CBSE Class 12 Business Studies Revision Notes
CBSE Class 12 Notes for Business Studies Followed By NCERT Guidelines
It talks about the genome, the “cookbook of life.”The notes of the molecular basis of inheritance, just like CoolGyan’s other NCERT solutions, are available in a freely downloadable PDF format. The entire document is structured under the following heads and subheads:
Packaging of DNA helix
DNA as genetic material- Griffith experiment
DNA is the genetic material- Experiment by Hershey and Chase
Central dogma of molecular Biology
Regulation of gene expression
Human Genome Project
Each of the above parts has been explained in an easy-to-understand manner with the help of perfectly labelled schematic diagrams. There are experiments and processes- all illustrated with utmost clarity. The best thing about the molecular basis of inheritance notes PDF is that all the important terms are either highlighted in bold or italics font and the main points are given in bullets. This presentation not only helps you to grasp the topic well but also memorize it easily. In one word, Chapter 6 Class 12 Biology notes are extremely handy and make learning one of the most crucial chapters in Biology a cakewalk.
An Overview of the Class 12 Biology Chapter 6 Notes
The molecular basis of inheritance Class 12 notes by CoolGyan under NCERT curriculum begins with an introductory note on DNA (deoxyribonucleic acid).
All genomes, except for viral genomes, are comprised of these nucleic acids. Under normal conditions, DNA exists as a double-stranded molecule in the form of a helix, essentially a ladder. This structure was discovered by the Nobel Laureate duo James Watson and Francis Crick, in 1955. So, it is also known as the Watson and Crick model. The two strands of the DNA double helix are configured anti-parallel to each other with the sense strand running in the 5' → 3' direction and the antisense strand running in the 3' → 5' direction.
Each DNA strand is made up of a sugar phosphate backbone. The linkers or steps of the ladder, consist of intricately bound pair of nucleotides. There are four nucleotides or nucleic acid molecules in DNA. Adenine (A) and Guanine (G) are the two purines, containing two carbon-nitrogen rings (one being an imidazole ring). Cytosine (C) and Thymine (T) are the two pyrimidines, containing one carbon-nitrogen ring structure. In RNA Thymine is replaced by Uracil (U).
Nucleotides are phosphate esters of nucleosides (sugar + base). Depending on the base composition, there can form 5 different types of nucleotide triphosphates, which covalently bind with each other by phosphodiester bond formation to give rise to the polynucleotides, namely- Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA).
The method of base pairing is termed “complementary” because specific geometry requirements need to be fulfilled to format the hydrogen bonds between the heterocyclic amines. It is a rule that adenine always pairs up thymine (or uracil in case of RNA), and guanine interacts with cytosine; Two hydrogen bonds are formed between adenine and thymine, while guanine and cytosine interact by three hydrogen bond formation.
According to Chargaff's rule, the number of purines in a given DNA is always equal to the number of pyrimidines.
Back to the ‘cookbook’ analogy, the genome is the book, the genes are the recipes, the works are the codons and the letters are the nucleotides.
The NCERT Class 12 Chapter 6 Biology notes by CoolGyan gives a clear concept of the basic unit of heredity that corresponds to a discrete functional segment of Deoxyribonucleic acid (DNA) – Gene. It is a gene that encodes a coherent set of amino acids specific for a particular polypeptide chain. The interaction of genes with each other and with environmental factors results in the physical development and observable characteristics (phenotype) of an organism.
DNA helix packaging
The packaging of DNA helix, as explained in the Biology Class 12 Chapter 6 notes, throws light on how positively charged histones (forming an eight-molecular unit called octamer) wrap around the negatively charged DNA to form nucleosomes. These are nothing but the repeating units of a structure called chromatin. A nucleosomal unit typically contains 200 bp (base pairs) of DNA helix. Isn’t it amazing that such a huge molecule is packaged in such a compact manner inside the nucleus of a cell!
The nucleosomes appear like beads on strings i.e. the chromatin fibres which remain coiled and condensed with the nucleus. The Class 12 molecular basis of inheritance notes explains this highly complex model in a simple way and further goes on to make you aware of the non-histone chromosomal (NHC) proteins, euchromatin, and heterochromatin.
To make your concept clearer, the Biology Chapter 6 Class 12 notes provide you with a diagrammatic comparative study between DNA, nucleosomes, chromatin, chromatin loops, condensed chromatin loops, and chromosome. The instant visualization of each chemical structure of the hereditary substance somewhat rivets the concept in your mind and you never forget it again in your entire career. Needless to say, you remain a step ahead in your preparation for Board exams of CBSE Class 12.
DNA as genetic material- An experimental proof
This section of the Biology Class 12 Chapter 6 notes deals with an experiment by Griffith were two strains of Pneumococcus bacteria and mice (medium) were used to prove that the transforming substance in a cell is nothing but DNA. Here also, you do not really need to memorize the entire section- just read it carefully and follow the diagram; you will be able to understand the experiment in one shot. Mind it- this is a very important experiment which you will be reading again and again in the future if you decide to take Life Sciences in your graduation and post-graduation. So, molecular inheritance Class 12 notes basically make your base strong upon which you can build your palace of knowledge when you go for higher studies.
Hershey and Chase Experiment to Prove DNA is Genetic Material
The Class 12 Biology Chapter 6 Notes has yet another key experiment of Genetics explained in it beautifully- Alfred Hershey and Martha Chase experiment. In this experiment, the scientist duo grew bacteriophage virus in two mediums- one rich in radioactive phosphorus and another rich in radioactive sulphur. Upon completion, they showed that DNA is the genetic material.’ A series of steps preceded this landmark discovery. The molecular basis of inheritance Class 12 notes PDF downloaded from the internet explains these steps in a diagrammatic format so that you see and understand what exactly is happening and not merely mug up the steps and the logic behind them.
Central dogma of molecular Biology
The Notes of Molecular Basis of Inheritance reaches its focal point at this part. The central dogma explains how genetic information flows in a biological system. It details about three key processes:
Replication: Production of two identical copies of (daughter) DNA from a single (parent) DNA molecule.
Transcription: Flow of information from DNA into messenger RNA (mRNA).
Translation: Formation of proteins through reading of codes in mRNA.
The Central Dogma of Molecular Biology is the basic organizing principle that forms the cornerstone of all genetic mechanisms. It states that the detailed residue-by-residue transfer of sequential information takes place from DNA and RNA to proteins. Once transmitted, such information cannot be transferred back from protein to either protein or nucleic acid.
The molecular basis of inheritance Class 12 notes explains these three processes in detail but without making them too complicated for the students. This is because like all other CoolGyan study materials this solution to aims at making you feel confident about your exam preparations. The expertise of the teachers is clearly evident in the content creation of this PDF.
The molecular basis of inheritance Class 12 notes rightly explains DNA replication as the transfer of genetic information from nucleic acids (DNA) to proteins. The process ensures the transfer of the same amount of genetic information present in the cell to its progeny cells post mitosis (cell division). The basis for biological inheritance, DNA replication involves copying of a double-helical DNA molecule to form two DNA double helices.
The synthesis or polymerization of DNA always takes place in the 5' → 3' direction and is steered by the enzyme DNA polymerase. The enzyme synthesizes a new DNA strand using one single strand as its template. The process is said to be semi-conservative because each nascent DNA molecule consists of a newly synthesized strand while the other one is derived from the pre-existing parent molecule.
The Chapter 6 Biology Class 12 notes explain this semi-conservative process in a compact and crisp manner. But while condensing the matter, it does not leave out important concepts like replication fork, the leading strand and lagging strand, origin of replication (OriC), and proofreading. Once you have an idea of the process you must study the diagram that follows this part carefully. Take it from us- you will not forget DNA replication even after your exams are over.
The Biology Notes for Class 12 Chapter 6 denotes transcription of RNA as the first stage of gene expression. It flags off the process of protein synthesis inside the cell’s nucleus.
Transcription involves the synthesis of a complimentary copy of RNA (messenger RNA) of a specific DNA sequence by the enzymes RNA polymerases. This phenomenon helps to amplify the DNA content of a cell by creating multiple copies of RNA, which can act as a template for protein synthesis- the final stage of gene expression. Transcription is a very well-orchestrated process that occurs in three distinct phases: Initiation, Elongation, and Termination. After the process is over, the post-transcriptional modification takes place in a number of ways namely splicing, capping, and tailing. The end result is the formation of various types of ribonucleic acids (RNA), each of which plays a key role in the protein biogenesis mechanism.
The three main types of RNA: Messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).
The Molecular Basis of Inheritance Class 12 solution talks about all three types of RNAs but focuses mainly on the process of RNA transcription.
CoolGyan’s Biology notes for Class 12 Chapter 6 deals with translation, again, in a pictorial manner. It is essentially the process of deciphering the genetic blueprint embedded in the DNA.
The process involves the delivery of amino acids to the ribosome by Transfer RNAs (tRNAs) in an order specified by the codon sequence in the messenger RNA.
Genetic information is encrypted in the mRNA as a sequence of ribonucleotides, which are “read” by the translational machinery in the form of triplets called codons. There are 64 codons, of which 3 are stop codons or termination codons (UAA, UAG and UGA). ATG or AUG, the codon for Methionine, on the other hand, is the translation initiation codon. It is these codons that “code” for specific amino acids. Complementary base-pairing between a codon on the mRNA and the anticodon of a tRNA forms the basis of correct placement of the amino acids.
More than one codon can code for the same amino acid. This is possible due to a specific characteristic of genetic code, known as third base degeneracy or wobble.
Like transcription, translation to proceeds in a stepwise fashion utilizing various components of the translational machinery that includes mRNA, ribosomal complex, tRNA, amino acids and individual sets of accessory proteins.
Translation is essentially an energy-intensive affair. Guanosine triphosphate (GTP) and adenosine triphosphate (ATP) are the two energy-rich molecules, which by hydrolysis supply this requisite energy to the cell.
Initiation of Translation
Initiation of translation is preceded by the binding of tRNA to its specific amino acid, a process called aminoacylation or charging. It involves the formation of a bond between the 3’-hydroxyl group of the terminal adenine of the acceptor arm of the tRNA and the carboxyl group of its corresponding amino acid. The entire reaction set is catalyzed by the enzymes called aminoacyl tRNA synthetases.
Elongation - The complete ribosomal complex (40S + 60S) bears two binding sites for tRNA molecules that follow the initiator tRNA- Peptidyl site or P site and Aminoacyl site or A site.
tRNAi base paired with AUG start codon occupies the first site or the P site, while the one charged with the amino acid, encoded by the second codon (sited corresponding to the A site) occupies the A site. A peptide bond is formed between the carboxyl group of the methionine borne by tRNAi and the amino group of the second amino acid that follows the sequence. The reaction is catalyzed by the enzyme peptidyl transferase and RNA deacetylase.
Termination - Elongation of the polypeptide chain comes to an end when a termination codon enters the A site. As there is no tRNA and corresponding amino acid to bind the stop codon, translation can proceed no more; and a set of release factors enter the A site to release the completed polypeptide chain.
The newly formed polypeptide chain needs to be modified before being used by the cell as a functional entity. This involves several processes, summed up together as post-translational modifications. Some of the major post-translational events include phosphorylation, acetylation, methylation, and hydroxylation.
The molecular basis of inheritance notes pdf explains translation in a brief manner but the way it explains strikes the right chord with the student’s heart, rather, mind!
The Biology notes for Class 12 Chapter 6 holds a special relevance in the NCERT Life Sciences curriculum because it talks about genetic code. Genetic codes comprise what we call the blueprint of life. The sequential arrangement of these nucleotides (in DNA) imbeds this blueprint. This information is deciphered using each triplet of bases at a time which specify the sequence of amino acids of a particular protein.
There are 64 genetic codes in the living world and they are highly similar across all organisms. Hence, these codes are thought to provide crucial evidence for the common origin of life on earth.
In the molecular basis of inheritance notes pdf, the genetic codes have been presented in a tabular format. You can learn the triplets easily and know the amino acids coded by them by just looking at the table. The table also gives you an idea of the basic properties of the amino acids coded- non-polar, aliphatic or polar, uncharged, aromatic, positively charged, or negatively charged. You will be amazed to see what a great variety of amino acids can be coded by the various permutations and combinations of only 4 nucleotides namely adenine, guanine, cytosine, and uracil.
Regulation of gene expression
What does this part of the Notes of Chapter 6 Biology Class 12 teaches you? – It says not always all the genes in a cell remain active. They become active only when there is a need. Gene expression is a highly controlled process and it is done by the regulatory genes.
Regulation of gene expression in eukaryotes occurs in the following levels:
Transport of mRNA from nucleus to the cytoplasm
Plain explanation of a process never seems to work in science. For a chapter as conceptual as molecular basis of inheritance Class 12, this is all the more applicable. So, the Notes of Chapter 6 Biology Class 12 explains the gene regulation process with the help of a real genetic system example- Lac operon or lactose operon.
An operon consists of many genes- structural, operator, promoter, regulator, and repressor genes. Lac operon too consists of lac Z, lac Y, and lac A genes. They code for galactosidase, permease, and transacetylase respectively. When a repressor molecule attaches with the operator, genes are not subscribed. It is only when a repressor molecule is free and instead, an inducer molecule binds the operator that the genes get switched on and transcription takes place. In lac operon, lactose is the inducer, which when binds the operator transcription gets switched on.
The explanation in the notes of the molecular basis of inheritance Class 12 is followed by a schematic diagram of the lac operon. Once you study this diagram closely, your concept regarding gene expression regulation becomes clear like crystal.
HGP or Human Genome Project
The last part of the molecular basis of inheritance Class 12 NCERT solution deals with the salient features of the Human Genome Project, an ambitious 13-year project launched internationally to determine the base pairs comprising the human DNA. The project, which saw completion in 2003, was also aimed at identifying and mapping all the 20,500 genes of the human genome not only from the physical standpoint but also from the functional perspective.
Some of the highlights of the HGP as pointed out in the notes of the molecular basis of inheritance are as follows:
There are 3164.7 million nucleotide bases in the human genome
On average, a gene consists of 3000 bases. The size, however, varies.
Human body is said to be a construct of about 30,000 genes
For more than 50 percent of the discovered genes, the functions are not known yet
Less than 2 percent of the human genome codes for functional proteins
Repeated sequences or consensus sequences comprise a major part of the human genome
Chromosome 1 has the maximum number of genes (2968)
The Y chromosome has the least number of genes (231)
Though HGP is now over, analyses of the data is still continuing in different renowned laboratories of the world. Efforts are being made to store the information gathered from it in robust databases.
The molecular basis of inheritance Class 12 notes PDF downloaded from the internet presents these facts in a bulleted format so that it is easier for you to remember and write in the exams. Too much of details tend to overwhelm an inquisitive mind. You may end up writing an inconclusive answer in your exam paper; hence, the crisp and compact approach. You gain knowledge and at the same time, you are prepared for your boards. However, if you want to learn more about the Project you can always hit the racks of your school library or browse the internet. There are umpteen books on Human Genetics. Read, enjoy, and be prepared for an exciting career in Life Sciences ahead!
Chapter 6 Biology Class 12 Notes Gives You a YouTube link too!
Yes, you read it right. The Molecular Inheritance Class 12 Notes has a link to a YouTube video for you too, at the end of the document. The video shows the process of molecular inheritance using 3D animation. The voiceover explains each step shown on the screen. Can anything get better than this! You read the chapter step by step from the PDF and then you watch it online. A never-to-forget learning experience- all made possible by the CoolGyan app!
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Reproduction in Organism
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Principles of Inheritance and Variation
Evolution- Lamarckism, Darwinism
Human Health and Diseases
Strategies for Enhancement in Food Production
Organisms and Populations
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