Chapter 11B - Proteins & Enzymes
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Describe the primary structure of proteins:
• covalent bonding (amide/peptide links) • order/sequence of amino acid residues in the protein/polypeptide
Describe the secondary structure of proteins:
• hydrogen bonding • coiling, folding, pleating of the primary structure to create the 3D shape • represented by dotted lines • α-helix structure • β-pleated sheet
What is the α-helix structure?
• hydrogen bonds form b/w oxygen of C=O group in each amide bond & hydrogen in N-H group in amide bond 4 amino acids below it in the helix
What is the β-pleated sheet?
• hydrogen bonds form b/w oxygen in one amide bond & hydrogen in the adjacent polypeptide chain
Describe the tertiary structure of proteins:
• covalent bonding (disulfide bridges) • hydrogen bonding • dispersion forces • ionic bonds • Folding of the protein into a particular 3D shape • Attraction arising from R/Z side chains • responsible for unique protein function
Where do ionic interactions form?
NH3+ and COO- on adjacent side chains
Where do disulfide bridges form?
Two cysteine -SH side chains only Note: Methionine cannot form disulfide bridges
Where do tertiary hydrogen bonds form?
N and H or O and H
Where do dispersion forces form in the tertiary structure of proteins?
Non-polar side chains
What are Enzymes?
• biological catalysts made of protein • catalyse biological reactions ensuring they proceed at a reasonable rate at body temperature • highly specific - responsible for catalysing one/small number of chemical reactions • lower activation energy by providing alternative pathway
Describe Enzyme function
• depends on tertiary/quaternary structures • has an active site which forms part of the 3D structure • binds to the reactant(s) (substrate) of a reaction • temporary bonds form b/w enzyme & substrate weakening bonds within substrate, lowering activation energy
Describe the quaternary structure of proteins?
• covalent bonding • hydrogen bonding • dispersion forces • ionic bonds • formed when individual protein molecules link together in a particular spatial arrangement • not all proteins have quaternary structures
Describe the Lock and Key model
• substrate fit perfectly into the active site of the enzyme • enzyme binds to the substrate forming an enzyme substrate complex • substrate breaks/rearranges into new products & products are released • enzyme remains unchanged & is free to bind to a new substrate
Positive catalyst
• Increases rate of reaction