Chemical Basis of Life 2

• Nucleic acids


  DNA and RNA

  
• Proteins (continued next week)
• Dr Michelle Coulson
• Campbell Biology, from Chapter 5 and Chapter 16
• Dehydration reaction: synthesizing a polymer

  1. Unlinked monomer

  2. Dehydration removes a water molecule, forming a new bond

  3. Short polymer

  4. Longer polymer

  
• Hydrolysis: breaking down a polymer


  1. Longer polymer

  2. Hydrolysis adds a water molecule, breaking a bond

  3. H

  4. Unlinked monomer

  
• Reminder from last lecture: Synthesis and Breakdown of Polymers
• HO


  OH = O+H = hydroxyl group
• Line indicates covalent bond
• Monomers are added to the growing polymer by a dehydration reaction
• Release of a water molecule
• Polymers are disassembled to monomers by hydrolysis
• These chemical reactions are sped up by specialized enzymes
• Lipids: summary of key concepts

  
• Carbohydrates: summary of key concepts

  
• Nucleic acids: summary of key concepts
• Proteins: summary of key concepts
• Four classes of large biological molecules

  • Carbohydrates (sugars, starch, cellulose)
  • Lipids (fats/oils, phospholipids of biological membranes)
  • Nucleic acids (DNA and RNA)
  • Proteins (made from amino acids)
• Macromolecules are very large, complex molecules
• Built from multiple, repeating units added together to make a polymer
• Macromolecules


  • Carbohydrates
  • Nucleic acids
  • Proteins
• Lipids aren't strictly macromolecules, but discussed here too

  
• Class of macromolecule


  • monomer
  • polymer
  • Name given to the chemical linkage
• polysaccharide


  • glucose (monomer is different for chitin)
  • starch, glycogen, cellulose
  • Glycosidic linkage
• nucleic acid


  • nucleotides (A, G, C, and T in DNA or U in RNA)
  • DNA (deoxyribonucleic acid)
  • RNA (ribonucleic acid)
  • oligonucleotide* (polymer of ~10-50 nucleotides, usually synthetically produced)
  • Phosphodiester bond
• * The prefix "oligo" come from the Greek word meaning "a few", i.e. a small but not specific number
• DNA structure


  • Thymine (T)
  • Guanine (G)
  • Cytosine (C)
  • Adenine (A)
  • Sugar–phosphate backbone
  • Nitrogenous bases
  • Phosphate group
  • Sugar (deoxyribose)
• • DNA: deoxyribose sugar
  • RNA: ribose sugar
• Nitrogenous bases


  • Pyrimidines (cytosine, thymine, and uracil) are smaller (single ring)
  • Purines (adenine and guanine) are smaller (double ring structure)
• Terms purine/pyrimidine are not needed in MGC
• DNA polarity: 5' end and 3' end


  • Carbons in the sugar component are identified as 1', 2', 3', 4' and 5'
  • 5' end of single DNA strand has the 5' carbon at the "end"
  • 3' end has 3' carbon at the "end"
  • the way we identify "ends" and direction/orientation
  • Two strands run antiparallel (opposite orientations)
  • Enzymes that make nucleic acids can only work in a certain direction (see DNA replication; transcription)

  
• Double-stranded DNA is anti-parallel
• DNA structure: double helix

  • Two strands of DNA, held together by H-bonds
  • A (adenine) pairs with T (thymine)
  • G (guanine) pairs with C (cytosine)
  • from the sequence of AGCT on one strand can determine the other strand
  • A G C T are called the bases
  • Different base sequences/orders can encode different proteins / different biological functions

  
• • Pentose sugar is deoxyribose
  • Bases are A, G, C, T
• • Complementary base pairing
  • Purine + purine: too wide
  • Pyrimidine + pyrimidine: too narrow
  • Purine + pyrimidine: width consistent with X-ray data (Rosalind Franklin)
• dsDNA is "right-handed"
• Simplified depictions of DNA
• Remember: Double-stranded DNA is always antiparallel
• There are two types of nucleic acids: Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA)
• dine + pyrimidine


  Too narrow