Ch 6. Molecular Basis of Inheritance (stack 3)

Question 1

Write any two differences between prokaryotic and eukaryotic transcription unit

Answer 1

Prokaryotic

1. It is polycistronic
2. Structural gene is uninterrupted

Eukaryotic

1. It is monocistronic
2. Structural gene is interrupted

Question 2

Differentiate between intrans and exons

Answer 2

Intrans - They do not code for any protein. Intrans or intervening sequences do not appear in mature or processed RNA.

Exons - The coding sequences or expressed sequences are defined as exons. Exons are said to be those sequence that appear in mature or processed RNA.

Question 3

Write the coding strand and the sequence of base on mRNA synthesized by DNA template with the sequence 3’-ATGCATAGCAT-5’.

Answer 3

Coding strand- 5’ -TACGTATCGTA - 3’

mRNA- 5’ - UACGTUTCGTU - 3’

Question 4

Write a note on the role of sigma factor and the rho factor in transcription in prokaryotes.

Answer 4

The sigma (σ) factor) binds to the RNA Polymerase to form the holoenzyme. It is responsible for promoter recognition and subsequent initiation of transcription of each bacterial gene.

Rho factor is a protein that recognizes and binds preferably to C-rich sites in the mRNA. It is required for the termination of transcription by an RNA polymerase and is essential for the viability of the cell.

Question 5

In bacteria, translation can begin much before the mRNA is fully transcribed. Justify with two reasons.

Answer 5

In bacteria, since the mRNA does not require any processing to become active, and also since transcription and translation take place in the same compartment (there is no separation of cytosol and nucleus in bacteria), many times the translation can begin much before the mRNA is fully transcribed.

Question 6

RNA polymerases in eukaryotes show a clear cut division of labour

Answer 6

• The RNA polymerase I transcribes rRNAs (28S, 18S, and 5.8S),
• RNA polymerase III is responsible for the transcription of tRNA, Ssr RNA, and snRNAs (small nuclear . RNAs).
• The RNA polymerase II transcribes the precursor of mRNA, the heterogeneous nuclear RNA (hnRNA).

Question 7

Explain the function of the following:

(a) Promoter
(b) tRNA
(c) Exons

Answer 7

It is a DNA sequence that provides a binding site for RNA polymerase.

Transfer amino acids from the cellular pool to the place of protein synthesis

Expressed sequences or coding sequences in matured mRNA

Question 8

Define genetic code

Answer 8

The sequence of nucleotides on DNA/mRNA specifying the sequence of amino acids in protein is called genetic code

Question 9

Name the Severo Ochoa enzyme

Answer 9

Polynucleotide phosphorylase

Question 10

What is the special property of Severo Ochoa enzyme (polynucleotide phosphorylase

Answer 10

Helpful in polymerising RNA with defined sequences in a template independent manner.

Question 11

Name the initiator codon

Answer 11

AUG

Question 12

What other function the initiator codon performs in addition to initiating translation?

Answer 12

It codes for the amino acid methionine

Question 13

Mention terminator codons

Answer 13

UAA, UAG and UGA

Question 14

Why UAA is considered as terminator or stop codon

Answer 14

Because it does not code for any amino acid and the translation will end at this codon.

Question 15

Why genetic code is said to be universal?

Answer 15

Because, the codons which specify the amino acids is same in all living organisms.

Question 16

Why genetic code is said to be unambiguous or specific

Answer 16

Because, a particular codon will code for a specific amino acid

Question 17

What is point mutation?

Answer 17

Point mutation is a type of mutation caused by the substitution of a nucleotide by another nucleotide, or the deletion or insertion of a nucleotide into the DNA resulting in a change from the normal or wild type gene sequence.

Question 18

What is frame shift insertion mutation?

Answer 18

Shifting of reading frame one or two steps forward due to addition of one or two nucleotides

Question 19

What is frame shift deletion mutation?

Answer 19

Shifting of reading frame one or two steps backwards due to deletion of one or two nucleotides

Question 20

Mention an example of a genetic disorder that is a result of point mutation.

Answer 20

Sickle cell anaemia

Question 21

Name Severo Ochoa enzyme. Mention its function

Answer 21

Severo Ochoa enzyme - Polynucleotide phosphorylase.

It was helpful in polymerising RNA with defined sequences in a template-independent manner (enzymatic synthesis of RNA).

Question 22

Explain any two properties of genetic code

Answer 22

• The codon is triplet. 61 codons code for amino acids and 3 codons do not code for any amino acids, hence they function as stop codons.
• One codon codes for only one amino acid, hence, it is unambiguous and specific

Question 23

Mention the initiator and terminator codons

Answer 23

AUG - Initiator codon

UAA, UAG and UGA - Terminator codon

Question 24

“Codon AUG has dual function”. Justify the statement

Answer 24

AUG has dual functions. It codes for Methionine.(met), and it also act as initiator codon

Question 25

Define translation.

Answer 25

The process of polymerisation of amino acids to form a polypeptide as defined by the sequence of codons on mRNA is called translation.

Question 26

Name the cellular factory responsible for synthesizing proteins

Answer 26

Ribosomes

Question 27

What do you mean by charging of tRNA with respect to translation

Answer 27

Linking of a specific amino acid to a specific tRNAin the presence of ATP energy is called charging of tRNA

Question 28

What do you mean by aminoacylation of tRNA with respect to translation

Answer 28

Linking of a specific amino acid to a specific tRNA in the presence of ATP energy is called charging of tRNA

Question 29

What is the function of ibosome during chain elongation of translation

Answer 29

Ribosomes acts as catalysts for linking the amino acids by peptide bonds.

Question 30

Which type of rRNA acts as ribozyme for the formation of peptide bonds during translation in bacteria

Answer 30

23S rRNA

Question 31

Mention the type of RNA that has anticodon

Answer 31

tRNA

Question 32

Expand UTR with reference to mRNA

Answer 32

Untranslated region

Question 33

What is an operon?

Answer 33

A group of genes clustered under common promoter, operator and reg ula to r gene is called operon.

Question 34

What is lac operon?

Answer 34

A group of genes involving in lactose metabolism clustered under common promoter, operator and regulator gene is called lac operon.

Question 35

Name the protein produced by lac ‘i’ gene

Answer 35

Repressor protein

Question 36

What is the function of regulatory gene of Lac-operon?

Answer 36

It codes for repressor protein.

Question 37

Why transcription in E.coli does not occur in the absence of lactose in the medium?

Answer 37

Because, the repressor protein binds to the operator region in the absence of lactose and prevents binding of RNA polymerase to the promoter region.

Question 38

How does repressor protein prevent the transcription of strnctural genes

Answer 38

The repressor protein binds to operator region in the absence of lactose and prevents binding of RNA polymerase to promoter region

Question 39

What is the function of- galactosidase in E.coli

Answer 39

Breaking lactose into glucose and galactose

Question 40

Mention the function of permease in E.coli

Answer 40

Transport lactose into the cells from outside medium

Question 41

What is the importance of operator in Lac-operon?

Answer 41

It provides site for binding of repressor protein

Question 42

Mention the inducer that inactivates Lac repressor protein

Answer 42

lactose

Question 43

Why lactose is termed as inducer with reference to Lac-operon?

Answer 43

Because, it induces the expression of lac- operon by binding to repressor protein

Question 44

What is negative regulation

Answer 44

Regulation of lac operon by repressor protein is referred to as negative regulation