Ch 6. Molecular Basis of Inheritance (stack 2)

Question 1

Mention any two criteria that a molecule must full fill to act as genetic material.

Answer 1

1. It should be able to generate its replica (Replication).
2. It should chemically and structurally be stable.

Question 2

DNA is a better genetic material than RNA. Justify with two reasons

Answer 2

1. DNA chemically is less reactive and structurally more stable when compared to RNA.
2. The presence of thymine at the place of uracil also confers additional stability to DNA.

Question 3

List any three criteria that a molecule has to fulfil to act as a genetic material

Answer 3

1. It should be able to generate its replica (Replication).
2. It should chemically and structurally be stable.
3. It should provide the scope for slow changes (mutation) that are required for evolution.

Question 4

Why is DNA molecule a more stable genetic material than RNA? Explain

Answer 4

• DNA is structurally more stable because of its double-stranded nature.
• 2’-0 H group present at every nucleotide in RNA is a reactive group and makes RNA labile and easily degradable. RNA is also now known to be catalytic, hence reactive. Therefore, DNA chemically is less reactive and structurally more stable when compared to RNA.
• The presence of thymine at the place of uracil also confers additional stability to DNA

Question 5

1. Define replication.

Answer 5

The process of synthesis of two new DNA from a parental DNA is called replication.

Question 6

Why replication in DNA is referred to as semi-conservative replication?

Answer 6

It is because , in the resulting daughter DNA only one strand is newly synthesised and the other strand is from the parental DNA conserved as it is.

Question 7

Name the enzyme involved in the polymerization of nucleotides during DNA replication.

Answer 7

DNA polymerase

Question 8

Mention the template polarity on which replication occurs continuously

Answer 8

3’ → 5

Question 9

Mention the template polarity on which replication occurs discontinuously.

Answer 9

5’ → 3’

Question 10

Name the enzyme which joins discontinuously synthesized fragments of DNA during DNA replication

Answer 10

DNA ligase

Question 11

What is origin of replication?

Answer 11

A definite region in DNA, where replication begins

Question 12

In which phase of the cell cycle DNA replication occurs?

Answer 12

S-Phase

Question 13

Mention the functions of DNA polymerase and DNA ligase during replication

Answer 13

DNA polymerase - Catalyse polymerisation of a large number of nucleotides in a very short time.

DNA ligase - The discontinuously synthesised fragments lagging strand are later joined.

Question 14

Draw a labelled diagram of replication fork

Explain the role of enzymes involved in DNA replication.

Answer 14

Unwindase/ Helicase - Unwinding of DNA double helix

Topoisomerase/gyrase-Reduces the strain between two strands of DNA

DNA polymerase - Synthesis of new strand by linking nucleotides

DNA ligase - joining of fragments in the lagging strand

Question 15

Define transcription

Question 16

” Both the strands of DNA do not act as templates during transcription”. Justify with a reason

Answer 16

Both the strands of DNA do not act as templates during transcription because:

1. If both strands act as a template, they would code for two different proteins, and this would complicate the genetic information transfer machinery.
2. The two RNA molecules if produced simultaneously would be complementary to each other, hence would form a double stranded RNA. This would prevent RNA from being translated into protein .

Question 17

Name the enzyme involved in polymerization of nucleotides during transcription

Answer 17

RNA polymerase

Question 18

What is a ‘coding strand’ with respect to transcription?

Answer 18

The DNA strand with 5’ → 3’ polarity and the sequence same as RNA (except thymine at the place of uracil) is called coding strand.

Question 19

What is ‘template strand’ with respect to transcription?

Answer 19

The DNA strand with 3’ → 5’ polarity and acts as template for the synthesis of RNA is called template strand.

Question 20

What is the significance of promoter site on a transcription unit

Answer 20

The promoter site is a DNA sequence that provides binding site for RNA polymers and its presence defines the template and coding stand.

Question 21

What is a cistron

Answer 21

A segment of DNA coding for a polypeptide

Question 22

What do you mean by monocistronic transcriptional unit

Answer 22

A transcription unit coding for a single polypeptide.

Question 23

What is polycistronic transcriptional unit?

Answer 23

A transcription unit coding for more than one polypeptide

Question 24

What are exons

Answer 24

The coding sequences or expressed sequences in eukaryotic gene are called exons.

Question 25

What are intrans

Answer 25

The non-coding or intervening sequences in eukaryotic gene are called intrans.

Question 26

What are split genes

Answer 26

The gene in which expressed sequences are interrupted by intervening sequences or intrans are called split genes.

Question 27

Mention the function of mRNA

Answer 27

It carries coded information in the form of codons to synthesis a polypeptide.

Question 28

Mention the function of tRNA

Answer 28

It transfers amino acid from cellular pool to the site of protein synthesis.

Question 29

Mention the function of rRNA

Answer 29

It is part of ribosomes and provide site for protein synthesis.

Question 30

Why tRNA is called an adaptor molecule

Answer 30

Because, it will read the code on one hand -and on the other hand would bind to specific amino acids.

Question 31

Mention the factor that temporarily associate with RNA polymerase during initiation of transcription in prokaryotes

Answer 31

Sigma factor

Question 32

Mention the factors that temporarily associate with RNA polymerase during termination of transcription in prokaryotes.

Answer 32

Rho factor

Question 33

Mention the enzyme that transcribes mRNA in prokaryotes

Answer 33

RNA polymerase

Question 34

In bacteria, translation can begin much before mRNA is fully transcribed. Give one reason

Answer 34

Since transcription and translation occurs in the same compartment, many times the translation can begin much before the mRNA is fully transcribed.

Question 35

Mention the enzyme that transcribes hnRNA in eukaryotes.

Answer 35

RNA polymerase II

Question 36

Which enzyme is involved in transcription of tRNA in eukaryotes

Answer 36

RNA polymerase III

Question 37

Which enzyme is involved in transcription of 28SrRNA in eukaryotes

Answer 37

RNA polymerase I

Question 38

What is hnRNA?

Answer 38

Heterogeneous nuclear RNA - precursor of **mRNA**

Question 39

What is 'capping' with reference to post-transcriptional stage in eukaryotes?

Answer 39

Addition of an unusual nucleotide (methyl guanosine triphosphate) to the 5' - end of hnRNA.

Question 40

What is ' tailing' with reference to post-transcriptional stage in eukaryotes?

Answer 40

Addition of adenylate residues (200-300) to the 3' - end of hnRNA.

Question 41

1. Define ' splicing' with respect to post-transcriptional stage in eukaryotes.

Answer 41

Removal of introns and joining of adjacent exons in a defined order is called splicing.