Q: Identify the correct statement with regard to G1 phase (Gap 1) of interphase.

During G1 phase the cell is metabolically active and continuously grows but does not replicate its DNA.DNA synthesis takes place in S phase. Nuclear division occurs during Karyokinesis.Reorganisation of all cell components takes place in M-Phase.

Q: The correct sequence of phases of cell cycle is:

The correct sequence of phases of cell cycle is G1→S→G2→M

Q: Cell in G0 phase :

Cells in G0 phase are said to exit cell cycle.These are at quiescent stage and do not proliferate unless called upon to do so.

Q: What is G0 (quiescent phase) of cell cycle?

G0 phase is the phase of inactivation of cell cycle due to non-availability of mitogens and energy rich compounds. Cells in this stage remain metabolically active but no longer proliferate i.e., do not grow or differentiate unless called on to do so depending on the requirement of the organism. E.g., Nerve and heart cells of chordates are in permanent G0 phase.

Question 1

Identify the correct statement with regard to G1​ phase (Gap 1) of interphase.

Accepted Answer

During G1​ phase the cell is metabolically active and continuously grows but does not replicate its DNA.DNA synthesis takes place in S phase. Nuclear division occurs during Karyokinesis.Reorganisation of all cell components takes place in M-Phase.

Question 2

Some dividing cells exit the cell cycle and enter vegetative inactive stage. This is called quiescent stage (G0​). This process occurs at the end of:

Accepted Answer

Some dividing cells exit the cell cycle and enter vegetative inactive stage, called quiescent stage (G0​). This process occurs at the end of M-phase and beginning of G1​ phase.

Question 3

The correct sequence of phases of cell cycle is:

Accepted Answer

The correct sequence of phases of cell cycle is G1​→S→G2​→M

Question 4

Cell in G0​ phase :

Accepted Answer

Cells in G0​ phase are said to exit cell cycle.These are at quiescent stage and do not proliferate unless called upon to do so.

Question 5

During which phase(s) of cell cycle, amount of DNA in a cell remains at4C  level if the initial amount is denoted as 2C  ?

Accepted Answer

During the S phase, the amount of DNA per cell doubles. Thus, at the G2​ phase, the  amount of DNA is 4C if the initial amount of DNA in the cell is 2C.

Question 6

In ' S ' phase of the cell cycle :

Accepted Answer

During the S phase, the DNA replicates and its amount in the cell doubles.

Question 7

The enzyme recombinase is required at which stage of meiosis:

Accepted Answer

Recombination occurs during pachytene, and thus, recombinase is needed during this  phase.

Question 8

Distinguish cytokinesis from karyokinesis.

Accepted Answer

Cytokinesis Karyokinesis (i) Cytokinesis is the biological process involving the division of a cell’s cytoplasm during mitosis or meiosis. (i) Karyokinesis is the biological process involving the division of a cell’s nucleus during mitosis or meiosis. (ii) Stages such as prophase, metaphase, anaphase, and telophase are not present in cytokinesis. (ii) It is divided into four stages – prophase, metaphase, anaphase, and telophase.

Question 9

Describe the events taking place during interphase.

Accepted Answer

Interphase involves a series of changes that prepare a cell for division. It is the period during which the cell experiences growth and DNA replication in an orderly manner. Interphase is divided into three phases :(i) G1​ phase(ii) S phase(iii) G2​ phaseG1​ phase – It is the stage during which the cell grows and prepares its DNA for replication. In this phase, the cell is metabolically active.S phase – It is the stage during which DNA synthesis occurs. In this phase, the amount of DNA (per cell) doubles, but the chromosome number remains the same.G2​ phase – In this phase, the cell continues to grow and prepares itself for the division. The proteins and RNA required for mitosis are synthesised during this stage.

Question 10

What is G0​ (quiescent phase) of cell cycle?

Accepted Answer

G0​ phase is the phase of inactivation of cell cycle due to non-availability of mitogens and energy rich compounds. Cells in this stage remain metabolically active but no longer proliferate i.e., do not grow or differentiate unless called on to do so depending on the requirement of the organism. E.g., Nerve and heart cells of chordates are in permanent G0 phase.

Question 11

Can there be mitosis without DNA replication in S phase?

Accepted Answer

Mitotic cell division cannot take place without DNA replication in S phase. Two important events take place during S phase – one is the synthesis or duplication of DNA and the other is the duplication of the centriole. DNA duplication is important as it maintains the chromosome number in the daughter cells and hence mitosis is an equational division. Therefore, the duplication of DNA is an essential step and without it, no mitosis can take place.

Question 12

Can there be DNA replication without cell division?

Accepted Answer

Yes. Endomitosis is the multiplication of chromosomes present in a set in nucleus without karyokinesis and cytokinesis result-ing in numerous copies within each cell. It is of 2 types.Polyteny: Here chromosomes divide and redivide without separation of chromatids so that such chromosomes become multistranded with many copies of DNA. Such polytene (many stranded) chromosomes remain in permanent prophase stage and do not undergo cell cycle e.g., polytene (salivary glands) chromosome of Drosophila has 512- 1024 chromatids. Here number of sets of chromosomes does not change.Polyploidy (endoduplication) : Here all chromosomes in a set divide and its chromatids separate but nucleus does not divide. This results in an increase in number of sets of chromosomes in the nucleus (4x, 8xÃ¢â‚¬Â¦.). This increase in sets of chromosomes is called polyploidy. It can be induced by colchicine and granosan. These chromosomes are normal and undergo cell cycle.

Question 13

Match List - I with List - II.Choose the correct answer from the options given below.

Accepted Answer

S phase - DNA replicationG2​ phase - Proteins are synthesizedQuiescent stage - Inactive phaseG1​ phase - Interval between mitosis and initiation of DNA replication.

Question 14

Cells in G0​ phase :

Accepted Answer

Some cells in the adult animals do not appear to exhibit division (e.g., heart cells) and many other cells divide only occasionally, as needed to replace cells that have been lost because of injury or cell death. These cells that do not divide further exit G1​ phase to enter an inactive stage called quiescent stage (G0​) of the cell cycle. Cells in this stage remain metabolically active but no longer proliferate unless called on to do so depending on the requirement of the organism.

Question 15

In ‘S’ phase of the cell cycle :

Accepted Answer

In S phase, the cell synthesizes a complete copy of DNA in its nucleus. It also duplicates a microtubule-organizing structure called the centrosome. The centrosomes help separate DNA during M phase.

Question 16

In the somatic cell cycle :

Accepted Answer

During S phase or synthetic phase the replication of DNA takes place. For replication of DNA, histone. proteins are required so they are also synthesized during this phase. It takes about 30%-50% of the total cell cycle.

Question 17

At what stage of the cell cycle are histone proteins synthesized in a eukaryotic cell?

Accepted Answer

During S phase or synthetic phase the replication of DNA takes place. For replication of DNA, histone. proteins are required so they are also synthesized during this phase. It takes about 30% - 50% of the total cell cycle.

Question 18

When cell has stalled DNA replication fork, which checkpoint should be predominantly activated?

Accepted Answer

If cell has stalled DNA replication fork, it implies that it has crossed  G1​  cell cycle check point and has entered S-phase of cell cycle, where it is preparing for chromosome replication. Stalled forks activate checkpoint signaling and pause replication. Afterwards it will enter G2​  phase and will soon approach second check point called mitotic cyclin (CM) which lies between G2​ and M-phase.

Question 19

During which phase(s) of cell cycle, amount of DNA in a cell remains at 4C level if the initial amount is denoted as 2C?

Accepted Answer

A cell cycle is divided into G1​ , S, G2​   and M phases. G1​ or first growth phase is followed by S phase or synthetic phase. DNA replication occurs in S phase and DNA amount doubles up i.e., a cell with 2C DNA in G1​  phase will now have 4C DNA. G2​  phase is second growth phase where DNA content remains 4C. M phase is the phase of division where DNA content either regains 2C level (mitosis) or becomes halved i.e. 1C (in meiosis). G0phase is the phase of differentiation where cell contains DNA as in the same amount as its parent cell and does not divide further.

Question 20

In which stage of cell cycle, DNA replication occurs?

Accepted Answer

During S phase or synthetic phase the replication of DNA takes place. For replication of DNA, histone. proteins are required so they are also synthesized during this phase. It takes about 30%-50% of the total cell cycle.

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