enzymes - substances that carry out most of the catalysis in living organisms  

• RNA may also carry out some catalysis
• substrates - molecules undergoing a reaction
• temporarily stabilizes an association between substrates, lowering activation energy
• carbonic anhydrase - increases production of carbonic acid from 200/hr to 600,000/sec
• active sites - pockets/clefts on the enzyme where substrates bind to form enzyme-substrate complex
• substrate must fit perfectly in an active site for catalysis to work; proteins adjust shapes into an induced fit between it and the substrate
• amino acid side groups of enzymes stress/distort certain bonds, weakening them

enzymes that take many forms - some function as parts of cell membranes/organelles

• multienzyme complex - associations of several enzymes catalyzing different steps in a reaction sequence
  • doesn't require that products of 1 reaction dissociate to move on to the next enzyme
  • no unwanted side reactions
  • all reactions within the complex can be controlled as a unit
• pyruvate dehydrogenase - controls entry to Krebs cycle
• fatty acid synthetase - catalyzes synthesis of fatty acids from 2-carbon precursors
• RNA catalysts - aka ribozymes
  • intramolecular catalysis - catalyze reactions on themselves
  • intermolecular catalysis - act on other molecules; ribozymes don't change
  • adds more support for belief that RNA came before proteins

factors affecting enzyme activity  

• temperature - increase in heat leads to increase in random molecular mov't
  • higher temperature adds stress to bonds
  • rate increases w/ temperature up until optimum temperature
  • proteins denature above the optimum temperature
• pH - controls balance between positively/negatively charged amino acids
  • ionic interactions hold enzymes together
  • optimum pH - ranges from 6 to 8
  • ionic interactions dependent on hydrogen ion concentration
• inhibitor - substance that binds to an enzyme and decreases its activity
  • feedback inhibition - end product of biochemical pathway acts as inhibitor of an earlier reaction on the pathway
  • competitive inhibitor - competes w/ substrates for same active site
  • noncompetitive inhibitor - binds to enzyme in a location other than the active site; changes the enzyme's shape so that the substrate won't fit
  • allosteric inhibitor - substance that binds to an allosteric site (chemical on/off switch) to reduce enzyme activity
• activators - binds to allosteric sites and increase enzyme activity
• enzyme cofactor - additional chemical components that assist enzyme function
  • coenzyme - nonprotein organic molecule
  • serves as an electron acceptor and transfers electrons to substrates in another reaction
• nicotinamide adenine dinucleotide (NAD+) - made of NMP and AMP bonded together
  • AMP acts as core
  • becomes NADH when reduced, can now supply 2 electrons and a proton for other reactions