Question

Read the sources given and answer any four from the questions given below:

Tryptophan is an amino acid which is always needed by the bacterial cells for protein synthesis and hence produced by a sequential action of five enzymes. In the tryptophan operon concept, when tryptophan is added in the medium, the switch in the bacterial cell is set off and the cell stops preparing it, as it is easily available without any effort. The repressor protein binds with tryptophan called the co-repressor to form a repressor-co-repressor complex called functional repressor molecule. The functional repressor molecule then binds with the operator gene switching it off and hence the structural genes are not expressed. There is a promoter gene present between the operator gene and the regulator gene. Promoter gene is the binding site for enzyme RNA polymerase which moves along the DNA during transcription ofmRNA. When the operator gene is on, the RNA polymerase transcribes mRNA but when the operator gene is switched off, the RNA polymerase also gets blocked and cannot transcribe. RNA polymerase also decides which strand of DNA would act as a template for synthesis of mRNA.

1. In the bacterial cell,functional repressor molecule binds with the operator gene when
   1. operator gene is switched on
   2. tryptophan is added in medium
   3. structural gene is switched off
   4. repressor protein binds with regulator gene
2. What is a co-repressor?
   1. repressor + RNA
   2. tryptophan + enzymes
   3. repressor + operator
   4. tryptophan
3. What is the position of promoter gene in tryptophan operon?
   1. after operator gene
   2. before regulator gene
   3. after structural genes
   4. between operator and regulator gene
4. Importance of promoter gene is
   1. binding site of RNA polymerase
   2. binding site for structural enzymes
   3. bind with tryptophan
   4. bind with repressor molecule
5. Function of RNA polymerase is to
   1. block operator gene
   2. bind with operator gene
   3. transcribe mRNA
   4. transcribe DNA

Answer 1

1. tryptophan is added in medium
2. tryptophan
3. between operator and regulator gene
4. binding site of RNA polymerase
5. transcribe mRNA