Molecular Basis of Inheritance Test - 4

Thymine and Adenine bond with each other so, they are equal in number. Sum of cytosine and guanine is equal to 100-60=40 percent. So, percentage of guanine is 40/2= 20 percent.

In biochemical genetics the term gene is being replaced by cistron. Cistron is a segment of DNA consisting of a stretch of deoxyribonucleotides which code for a biochemical controlling other cistron.

In lac operon, Francois Jacob and Jacque Mono elucidated that in absence of lactose the repressor binds with the operator gene and forms the particular protein to express itself.

Bacterium E.coli with a mutated z gene of the lac operon cannot grow in medium containing only lactose as the source of energy because E.coli cannot synthesize functional beta galactosidase essential for cell wall formation.

Transcription is the process of copying DNA code into mRNA. It occurs in the nucleus of the cell. The mRNA comes out of nucleus then its translation occurs into cytoplasm to form protein.

In lac operon, lactose is the substrate for enzyme beta-galactocidase and it regulates switching ON and OFF of the operon. Hence, lactose is called the inducer.

Lac Operon consists of one regulator gene, i and three structural genes z, y and a. I gene code for repression of the lac Operon. Z gene code for beta-galactosidase, y code for permease and a gene code for transactylase.

An operon is a cluster of coordinately regulated genes. It includes structural genes (generally encoding enzymes), regulatory genes (encoding, e.g. activators or repressors) and regulatory sites (such as promoters and operators).

The type of control is defined by the response of the operon when no regulatory protein is present.

The inducer–repressor control of the lac operon is an example of negative control, in which expression is normally blocked.

In contrast, the CAP-cAMP system is an example of positive control, because expression of the lac operon requires the presence of an activating signal.

The correct sequence of events involving gene expression includes formation of primary transcript, regulation of splicing, transport of mRNA from nucleus to cytoplasm and translation.