nucleic acid

• Nucleic Acid


  A polymer in which the monomer units are nucleotides
• Types of Nucleic Acids

  • Deoxyribonucleic acid (DNA)
  • Ribonucleic acid (RNA)
• Nucleotide

  Building blocks of Nucleic Acids, a three-subunit molecule in which a pentose sugar is bonded to both a phosphate group and a nitrogen-containing heterocyclic base
• Pentose Sugars


  The sugar unit of a nucleotide is either the pentose ribose or the pentose 2'-deoxyribose
• Nitrogen-Containing Heterocyclic Bases


  • Thymine (T)
  • Cytosine (C)
  • Uracil (U)
  • Adenine (A)
  • Guanine (G)
• Phosphate


  The third component of a nucleotide, derived from phosphoric acid (H3PO4)
• Nucleotide Formation

  Condensation: removal and formation of water molecule, occurs between sugar and base, sugar and phosphate
• Nucleotide Nomenclature

  1. Names end in 5-monophosphate

  2. Preceding monophosphate is name of base (purine bases use -osine suffix, pyrimidine bases use -idine suffix)

  3. Prefix deoxy- signifies deoxyribose sugar, no prefix is ribose

  4. Abbreviations use one-letter base symbols, MP for monophosphate, d for deoxyribose
• Primary Nucleic Acid Structure

  Nucleotide units linked through sugar-phosphate bonds (backbone), sequence of bases is the variable portion
• Difference between Nucleic Acids and Proteins
• DNA Double Helix

  • Two polynucleotide strands coiled around each other

  Amounts of A and T are equal, amounts of C and G are equal

  Strands are antiparallel, one 5'-to-3', other 3'-to-5'

  Unequal spaces between base pairs
• Base Pairing

  Only pairs of one small base (pyrimidine) and one large base (purine) fit

  1. T and G-C pairings are complementary and most favorable
• Wherever G occurs in one DNA strand, there is a C in the other strand; wherever T occurs in one strand, there is an A in the other strand
• Base-Stacking Interactions

  • Bases positioned with planes parallel, stabilizing the DNA double helix
• DNA Replication

  Helicase breaks hydrogen bonds, DNA unzips

  2. Free nucleotides match complementary bases, DNA polymerase verifies and forms new phosphodiester linkages

  DNA polymerase operates 5'-to-3', one strand grows continuously, other in short segments (Okazaki fragments)
• DNA replication

  The process where DNA makes a copy of itself
• DNA replication

  • It is conservative
  • It is bidirectional (5' to 3' and 3' to 5')
• DNA replication step 1

  1. Hydrogen bonds between base pairs are broken by helicase

  2. DNA molecule unzips into complementary halves
• DNA replication step 2

  1. Nucleotides match up with complementary bases

  2. DNA polymerase verifies base pairing and catalyzes formation of new phosphodiester linkage
• DNA polymerase

  • Can only operate in 5' to 3' direction
  • One strand grows continuously (leading strand)
  • Other strand is formed in short segments (Okazaki fragments)
• Okazaki fragments

  Short segments that the lagging strand is formed in
• Nicks

  Breaks or gaps in the lagging strand
• DNA ligase

  Enzyme that connects the Okazaki fragments to complete the lagging strand
• Topoisomerase

  Makes temporary nicks in the helix to release tension, then seals the nicks
• Helicase

  Enzyme that breaks hydrogen bonds and unzips the DNA
• DNA polymerase

  Enzyme that catalyzes the connection of nucleotides to form the complementary DNA strand
• Leading strand

  Transcribed continuously in 5' to 3' direction
• Lagging strand

  Transcribed in segments (Okazaki fragments) in 5' to 3' direction
• Primase

  Enzyme that catalyzes formation of RNA starting segment (RNA primer)
• DNA ligase

  Enzyme that catalyzes connection of two Okazaki fragments
• Types of RNA molecules

  • Heterogenous nuclear RNA (hnRNA)
  • Messenger RNA (mRNA)
  • Small nuclear RNA (snRNA)
  • Ribosomal RNA (rRNA)
  • Transfer RNA (tRNA)
• Heterogenous nuclear RNA (hnRNA)


  RNA formed directly by DNA transcription, also known as pre-mRNA
• Messenger RNA (mRNA)

  RNA that carries instructions for protein synthesis (genetic information) to the sites for protein synthesis
• Small nuclear RNA (snRNA)

  RNA that facilitates the conversion of heterogenous nuclear RNA to mRNA
• Ribosomal RNA (rRNA)

  RNA that combines with specific proteins to form ribosomes
• Transfer RNA (tRNA)

  RNA that delivers amino acids to the sites for protein synthesis
• Total cellular RNA: rRNA 75-80%, tRNA 10-15%, mRNA & hnRNA 5-10%
• Transcription

  1. RNA is made from a DNA template in the nucleus

  2. mRNA carries the message of DNA into cytoplasm to the ribosomes
• Post-Transcription Processing: Formation of mRNA

  This is a splicing method
• Genetic code

  The assignment of the 64 mRNA codons to specific amino acids (or stop signals)