Biology Class 12 NCERT Solutions: Chapter 6 Molecular Basis of Inheritance Part 2

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Q.6 Depending upon the chemical nature of the template (DNA or RNA) and the nature of nucleic acids synthesized from it (DNA or RNA), list the types of nucleic acid polymerases.

Answer:

  • There are two different types of nucleic acid polymerases.

  • DNA-dependent DNA polymerases

  • DNA-dependent RNA polymerases

  • The DNA-dependent DNA polymerases use a DNA template for synthesizing a new strand of DNA, whereas DNA-dependent RNA polymerases use a DNA template strand for synthesizing RNA.

Q.7 How did Hershey and Chase differentiate between DNA and protein in their experiment while proving that DNA is the genetic material?

Answer:

  • Hershey and Chase worked with bacteriophage and E.coli to prove that DNA is the genetic material. They used different radioactive isotopes to label DNA and protein coat of the bacteriophage.

  • They grew some bacteriophages on a medium containing radioactive phosphorus (32P) to identify DNA and some on a medium containing radioactive sulphur (35S) to identify protein.

  • Then, these radioactive labelled phages were allowed to infect E.coli bacteria. After infecting, the protein coat of the bacteriophage was separated from the bacterial cell by blending and then subjected to the process of centrifugation.

  • Since the protein coat was lighter, it was found in the supernatant while the infected bacteria got settled at the bottom of the centrifuge tube.

  • Hence, it was proved that DNA is the genetic material as it was transferred from virus to bacteria.

Image of Hershey - Chase Experiment

Image of Hershey - Chase Experiment

Q.8 Differentiate between the followings:

(a) Repetitive DNA and Satellite DNA

(b) mRNA and tRNA

(c) Template strand and Coding strand

Answer:

(a) Repetitive DNA and satellite DNA

Table of Repetitive DNA and Satellite DNA
Table of Repetitive DNA and satellite DNA

Repetitive DNA

Satellite DNA

1.

Repetitive DNA are DNA sequences that contain small segments, which are repeated many times.

Satellite DNA are DNA sequences that contain highly repetitive DNA.

(b) mRNA and tRNA

Table of mRNA and tRNA
Table of mRNA and tRNA

mRNA

tRNA

1.

mRNA or messenger RNA acts as a template for the process of transcription.

tRNA or transfer RNA acts as an adaptor molecule that carries a specific amino acid to mRNA for the synthesis of polypeptide.

2.

It is a linear molecule.

It has clover leaf shape.

(c) Template strand and coding strand

Table of Template Strand and Coding Strand
Table of Template strand and coding strand

Template strand

Coding strand

1.

Template strand of DNA acts as a template for the synthesis of mRNA during transcription.

Coding strand is a sequence of DNA that has the same base sequence as that of mRNA (except thymine that is replaced by uracil in DNA).

2.

It runs from.

It runs from.

3.

Produces working copies of RNA molecule and is also known as master strand or sense strand.

It does not participate in transcription and is also called non template strand.

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