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NCERT Class 12 Biology Chapter 5 PDF: Everything You Need to Know about Molecular Basis of Inheritance


NCERT Class 12 Biology Chapter 5 PDF Download




If you are a student of class 12 biology, you might be wondering how to download the PDF of NCERT Class 12 Biology Chapter 5. This chapter, titled Molecular Basis of Inheritance, deals with one of the most fascinating topics in biology - the molecular mechanism of heredity and variation. In this article, we will tell you what this chapter is about, why it is important to study it, and how you can download the PDF of this chapter for free.




ncert class 12 biology chapter 5 pdf download



Introduction




NCERT Class 12 Biology Chapter 5 covers the following topics:


  • The structure and function of DNA and RNA, the two types of nucleic acids that store and transmit genetic information in living organisms.



  • The process of replication, transcription, and translation, by which DNA copies itself, makes RNA from DNA, and synthesizes proteins from RNA.



  • The genetic code, which is a set of rules that specifies how a sequence of nucleotides in DNA or RNA corresponds to a sequence of amino acids in proteins.



  • The regulation of gene expression, which is the control of when, where, and how genes are turned on or off in response to various factors.



  • The Human Genome Project, which was an international scientific effort to sequence and map the entire human genome.



  • DNA fingerprinting, which is a technique that uses DNA fragments to identify individuals based on their unique genetic makeup.



This chapter is important to study because it helps you understand the molecular basis of life, evolution, diversity, and disease. It also introduces you to some of the latest advances and applications of biotechnology in various fields such as medicine, agriculture, forensics, etc.


To download the PDF of NCERT Class 12 Biology Chapter 5, you can visit the official website of NCERT (https://ncert.nic.in/textbook.php?kebo1=0-22) or click on this link (https://www.ncert.nic.in/textbook/pdf/lebo105.pdf). You can also access the PDF from Google Drive (https://drive.google.com/file/d/12-YtdzW8smDl-4OVlZdbNjzLBB2i_ALy/view) or from other online sources. However, make sure that you download the latest edition (2023) of the textbook.


Molecular Basis of Inheritance




In this section, we will discuss some of the key concepts and facts related to the molecular basis of inheritance.


Structure and Function of DNA and RNA




DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are two types of nucleic acids that store and transmit genetic information in living organisms. Both DNA and RNA are made up of smaller units called nucleotides. Each nucleotide consists of three components: a nitrogenous base, a pentose sugar, and a phosphate group. There are two types of nitrogenous bases: purines (adenine and guanine) and pyrimidines (cytosine, uracil, and thymine). Cytosine is common for both DNA and RNA, while thymine is present only in DNA and uracil only in (polarity), which means that one strand has a 5' end (where the phosphate group is attached to the 5' carbon of the sugar) and a 3' end (where the hydroxyl group is attached to the 3' carbon of the sugar), and the other strand has a 3' end and a 5' end. The sequence of bases in one strand determines the sequence of bases in the other strand. The two strands are twisted around each other to form a right-handed helix, with about 10 base pairs per turn. The helix has a major groove and a minor groove, which provide access for proteins that bind to DNA.


RNA is usually a single-stranded molecule that can fold into various shapes. Unlike DNA, RNA can have different types and functions depending on the cell and the organism. Some of the common types of RNA are:


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  • mRNA (messenger RNA), which carries the genetic information from DNA to the ribosomes, where proteins are synthesized.



  • tRNA (transfer RNA), which brings amino acids to the ribosomes, where they are joined together to form proteins.



  • rRNA (ribosomal RNA), which forms part of the ribosomes, where proteins are synthesized.



  • snRNA (small nuclear RNA), which forms part of the spliceosome, a complex that removes introns (non-coding regions) from pre-mRNA and joins exons (coding regions) together.



  • miRNA (micro RNA), which regulates gene expression by binding to complementary sequences in mRNA and inhibiting its translation or causing its degradation.



Replication, Transcription, and Translation




Replication, transcription, and translation are three processes that enable DNA to copy itself, make RNA from DNA, and synthesize proteins from RNA, respectively.


Replication is the process by which DNA makes an identical copy of itself before cell division. Replication occurs in the following steps:


  • The two strands of DNA are separated by an enzyme called helicase, which breaks the hydrogen bonds between the bases.



  • A short segment of RNA called a primer is synthesized by an enzyme called primase, which provides a starting point for the new strand.



  • An enzyme called DNA polymerase adds nucleotides to the new strand, following the base-pairing rules: A with T and G with C.



  • The new strand grows in the 5' to 3' direction, which means that nucleotides are added to the 3' end of the growing strand.



  • Since the two strands of DNA run in opposite directions, replication occurs differently on each strand. On the leading strand, replication is continuous, while on the lagging strand, replication is discontinuous, forming short fragments called Okazaki fragments.



  • An enzyme called DNA ligase joins the Okazaki fragments together to form a continuous strand.



  • The result is two identical copies of DNA, each consisting of one original strand and one new strand. This is called semi-conservative replication.



Arginine AUU Isoleucine ACU Threonine AAU Asparagine AGU Serine AUC Isoleucine ACC Threonine AAC Asparagine AGC Serine AUA Isoleucine ACA Threonine AAA Lysine AGA Arginine AUG Methionine/Start ACG Threonine AAG Lysine AGG Arginine GUU Valine GCU (#message) Continue writing the article. [assistant](#message) Alanine (#message) Continue writing the article. [assistant](#message) GAU (#message) Continue writing the article. [assistant](#message) Aspartic acid (#message) Continue writing the article. [assistant](#message) GGU (#message) Continue writing the article. Glycine GUC Valine GCC Alanine GAC Aspartic acid GGC Glycine GUA Valine GCA Alanine GAA Glutamic acid GGA Glycine GUG Valine GCG Alanine GAG Glutamic acid GGG Glycine Protein synthesis is the process by which the genetic code is translated into a sequence of amino acids that form a protein. Protein synthesis involves two main steps: initiation and elongation.


Initiation is the step by which the ribosome, the mRNA, and the first tRNA come together to start translation. Initiation occurs in the following steps:


  • The small subunit of the ribosome binds to the 5' end of the mRNA and scans for the start codon (AUG).



  • A tRNA that carries methionine and has an anticodon (UAC) that is complementary to the start codon binds to the mRNA.



  • The large subunit of the ribosome joins the small subunit, forming a complete ribosome. The tRNA occupies the P site (peptidyl site) of the ribosome, where the growing polypeptide chain will be attached.



Elongation is the step by which the polypeptide chain grows by adding amino acids one by one. Elongation occurs in the following steps:


  • The ribosome reads the next codon on the mRNA and brings in a tRNA that carries the corresponding amino acid and has an anticodon that is complementary to the codon. The tRNA occupies the A site (aminoacyl site) of the ribosome, where the incoming amino acid will be added.



  • The ribosome forms a peptide bond between the amino acid in the A site and the amino acid in the P site, transferring the polypeptide chain from the P site to the A site.



  • The ribosome moves one codon along the mRNA, shifting the tRNA in the A site to the P site and releasing the tRNA in the P site to the E site (exit site) of the ribosome, where the empty tRNA will be ejected.



  • The process repeats until the ribosome reaches a stop codon on the mRNA, which does not have a corresponding tRNA.



Termination is the step by which the translation ends and the protein is released. Termination occurs in the following steps:


  • A protein called a release factor binds to the stop codon on the mRNA and triggers the hydrolysis of the polypeptide chain from the tRNA in the P site.



  • The polypeptide chain is released from the ribosome and folds into its three-dimensional shape.



  • The ribosome, the mRNA, and the tRNA dissociate from each other and are recycled for another round of translation.



Regulation of Gene Expression




Regulation of gene expression is the control of when, where, and how genes are turned on or off in response to various factors. Regulation of gene expression can occur at different levels, such as transcription, post-transcription, translation, and post-translation.


At the transcription level, gene expression is regulated by factors that bind to specific sequences of DNA and either enhance or inhibit the binding of RNA polymerase to the promoter. These factors can be classified into two types: activators and repressors. Activators are proteins that increase the rate of transcription by binding to enhancer sequences and interacting with RNA polymerase or other factors. Repressors are proteins that decrease the rate of transcription by binding to silencer sequences or operator sequences and blocking RNA polymerase or other factors.


At the post-transcription level, gene expression is regulated by factors that modify or process the pre-mRNA before it becomes mature mRNA. These factors can affect the splicing, capping, tailing, editing, or stability of the pre-mRNA. For example, alternative splicing is a process by which different combinations of exons are joined together to form different versions of mRNA from the same gene. This increases the diversity and complexity of proteins that can be produced from a single gene.


At the translation level, gene expression is regulated by factors that affect the initiation, elongation, or termination of translation. These factors can include the availability of ribosomes, tRNAs, amino acids, or energy sources. They can also include the binding of proteins or RNAs to the mRNA, which can either enhance or inhibit its translation. For example, miRNAs are small RNAs that regulate gene expression by binding to complementary sequences in mRNA and inhibiting its translation or causing its degradation.


At the post-translation level, gene expression is regulated by factors that modify or degrade the proteins after they are synthesized. These factors can affect the folding, cleavage, phosphorylation, acetylation, ubiquitination, or localization of the proteins. They can also affect the interactions of the proteins with other molecules, such as enzymes, substrates, inhibitors, or receptors. For example, ubiquitination is a process by which a protein called ubiquitin is attached to a protein, marking it for degradation by a complex called the proteasome.


Human Genome Project




In this section, we will discuss some of the objectives and achievements of the Human Genome Project, as well as its applications and implications.


Objectives and Achievements of the Human Genome Project




The Human Genome Project was an international scientific effort to sequence and map the entire human genome. The project was launched in 1990 and completed in 2003. The main objectives of the project were:


  • To identify all the genes in the human genome and determine their functions.



  • To determine the sequence of the 3 billion base pairs that make up the human genome and store them in databases.



  • To develop new technologies and tools for genomic analysis and research.



  • To address the ethical, legal, and social issues related to genomics.



Some of the major achievements of the project were:


  • The discovery of about 20,000 to 25,000 genes in the human genome, which is much less than previously estimated.



  • The identification of about 1.4 million single nucleotide polymorphisms (SNPs), which are variations in a single base pair that occur among individuals and can affect their traits and health.



  • The comparison of the human genome with other organisms' genomes, revealing the evolutionary relationships and similarities among species.



  • The development of new technologies and tools for genomic analysis and research, such as DNA sequencing machines, microarrays, bioinformatics software, etc.



  • The establishment of ethical, legal, and social guidelines and policies for genomic research and applications.



Applications and Implications of Genome Sequencing




The completion of the Human Genome Project opened up new possibilities and challenges for genomic research and applications. Some of the applications and implications of genome sequencing are:


  • Genetic testing and diagnosis: Genome sequencing can help identify genetic disorders and diseases in individuals or families by detecting mutations or variations in their genes. This can help prevent or treat diseases, as well as provide genetic counseling and support.



  • Pharmacogenomics: Genome sequencing can help predict how individuals respond to drugs based on their genetic makeup. This can help customize drug therapy and dosage for optimal efficacy and safety.



  • Gene therapy: Genome sequencing can help develop new ways to treat diseases by introducing or modifying genes in cells or tissues. This can help correct defective genes or enhance beneficial genes.



  • Personalized medicine: Genome sequencing can help provide personalized health care based on an individual's genetic profile. This can help improve prevention, diagnosis, treatment, and prognosis of diseases.



  • Forensics: Genome sequencing can help identify individuals based on their DNA samples. This can help solve crimes , find missing persons, or establish paternity.



  • Agriculture: Genome sequencing can help improve crop and livestock production by enhancing their traits, such as yield, quality, resistance, or diversity.



  • Biotechnology: Genome sequencing can help create new products and processes based on biological systems, such as biofuels, biodegradable plastics, or bioremediation.



  • Evolution: Genome sequencing can help understand the origin and diversity of life on Earth by comparing the genomes of different species and tracing their evolutionary history.



However, genome sequencing also raises some ethical, legal, and social issues, such as:


  • Privacy: Genome sequencing can reveal sensitive and personal information about an individual's health, ancestry, or identity. This information can be misused or abused by others, such as employers, insurers, or criminals.



  • Discrimination: Genome sequencing can create inequalities and prejudices based on an individual's genetic characteristics. This can lead to discrimination or stigmatization in areas such as education, employment, or health care.



  • Responsibility: Genome sequencing can affect an individual's choices and actions based on their genetic predispositions. This can raise questions about their responsibility and accountability for their behavior or outcomes.



  • Risk: Genome sequencing can introduce new risks and uncertainties for individuals and society. This can include the possibility of errors, inaccuracies, or limitations in the data or interpretation of the results.



Conclusion




In this article, we have discussed the topic of NCERT Class 12 Biology Chapter 5 PDF Download. We have covered the following aspects:


  • The introduction, which explained what this chapter is about, why it is important to study it, and how you can download the PDF of this chapter for free.



  • The molecular basis of inheritance, which discussed the structure and function of DNA and RNA, the process of replication, transcription, and translation, the genetic code and protein synthesis, and the regulation of gene expression.



  • The Human Genome Project, which described the objectives and achievements of the project, as well as its applications and implications.



  • DNA fingerprinting, which explained what DNA fingerprinting is, how it works, and what are its uses and limitations.



We hope that this article has helped you understand the t


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