YIJC [H2] CI2.1_Struct & Fn of Nucleic Acids (N) vf

JC1 BIOLOGY LECTURE NOTES CORE IDEA 2: GENETICS AND INHERITANCE TOPIC 2.1: STRUCTURE & FUNCTION OF NUCLEIC ACIDS Learning Outcomes: (a) Describe the structure and roles of DNA and RNA (tRNA, rRNA and mRNA) (knowledge of mitochondrial DNA is not required). Use the knowledge gained in this section in new situations or to solve related problems. References: Reece, J. B., et al. (2011). Campbell Biology (9th Ed) Chapter 16 The Molecular Basis of Inheritance, p351 – 365 Note: These textbooks and references are available in our library. You may wish to borrow them to supplement your reading when necessary. A Bridge to O Level Biology (6093 syllabus and 5078 syllabus) You should have learnt to: (a) outline the relationship between DNA, genes and chromosomes (b) state the structure of DNA in terms of the bases, sugar and phosphate groups found in each of their nucleotides (c) state the rule of complementary base pairing (d) state that DNA is used to carry the genetic code, which is used to synthesise specific polypeptides (details of transcription and translation are not required) (e) state that each gene is a sequence of nucleotides, as part of a DNA molecule 1 INTRODUCTION Genetic information is stored in an organism’s DNA; expression of genes results in the synthesis of functional products, such as rRNA, tRNA and proteins. These products play a role in intra- and extra- cellular biochemical pathways and influence the physiological processes in organisms. Genomes contain heritable information necessary for continuity of life at all levels: cell, organism and system. This information is stored and passed on to subsequent generations via DNA. Reproduction can occur at the cellular or organismal level; each progeny needs to receive heritable genetic information from its parent(s). H2

2 Check Your Prior Knowledge Fill in the blanks in the diagram below. 2 BASIC STRUCTURE OF NUCLEIC ACIDS • There are two types of nucleic acids found in living cells: (i) deoxyribonucleic acid (DNA) (ii) ribonucleic acid (RNA) • Both DNA and RNA exist as polynucleotide chains, made up of many nucleotides (monomer) joined together via condensation reactions. 2.1 STRUCTURE OF A NUCLEOTIDE • A nucleotide is made up of three components bonded together via condensation reactions: (i) a pentose sugar (ii) a nitrogenous base (iii) one or more phosphate groups attached at the carbon 5 of the pentose sugar Fig. 2.1.1: Structure of a nucleotide phosphate group base sugar

3 Pentose Sugar • A pentose sugar is a monosaccharide with five carbon atoms. • The pentose sugar in DNA is known as deoxyribose, and the pentose sugar in RNA is known as ribose. Fig. 2.1.2: Deoxyribose (left) and ribose (right) Nitrogenous base • Nitrogenous bases are cyclic organic compounds containing the atoms C, H, O, N. • There are two types of nit