Q. 25

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Answer :

(a)The region where the repressor protein will attach normally is the ‘operator region’ or O. It is a short region of DNA which interacts with the regulatory protein that controls the transcription of the operon.

(b) Repressor is unable to attach at this site in presence of an inducer which is Lactose.

(c) If repressor fails to attach to the said site following products would be formed at the following sites.

z: -β galactosidase

y: permease

a: Transacetylase

(d)This kind of regulation is called negative regulation because it has repressor attached to it all the time. It is also known as constitutive repressor because of which the operon is always in off position. It gets switched on only when an inducer such as Lactose or Allolactose gets attached to the site.


Transcription in eukaryotes is more complex process than in prokaryotes because:

1. In prokaryotes only one RNA polymerase enzyme is involved. Whereas in eukaryotes three RNA polymerase enzymes are involved.

2. In prokaryotes translation and transcription occurs at the same time inside the cytoplasm. Whereas in eukaryotes translation and transcription occurs at different sites.



It takes place with the help of three different RNA polymerase enzymes and several initiation factors.


Elongation in eukaryotes requires different elongation factors which stimulate the elongation of RNA.Here the addition of nucleotides takes place in the DNA strand. This makes the DNA strand longer.


Termination marks the end of transcription and release of RNA polymerase also takes place.

In eukaryotes post transcription changes also takes place which includes:

1. Cleavage: In this process large RNA strand is cleaved into smaller DNA strands.

2. Splicing: In this process extra segments from the DNA strands are removed (introns) by the enzyme nucleases.

3. Terminal additions: In this process extra nucleotides may be added for particular fuctions.

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