FOB 6 enzymes

• enzyme


  molecule that increases the rate of biochemical reactions by decreasing the activation energy needed. it does this by interacting with substrates in the activation site of the enzyme, which promotes/stabilises their transition state. does not force an unfavourable reaction. in the body, most reactions do not occur at an approachable rate therefore need enzymes
• characteristics of enzymes


  biological catalysts, most are globular proteins (exception: ribosomes are RNA based enzymes), enzymes do not alter the equilibrium of a reaction but enhance the rate of reaction, decreasing the time to equilibrium
• enzyme general reaction


  general formula: S (substrate) <-> ES (enzyme-substrate complex)<-> P (product) full formula: S <-> ES <-> EP (enzyme product complex) <-> P . transition state between ES and EP
• enzyme specificity


  comes from the shape and characteristics of the R-groups of the amino acid residues that form the active site of the enzyme (charge).
• cofactor


  in addition to the R-groups present, and the 3-dimensional structure, some enzymes require additional chemical components: cofactors. inorganic and organic.
• inorganic co factors


  ions: Mg2+ Ca2+ etc. ionic interactions (pull substrate into favourable orientation or nuetralise charge on the substrate through ionic bonds), help orientate substrate and or stabilise charged intermediates. redox electron transfer reactions .
• organic (cofactors) co-enzymes


  many derived from vitamins. more diverse functions: transfer of functional groups (transfer hydroxyl groups), substrate binding stabilisation, redox reactions, acid/base reactions (transfer H ions)
• types of cofactors


  prosthetic group, apoenzymes or apoproteins, holoenzyme
• prosthetic group


  cofactor is very tightly or covalently bound to an enzyme
• apoenzymes or apo proteins 


  an enzyme that requires a cofactor but does not currently have one bound
• holoenzyme


  complete catalytically active enzyme with its bound cofactors
• how do enzymes work (1)

  provide a specific environment in which chemical reactions are more favourable: alignment of substrate functional groups in the correct catalytic orientation, increase the likelihood of interactions between substrates, co-substrates and co-factors (entropy reduction),
• how do enzymes work (2)

  removes substrate(s) from the solvent shell of water that surrounds and stabilises these biomolecules (bury substrate in catalytic active site, replacing water bonds), induces distortion in the substrate that is normally required for a reaction to occur (formation of transition state), formation of covalent and non-covalent bonds to offset the energy needed to break the original bonds. all this reduces activation energy
• how do enzymes lower Ae


  when equilibrium favours the product (the product is a lower Gibbs free energy ground state). the active site of an enzyme promotes the formation of the transition state which reduced ae.
• induced fit model


  not quite a perfect fit for the substrate as it needs to force the product into a shape. continues to change once the substrate has bound which will cause a change in the substrate, pushing into transition state and formation of product
• enzyme activity


  1 unit of enzyme activity is defined as the amount of enzyme causing the transformation of 1 umol of substrate S to product P per minute at 25 D C. The amount of enzyme activity in a solution equals the total number of units in the solution.
• factors that affect enzyme activity


  enzyme concentration, pH temp, substrate conc, inhibitors.
• enzyme conc and enzyme activity


  linear relationship only if unlimited substrate present and until a concentration maximum is reached for the enzyme (when no more enzyme or substrate can be dissolved, can't work undissolved)
• effect of pH


  designed to work in specific environments, if it works in cells 7.4, or in the stomach lower etc. due to ionisation of enzymes which changes structure and function.
• temp 


  increases until a certain extent when proteins denature
• substrate conc

  can be limiting reagent. k1 (rate of free e and s to es complex) K2 ( rate of es to e and P) k-1 (rate of es to e and s). k1 is infinity for substrate. michaelis-menton kinetics (hyperbolic graph of velocity of enzyme) vmax is maximum amount of activity that can be generated from an enzyme (all substrate is bound). km michaelis constant (substrate conc which can be used to measure substrate affinity (lower more affinity and higher velocity)) at substrate conc below km value initial velocity is driven by substrate present, above km more by enzyme kinetics
• km calc


  k2 + k-1 (reduced affinity) / k1 (increased affinity)
• Lineweaver burk plot


  reciprocal plot. x-intercept 1/km. y intercept 1/vmax
• Vo


  initial velocity
• enzyme inhibitors


  reversible (can be removed). irreversible (bind and cannot be removed until the enzyme is broken down). 3 types: competitive, uncompetitive, mixed / non-competitve.
• competitive inhibitor


  competes with substrate to bind in active site, if enough substrate is added it be out-competed. km increases as there is less theoretically affinity, v max is unaffected.
• uncompetitive inhibitor


  binds at a location other than the active site. binds to the enzyme-substrate complex. reduces Vmax as it cant be out-competed. appears to have a greater affinity for substance and km reduces
• mixed inhibitor


  can remove free enzyme or enzyme substrate complex. binds to a separate place to substrate binding. can't out compete so v max goes down if ei is greater than esi, km increases. non-competive equally removed ei and esi which unaffects km