Nucleotides and Nucleic acids

• Nucleosides


  Nucleotides without the phosphate group
• Nucleotides


  Consist of a nitrogenous base, a 5 carbon sugar, and a phosphate group

  
• Purines


  Nitrogenous bases with 2 rings (adenine, guanine)

  
• Pyrimidines


  Nitrogenous bases with 1 ring (cytosine, thymine, uracil)

  
• RNA


  Ribonucleic acid, contains ribose sugar and uracil base

  
• DNA


  Deoxyribonucleic acid, contains deoxyribose sugar and thymine base

  
• Functions of nucleotides


  • Building blocks of nucleic acids
  • Sources of energy used to drive unfavourable reactions
  • Components of coenzymes
• Phosphodiester bridge


  Gives polarity to polynucleotides, more labile in RNA than DNA

  
• Specific base pairing is facilitated by factors, and Erwin Chargaff made observations on DNA composition
• Watson-Crick model of DNA (B-DNA)

  • 2 polynucleotide strands wound around each other
  • Hydrophilic backbone on outside, hydrophobic bases stacked inside
  • Antiparallel strands with complementary base pairing
  • Factors contributing to stability of double helix
• Flexibility of DNA molecule

  • Different conformations of deoxyribose
  • Rotation about C'-N glycosyl bonds
  • Rotation about phosphodiester bonds

  
• Spontaneous reactions which can take place in DNA: deamination, depurination, reactions between adjacent thymine bases

  
• Hyperchromic effect


  Increase in UV absorption when double-stranded DNA is denatured
• Melting temperature of double-stranded DNA

  Increases with higher salt concentration
• Factors promoting hydrolysis of ATP

  Charge separation, formation of phosphate, ionization, solvation
• Substrate-level phosphorylation differs from oxidative phosphorylation
• 1. DNA


  • Predominates in organic solvents, right-handed helix, 11 bp/turn, base pairs not perpendicular to axis

  
• 1. DNA


  • Left-handed helix, 12 bp/turn, narrower double helix, major groove barely apparent
• Relationship between DNA and chromosomes
• Theodore Roosevelt: 'When you play, play hard. When you work, don't play at all.'
• Molecular biology is the practice of biochemistry without a license (Erwin Chargaff)
• Chargaff's observations on DNA composition
• Consequences of DNA containing uracil instead of thymine

  
• TATA box in DNA
• Effect of salt concentration on DNA melting temperature
• mRNA may be monocistronic or polycistronic
• Charles Caleb Colton: 'Examinations are formidable even to the best prepared, for the greatest fool may ask more than the wisest man can answer.'
• Nucleotides as energy intermediates or "currency"