nucleic acids

• 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
• Nitrogen base is attached at Carbon 1 (C1), while phosphate group is attached at Carbon 5 (C5)
• RNA and DNA differ at Carbon 2 (C2) - RNA has -OH, DNA has -H

  
• Nucleic acid backbone


  Phosphate - sugar

  
• 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
• Pyrimidines and purines both contain amine functional groups

  
• Phosphate

  Derived from phosphoric acid (H3PO4 → HPO42-)
• 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 nomenclature

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

  
• RNA nucleotide nomenclature


  • 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


  • Double helix/double stranded
  • Located in the nucleus
  • Used for replication and storing genetic information
  • Complementary base amounts are equal (A=T, C=G)
  • Strands are antiparallel
• 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 the segments

  3. Replication fork is the point where the double helix is unwinding
• Antimetabolites are drugs that inhibit the DNA replication process
• 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 a protein

  
• RNA


  • Single stranded
  • Located outside the nucleus
  • Used for protein synthesis
  • Has ribose sugar, uracil instead of thymine
  • Does not have equal amounts of specific bases
  • 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 strand

  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 - process of removing introns and joining exons to form mRNA

  4. Spliceosome - complex of snRNA and proteins that facilitates splicing

  
• 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
• Small nuclear ribonucleoprotein particle (snRNP)

  Complex formed from an snRNA molecule and several proteins; always further collect together into a larger complexes called spliceosomes