Cell cycle & DNA synthesis

Question 1

why do cells need to divide?

Answer 1

1) Growth
2) repair
3) replacement
4) Germ cells (formation of gametes)

Question 2

What is cell division?

Answer 2

1) Mitosis: Occurs in somatic cells
- Leads to the formation of two diploids (2N)
- Genetically identical to the parent cells
- Crucial for growth and regeneration

2) Meiosis: occurs in germ cells
- Leads to the formation of four haploid (n) daughter cells
- Genetically non-identical to the parent cell
- Cell division where chromosome number reduces to half

Question 3

what are the phases of the cell cycle?

Answer 3

interphase (most cells spend their time here where they grow & double their mass protein & duplicate their chromosome) & mitotic phase

Question 4

what are the stages of interphase?

Answer 4

1) G-1 (RNA & Protein synthesis)

2) G0 phase (cell decides whether to proceed or not)

3) S Phase (DNA replication)

4) G2 phase (Cell further grows and prepares for mitosis, Double check for DNA error
and performs the repair)

Question 5

what are the cells that do not divide at all once they are differentiated and are said to be arrested in the G0 “Restriction phase”?

Answer 5

Neurons & Cardiac cells, and others might enter this phase after organ damage

Question 6

what are the function checkpoints?

Answer 6

Checkpoints monitor and control the accuracy of DNA synthesis as well as the assembly and attachment of an elaborate network of microtubules that facilitate chromosome movement

Question 7

How many hours does does the mitiosis take?

Answer 7

1-2 hours

Question 8

what is the DNA structure?

Answer 8

Backbone made of pentose sugar
Deoxyribose bonded to the phosphate (PO4) group via a phosphodiester bond, and the center is made of nitrogenous bases bonded together by a hydrogen bond

Question 9

What are the characteristic features that ensure the high accuracy of replication (which is 50/nucleotide/sec)

Answer 9

1) Semi-conservative
2) Starts at several replication origins
3) Semi-Discontinuous
4) Always occurs in the 5’ - 3’ direction
5) Requires several proteins

Question 10

What are the proteins required for replication?

Answer 10

1) Topoisomerases- Relaxes the supercoil DNA

2) Helicases- Separates 2 strands (Cleaves the Hydrogen-bonds between nucleotides of double strand)

3) Single strand binding proteins- prevent re-annealing of single strands

4) DNA polymerase- Synthesis of new strand, Primer removal and
Proofreading (3’🡪5’ direction)

5) Primase- RNA primer synthesis (DNA Primase (RNA polymerase) synthesizes an RNA primer to initiate DNA synthesis)

6) DNA ligase- Seals nick via a phosphodiester bond, Gap filling on lagging strands, Catalyzes the joining of DNA fragments by Phosphodiester bond formation

Question 11

what is the difference between the replication process that occurs in the leading and lagging strand?

Answer 11

in the leading strand, it is continuous while in the lagging strand, it is discontinuous forming okazaki fragments both are replicated from 5’ to 3’ while the leading is towards the replication fork and the lagging is away

Question 12

what are the requirements for a continuous replication?

Answer 12

1) Single RNA primer
2) Primase

Question 13

What are the requirements for a discontinuous DNA replication?

Answer 13

Multiple RNA primers
Primase
DNA ligase

Question 14

What are the stages of mitosis?

Answer 14

1) Prophase
2) pro-metaphase
3) Metaphase
4) Anaphase
5) Telophase

Question 15

What happens in prophase?

Answer 15

1) Chromosomal condensation
2) Centromeres moves to the opposite side of the poll
3) Spindle fiber forms

Question 16

what happens during metaphase?

Answer 16

1) Nuclear envelop disappears
2) Kinetochore attaches to spindle fiber

Question 17

what happens during the metaphase?

Answer 17

the chromosomes are maximally condensed and are aligned at the equator

Question 18

what happens during anaphase?

Answer 18

The centromere of each chromosome splits and they are pulled away

Question 19

What happens during telophase?

Answer 19

the sets of chromosome arrive at the opposite pole, and the nuclear envelope begins to reassemble while the cytoplasmic division starts

Question 20

what is cytokinesis?

Answer 20

the process where the cytoplasm is physically separated with the help of the contractile ring of actin and myosin filaments forming two new cells

Question 21

what does meiosis consist of?

Answer 21

one round of DNA replication and two rounds of chromosome segregation and cell division

Question 22

what are the stages of meiosis?

Answer 22

1) Metaphase 1
3) Metaphase 2

Question 23

what are the stages in prophase 1?

Answer 23

1) Leptotene (Chromosomal condensation)
2) Zygotene (Synapsis starts (homologous chromosome lines up together)
3) Pachytene (Chiastma forms between chromatids and cross-over occurs
4) Diplotene (Disassembly of the synaptonemal complexes followed by the condensation and shortening of the chromosomes
5) Diakinesis (Formation of the spindle fibers and the disappearance of the nuclear membrane)

Question 24

what is the most significant event that happens during prophase 1?

Answer 24

Genetic recombination (crossing over) occurs between non-sister chromatids

Question 25

where in the male sex chromosome does the pairing occur?

Answer 25

pairing between the homologous segments occurs in the pseudoautosomal region

Question 26

what are the stages in meiosis 1?

Answer 26

1) Prophase 1: discussed already in detail 2) metaphase 1: pairs of homologous chromosomes align at the equator held in the center by the spindle fiber 2) Anaphase 1: chromosomes are pulled to opposite sides as the spindle fiber contracts 3) Telophase 1: chromosomes reach opposite pole of the cell 4) Cytokenisis: two haploid cells are formed

Question 27

What happens in meiosis 2?

Answer 27

1) Prophase 2: The nuclear membrane disappears again and centrioles move to opposite poles 2) Metaphase 2: chromatids line along the equator 3) Anaphase 2: centromeres contracts pulling sister chromatids away 4) Telophase 2: chromatids are pulled to either pole, the nuclear membrane reforms and the nucleolus reappears

Question 28

what are the checkpoints in the cell cycle?

Answer 28

1) G1 checkpoint: determines whether - Cell has the appropriate size - has adequate energy reserves - No DNA damage 2) G2 checkpoint: - Determines whether Chromosomes have been accurately replicated without damage 3) M checkpoint (Spindle checkpoint): - Determines whether all the sister chromatids are correctly attached to the spindle microtubules

Question 29

How is the cell cycle initiated?

Answer 29

via Activated cyclin-dependent protein kinases (Cdks)

Question 30

What is the most important regulator of Cdks?

Answer 30

Cyclins

Question 31

how is the cell cycle-regulated?

Answer 31

Two key components of the cell-cycle control system. When Cyclin forms a complex with Cdk, the protein kinase is activated to trigger Specific cell-cycle events. Without cyclin, Cdk is inactive.

Question 32

What are the different types of cell cyclin?

Answer 32

1) A 2) B 3) D 4) E

Question 33

what are the Cdks partners of Cyclin A?

Answer 33

Cdk2 & 1

Question 34

what are the Cdks partners of Cyclin B?

Answer 34

Cdk 1

Question 35

what are the Cdks partners of Cyclin D?

Answer 35

Cdk4 & 6

Question 36

what are the Cdks partners of Cyclin E?

Answer 36

Cdk2

Question 37

Which cyclin is expressed from G1 till the end?

Answer 37

CyclinD

Question 38

Which cyclin is expressed during the G1-S phase?

Answer 38

Cyclin E

Question 39

Which cyclin is expressed during S-G2 phase?

Answer 39

Cyclin A

Question 40

Which cyclin is expressed during mitotic phase?

Answer 40

Cyclin B

Question 41

How is the Cdk activated?

Answer 41

first it is blocked by the T-loop, cyclin binding partially activates it then the Cdk-activating kinase (CAK) by phosphorylation it at the threonine residue further activating it

Question 42

what are the Cdk-inhibitory proteins?

Answer 42

1) Wee1-kinase phosphorylates two close sites above the active site, opposed by the action of (Cdc25 phosphatase, which removes the added phosphate group) 2) P21 3) P27 (forms a CKI complex binding to both the cyclin and the Cdk distorting the active site)