Test: Translation & Regulation of Gene Expression - NEET MCQ

The lac operon consists of the following parts:

• Structural Gene - It consists of 3 genes:
  • z - codes for β-galactosidase
  • y - codes for permease
  • a - codes for transacetylase
• Operator -
  • It is present adjacent to the structural gene.
  • It is the site for the binding of repressor protein.
• Regulator -
  • It comprises of the i-gene, which codes for the repressor protein.
  • The repressor protein is synthesized all the time constitutively.
• Promoter -
  • It is the transcription initiation site where RNA polymerase binds.
• Inducer -
  • It is the molecule that determines whether the repressor will bind to the operator or not.
  • Hence, it regulates the operon.
  • Example - Lactose in lac operon.

The central dogma illustrates the flow of genetic information in cells, the DNA replication, and coding for the RNA through the transcription process and further RNA codes for the proteins by translation. The concept of a sequence of interaction can be understood through the framework. The most common includes biopolymers. 

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.

Option 1:

• Alec Jeffreys discovered a technique known as DNA fingerprinting. It is used for the identification of organisms based on their DNA profiles.
• Streptococcus pneumoniae is a gram-positive anaerobic bacterium that causes pneumonia. It also causes middle ear infections in children.

Option 2:

• Francois Jacob and Jacques Monod discovered the lac operon.
• Lac operon or lactose operon is found in E. coli for the metabolism of lactose and its utilization and uptake.
• Genes in lac operon code for a protein that allow them to use lactose as a source of energy.

Option 3:

• Hershey and Chase experimented to prove that DNA is the genetic material. They used bacteriophages to perform this experiment. Bacteriophages are viruses that infect bacteria.
• TMV stands for tobacco mosaic virus. It contains a single-stranded RNA virus that causes mosaic disease in tobacco. This virus affects tomatoes also.

Option 4:

• Mathew Meselson and F. Stahl discovered the semi-conservative nature of DNA replication. It means that during DNA replication, one new strand and one old strand are synthesized.
• Pisum sativum, a pea plant was used by Mendel to carry out his genetic experiments. He took seven contrasting characters of Pisum sativum and carried out crossing experiments for several generations to understand the inheritance pattern of genes.

So, the correct answer is option 2.

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.

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.