Molecular Basis of Inheritance Test 8

The gene product of lacZ is beta- galactosidase which cleaves lactose, a disaccharide, into glucose and galactose. LacY encodes Beta-galactoside permease, a membrane protein which becomes embedded in the cytoplasmic membrane to enable the cellular transport of lactose into the cell.

Gene is a sequence of nucleotides in DNA or RNA that encodes the synthesis of a gene product, either RNA or protein. When we divide gene, it gets divided into 3 parts - Cistron, Recon and Muton . Cistron is the largest one in the gene. It encodes for the polypeptide during protein synthesis. Recons are the locations within a gene which takes part in recombination and Muton are the elements which undergoes mutation. Hence, the correct sequence is b.

Regulator gene controls the expression of operon and produces a small protein molecule known as repressor. It is a DNA or RNA binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers. It blocks the attachment of RNA polymerase to the promoter.hence, it prevents translation of mRNA into protein and this entire process is known as repression.

Joint joining of nucleotide in RNA and DNA is done by DNA/RNA ligase.

It consists of three adjacent structural genes, a promoter, a terminator, and anoperator. The lac operon is regulated by several factors including the availability of glucose and lactose. It can be activated by allolactose. Lactose binds to the repressor protein and prevents it from repressinggene transcription.

In case of lactose presence
(i) Lactose acts as an inducer which binds to the repressor and forms an inactive repressor.
(ii) The repressor fails to bind to the operator region.
(iii) The RNA polymerase binds to the operator and transcript lac mRNA.
(iv) lac mRNA is polycistronic, i.e., produces all three enzymes, β -galactosidase, permeaseand transacetylase.
(v) The lac operon is switched on.

In case of lactose absence
(i) When lactose is absent, i gene regulates and produces repressor mRNA which translate repression.
(ii) The repressor protein binds to the operator region of the operon and as a resultprevents RNA polymerase to bind to the operon.
(iii) The operon is switched off.   

The cellular factory responsible for synthesising proteins is the ribosome. The ribosome consists of structural RNAs and about 80 different proteins. In its inactive state, it exists as 2 subunits, as a large subunit and a small subunit. When the small subunit encounters an mRNA, the process of translation of the mRNA to protein begins.

Single nucleotide polymorphisms(SNP), represents a difference in a single DNA building block, called a nucleotide.it is a location on sites in human DNA where single base DNA differences occurs.