Tag: expression of gene

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Multiple choice expression of gene inherited changes biology

Inducible operons differ from repressible operons in that

  1. operator of inducible operons is switched off by a repressor protein

  2. inducible operons have an operator that controls binding of RNA polymerase to the promoter region

  3. inducible operons use activators and positive control to regulate their transcription

  4. inducible operons usually include structural genes that function in catabolic pathways
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The inducible operon is usually off and it can be induced in the presence of inducer like lactose. After getting induced, the operon is turned on and transcription takes place to catabolize these inducers. Hence, the inducible operon is usually involved in catabolism. 

While repressible operon is on normally and results in transcription of structural genes to produce the desired product for e.g. tryptophan. Hence, it works at times when the bacterial cell does not require these products like tryptophan and the presence of tryptophan from external source turns off this operon. 
So, the correct option is 'inducible operons usually include structural genes that function in catabolic pathways'.

Multiple choice expression of gene inherited changes biology

Choose the correct answer from the alternatives given :
Repressible operon system is usually found in (i) pathways. The pathways end product serves as a (ii) to activate the repressor, turn off enzyme synthesis and prevent overproduction of the end product of the pathway. Genes for this operon are usually switched (iii) and the repressor is synthesised in an (iv) form.

  1. (i) anabolic, (ii) corepressor, (iii) on, (iv) - inactive

  2. (i) anabolic, (ii) inducer, (iii) off, (iv) - active

  3. (i) catabolic, (ii) inducer, (iii) off, (iv) - active

  4. (i) catabolic, (ii) corepressor, (iii) on, (iv) - inactive
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Repressible operons are generally involved in anabolic pathways, or the synthesis of an essential component, while inducible operons are generally involved in catabolic pathways or the breakdown of a nutrient. Positive control of an operon is when gene expression is stimulated by the presence of a regulatory protein. The repressible operon work on the feedback inhibition mechanism which is the phenomenon where the output of a process is used as an input to control the behavior of the process itself and the co-repressor serves as to activate the repressor. Genes of a repressible operon are switched off as they are required to synthesize the structural/functional genes in the absence of the repressor. The presence of the repressor can stop this process and hence the repressor is present in the inactive form. 

So, the correct option is '(i) anabolic, (ii) corepressor, (iii) on, (iv) - inactive'.