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3.2  Amino Acids And Peptide Bonds
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3.2 Amino Acids And Peptide Bonds

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  • 2.2.2
  • Do not need to know names or structure of amino acids – interest only
  • Some other amino acids do occur in proteins e.g. selenocysteine (some enzymes), hydroxyproline (in collagen) – these are produced by modification of other amino acids after incorporation into proteins. Other amino acids occur as intermediaries in metabolic pathways (ornithine – urea production). D-alanine, D-glutamic acid, mesodiaminopimelic acid are found in the peptide cross-links in bacterial peptidoglycan: only L-forms are found in proteins. Also dopamine (neurotransmitter), creatine (energy store in muscles)
  • Interest only but see Option A 2.8
  • Interest only: students may have seen ‘ contains a source of phenylalanine ’ on food packaging
  • 2.2.6
  • Part of 2.2.5
  • Part of 2.2.5

Transcript

  • 1. Amino Acids and Dipeptides CH 2 H H N C C OH O H C O OH H H N C C O H R 1 H N C C OH O H R 2
  • 2. Polymer: large molecules consisting of large numbers of repeating units connected by covalent bonds Monomer: a small molecule that may become chemically bonded to other monomers to form a polymer amino acid = monomer polypeptide = polymer
  • 3. amino group carboxyl group R group General structure of an amino acid (basic) (acidic) H H N C C OH O H R
  • 4. Different amino acids have different R groups Their different properties depend on their R groups Hydrophobic (‘Water-hating’) R groups CH 3 H H N C C OH O H alanine CH 2 H H N C C OH O H phenylalanine (aromatic)
  • 5. Hydrophillic (‘Water-loving’) R groups CH 2 H H N C C OH O H SH cysteine CH 2 H H N C C OH O H OH serine
  • 6. aspartic acid (acidic) First isolated from asparagus juice! CH 2 H H N C C OH O H C O NH 2 asparagine (basic) CH 2 H H N C C OH O H C O OH
  • 7. You do NOT need to know their names! There are 20 amino acids naturally incorporated into proteins Alanine Arginine Asparagine Aspartic acid Cysteine Glutamic acid Glutamine Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tryptophan Tyrosine Valine
  • 8. Other amino acids do exist… used in the human body as a hormone to regulate metabolic rate … but are not normally found in proteins CH 2 H H N C C OH O H O I I I I Thyroxine:
  • 9. Humans can synthesis some amino acids by altering other amino acids, however… … some amino acids cannot be synthesised and are therefore needed in the diet. These are the essential amino acids Arginine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine
  • 10. Phenylketonuria or Maple Syrup Urine Disease Patients lack the enzyme phenylalanine hydroxylase – needed to dispose of the amino acid phenylalanine properly Penylalanine rapidly builds up in the blood stream - it converted to unusual metabolites which give the patient’s urine a characteristic smell - it also rapidly causes brain damage! Treatment: A diet low in phelylalanine No meat, fish, poultry, eggs, cheese, milk, beans, or peas
  • 11. Formation of a dipeptide: carboxyl group of one amino acid reacts with amino group of second amino acid H 2 O water molecule formed peptide linkage a dipeptide H H N C C OH O H R 2 H H N C C OH O H R 1 H H N C C O H R 1 H N C C OH O H R 2
  • 12. H 2 O Formation of a dipeptide produces a molecule of water, therefore… … this is a condensation reaction 2 amino acids  dipeptide + water H H N C C OH O H R 1 H H N C C OH O H R 2 H H N C C O H R 1 H N C C OH O H R 2
  • 13. H 2 O Splitting a dipeptide to form two amino acids consumes one molecule of water, therefore… … this is a hydrolysis reaction dipeptide + water  2 amino acids H H N C C OH O H R 1 H H N C C OH O H R 2 H H N C C O H R 1 H N C C OH O H R 2
  • 14. Tripeptide: three amino acids linked together Oligopeptide: a short chain of a few amino acids Polypeptide: a chain of many amino acids A protein may consist of one or more polypeptide chains Structure of haemoglobin – a protein consisting of four polypeptides