NCERT Solutions Class 12 Biology Chapter 6
The study of living beings, their origins, anatomy, morphology, physiology, behaviour, and distribution is called biology. It is a broad-ranging natural science with various unifying elements that unite it as a single, cohesive topic. In the past, there was a phrase for biology in English called lifelore, but it is no longer used.
NCERT Class 12 Biology Chap 6: The Molecular Basis of Inheritance.
The study of genes is part of the molecular foundation of heredity. DNA as genetic material, DNA replication, transcription, translation, genetic code, gene expression control, and many other topics are covered in the research. As you’ve read, DNA has a double-helical structure, which was discovered in the 1950s by James Watson and Francis Crick using their theory, model, and experiment. Each strand of DNA helix is made up of nucleotide repeating units.
Chapter 6 Class 12 Biology is a study of genetics. Students may find it a little challenging to get a hold of this chapter. Extramarks lends a helping hand by providing NCERT Solutions Class 12 Biology Chapter 6. These Solutions will give students an idea of the answer writing pattern for the upcoming board examinations and further guide them with the help of sample papers, notes, so that they can be confident in their preparation and add to their academic excellence.
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Key Topics Covered in NCERT Solutions Class 12 Biology Chapter 6
Mentioning below the key concepts covered in NCERT Solutions Class 12 Biology Chapter 6- Molecular basis of Inheritance:
| What is DNA? |
| Structure of Polynucleotide |
| Talking about a Gene |
| Packaging DNA Helix |
| RNA World |
| Genetic Code |
| Regulation of Gene Expression |
Extramarks’ briefly explains each subtopic in NCERT Solutions Class 12 Biology Chapter 6- Molecular Basis of Inheritance.
What is DNA?
DNA, or deoxyribonucleic acid, is the molecule of heredity in all living beings since it conveys genetic information. It’s a lengthy deoxyribonucleotide polymer chain. The amount of nucleotide base pairs in it determines its length.
Based on X-ray crystallography of DNA, Watson and Crick were the first scientists to suggest a double-helical model for the molecule. Every strand of DNA is made up of nucleotides, each of which comprises deoxyribose sugar, a nitrogen base, and a phosphate.
According to the central dogma of molecular biology, genetic information passes from DNA to RNA to Protein.
The whole structure of DNA resembles a twisted ladder. Weak hydrogen bonds between the nitrogen bases hold the two strands of DNA together. Purine bases always couple with pyrimidine bases, such as adenine (A) with thymine (T) and guanine (G) with cytosine (C).
Students can refer to NCERT Solutions Class 12 Biology Chapter 6 for a detailed explanation of DNA and its aspects. In addition, they can register with Extramarks to access concise, authentic study material in abundance.
Structure of Polynucleotide
NCERT Solutions Class 12 Biology Chapter 6 explains the structure of Polynucleotide in the following section.
The three constituents that make up a nucleotide are the nitrogenous base, sugar, and phosphate group. Purines (Adenine and Guanine) and Pyrimidines are nitrogenous bases (Cytosine and Thymine). The pentose sugar (ribose in RNA and deoxyribose in DNA) makes up the sugar portion, while the nucleoside and nucleotide make up the phosphate group.
Talking about a Gene
NCERT Solutions Class 12 Biology Chapter 6 describes that the functional unit of Inheritance is the gene. DNA comprises both coding and non-coding nucleotide sequences in all eukaryotic species. Exons and introns are the terms for coding and non-coding sequences, respectively. The Exons are visible in mature RNA, while the introns are not.
RNA stands for Ribonucleic Acid. It is a single strand of nucleic acid found in all living cells that serves as a messenger for DNA’s instructions on protein synthesis regulation. The three main kinds of RNA molecules are:
- Ribosomal RNA (rRNA)
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
Packaging DNA Helix
- In prokaryotes, DNA is organised in a massive loop in the nucleoid region, with positively charged proteins holding negatively charged DNA tightly.
- In prokaryotes, DNA is organised in chromosomes in a complicated manner. First, DNA is twisted around the centre of a histone octamer (a unit with eight histone molecules) to create a nucleosome.
- Positively charged proteins in the form of histones, which are high in the essential amino acids lysine and arginine, have been discovered. H1, H2A, H2B, H3, and H4 are the five kinds. The histone octamer comprises two molecules of four histone proteins that are important for gene regulation.
- The nucleosome is a chromatin repeating unit that prevents DNA from tangling and contains about 200 bp of DNA.
- NHC makes it easier for chromatin to be packaged further (Non-histone chromosomal proteins).
- Euchromatin: Euchromatin is a transcriptionally active region with loosely packed chromatin that absorbs light stains.
- Heterochromatin: Heterochromatin is a transcriptionally dormant region with tightly packed chromatin that absorbs the black dye.
RNA World
NCERT Solutions Class 12 Biology Chapter 6 states that RNA was the initial genetic material, and there is sufficient evidence to show that critical life processes originated around it. It is employed as a genetic material as well as a catalyst. However, as a catalyst, RNA was extraordinarily reactive and hence unstable. As a result, DNA developed from RNA, with chemical changes that made it more stable.
Replication
- Watson and Crick presented a semiconservative model for DNA replication.
- Meselson and Stahl demonstrated that DNA replicated semi-conservatively in 1958.
- Taylor established that DNA replication is semiconservative in another experiment on faba beans (Vicia faba) using radioactive thymidine.
- Enzyme DNA replication is catalysed by DNA polymerase. Only in the 5’3′ direction can it polymerise.
- Replication is continuous in a strand with a 5 ‘3’ direction, referred to as the leading strand, with a 3′ 5′ polarity, referred to as the leading strand template.
- When using a trailing strand template with a polarity of 5’3′, replication is interrupted.
Transcription
NCERT Solutions Class 12 Biology Chapter 6 describes that only one section of the genetic information in DNA gets transcribed into RNA. In RNA, instead of Thymine, Adenine interacts with Uracil. The structural gene, promoter, and terminator are all involved in DNA transcription. Transcription is catalysed by RNA polymerase, and the direction of transcription is the same as that of replication by DNA polymerase, i.e. 5’3′. The antisense strand template strand has a 3’5′ polarity and is a template for RNA synthesis. The coding strand, also known as a sense strand, has a polarity of 5’3′. It also has a structural gene, a promoter, a terminator, exons, and introns.
Genetic Code
These are the base sequences in mRNA that code for a particular amino acid in protein production. Every code is made up of three nucleotides called triplets. There are 64 codons in all, with 61 coding for amino acids. The remaining three are called stop codons since they do not code for any amino acids. For example, the start codon, AUG, also codes for the amino acid methionine.
Mutations and Genetic Code
Point mutation is caused by a change in a single base pair. For example, sickle cell anaemia is caused by a mutation in the gene that codes for the -globin chain. As a result, Glutamate in the normal protein is changed to Valine in the sickle cell. When one or two base pairs are lost or gained, the reading frame at the location of deletion or insertion is altered. A frameshift mutation is a term for this type of mutation.
Translation
NCERT Solutions Class 12 Biology Chapter 6 explains Translation as the polymerisation of amino acids. Peptide bonds link amino acids together. The three RNAs (mRNA, tRNA, and rRNA) play a unique function in the translation process. The aminoacylation of tRNA is the first step in the translation process. Ribosomes catalyse the synthesis of peptide bonds, operating as a protein-making factory. The translation procedure is always in the 5’3′ direction. The large subunit of a ribosome has two places where two tRNAs with amino acids near enough to form a peptide bond can be accommodated.
Regulation of Gene Expression
- In eukaryotes, the expression of a gene that produces polypeptide can be controlled at many levels:
- When the primary transcript, i.e. transcription, is created.
- At the time of splicing or processing.
- When mRNA is being transported from the nucleus to the cytosol.
- When it comes to protein synthesis or translation.
- Environmental, physiological, and metabolic factors all influence gene expression.
- The coordinated control and expression of numerous genes are responsible for the embryo’s growth and differentiation.
- In prokaryotes, gene expression is mainly controlled at the transcriptional start.
- Regulatory proteins, which can be repressors or activators, control the activity of RNA polymerase at the start site.
- The promoter region’s accessibility is controlled by a neighbouring operator sequence that binds to a particular protein, usually a repressor. In a specific operator, there is a particular operator and repressor protein.
NCERT Solutions Class 12 Biology Chapter 6 Exercise and Solutions
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By getting access to NCERT Solutions Class 12 Biology Chapter 6, students can easily understand all the concepts relating to the Molecular Basis of Inheritance.
Key Features of NCERT Solutions Class 12 Biology Chapter 6
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