NCERT Questions for Class 12 Biology Chapter 5 – Molecular Basis of Inheritance

Important Questions with Solutions of Class 12 Biology Chapter 5 – Molecular Basis of Inheritance

1) What are the 4 criteria that convert a molecule into a genetic material?

Ans – The criteria that convert a molecule into genetic material are:

1. Rising of the replica.
2. Chemical and structural stability is important.
3. It should suffice its expressions with the Mendelian characters.

Mutation as a slow change is a must priority for evolution.

2) The strands of DNA are not copied during transcription. Give reason.

Ans –

a. In a situation where the DNA is copied results in 2 different RNAs as complementary. It also paves the way for the rise of two polypeptides. In a segment of DNA where two polypeptides are produced, the genetic information machinery automatically becomes complicated.

• Recognition of criminals in the forensic laboratory.
• Identification of real parents in a time of dispute.
• Determining racial groups to rewrite biological evolution.

b. Instead of translating into polypeptides, the 2 complementary RNA would result in a double standard RNA.

c. The polymerization is carried out by the RNA polymerase in 53 angles thus creating the template strand i.e. the DNA strand with 35 polarity acts.

3) Explain the fact that DNA polymerase plays a dual function during the time of DNA replication.

Ans – There are two functions played by DNA polymerase. They are:

1. Provides a hand in the synthesis of new strands.
2. Assists in proofreading, i.e. replacing RNA strands into DNA fragments.

4) Why does both the strands of DNA are not copied during the transcription of the DNA?

Ans – The strands of DNA are not copied during the transcription of the DNA because:

1. Genetic machinery would face complications if the strands coding for RNA can build 2 different RNA molecules & 2 different proteins.
2. Two RNA molecules, as complementary to each other will accumulate together. It forms dsDNA without any translation making the transcription process more futile.

5) The binding of tRNA to amino acids and mRNA codons during protein synthesis is necessary. Give reason.

Ans – The binding of tRNA to both amino acids and mRNA codons during protein synthesis is necessary because tRNA working as an adapter molecule gets hand into the cytoplasm accumulating the particular activated amino acid and later transferred to the ribosomal present within the cytoplasm, where proteins are synthesized. It eventually gets attracted towards the ribosome in a pattern marked by mRNA and ends with the transmission of the amino acid to a polypeptide chain.

6) Explain frameshift mutation and a disease caused by this disorder.

Ans – Adding/deleting one or two bases, the reading from the site of mutation changes which results in a protein with different sets of amino acids. This whole process is known as frameshift mutation.

7) Distinguish between DNA and RNA based on their structure/chemistry and function.

Ans – The difference between DNA and RNA based on their structure/chemistry and function:

DNA	RNA
Molecules with two strands.	Molecules with only one strand.
As a pyrimidine base, thymine is used.	As a pyrimidine base, uracil is used.
Deoxyribose replicates into pentose sugar.	Ribosome replicates into sugar.
Without being reactive, it’s quite stable.	It’s reactive due to the presence of 2’-OH.
The synthesis of polypeptides is commanded.	Helps in protein synthesis.
The location is in the nucleus itself.	Transported into the cytoplasm.

8) Elaborate on the conversion of the hnRNA into the mRNA or the procedure of splicing, capping & tailing occurring during transcription in Eukaryotes.

Ans – hnRNA followed by mRNA undergoes:

1. Splicing: Exons accumulate together and removal of introns happens.
2. Capping: Methyl guanosine triphosphate, an unusual nucleotide provides as an add-on at the 5’ in the end of hnRNA.
3. Adenylate residues (200-300) offer an add-on at the 3’ during hnRNA.

9) How can such a huge DNA (sized as N 2.2 m in a eukaryotic cell) be packed into a nucleus of micrometers in diameter?

Ans – Nucleosome is a structure in eukaryotes, in which the DNA is packed around a positively charged histone octameter. In an atypical nucleosome, the range of DNA Felix is around 200bp.

Chromatin fibers are formed from the repeating units of nucleosomes.

Chromatin fiber condenses into chromosomes at the metaphase stage of cell division. Non-histone chromosome protein is an additional set of proteins needed for the chromatin package at a higher level in the nucleus. Euchromatin is the certain chromatin regions that are loosely packed compared to the other areas where it’s stainless. Meanwhile, heterochromatin is the other region that is lightly packed & the stains darker.

Key concepts covered in Chapter 5 of Class 12 Biology – Molecular Basis of Inheritance

Chapter 5 of Class 12 Biology covers a variety of essential topics related to the molecular basis of inheritance. Some key concepts covered in this chapter include:

• Structure of DNA and RNA
• DNA replication
• Genetic code and gene expression
• Regulation of gene expression
• Genetic variations and mutations

Structure of DNA

Two long nucleotide chains twist into a double-helix shape to form DNA. Each nucleotide consists of a sugar molecule, a phosphate group, and one of the nitrogenous bases: adenine, thymine, cytosine, or guanine. The pairing of these DNA strands through complementary pairing holds them together and replicates accurate genetic information.

Replication of DNA

Before the division of a cell, a basic process called replication makes a copy of the cell’s genetic material. In replication, the unwinding double helix forms two strands of DNA. It does semiconservative duplication with the aid of enzymes called DNA polymerases. Each daughter cell passes on genetic information in this way.

Transcription and Translation

Transcription is the process whereby the transfer of genetic information from DNA occurs in messenger RNA. This mRNA thus holds the genetic code of DNA in the nucleus, transporting it into the cytoplasm to the ribosomes for translation into protein. The ribosomes are where translation occurs, with the task of translating the genetic code into a precise sequence of amino acids that compose a protein.

Genetic Variation and Inheritance

Gene expression, genetic recombination, and mutations are part of the processes that bring about genetic variation. Such differences are important for evolution, increasing diversity in characteristics within a population. This refers to inheritance—the transfer of genetic information from parents to offspring that enables life to go from one generation to the next.

How do these concepts contribute to our understanding of genetics?

By understanding the structure of DNA and RNA, students can learn how it stores and passes on the genetic information in cells. The mechanism of DNA replication is critical to understand that an adequate and proper form of duplication of genetic material occurs in cell division. Furthermore, understanding the genetic code and gene expression explains how genes convert into functional proteins that carry out biological functions.