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Introduction

  • We are made up of 3 main fuel types:
    • Fat
    • Carbohydrate
    • Protein

Carbohydrates

  • Aldehydes or ketones
    • Have multiple hydroxyl groups
      • Eg: glucose (aldehyde) and Fructose (ketone)
  • Function:
    • Storage of metabolic fuel in cells
      • Starch in plants, glycogen in animals
    • Structural materials
      • Cellulose in plants, connective tissue in animals
    • Molecular recognition
      • Blood groups
  • Types:
    • Monosaccharide – single unit/monomer
      • Eg: glucose
    • Oligosacchardie – a few, 2-20 joined by covalent bonds
      • Eg: sucrose, lactose
    • Polysacchardie – more than 20 joined together by covalent bonds
      • Eg: cellulose, glycogen
  • Structure of monosaccharides:
    • Have a carbonyl group: aldehyde, ketone + structural isomers
    • 3-7 carbons in length
    • Stereoisomers
      • Some have chiral centres
      • Mostly are ‘R’ since human body mostly processes R-stereoisomers
  • Polymerisation:
    • Synthesis involves a loss of H2O (dehydration) to form a new covalent bond
    • Breakdown involves the addition of H2O (hydrolysis) to split a covalent bond
      • Both reactions are often catalysed by enzymes
    • Egs:
      • Cellulose is glucose with a β-1,4 glycosidic link
      • Amylose is glucose with an α-1,4 glycosidic link
  • Storage polysaccharides
    • Amylopectin is branched at every 25th glucose
    • Glycogen is branched at every 10th glucose
      • Used as a short term energy store
    • The Spaghetti hypothesis
      • Single strand is neat and slow to eat
      • Multiple strands (branching) means that strands are ‘eaten’ faster by enzyme catalysis

Lipids

  • Have many different chemical structures
  • Insoluble in water, soluble in organic solvents
  • Types:
    • Triacyglycerols (triglycerides)
    • Phopholipids
    • Steroids
  • Functions:
    • Storage of metabolic fuel in specialised cells
      • Eg: triglycerides in adipose cells
        • Stores twice as much energy as carbohydrates and is anhydrous
        • Structure: long hydrocarbons joined to a glycerol backbone
    • Cell membranes
      • Eg: phospholipids, cholesterol
        • Hydrophobic (fatty acids) and hydrophilic ends (alcohol, phosphate)
        • In phospholipid bi-layers proteins are like icebergs free to diffuse in a sea of lipid
    • Hormones
      • Eg: steroids