enzymes and co-factors

Question 1

what is gibbs free energy

Answer 1

• energy available in a system to do work
• △G = change in gibbs’ free energy (+ or -).
  △G = Gfinal state - Ginitial state

Question 2

what is an endergonic reaction

Answer 2

• require energy input to happen (uphill), graph starts down, endothermic
• not spontaneous
• +△G = increase energy and instability

Question 3

what is an exergonic reaction

Answer 3

• spontaneous (downhill) and releases energy, exothermic
• energy of products - energy of reactants = -ve
• △G = decrease energy and increase stability

Question 4

what is activation energy

Answer 4

• energy required to destabilise existing chemical bonds and initiate a chemical reaction (transition state)
• rate of reaction depends on activation energy (necessary to begin)
• catalyst: lower activation energy, provide alternate pathway, not consumed

Question 5

what are enzymes

Answer 5

• biological catalyst
• conformational shape change (functional shape, active site, affinity), enables it to stabilise a temporary association between reactants
• not consumed
• specific to substrates (lock and key)
• combines in correct orientation, stresses bonds and provides a surface to facilitate reactants coming together
• carbonic anhydrase: CO2 + H2O -(carbonic anhydrase)-> H2CO3, exergonic (spontaneous) but significant activation energy (enzyme - carbonic anhydrase)

Question 6

what are the function of enzymes

Answer 6

• most are globular proteins with active site(s) for substrates to bind
  1. R-groups of AA interact chemically with substrate
  2. stress or distortion of a bond = lower activation energy
  3. product forms and dissociates from enzyme (due to lower affinity for enzyme)
• enzyme fits precisely into active site to form enzyme substrate complex, substrate binding induces shape change
• activates enzyme to produce a snug fit or receive other substrates

Question 7

what are multi-enzyme complexes

Answer 7

• teams of loosely associated enzymes catalysing different steps of a sequence
• increases catalytic efficiency
• produce of one reaction passed to next enzyme
• unwanted side reactions limited
• all reactions can be controlled as a unit

Question 8

what are factors effecting enzyme activity (6)

Answer 8

• conc: of substrate / enzyme type (limitation, complete saturation = plateau)
• temp: rate increases with temp to an optimum, denaturation / deactivation can occur, too high (h bonds and hydrophobic interactions are too weak = no shape), too low (interactions are too inflexible to allow precise fit)
• pH: affects +ve and -ve charges of AA, charges = maintain shape
• inhibitors: decrease enzyme activity (regulate activity of enzymes), competitive (compete with substrate for same binding site), non-competitive (bind to allosteric site, alters shape, loses affinity)
• activators: keep enzymes in active configurations (regulate activity), bind to allosteric sites, stabilise active / inactive form (ADP / ATP)
• enzyme co-factors: enzyme function assisted by additional chemical components, non-protein ion / organic molecule, haemoglobin (cofactor = iron)

Question 9

what is feedback inhibition

Answer 9

• biochemical pathways

- products of a pathway inhibit early reactions, if not products are produced unnecessarily (not a feedback loop)