Cell Cycle Flashcards
What are cells that continue to divide regularly known as?
Cycling cells
What are the 3 stages of interphase?
G1, S and G2
How long after mitosis does the S phase begin?
8 hours
How long does the S phase take to complete?
7-8 hours
What process occurs during the S phase?
Semi-conservative replication of DNA
What occurs during the G1 phase?
Most of the molecular machinery required to complete another cell cycle is generated. Cells in the phase respond to growth factors, directing the cell to initiate another cycle
What occurs during the G0 phase, outside of the cell cycle?
The cell remains in a state of quiescence in which the cell is not active in the cell cycle
What can stimulate a cell to leave the G0 phase and reenter the cell cycle?
Growth factors
In which phase do the tumour suppressant genes, that mutate to cause a retinoblastoma, block using proteins to prevent tumour formation
The G1 phase
What occurs during the G2 phase of interphase?
The cell prepares for division
How does the G2 phase end?
The nuclear membrane breaks down and chromosome condensation begins as mitosis starts
How long does the G2 phase usually last?
2-4 hours
What are the 4 main stages of mitosis?
Prophase, Metaphase, Anaphase and Telophase
What occurs during prophase?
Chromosomes tightly coil along their entire length. Each chromosome splits longitudinally except at the centromere. Two paired centriole are separated from each other by the elongation of continuous microtubules of the achromatic spindle and occupy opposite poles.
What occurs during prometaphase?
The nuclear membrane and nucleolus disappear. The chromosomes become entangled in a meshwork of continuous microtubules.
How long does prometaphase last?
Around 1.5 hours
What occurs during metaphase?
The centromere region from each chromosome presents a bilateral disc (kinetochores). From the kinetochores, a set of chromosomal microtubules are organised and extend towards opposite centrioles. The extension of these microtubules allows the chromosomes to line up along the equator
For how long does metaphase occur?
20 minutes
How does colchicine disrupt mitosis?
Colchicine prevents the formation of microtubules of the spindle. This means the chromosomes assemble around the centrioles
What are the applications of colchicine?
They are an important tool in karyotyping, which underpins the rational for many types of cytotoxic drugs
What is karyotyping?
Karyotyping is the process of pairing and ordering all the chromosomes of an organism, thus providing a genome-wide snapshot of an individual’s chromosomes.
What occurs during anaphase?
The centromeres split longitudinally and chromatids separate to form 2 separate chromosomes. This occurs as chromosomal microtubules contract, exerting a centrifugal force on the centromere region. The separate chromosomes are pulled to opposite poles.
What is non-disjunction?
Due to abnormal function of the spindle apparatus, one or more chromosomes fail to migrate properly during anaphase. This leads to one daughter cell receiving extra chromosomes and one being deficient in this chromosome.
What is an isochromosome?
The centromere of a chromosome splits transversely instead of longitudinally, forming two daughter chromosomes of unequal lengths. These are isochromosomes.
What occurs during telophase?
The daughter chromosomes are enveloped by new nuclear membranes and a nucleolus appears. The chromosomes become uncoiled.
What occurs during cytokinesis?
A cleavage furrow develops around the equator region. The contract of the fibrillar component of the cytoplasm (the actin and myosin belt) helps in the hour glass constriction of the cleavage.
What family of proteins controls the cell cycle?
Cyclin
What are the 3 checkpoints within the cell cycle?
Restriction point (G1 checkpoint)
G2-Mitosis checkpoint
Metaphase-Anaphase checkpoint
What occurs in the Restriction checkpoint (G1 checkpoint)?
This checkpoint ensures all conditions are favourable before progressing into S phase
Cyclin D1-3 and CDK4 or 5 phosphorylate the retinoblastoma protein
This is usually bound to E2F but releases it so progression can occur
What occurs during the G2-Mitosis checkpoint?
Damaged DNA stimulates kinases that phosphorylate p53
p53 then can repair the damaged DNA or stimulate apoptosis
