Nucleic Acids

• Nucleic acids


  Polymeric molecules in which the repeating units are nucleotides
• Types of nucleic acids

  • Deoxyribonucleic acids (DNA)
  • Ribonucleic acids (RNA)
• Functions of DNA and RNA

  DNA - transfer of genetic information

  RNA - synthesis of proteins
• Nucleic acid building blocks

  • Pentose sugar (ribose or deoxyribose)

  Nitrogen-containing base (purine or pyrimidine derivative)

  Phosphate group
• Nitrogen-containing bases


  • Adenine (A)

  Guanine (G)

  Cytosine (C)

  Thymine (T)

  Uracil (U)
• Nucleoside


  Compound formed from a pentose sugar and a purine or pyrimidine base derivative
• Nucleotide


  Nucleoside to which a phosphate group has been added
• Nucleotide


  Monomers for nucleic acid polymers
• Primary nucleic acid structure

  Backbone is a constant alternating sequence of sugar and phosphate groups, with a nitrogen-containing base attached to each sugar unit
• Complementary bases


  Specific pairs of bases in nucleic acid structures that hydrogen-bond to each other
• Secondary DNA structure


  Two polynucleotide chains coiled around each other in a double-helix arrangement, held together by hydrogen bonding between complementary pairs of bases (A with T, C with G)
• DNA replication


  Two strands of a parent DNA double helix separate and act as templates for the synthesis of new chains using the principle of complementary base pairing
• Chromosome


  Structure consisting of an individual DNA molecule bound to a group of proteins
• Types of RNA molecules


  • Ribosomal RNA (rRNA)

  Messenger RNA (mRNA)

  Heterogeneous nuclear RNA (hnRNA)

  Transfer RNA (tRNA)

  Small nuclear RNA (snRNA)
• Transcription


  Genetic information encoded in the base sequence of DNA is copied into hnRNA/mRNA molecules
• Gene


  Portion of a DNA molecule that contains the base sequences needed for the production of a specific hnRNA/mRNA molecule, with exons containing genetic information and introns not conveying genetic information
• Codon


  Three-nucleotide sequence in mRNA that codes for a specific amino acid needed during protein synthesis
• Genetic code


  All the mRNA codons that specify either a particular amino acid or the termination of protein synthesis
• Anticodon


  Three-nucleotide sequence in tRNA that binds to a complementary sequence (a codon) in mRNA
• Translation


  Codons in mRNA are translated into amino acid sequences of new proteins, involving interactions between the codons of mRNA and the anticodons of tRNA
• Types of mutations


  • Point mutation - one base in a DNA sequence is replaced with another base

  Frameshift mutation - insertion or replacement of a base in a DNA sequence
• Recombinant DNA


  Synthesized by splicing a segment of DNA, usually a gene, from one organism into the DNA of another organism
• Polymerase chain reaction


  Method for rapidly producing many copies of a DNA sequence
• Nucleoside


  A two-subunit molecule in which a pentose sugar is bonded to a nitrogen containing heterocyclic base
• Nucleoside formation


  1. Base

  2. Sugar

  3. Water
• Nucleoside formation


  • The base is always attached to C1' of the sugar (the anomeric carbon atom) in a β-configuration
  • For purines, attachment is through N9; for pyrimidines, N1 is involved
  • A molecule of water is formed as the two molecules bond together
• RNA nucleosides


  • ribose-adenine
  • ribose-cytosine
  • ribose-guanine
  • ribose-uracil
• DNA nucleosides


  • deoxyribose-adenine
  • deoxyribose-cytosine
  • deoxyribose-guanine
  • deoxyribose-thymine
• Nucleoside naming


  Pyrimidine bases use the suffix -idine

  Purine bases use the suffix -osine

  The prefix deoxy- indicates deoxyribose sugar
• Nucleotide


  A nucleoside with a phosphate group bonded to the pentose sugar
• Nucleotide formation


  1. Nucleoside

  2. Phosphate group

  3. Water
• Nucleotide formation


  • The phosphate group is attached to the sugar at the C5' position through a phosphoester linkage
  • A molecule of water is produced in the process
• Nucleotides


  • Adenosine 5'-monophosphate (AMP)

  Guanosine 5'-monophosphate (GMP)

  Cytidine 5'-monophosphate (CMP)

  Uridine 5'-monophosphate (UMP)

  Deoxyadenosine 5'-monophosphate (dAMP)

  Deoxycytidine 5'-monophosphate (dCMP)

  Deoxyguanosine 5'-monophosphate (dGMP)

  Deoxythymidine 5'-monophosphate (dTMP)
• Ribonucleic Acid (RNA)


  A nucleotide polymer in which each of the monomers contains ribose, phosphate group, and one the heterocyclic bases: adenine, guanine, cytosine, or uracil
• Deoxyribonucleic Acid (DNA)


  A nucleotide polymer in which some of the monomers contain deoxyribose, phosphate group and one of the heterocyclic bases: adenine, guanine, cytosine and thymine
• Nucleic Acid Backbone


  • The alternating sugar-phosphate chain in nucleic acid structure
  • Constant through the entire nucleic acid structure
  • For DNA molecules, it consist of alternating phosphate and deoxyribose sugar units
  • For RNA molecules, it consists of alternating phosphate and ribose sugar units
• Primary Nucleic Acid Structure


  • The sequence in which nucleotides are linked together in a nucleic acid
  • Depends only on the sequence of bases present
• Important Points about Nucleic Acid Structure

  • Each nonterminal phosphate group of the sugar-phosphate backbone is bonded to sugar molecules through a 3',5'-phosphodiester linkage
  • A nucleotide chain has directionality. The 5'end normally carries a free phosphate group attached to the 5' carbon atom. The 3' end normally has a free hydroxyl group attached to the 3' carbon atom
  • Each nonterminal phosphate group in the backbone of a nucleic acid carries a 1- charge
• DNA Double Helix

  • Involves two polynucleotide strands coiled around each other in a manner similar to a spiral staircase
  • The sugar-phosphate backbone as the outside banisters of the spiral staircase
  • The bases (side chains) extend inward toward the bases of the other strand
  • The two strands are connected by hydrogen bonds between their bases
  • The two strands is antiparallel–as they run in opposite direction: one runs in the 5' to 3' direction, the other runs in 3' to 5' direction
  • Two strands of DNA in a double helix are not identical —they are complementary
• Base Pairing


  • One small base (a pyrimidine) and one large base (a purine)
  • Most favorable combinations that normally occur in DNA are the A–T and G—C pairing