Title MOLECULAR BASIS OF INHERITANCE-(1-63).pdf ✅

NEET BOTANY VOL-II CH-6: MOLECULAR BASIS OF INHERITANCE NARAYANA GROUP 1 Molecular Basis of Inheritance C O N T E N T S  Introduction  The DNA  The Search for Genetic Material  RNA World  Replication  Transcription  Genetic Code  Translation  Regulation of Gene Expression  Human Genome Project  DNA Fingerprinting  Search for genetic material and DNA as genetic material;  Structure of DNA and RNA;  DNA packaging;  DNA Replication;  Central dogma;  Transcription,  Genetic code,  Translation;  Gene expression and regulation- Lac Operon;  Genome and Human genome project; NEET SYLLABUS 6
NEET BOTANY VOL-II CH-6: MOLECULAR BASIS OF INHERITANCE NARAYANA GROUP 2 INTRODUCTION  Molecular Biology is a relatively young branch of Biology.  Warren Weaver recognised the importance of physical and chemical approach to Biology and introduced the term Molecular Biology.  Molecular Biology was developed due to convergence of Genetics, Physics and Biochemistry  Molecular Biology began in 1953 with the proposal of double helix model of DNA by Watson & Crick  FHC Crick prosposed a thesis on x-ray diffraction of polypeptides and proteins THE DNA * DNA is a long polymer of deoxyribonucleotides. * The length of DNA is usually defined as number of nucleotides (or a pair of nucleotide referred to as base pairs) present in it. * This also is the characteristic of an organism. For example, a bacteriophage known as  174 has 5386 nucleotides. Bacteriophage lambda has 48502 base pairs (bp) , Escherichia coli has 6 4.6 10  bp and haploid content of human DNA is 9 3.3 10  bp. NH2 H N2 N N N N N H H N HC HN N C C C C O C C C CH CH PURINES Adenine (A) Guanine (G) 1 1 6 6 5 5 4 4 3 3 2 2 7 7 8 8 9 9 PYRIMIDINES Uracil(U) HN CH CH H O O C C N 2 3 4 5 6 1 HN C CH3 CH H O O C C N 2 3 4 5 6 1 Thymine (T) N CH CH H O N H2 C C N 2 3 4 5 6 1 Cytosine (C)
NEET BOTANY VOL-II CH-6: MOLECULAR BASIS OF INHERITANCE NARAYANA GROUP 3 H C2 CH2 HO OH phosphate group OH A deoxyribose sugar molecule linked with phosphate group at 5 position  CH HC CH 5 2 4 1 3 OH O O O P deox yribose su gar STRUCTURE OF POLYNUCLEOTIDE CHAIN * The chemical structure of a polynucleotide chain (DNA or RNA) . * A nucleotide has three components - a nitrogenous base, a pentose sugar (ribose in case of RNA, and deoxyribose for DNA) , and a phosphate group. * There are two types of nitrogenous bases -Purines (Adenine and Guanine) and Pyrimidines (Cytosine, Uracil and Thymine) . Cytosine, adenine, guanine are common for both DNA and RNA and Thymine is present in DNA. Uracil is present in RNA at the place of Thymine. * A nitrogenous base is linked to the OH of 1'C pentose sugar through a N-glycosidic linkage to form a nucleoside, such as adenosine or deoxyadenosine, guanosine or deoxyguanosine, cytidine or deoxycytidine and uridine or deoxythymidine. * When a phosphate group is linked to OH of 5'C of a nucleoside through phosphoester linkage, a corresponding nucleotide (or deoxynucleotide depending upon the type of sugar present) is formed. Two nucleotides are linked through 3’-5’ phosphodiester linkage to form a dinucleotide. * More nucleotides can be joined in such a manner to form a polynucleotide chain. * A polymer thus formed has at one end a free phosphate moiety at 5’ phosphate 5’-end of ribose sugar, which is referred to as 5’-end of polynucleotide chain. * Similarly, at the other end of the polymer the sugar has a free of 3'-OH group which is referred to as 3’-end of the polynucleotide chain. * The backbone in a polynucleotide chain is formed by sugar and phosphates. The nitrogenous bases linked to sugar moiety project from the backbone * In RNA, every nucleotide residue has an additional -OH group present at 2’-position in the ribose, Also, in RNA the uracil is found at the place of thymine (5-methyl uracil, another chemical name for thymine) . * DNA as an acidic substance present in nucleus was first identified by Friedrich Miescher in 1869. * He named it as ‘Nuclein’ However, due to technical limitation in isolating such a long polymer intact, the elucidation of structure of DNA remained elusive for a very long period of time. * It was only in 1953 that James Watson and Francis Crick, based on the X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin, proposed a very simple but famous Double Helix model for the structure of DNA.