3. The cell cycle

Question 1

how long does the cell cycle take to comple

Answer 1

12 hrs at least

Question 2

cell cycle is divided into 2 parts. what are they

Answer 2

mitosis (M phase)
Interphase
aka - G1, S and G2 phase

Question 3

what is the role of cyclins in the cell cycle

Answer 3

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

Question 4

describe S phase

Answer 4

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

Question 5

The S phase is promoted by who

Answer 5

The phase is promoted by cyclin A and CDKs

Question 6

name 3 Disorders from defective DNA repairing

Answer 6

1. Xeroderma Pigmentosum
2. Homologous Recombination
3. Hereditary Nonpolyposis Colon Cancer (HNPCC)

Question 7

describe G1 phase

Answer 7

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

Question 8

G1 phase is controlled by who

Answer 8

This phase is controlled by cyclin E and CDKs

Question 9

what phase is during G1

Answer 9

G0 - resting phase

Question 10

describe G2 phase

Answer 10

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

Question 11

G2 phase is controlled by who

Answer 11

This phase is controlled by cyclin B and CDK

Question 12

are individual chromosomes visible at interphase

Answer 12

No They are uncoiled into very long narrow structures

Question 13

In interphase the nucleus of the cell possesses a nuclear envelope and contains a network of …….threads or …….and a nucleolus….

Answer 13

chromatin
granules

Question 14

Mitosis
The nuclear changes that achieve distribution and conventionally divided into 4 phases.
Name them.

Answer 14

1. prophase
2. metaphase
3. anaphase
4. telophase
   then cytokinesis

Question 15

describe prophase

Answer 15

Subsequently, the nuclear membrane and nucleolus disappear

The chromosomes are now entangles in a meshwork of continuous microtubules

This stage is called prometaphase

Question 16

describe metaphase

Answer 16

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

Question 17

what is the difference between centromeres and kinetochores

Answer 17

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

Question 18

what is the role of colchicine

Answer 18

arrest the cell division at metaphase

Prevents the formation of microtubules of the spindle fibres

Question 19

describe anaphase

Answer 19

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

Question 20

what is non- disjunction

Answer 20

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

Question 21

what is isochromosome

Answer 21

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

Question 22

what is telophase

Answer 22

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