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CBSE 12th Standard Biology Subject Molecular Basic of Inheritance Ncert Exemplar 2 Marks Questions 2021

Published on: 25/05/2021

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Questions:

Generic 2

5 x 2 = 10

Name a few enzymes involved in DNA replication other than DNA polymerase and ligase. Name the key function for each of them.

Explain when is a genetic code said to be
(i) Degenerate (ii) Universal

What are the functions of
(i) methylated guanosine cap and
(ii) poly A-tail in a mature mRNA?

What is the cause of discontinuous synthesis of DNA on one of the parental strands of DNA?What happens to these short stretches of the DNA synthesised?

Recall the experiment of Frederick Griffith.If RNA instead of DNA was the genetic material would the heat-killed S-strain of the bacteria have transformed the R-strain into S-strain? Explain your answer

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Answers Key:

Generic 2

5 x 2 = 10

The enzymes involved in DNA replication other than DNA polymerase and ligase are listed below with their functions:

Helicase	-opens the helix
Topoisomerases	-Removes the tension caused due to unwinding
DNA ligase	-Joins the cut DNA strands

The differences between unambiguous and universal genetic codes are as follows

Unambiguous	Universal
In genetic code, one codon codes for only one amino acid hence, it is unambiguous	The genetic code is universal.i.e. each codon codes for same amino acid in all organisms

(ii) The differences between degenerate and initiator codes are as follows

Degenerate	Initiator
Some amino acids are coded by more than one codon, hence the code is degenerate, e.g. serine, leucine, arginine are encoded by 6 codons.	These codons act as start signal for translation. e.g. AUG acts as initiator codon and it codes for methionine

(i) The methylated guanosine cap helps in the binding of mRNA to the smaller subunit of ribosome during initiation of translation.
(ii) Poly-A tail has a direct relatioship with the logevity of mRNA.

1. DNA polymerase can polymerise the nucleotides only in 5' -> 3' direction.
2. Hence on the template strand of DNA with 5' -> 3' polarity there is discountinuous synthesis.
3. These short stretches of DNA are joined together by DNA-ligase into a new strand of DNA.

1.The presence of 2'OH-group of ribose makes RNA more labile and prone to degradation.
2.In the heat-killed S-strain,it would not have remained functional and hence would not have transformed the R-cells into S-cells.