3. The cell cycle Flashcards
how long does the cell cycle take to comple
12 hrs at least
cell cycle is divided into 2 parts. what are they
mitosis (M phase)
Interphase
aka - G1, S and G2 phase
what is the role of cyclins in the cell cycle
The cyclins are a family of proteins whose conc. Increases and decreases through the cell cycle
Cell cycle molecules are cyclins, A, B and E
The cyclins activate Cyclin dependent kinase (CDKs) which act in conjunction with cyclins
Upon completion of cell cycle
describe S phase
Relation of DNA to genes is established
DNA replicated to have enough genes for 2 daughter cells
DNA duplicates not in mitosis but during interphase long before the chromosomes are detected as thread like bodies
Begins 8 hrs after the end of mitosis and takes 7-8 hrs to complete
The S phase is promoted by who
The phase is promoted by cyclin A and CDKs
name 3 Disorders from defective DNA repairing
- Xeroderma Pigmentosum
- Homologous Recombination
- Hereditary Nonpolyposis Colon Cancer (HNPCC)
describe G1 phase
When cells respond to growth factors directing the cell to initiate another cycle
This decision is irreversible
Phase where most molecular machinery required to complex another cell cycle is generated
G1 phase is controlled by who
This phase is controlled by cyclin E and CDKs
what phase is during G1
G0 - resting phase
describe G2 phase
The gap between the end of the S phase and beginning of mitosis is the g2 phase
During this phase the cell prepares for division
This period ends with the breakdown of the nuclear membrane and the onset of chromosome condensation
Takes 2 hrs to completes
G2 phase is controlled by who
This phase is controlled by cyclin B and CDK
are individual chromosomes visible at interphase
No They are uncoiled into very long narrow structures
In interphase the nucleus of the cell possesses a nuclear envelope and contains a network of …….threads or …….and a nucleolus….
chromatin
granules
Mitosis
The nuclear changes that achieve distribution and conventionally divided into 4 phases.
Name them.
- prophase
- metaphase
- anaphase
- telophase
then cytokinesis
describe prophase
Subsequently, the nuclear membrane and nucleolus disappear
The chromosomes are now entangles in a meshwork of continuous microtubules
This stage is called prometaphase
describe metaphase
Chromosomes are lined up of the metaphase plate
Centromere region from each chromosome presents a bilateral disc - Kinetochores
From kinetochores a set of chromosomal microtubules are organized and extend bilaterally toward opposite centrioles
what is the difference between centromeres and kinetochores
centromere is the exact middle of a chromosome
kinetochore is next the the centromere kind of on the outside edge of both chromatids so that the microtubules can attach on
what is the role of colchicine
arrest the cell division at metaphase
Prevents the formation of microtubules of the spindle fibres
describe anaphase
The centromeres split longitudinally and chromatids separate to form 2 new chromosomes
The spindle fibres contract, each pain of newly formed chromosomes separates and migrates
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 is isochromosome
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 telophase
It is a re organization period
The daughter cells are enveloped by new nuclear membrane and nucleolus appears
The chromosomes become uncoiled and their identity is lost
The cytoplasm divides and two complex cells are formed
In the process of cytokinesis, the cleavage furrow develops around the equator region of achromatic spindle
The contraction of fibrillar component of cytoplasm
