Cell Cycle Flashcards
Describe the stages of a cell cycle.
The cell cycle is split into Mitosis and Interphase which consists of 3 phases ( G1, S & G2)
Describe the events occurring in the G1, S and G2 phase of a cell cycle.
G1- Initial Growth Phase
S- DNA replication
G2- Grows more in preparation for Mitosis.
What occurs in G1 in depth?
G1 is the period when cells respond to growth factors directing the cell to initiate another cycle; once made, this decision is irreversible. It is also the phase in which most of the molecular machinery required to complete another cell cycle is generated
What is the G1 stage controlled by?
The phase is controlled by cyclin E and CDKs)
Which cells enter the G0 phase?
Cells that retain the capacity for proliferation and in the process of differentiation, but which are no longer dividing, have entered a phase called G0 and are described as quiescent. They do not enter S phase
What occurs in the G2 phase in depth?
During G2, the cell prepares for division; this period ends with the breakdown of the nuclear membrane and the onset of chromosome condensation.
What is the G2 phase controlled by?
The phase is controlled by cyclin B and CDKs)
Where does replication of DNA occur?
In the Chromosome.
What does Mitosis consist of?
PMAT
Prophase?
- The individual chromosome are first visualized as thin threads and are tightly coiled along the entire length of the chromosome.
- Each chromosome splits longitudinally into two chromatids except at the centromere.
- The two paired centriole are separated from each other by elongation of continuous microtubules of the achromatic spindle and occupy the opposite pole of nucleus.
Prometaphase?
- Subsequently, the nuclear membrane and nucleolus disappear.
- The chromosomes are now entangled in a meshwork of continuous microtubules.
- This stage is prometaphase; The prophase take about 1.5 hours to complete.
Metaphase?
- Centromere region from each chromosome presents a bilateral disc Kinetochores.
2.From kinetochores, a set of chromosomal microtubules are organized and extend bilaterally towards opposite centrioles.
- The growth of the chromosomal microtubules allows centromere of individual chromosomes with their paired chromatids to occupy equatorial plane of the spindle.
- Metaphase persists for 20 minutes
Anaphase?
- The centromeres split longitudinally and chromatids separate to form two new chromosome.
- The spindle fibres contract, each pair of newly formed chromosomes separates and migrates to the opposite pole of the spindle. Two identical and complete chromosomes are formed.
- The separation of the chromatids to form new chromosomes occurs by contraction of chromosomal microtubules which exert a centrifugal force in centromere region.
Telophase? (process)
- It is a reorganization period
The daughter chromosomes are enveloped by new nuclear membrane and nucleolus appears. - The chromosomes become uncoiled and their individual identity is lost.
- The cytoplasm divides and two complete cells are formed
Telophase? (complete)
- In the process of cytokinesis, the cleavage furrow develops around the equator region of achromatic spindle.
- The contraction of fibrillar component of cytoplasm help in hour glass constriction of cleavage
What is Non-disjunction?
Due to abnormal function of spindle apparatus one or more chromosomes fail to migrate properly in anaphase.
This leads to non-disjunction where one daughter cell receives extra chromosomes and other daughter cell is deficient in this chromosome
What are isochromosomes?
Sometimes, the centromere splits transversely instead of longitudinal division.
This leads to formation of two daughter chromosome of unequal length. This is known as Isochromosome
What is the role of Colchicine?
Colchicine arrest the cell division at metaphase.
Colchicine prevents the formation of microtubules of the spindle.
In colchicine treated metaphase the chromosomes are found to assemble around centriole.
Application of colchicine in cell culture is a important tool in karyotyping.
This underpins the rationale for many types of cytotoxic drugs used in cancer therapy.
