Cell cycle

Question 1

Phases of cell cycle

Answer 1

G1 = Gap 1 = interval between mitosis and DNA replication. in this phase RNA and protein synthesis occurs.
S phase = Synthesis phase = DNA replication occurs
G2 = Gap 2 = interval between S phase and mitosis. In this stage DNA repair takes place and cell prepares for mitosis.
G1, S and G2 phase collectively known as interphase when DNA replication and protein synthesis takes place.
Mitosis phase: somatic cell division occurs to produce two daughter cells.
G0 phase : some cells they leave the cell cycle to differentiate into a specialized cells called stem cells.
Facultative divider: Liver stem cells has ability to re-enter cell cycle when signaled until then they stay differentiated.

Question 2

Who does the regulation of cell cycle?

Answer 2

Complex of cyclin dependent kinases (CDKs) and cyclin (proteins generated during cell cycle)

Question 3

Cell cycle check points

Answer 3

G1/S check point (restriction point): makes sure raw material is available for DNA replication
G2/M check point: checks for DNA damage and repairs it. If not repairable then apoptosis
Mitosis check point (spindle checkpoint): ensures that both the daughter cells have equal number of chromosomes.

Question 4

Mitosis

Answer 4

Somatic cell division produces two identical daughter cells with equal number of chromosomes (diploid)

Question 5

Meiosis

Answer 5

Gamet cell division produces 4 daughter cells with haploid number of chromosomes. Also called gametogenesis

Question 6

Mitosis Phases

Answer 6

Prophase, Prometaphase, Metaphase, Anaphase, Telophase + cytokinesis

Question 7

Karyotyping

Answer 7

Examination of the chromosomes of dividing cells, karyotyping, can give diagnostic information about the chromosomal complement of an individual or of a malignant tumour

Question 8

Meiosis process

Answer 8

S phase: Duplication of chromosomes occurs

Prophase I: Chromatids cross over to exchanged genetic information and this process is called chiasma formation.

First Meiotic cell division (metaphase I and anaphase I)- produces two daughter cells containing pair of homologous chromosomes where chromatids are still attached to centromere.

Second meiotic division - Chromatids in each pair of chromosomes are pulled apart from the centromere (metaphase II) and produces 4 daughter cells with haploid number of chromosomes (Anaphase II and Telophase II).

Question 9

Apoptosis and activating signals

Answer 9

Programmed cell death. Activators are intrinsic or extrinsic
Eg: activation of Fab receptor (death receptor), damage to DNA and leakage of cytochrome C, interaction with Bcl2 and inhibitors of apoptosis family of receptor - enhances caspase cascade - leading to cell death.
1. Pyknosis - condensation of nucleus
2. detachment of cell membrane from the neighbour cells
3. Karryorrhexis - breaking down of nuclear material into the fragments called cytoplasmic blebs
4. Karyolysis - breaking down of entire cell into membrane bound fragments called apoptotic bodies which are phagocytosed by phagocytosis.

Question 10

Prophase

Answer 10

• Chromosomes condensation
• Nucleoli disappear
• Centrioles starts moving to opposite poles
• Mitotic spindle formation

Question 11

Prometaphase

Answer 11

• Nuclear membrane disappears
• Chromosomes binds to mitotic spindle by kinetochore

Question 12

Metaphase

Answer 12

• Chromosomes aligned to spindle equator
• Kinetochore controls the entry into next phase until all chromosomes are aligned

Question 13

Anaphase

Answer 13

• Mitotic spindle extends in length
• Centrosome attaches to the cell membrane
• Chromatids are pulled apart from centromere
• Transfer towards the opposite poles

Question 14

Telophase + Cytokinesis

Answer 14

• Nuclear membrane and nucleoli reappear
• Chromosomes starts uncoiling to gain their original shape
• cytokinesis begins at the point of spindle equator by indentation of membrane by forming a cleavage furrow which divides them into two daughter cells.