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

  
• 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 derivatives

  Thymine (T), cytosine (C), uracil (U)

  
• Purine derivatives

  Adenine (A), guanine (G)

  
• Phosphate

  Derived from phosphoric acid (H3PO4 → HPO42-) to hydrogen phosphate ion
• 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

  
• Nucleoside


  Sugar and nitrogen base
• Nucleotide


  Sugar, phosphate, and base

  
• 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

  
• Nucleotide chain has directionality - 5' end has free phosphate, 3' end has free hydroxyl

  
• end product of nucleic acids re protein or amino acids
• 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)
  • Two 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 segments

  3. Replication fork is the point where the double helix is unwinding
• 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 directs synthesis of hnRNA/mRNA

  2. hnRNA is edited to form mRNA

  
• Gene


  Segment of DNA that contains the base sequence for a specific hnRNA/mRNA

  
• Genome


  All of the genetic material (total DNA) contained in the chromosomes
• Transcription process

  Unwinding of DNA double helix

  2. Alignment of free ribonucleotides along exposed DNA strand

  3. RNA polymerase links ribonucleotides to growing hnRNA

  4. Transcription ends when RNA polymerase encounters stop signal
• Post-transcription process


  Conversion of hnRNA to mRNA by splicing - removing introns and joining exons
• Exons


  Gene segments that convey genetic information