Proteins

• COOH carboxyl/carboxylic acid group • R variable side group • NH2 amine/amino group • Central carbon atom • A hydrogen atom

Biuret test confirms presence of peptide bond • Add equal volume of sodium hydroxide to sample at room temperature • Add drops of dilute copper (II) sulfate solution, swirl to mix (1 & 2 make biuret reagent) • Results: - Positive result: colour changes from blue to purple - Negative result: solution remains blue

• 20 - Differ only by one side ‘R’ group

• Condensation reaction forms peptide bond (-CONH-) & eliminates molecule of water • Dipeptide: 2 amino acids • Polypeptide: 3 or more amino acids

4

• Sequence, number & type of amino acids in the polypeptide - Determined by sequence of codons on mRNA, and determines the proteins function in the end

• The shape that the chain of amino acids chains – either alpha helix or beta pleated sheet • The hydrogen in the -NH has a slight positive charge whilst the oxygen in the -C=O has a slight negative charge • As a result weak hydrogen bonds can form leading to alpha helices or beta pleated sheets

α-helix: - All N-H bonds on same side of protein chain - Spiral shape - H-bonds parallel to helical axis β-pleated sheet: - N-H & C=O groups alternate from one side to the other

3D structure formed by further folding of polypeptide • Disulfide bridges • Ionic bonds • Hydrogen bonds

• Disulfide bridges: strong covalent S-S bonds between molecules of the amino acid cysteine • Ionic bonds: relatively strong bonds between charged R groups (pH changes cause these bonds to break) • Hydrogen bonds: numerous & easily broken

• Functional proteins may consist of more than one polypeptide • Precise 3D structure held together by the same types of bond as tertiary structure • May involve addition of prosthetic groups e.g. metal ions (haemoglobin) or phosphate groups

• Spherical & compact • Hydrophilic R groups face outwards & hydrophobic R groups face inwards = usually water-soluble • Involved in metabolic processes e.g. enzymes & haemoglobin

• Can form long chains or fibres • Insoluble in water • Useful for structure and support e.g. collagen in skin

• Use capillary tube to spot mixture onto pencil origin line & place chromatography paper in solvent • Allow solvent to run until it almost touches other end of paper, amino acids move different distances based on relative attraction to paper & solubility in solvent • Use revealing agent or UV light to see spots • Calculate Rf values & match to database

• Biological catalysts for intra & extracellular reactions • Specific tertiary structure determines shape of active site, complementary to a specific substrate • Formation of enzyme-substrate (ES) complexes lowers activation energy of metabolic reactions

• Shape of active site is not directly complementary to substrate & is flexible • Conformational changes enables ES complexes to form • This puts strain on substrate bonds, lowering activation energy

• Initially lock & key model: rigid shape of active site complementary to only 1 substrate • Currently induced fit model: also explains why binding at allosteric sites can change shape of active site

Difference between free energy of substrate & peak of curve

• Enzyme concentration • Substrate concentration • Concentration of inhibitors • pH • Temperature

• Given that enzyme concentration is fixed, rate increases proportionally to substrate concentration • Rate levels off when maximum number of ES complexes form at any given time

• Given that substrate is in excess, rate increases proportionally to substrate concentration • Rate levels off when maximum number of ES complexes form at any given time

• Rate increases as kinetic energy increases & peaks at optimum temperature • Above optimum, ionic & H-bonds in tertiary structure break = active site no longer complementary to substrate (denaturation)

• Enzymes have a narrow optimum pH range - Outside range, H+/OH- ions interact with H-bonds & ionic bonds in tertiary structure = denaturation

• Similar shape to substrate = bind to active site • Do not stop reaction; ES complexes forms when inhibitor is released • Increasing substrate concentration decreases their effect