhibitor proteins are deployed to muffle the activity of cyclin-Cdk complexes and synthesis of new cyclins is stopped
What is the role of p53 in the cell cycle?
DNA damage in G1 causes an increase in both the concentration and activity of p53
p53 can induce the cell to undergo programmed cell death (apoptosis) if the DNA damage is too severe to be repaired
What happens if there is a mutation in the p53 gene?
there will be unrestrained replication of damaged DNA leading to a high rate of mutation and cells that tend to become cancerous
What is a kinetochore?
protein complexes that assemble on the centromere of each condensed chromosone during late prophase
they attach chromosones to the mitotic spindle
What are the main events of prophase?
chromosones condense
mitotic spindle assembles between the two centrosomes which have begun to move apart
What are the main events of prometaphase?
breakdown of the nuclear envelope
chromosones attach to spindle microtubules via their kinetochores
What are the 5 stages of mitosis?
prophase
prometaphase
metaphase
anaphase
telophase
What are the main events of metaphase?
chromosones are aligned at the equator of the spindle midway between the spindle poles
What are the main events of anaphase?
sister chromatids separate and are slowly pulled towards spindle pole
kinetochore microtubules get shorter and the spindle poles move apart
What cells undergo mitosis?
all somatic cells (occurs only in eukaryotic cells)
What is the purpose of meiosis?
to provide genetic variety
to produce gametes
What are the main events of telophase?
nuclear membranes form
division of cytoplasm begins with the assembly of the contractile ring
How does a cell divide during cytokinesis?
contractile ring of actin and myosin pinches the cell into two daughter cells
What are the main differences between mitosis and meiosis?
MITOSIS
- preserves chromosone number
- diploid
- clonal
- genetic conformity
MEIOSIS
- reduction division
- chromosone number halved
- haploid
- genetic variation
- inter-chromosonal crossing over
What is the purpose of apoptosis?
to get rid of cells that are no longer needed
important for development and cellular defense
What is cell necrosis?
when cells die as a result of acute injury
What is the difference between necrosis and apoptosis?
necrosis - a comprimised cell membrane as a result of acute injury leads to cell swelling, the cell bursts and releases intracellular components triggering an inflammatory response (messy death)
apoptosis - cell shrinks and nuclear DNA breaks up into fragments, the cell develops irregular bulges (blebs) on surface, macrophage phagocytoses cell before it spills its contents (clean death)
Outiline the process of meiosis
- chromosones replicate
- chromosones condense
- chromosones pair with homologous partner
- crossover occurs (genetic variation)
- homologous pairs separate
- cytokinesis
- chromosones condense
- chromosones line up individually at equator
- chromatids separate
- cytokinesis
Give an example of a ‘post-mitotic’ cell?
differentiated neurons and muscle cells that comprise the brain, heart and skeletal muscle
What is a ‘post-mitotic’ cell?
cells that are incapable of proliferation and are irreversible blocked from re-entering the cell cycle
DNA damage can cause arrest at which two stages of the cell cycle?
G1 (if damage to DNA is already present) and G2 (if damage has occured during S phase)
What are gametes that receive and incorrect number of chromosones called?
aneuploid
