CHEM 113

• Nucleic acids discovered by Swiss Physiologist Friedrich Miescher


  1869
• Nucleic acids


  Unbranched polymer containing monomers called nucleotides; repeating unit is nucleotides
• Types of nucleic acids

  • DNA
  • RNA
• Nucleotide


  Three-subunit molecule; building block of nucleic acids
• Components of a nucleotide

  • Pentose sugar (monosaccharide)
  • Phosphate group
  • Nitrogen base (heterocyclic base)

  
• Pentose sugar


  • 5 carbons
  • RNA has ribose, DNA has deoxyribose

  
• Phosphate group is attached at Carbon 5 (C5), base is attached at Carbon 1 (C1)

  
• RNA and DNA differ at Carbon 2 (C2) - RNA has -OH, DNA has -H

  
• Nitrogen bases


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

  
• Adenine (A), guanine (G), and cytosine (C) are found in both RNA and DNA

  
• Uracil (U) is found only in RNA, thymine (T) is found only in DNA
• Pyrimidine


  Monocyclic (single ring) base with a six-membered ring
• Purine


  Bicyclic (double ring) base with fused five and six-membered rings

  
• Pyrimidines and purines both contain amine functional groups
• Nucleoside


  Two-subunit molecule composed of pentose sugar bonded with a nitrogen base
• Nucleosides

  • Adenosine
  • Guanosine
  • Cytidine
  • Uridine (RNA)
  • Deoxyadenosine
  • Deoxyguanosine
  • Deoxycytidine
  • Deoxythymidine (DNA)

  
• Nucleotide formation


  1. Phosphate attached to C5, base attached to C1 of pentose

  2. Molecule of water produced

  
• DNA nucleotide names


  • Deoxyadenosine 5'-monophosphate
  • Deoxyguanosine 5'-monophosphate
  • Deoxycytidine 5'-monophosphate
  • Deoxythymidine 5'-monophosphate

  
• RNA nucleotide names


  • Adenosine 5'-monophosphate
  • Guanosine 5'-monophosphate
  • Cytidine 5'-monophosphate
  • Uridine 5'-monophosphate

  
• Primary nucleic acid structure

  Sequence in which nucleotides are linked together
• RNA


  • Nucleotide polymer with ribose, phosphate, and one of the four nitrogen bases
  • Backbone - alternating phosphate and ribose
• DNA


  • Nucleotide polymer with deoxyribose, phosphate, and one of the four nitrogen bases
  • Backbone - alternating phosphate and deoxyribose

  
• Each nonterminal phosphate group is bonded to two sugar molecules through a 3', 5' phosphodiester linkage

  
• Nucleotide chain has directionality - 5' end has free phosphate, 3' end has free hydroxyl
• DNA is double helix/double stranded, located inside the nucleus, used for replication and genetic information
• Amounts of complementary bases in DNA are always equal (A% = T%, C% = G%)
• DNA strands are anti-parallel, running in opposite directions (5'-to-3' and 3'-to-5')
• Base pairing


  • One small base (pyrimidine) and one large base (purine) can fit within the helix interior
  • Hydrogen bonding is stronger with A-T and G-C
• Complementary bases


  Pairs of bases in a nucleic acid structure that are hydrogen-bonded to each other (A↔T, G↔C)
• DNA replication


  1. DNA helicase breaks hydrogen bonds between complementary bases

  2. DNA ligase connects segments

  3. Replication fork moves as double helix unwinds
• Chromosomes


  • Histone-DNA complexes; 15% DNA, 85% protein
  • Different organisms have different numbers of chromosomes
• Protein synthesis


  1. Transcription - DNA directs synthesis of mRNA

  2. Translation - mRNA is used to synthesize proteins

  
• RNA


  • Single stranded, located outside nucleus, involved in protein synthesis
  • Sugar unit is ribose, uses uracil instead of thymine
  • Does not contain equal amounts of specific bases
  • Much smaller than DNA

  
• Types of RNA


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

  
• Transcription


  1. DNA helicase unwinds DNA double helix

  2. RNA polymerase aligns ribonucleotides along exposed DNA template

  3. RNA polymerase links ribonucleotides to form hnRNA

  4. Transcription ends when RNA polymerase encounters stop signal

  
• Post-transcription


  1. Exons - gene segments that convey genetic information

  2. Introns - gene segments that do not convey genetic information

  3. Splicing - removal of introns and joining of exons by snRNPs and spliceosomes to form mRNA

  
• Alternative splicing


  Process by which several different proteins can be produced from a single gene
• Exon


  Gene segment that conveys (codes for) genetic information; DNA segment that help express a genetic message

  
• Intron

  Gene segment that does not convey (code for) genetic information; DNA segment that interrupt a genetic message
• Splicing

  Removing introns from an hnRNA molecule and joining the remaining exons together to form an mRNA molecule; involves snRNA molecules