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Molecular Basis of Inheritance

Short Answer Type

131.

The base sequence in one of the strands of DNA is TAGCATGAT.

(i) Give the base sequence of its complementary strand.

(ii) How are these base pairs held together in a DNA molecule?

(iii) Explain the base complementarity rules. Name the scientist who framed this rule.

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132.

What is a cistron?

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Long Answer Type

133. How do m-RNA, t-RNA and ribosomes help in the process of translation?

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134.

Describe how the lac operon operates, both in the presence and absence of an inducer in E.coli.

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Short Answer Type

135.

(a) Draw a neat labelled diagram of a nucleosome.

(b) Mention what enables histones to acquire a positive charge.

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136. List the salient features of double helix structure of DNA.

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137. How are the structural genes activated in the lac operon in E.coli

The Lac operon in E.coli consists of one regulatory gene (the i gene ) and three structural genes (z, y, and a).Lactose acts as the inducer and it regulates switching on and off of the operon. The i gene produces repressor all-the-time (constitutively) which inactivates the structural gene.The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon. Lactose inactivates the repressor allowing the RNA polymerase access to the promoter and transcription proceeds. The structural genes are activated and transcribed.

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