Which of the following statements are correct with reference to a transcription unit? A. A transcription unit in DNA is defined primarily by three regions : promoter, structural gene and terminator. B. The promoter is said to be located towards the 5'-end of the structural gene. C. The promoter is a DNA sequence that provides binding site for RNA polymerase. D. The promoter defines the template and coding strands. E. The terminator is located towards the 3'-end of the coding strand and it defines the end of the process of transcription. Choose the correct answer from the options given below:

Core Logic

The technique of DNA fingerprinting involves the following sequential steps:

• Isolation of DNA and digestion by restriction endonucleases (A).
• Separation of the digested DNA fragments based on their size by gel electrophoresis (E).
• Blotting (transferring) of separated DNA fragments from the gel to synthetic membranes like nitrocellulose or nylon (C).
• Hybridisation using a labelled VNTR probe (B).
• Detection of hybridised DNA fragments under X-rays by autoradiography (D).

Step 1: Final Conclusion

The correct logical progression is A → E → C → B → D.

Pattern Recognition

Cut (Digestion) -> Run (Electrophoresis) -> Transfer (Blotting) -> Bind (Hybridisation) -> See (Autoradiography). A-E-C-B-D.

Chapter Mix

Class 12 Biology: Molecular Basis of Inheritance

Core Logic

• Statement A is correct. Histones assemble to form a histone octamer (core of 8 molecules).
• Statement B is incorrect. Histones are positively charged basic proteins. (DNA is negatively charged).
• Statement C is correct. The positive charge of histones is due to the abundance of basic amino acid residues like lysine and arginine.
• Statement D is incorrect. DNA is negatively charged (due to phosphate groups), not positively charged.
• Statement E is correct. Higher-level packaging of chromatin requires non-histone chromosomal (NHC) proteins.

Step 1: Final Conclusion

Only statements A, C, and E are correct.

Pattern Recognition

Electrostatics in genetics: DNA = Acid = Negative. Histones = Basic = Positive. Statements B and D invert these fundamental facts, making them both false.

Chapter Mix

Class 12 Biology: Molecular Basis of Inheritance

Core Logic

In the lac operon model, the structural genes code for specific enzymes involved in lactose metabolism:

• z gene: Codes for beta-galactosidase (β$\beta$-gal), which hydrolyzes lactose into galactose and glucose.
• y gene: Codes for permease, increasing cell permeability to β$\beta$-galactosides.
• a gene: Codes for transacetylase.
• i gene: (Regulatory gene) codes for the repressor protein of the lac operon.

Step 1: Final Conclusion

The z gene codes for beta-galactosidase.

Pattern Recognition

Acronym to remember order and function: ZYA = β$\beta$-gal, Permease, Transacetylase.

Chapter Mix

Class 12 Biology: Molecular Basis of Inheritance