Class 12 Biology Chapter 5 is “Molecular Basis of Inheritance”. Here, you will get chapter 5 study materials, notes along with important questions with answers. You can not only study this online but can get all of these study materials in PDF form for free download. This will help you to understand the chapter 5 more easily and learn quickly.
Below, you will get the class 12 Biology subject books pdf download links. Students can visit the link and download the Biology book pdf from the official NCERT website links –
Class 12 Biology Book pdf free download – https://ncert.nic.in/textbook.php?lebo1=1-13
Class 12 Biology Chapter 5 “Molecular Basis of Inheritance” notes
This chapter “Molecular Basis of Inheritance” explain how genetic information is transfer from one generation to another through molecular mechanisms. It looks into the role of DNA, the key molecule in storing and passing on genetic information.
Deoxyribonucleic Acid (DNA)
DNA, also known as deoxyribonucleic acid, is a crucial molecule present in all living beings. In 1953, James Watson and Francis Crick put forward the idea of the double helix structure of DNA. They figured out how DNA is shaped by studying X-ray diffraction data gathered by Rosalind Franklin and Maurice Wilkins. Their model of the DNA double helix, where two strands run in opposite directions and are twisted together, connected by hydrogen bonds between matching bases, gave a new perspective on how traits are passed down and changed the way we look at biology.
DNA is a double-stranded molecule made up of two polynucleotide chains twisted around each other to create a double helix. Each chain consists of nucleotides containing a sugar (deoxyribose), a phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G).
The two DNA strands are connected by hydrogen bonds between complementary bases: adenine pairs with thymine (A-T), and cytosine pairs with guanine (C-G). This base pairing guarantees accurate DNA replication during cell division.
DNA carries the genetic instructions essential for the growth, development, functioning, and reproduction of all living organisms. These instructions are stored in the sequence of nucleotide bases along the DNA molecule.
The sequence of bases in DNA creates the genetic code, determining the sequence of amino acids in proteins. The genetic code is read in sets of three nucleotides known as codons, with each codon coding for a specific amino acid.
Prior to cell division, DNA replicates to produce two identical copies of the genetic material. DNA replication is a semi-conservative process where the two DNA strands separate, and each strand acts as a template for the creation of a new complementary strand.
Ribonucleic Acid (RNA)
RNA, also known as ribonucleic acid, is an extremely important molecule that can be found in all living cells. RNA is made up of a single strand of nucleotides. Each nucleotide consists of a ribose sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), uracil (U), cytosine (C), and guanine (G). Unlike DNA, RNA contains uracil instead of thymine. Due to its single-stranded nature, RNA can form various secondary structures.
Types of RNA: There are different types of RNA, each with its own specific functions:
- Messenger RNA (mRNA): It carries genetic information from DNA to the ribosomes, where proteins are synthesized.
- Transfer RNA (tRNA): It transfers amino acids to the ribosomes during protein synthesis, matching them with the codons on the mRNA.
- Ribosomal RNA (rRNA): It forms the core structure of the ribosome, which is where protein synthesis takes place.
- Other regulatory RNAs: These include microRNA (miRNA), small interfering RNA (siRNA), and long non-coding RNA (lncRNA). They play important roles in regulating gene expression.
Function: RNA plays a central role in gene expression and protein synthesis:
- Transcription: RNA polymerase creates mRNA by transcribing the DNA template strand, resulting in a complementary RNA molecule.
- Translation: mRNA carries the genetic code from DNA to the ribosome. tRNA molecules then bring amino acids to the ribosome, matching them with the codons on the mRNA. This process forms a polypeptide chain, which eventually folds into a functional protein.
- Regulation of Gene Expression: RNA molecules, especially non-coding RNAs, have crucial roles in regulating gene expression at different levels, including transcription, mRNA processing, stability, and translation.
DNA Replication
Semiconservative Replication: DNA replication follows a semiconservative model, where each newly made DNA molecule consists of one original (parental) strand and one newly made (daughter) strand. This was proven by the Meselson-Stahl experiment in 1958.
- Replication begins at specific spots on the DNA molecule called origins of replication. Enzymes called helicases unwind and separate the DNA double helix, creating a replication fork.
- DNA polymerases help create new DNA strands by adding nucleotides to the 3′ end of an existing DNA or RNA primer. The leading strand is made continuously in the 5′ to 3′ direction, while the lagging strand is made in short fragments called Okazaki fragments.
- Primase makes a short RNA primer that matches the DNA template strand, giving DNA polymerase a starting point to begin synthesis.
- DNA polymerases make sure replication is accurate by choosing the correct nucleotide to match the template strand. Proofreading mechanisms find and fix errors in base pairing.
- Replication moves in both directions from each origin of replication until the whole DNA molecule is copied. Termination happens when replication forks from neighboring origins meet and the newly made DNA strands are joined together.
- The replisome is a group of enzymes and proteins involved in DNA replication. It includes helicases, DNA polymerases, primases, DNA ligases, and other helper proteins that coordinate the replication process.
- Telomeres are repetitive DNA sequences found at the ends of linear chromosomes. They protect against the loss of genetic material during replication. Telomerase is an enzyme that maintains telomere length by adding repetitive nucleotide sequences to the ends of chromosomes.
- Replication is tightly controlled to ensure that DNA is accurately replicated only.
Transcription
Transcription is a process where a complementary RNA molecule is made from a DNA template. It involves the following steps:
- Initiation: Transcription starts when RNA polymerase binds to a specific DNA region called the promoter. Promoters act as signals for the beginning of transcription.
- Elongation: RNA polymerase unwinds the DNA double helix and creates a complementary RNA molecule using one strand of the DNA as a guide. The RNA strand grows in the 5′ to 3′ direction as nucleotides are added.
- Base Pairing: During transcription, RNA nucleotides are added to the growing RNA strand based on complementary base pairing with the DNA template. Adenine (A) in DNA pairs with uracil (U) in RNA, while cytosine (C) in DNA pairs with guanine (G) in RNA.
- Termination: Transcription ends when RNA polymerase reaches a termination signal on the DNA template. In prokaryotes, specific sequences cause RNA polymerase to detach from the DNA. In eukaryotes, termination involves cutting and adding a poly(A) tail to the RNA transcript.
Post-Transcriptional Modifications
Newly synthesized RNA molecules undergo modifications before they become functional. These include adding a modified guanine nucleotide to the 5′ end (capping), adding a poly(A) tail to the 3′ end (polyadenylation), and removing non-coding sequences (introns) and joining coding sequences (exons) to create mature mRNA in eukaryotes.
Transcription is tightly controlled to ensure genes are only transcribed when needed. Regulatory proteins, transcription factors, and other elements influence the activity of RNA polymerase and the accessibility of DNA to the transcription machinery.
Class 12 Biology Chapter 5 “Molecular Basis of Inheritance” notes PDF Free Download
For your better understanding of the chapter 5, the notes is given in the PDF format below. Hope, the notes given in these PDF help you to better understand the chapter and to solve the extra questions based on the chapter. Notes of the chapter is given in the PDF form. You can either read it online or download in PDF for free and study offline.
Class 12 chapter 5 notes –
Class 12 Biology chapter 5 “Molecular Basis of Inheritance” important questions with answers are also given below. You can directly download it, in the PDF form. It will help you to understand the chapter better.
Chapter 5 “Molecular Basis of Inheritance” Important Questions with Answers
For your better understanding of the chapter 5, students must study the question based on the chapter. It will give you the idea to better understand the chapter. Here’s given some important very short, short and long types of questions with answers. Click the link below to download the PDF directly. You can also visit the CBSE 12 Board Previous questions papers page to directly download 5-10 years papers with answer. It will help you to understand the types of questions come in the CBSE 12 Board exam. For your better preparation for the exam, don’t skip to practise previous years papers along with sample papers.
Click in the link to directly download the important questions with answer –
Short types questions with answers
Long types questions with answers
Study Materials for remaining Class 12 Biology chapters:
Unit 6: REPRODUCTION
Chapter 2 – Human Reproduction
Chapter 3 – Reproductive Health
Unit 7: GENETICS AND EVOLUTION
Chapter 4 – Principles of Inheritance and Variation
Chapter 5 – Molecular Basis of Inheritance
Chapter 6 – Evolution
Unit 8: BIOLOGY IN HUMAN WELFARE
Chapter 7 – Human Health and Disease
Chapter 8 – Microbes in Human Welfare
Unit 9: BIOTECHNOLOGY
Chapter 9 – Biotechnology : Principles and Processes
Chapter 10 – Biotechnology and Its Applications
Unit 10: ECOLOGY
Chapter 11 – Organisms and Populations
Chapter 12 – Ecosystem
Chapter 13 – Biodiversity and Conservation
Students can get all the study materials that are required for class 12 Biology in Your Mentor Guru website. So, click in the links above to get all the chapters study materials including note and important questions with answer of class 12 Biology in PDF format to study offline. It is free PDF download. And don’t forget to check out previous years question papers of CBSE 12 Board exam.
Also check out –
- Class 12 Chemistry Study Materials
- Class 12 Physics Study Materials
- Class 12 English Study Materials
- Class 12 Mathematics Study Materials