Carbohydrates, Lipids and Proteins


Monomers and Polymers

  • Monomers are individual molecules that make up a polymer
  • Polymers are long chains that are composed of many individual monomers that can be bonded together in a repeating pattern
  • Condenstaion reactions join them, releasing water
  • Hydrolysis reactions occur to break down larger molecules by adding water
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  • Monosaccarides are the simplest carbohydrate, consisting of only one molecule
  • Ribose sugars are found in many biological molecules such as RNA, ATP and NAD
  • Glucose is a hexose sugar with 2 isomers
  • Disaccaharide are sugars that are somposed of two monosaccharides joined together in a condensation reaction, forming a glycosidic bond

Maltose= 2 alpha glucose

Sucrose= alpha glucose and fructose

Lactose= beta glucose and galactose

Polysaccahrides are formed by many monosaccarides joined together 

  • Amylose, amylopectin is the main polysaccahride energy store in plants,is composed of a-glucose
  • In animals, the polysaccharide energy store is called glycogen, composed of a-glucose
  • Cellulose is a structural component of plant cell walls, composed of long unbranched chains of b-glucose
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  • Saturated= no double bonded Carbons
  • Unsaturated= at least one double bonded Carbon atoms, meaning there is less hydorgen molecules
  • A triglyceride molecule is formed by joining one glycerol and three fatty acid tails by condensation reacts to form ester bonds
  • Triglycerides have key roles in respiration and energy storage due to its insolubility and high Carbon to Hydrogen ratio
  • Phospholipids replace one of the fatty acid chains in triglycerides with a phosphate molecule
  • Hydrophobic tails and Hydrophillic heads allow them to form phospholipid bilayers

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Inorganic Ions

  • Inorganic ions are atoms or molecules with an electric charge containinng no carbon
  • Cations are positively charged
  • Anions are neagtively charged
  • Inorganic ions occur in solution in the cytoplasm and body fluids of organisms, some in high concentrations and others in very low concentrations
  • Each ion has a specific role, depending on its properties
    • Hydrogen ions determine the pH of bodily fluids, the higher the concentration the lower the  pH
    • Na+ ions are used in the co-transport of glucose and amino acids across cell membranes and transmissionof nervous impulse
    • Phosphate ions are essential components of DNA, RNA nucleotides & ATP
    • Calcium ions regulate protein channels, impulse transmission and harden body parts like teeth
    • K ions play a role in muscle contraction, nervous transmission, active transport and maintaining turgidity in plant cells
    • Ammonium ions and nitrate ions are part of the nitrogen cycle
    • hydrogencarbonate ions are formed when CO2 dissolves in the blood. They are important in the transport of carbon dixoide in the blood and the regulation of blood pH
      • CO2+H20 = HCO-3 + H+
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  • Amino acids are the monomers units, there are 20 naturally occuring amino acids
  • Dipeptides are formed when two amino acids are joined togther by a condensation reaction forming a peptide bond
  • A polypeptide is a polymer made of many amino acids joined togther by peptide bonds
  • A protein may contain one or more polypeptide chains
    • Primary
      • the specific sequence of amino acids in a polypeptide chains
      • peptide bonds
    • Secondary
      • the curling or folding of the polypeptide chain into a-helices and b-pleated sheets due to the formation of hydrogen bonds
      • Hydrogen bonds
    • Tertiary
      • The overall 3D shape of a protein, determined by the interactions between R groups
      • Hydrogen, ionic and disulphide bridges
    • Quaternary
      • The 3D shape that is determined by either multiple polypeptide chains or a prosthetic group
      • Hydrogen, Ionic and disulphide bridges
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Globular Proteins

  • A globular protein is a protein with a spherical shape that is soluble in water; they typically have metabolic roles
  • Globular proteins have a few important properties
    • they are roughly spherical in shape, with hydrophobic R groups on the inside and hydrophillic R groups on the outside making them soluble in water
    • they have very sepcific shapes: this allows them to perform specfic functions
  • Haemoglobin is a conjugated globular protein made up of 4 polypeptide chains and 4 haem groups which contain iron ions
  • Insulin consists of 2 polypeptide chains, joined together by disulphide links. The specificity of the shape allows binding to cell membrane receptors
  • Pepsin has hydrogen bonds, disulphide link and few basic R groups to keep it functional in low pH stomach acid.
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Fibrous Protein

  • Fibrous proteins have some similar properties to each other:
    • They contain long polypeptide chains with repeating sequences of amino acids
    • non-polar R group making them insoluble in water
    • they can form fibres which make the protein stronger
  • Collagen is used to make bones, tendons and are found in the walls of arteries to help resist the high pressure
  • Keratin contains high amounts of cysteine, resulting in disulphide links forming between the two polypeptide chains, which makes the molecule very hard and strong. It is found in fingernails, hooves and horns
  • Elastin has the ability to stretch and recoil. Elastin is stretchy due to coiling of the elastin molecules and cross-links that keep the molecules together. It is found in the lungs, bladder and blood vessel walls.
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Biochemical Tests

  • Reducing sugars
    • benedicts (heat)
      • red/orange precipitate
    • reagent strips
      • compare with calibration card
  • Non-reducing sugars
    • hydrochloric acid, heat sodium hydrogencarbonate, Benedicts, heat
      • red/orange recipitate
  • Starch
    • iodine in potassium iodide solution
      • blue/black
  • Protein
    • biruet
      • purple
  • Lipid
    • ethanol, water, shake
      • cloudy white
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