Molecular Basis of Inheritance — Practice

Question 1

Why was the Hershey-Chase experiment decisive in proving DNA is the genetic material?

Accepted Answer

They labelled phage protein with 35S and DNA with 32P. After infection, only 32P (DNA) entered the bacteria and appeared in progeny phages, while 35S (protein) stayed outside, showing DNA is the genetic material.

Question 2

What is semiconservative replication and how did Meselson-Stahl prove it?

Accepted Answer

Each daughter DNA has one parental and one new strand. Meselson and Stahl grew E. coli in heavy 15N, switched to light 14N, and after one generation found DNA of intermediate density (15N-14N), confirming semiconservative replication.

Question 3

How many amino acids would a polypeptide encoded by 150 codons have?

Accepted Answer

Roughly 150 (one per codon); excluding the stop codon, about 149 amino acids.

Question 4

What is the function of the lac operon repressor?

Accepted Answer

In the absence of lactose, the repressor binds the operator and blocks RNA polymerase, switching the genes off. When lactose (allolactose) binds the repressor, it releases from the operator, allowing transcription of lacZ, lacY, and lacA.

Question 5

What is the significance of VNTRs in DNA fingerprinting?

Accepted Answer

VNTRs (variable number tandem repeats) differ in copy number between individuals (except identical twins), producing a unique banding pattern used to identify people.

Practice — Molecular Basis of Inheritance

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