Nucleic Acids

• DNA


  Deoxyribose nucleic acid, a chemical substance present in the nucleus of all cells in all living organisms that controls all the chemical changes which take place in cells and determines the kind of cell and organism produced
• DNA


  • It is a very large molecule made up of a long chain of sub-units called nucleotides
  • Each nucleotide is made up of a sugar called deoxyribose, a phosphate group, and an organic base
• Ribose


  A sugar like glucose, but with only five carbon atoms in its molecule
• Deoxyribose


  Almost the same as ribose, but lacks one oxygen atom
• Common organic bases


  • Adenine (A)
  • Thymine (T)
  • Cytosine (C)
  • Guanine (G)
• Formation of a nucleotide

  Deoxyribose, phosphate, and one of the bases (adenine) combine
• DNA molecule


  • Usually consists of a double strand of nucleotides
  • The sugar-phosphate chains are on the outside
  • The strands are held together by chemical bonds between the bases
• Bonding between bases


  Adenine forms a bond with Thymine, and Cytosine bonds with Guanine
• Double helix


  The paired strands are coiled into a spiral
• DNA replication


  1. Before a cell divides, the DNA strands unwind and separate

  2. Each strand makes a new partner by adding the appropriate nucleotides

  3. The result is two double-stranded DNA molecules in the nucleus
• Genetic code


  • The sequence of bases in DNA forms the genetic code
  • A group of three bases (a triplet) controls the production of a particular amino acid in the cytoplasm of the cell
  • The different amino acids and the order in which they are joined up determines the sort of protein being produced
• Amino acids coded for by triplets

  • Serine, Cysteine, Valine, Glycine, Alanine
• Triplet code


  Each triplet codes for a specific amino acid
• DNA controls


  Which enzymes are made, and the enzymes determine what reactions take place in the cell, which determines the type and function of the cell
• Gene


  A sequence of triplets in the DNA molecule that may code for a complete protein, with a thousand or more bases in one gene
• Nucleic acids are molecules capable of transmitting biological information from parent cells to its daughter cells, and if we look into a wider lens, from one generation to another
• Nucleotides


  Basic building blocks of nucleic acids, made up of a sugar-phosphate backbone and a nitrogenous base

  
• Nitrogenous bases


  • May either be a purine or a pyrimidine, attached to the first carbon of the pentose sugar
• DNA


  Most commonly found to be double stranded, has deoxyribose sugar backbone, contains adenine, guanine, cytosine and thymine

  
• RNA


  More commonly found to be single stranded, has ribose sugar backbone, contains adenine, guanine, cytosine and uracil

  
• Central dogma of molecular biology

  1. DNA replication (synthesis of DNA)

  2. Transcription (synthesis of RNA)

  3. Translation (synthesis of protein)

  
• DNA replication


  • Semi-conservative, contains an old strand from the parent DNA and a newly formed strand

  
• Phases of DNA replication

  1. Initiation

  2. Elongation

  3. Termination

  
• Initiation of replication


  Separation of complementary DNA strands, unwinding by helicase, binding of single-stranded binding proteins, relaxation by topoisomerases, synthesis of RNA primers by primase

  
• Elongation of replication


  DNA Polymerase III adds nucleotides complementary to the DNA template, leading strand synthesized continuously, lagging strand synthesized discontinuously as Okazaki fragments

  
• DNA Polymerase I


  Proofreads the DNA molecule, removes RNA primers and replaces them with DNA nucleotides
• Ligase


  Seals the nicks left by DNA Polymerase I in the sugar-phosphate backbone
• Enzymes and proteins involved in DNA replication


  • Helicase
  • Single-stranded binding proteins
  • Topoisomerases
  • Primase
  • DNA Polymerase III
  • DNA Polymerase I
  • Ligase