Pack 4 - proteins, enzymes and digestion

Proteins
1. C, H, O, N are always present
2. NH2 is the amine group
  1. COOH is carboxyl group
  2. R is variable group
    1. The R group is what varies amino acids
      1. When R = H amino acid is called glycine
      2. When R = CH3 amino called alanine
3. Formation of a Protein
  1. Primary structure
    1. This is the number and the sequence of amino acids joined by peptide bonds
    2. Joining of two amino acids results in the loss of a water molecule
      1. This is condensation reaction
      2. Two joined amino acids is a di-peptide etc.
    3. The R group has positive and negative charges this causes the protein to fold
      1. As opposites attract
    4. Features of the R groups
      1. Could be hydrophilic/phobic
      2. Some are + some are -
      3. Could be second amine or carboxyl group
      4. Could have sulfur
    5. Chromotography can be used to separate out individual amino acids
      1. This is done using properties of the R group
      2. Find the RF
    6. Relationship between primary structure and protein function (3 marks)
      1. Primary structure = sequence and number of amino acids joined by peptide bonds
      2. R groups bond with R groups forming hydrogen bonds
      3. The shape must be right - active site and substrate must fit
  2. Secondary structure
    1. This is the folding of proteins chains due to hydrogen bonds forming between amino acids
    2. Alpha helix
      1. Helical coiling of the polypeptide chain maintained by H bonds at each peptide link
      2. Structural proteins
        e.g. keratin (hair) twist to form two stranded helix
        e.g. collagen (bones and tendons) forms three stranded helix
        Linked by cross bridges so are very stable
        These fibrous proteins provide strength
    3. Beta - pleating
      1. Pleated sheets, the sheets provide flexibility
  3. Tertiary structure
    1. This is where the protein chain is further folded to form a coiled 3D structure
    2. Tertiary contains:
      1. Disulfide bonds
        Strong bonds between two sulphur atoms
      2. Ionic bonds
        Form between carboxyl and amino groups that are not used to form peptide bonds
        Easily broken by pH
      3. Hydrogen bonds
        Weak bonds but lots that gives structure stability
  4. Quaternary structure
    1. Proteins that are made up of more than one polypeptide chain
  5. Fibrous and globular proteins
    1. Proteins that only have a secondary structure are said to be fibrous
      1. Non-polar
    2. Proteins that have a tertiary structure are said to be globular
      1. Very soluble
4. Testing for proteins
  1. Add Biuret reagent
    1. If protein present solution will turn purple
Enzymes
1. Anabolic = building
  1. Catabolic = breaking
2. Any reaction needs a certain amount of ACTIVATION ENERGY
  1. An enzyme binds with substrate and lowers activation energy
3. How an enzyme works
  1. Induced fit model
    1. When the substrate combines with the enzyme it causes the active site to change shape
      1. This puts strain on the substrate molecule, distorting particular bonds and lowering the activation energy
4. Properties
  1. Enzymes work quickly
  2. Enzymes remain unchanged by the reaction
  3. Enzymes work in both directions of a reaction
  4. Enzymes are specific
  5. Enzymes are affected by temperature
    1. As temp. increases below optimum temp.:
      1. Increased KE
        So increased collisions
      2. Reduction of activation energy
        Increased production of enzyme-substrate complexes
    2. As temp. increases above the optimum temp,:
      1. Hydrogen and ionic bonds break
      2. Tertiary structure is lost
        Active site changes shape
      3. Enzyme denatures
      4. Fewer enzyme/substrate complexes formed
  6. Enzymes are affected by pH
    1. Low pH
      1. Ionic and hydrogen bonds are broken due to lots of H+
    2. High pH
      1. Ionic and hydrogen bonds are broken due to lots of OH-
  7. Enzymes are affected by substrate conc.
    1. Diagonal then straight line
      1. enzyme conc. becomes limiting factor, substrate can't bind to anymore enzymes as all are being used
  8. Enzymes are affected by enzyme conc.
    1. Diagonal then straight line
      1. Substrate conc. becomes the limiting factor, more enzyme added but cannot bind to anyy substrate as no more substrate molecules available
  9. Enzymes are affected by inhibitors
    1. Competitive inhibition:
      1. These compete with the substrate for the enzyme's active site
        Inhibition is temporary
      2. Substrate and inhibitor have similar shapes
        They are complimentary in shape
    2. Non-competitive
      1. This does not have a similar shape to the substrate
      2. It binds to the enzyme at a site other than the active site
      3. The binding of the inhibitor causes a change in the shape of the active site
      4. The substrate is no longer able to bit as it does not have a complimentary shape
    3. You can use the product of a reaction to act as an inhibitor for earlier on in the reaction
5. Intra cellular = inside cells
  1. Extra cellular = outside the cell
Digestion
1. This is the hydrolysis of complex foods down into simple soluble substances by enzymes
2. Disaccharides
  1. Maltose
    1. 2 alpha glucose
  2. Sucrose
    1. Alpha glucose and fructose
  3. Lactose
    1. Alpha glucose and galactose
  4. These 3 are all found in the membrane of the epithelial lining of the small intestine
3. Amylase breaks down starch
4. Lipids in mammals
  1. Broken down by lipase
  2. Bile salts emulsify the fats
  3. (3 fatty acids and glycerol)
5. Proteins in mammals
  1. Protease breaks down amino acids
    1. This is inactive when first synthesised otherwise it would break down all protein in the cell
  2. Endopeptidases breaks down middle of peptide bond
    1. Exopeptidases breaks down outer peptide bond
  3. Di-peptidases are found on the intestinal lining of the epithelial cells
6. Absorption
  1. Co-transport for monosaccharides
    1. Protein that moves two molecules in same direction = symporter
      1. Sodium ions are co transported with glucose molecules
        Passive
    2. Active transport keeps the conc. gradient of sodium ion so that its always lower in the cell than the lumen
      1. High conc. difference between lumen and outside of cell keeps sodium moving and therefore glucose too
  2. Co transport for absorption of amino acids
    1. Exactly the same as monosaccharides but sodium enters with amino acids
  3. The role of micelles in the absorption of lipids
    1. A micelle is made of monoglycerides and fatty acids
    2. Bile salts help form micelles by:
      1. Bind to hydrophilic sites
        Bile salts surround it and stop fats sticking together
      2. Micelles help cells absorb lipids by:
        Free fatty acids + bile salts create bile salts around the fatty acids
        This makes it lipid soluble so they go into the epithelial layer
        They are then packed together to form chylomicrons which then leave the cell by exocytosis

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Pack 4 - proteins, enzymes and digestion

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	Created by Jacob Shepherd over 8 years ago