BIOL 112 Lecture Notes - Lecture 7: Titration, Activation Energy, Allosteric Regulation

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21 Jul 2016
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o!Reducing dimensionality (orienting substrate molecules, bringing together
atoms that will bond)
o!Physical strain (can stretch bonds in substrate molecules, making them
unstable)
o!Chemical charge (can temporarily add chemical groups to substrates)
!Shape of enzyme active sites allows a specific substrate to fit (lock and key)
o!Binding depends on hydrogen bonds, electrostatic attraction, hydrophobic
interactions
o!Many enzymes change shape when they bind to the substrate - induced fit
!Some enzymes require partners:
o!Prosthetic groups: non-amino acid groups, e.g. lipids bound to enzymes to
stabilise
o!Cofactors: inorganic ions
o!Coenzymes: small carbon-containing molecules, not bound permanently to
enzymes; e.g. ligands
!The rate of a catalysed reaction depends on substrate concentration
o!Concentration of enzyme usually lower than concentration of substrate
o!At saturation, all enzymes are bound to substrate - maximum rate
o!Used to calculate enzyme efficiency - turnover (molecules of substrate
converted per unit of enzyme)
!Reactions organised in metabolic pathways, interconnected both in space and in
time
!Inhibitors: regulate enzymes by binding to them and slowing reaction rates
o!Naturally-occurring inhibitors regulate metabolism
o!For example, you're a bacterium, feasting on sugar, so you start
metabolising
o!But then you run out of sugar ... so you need to stop metabolising otherwise
you end up losing energy
o!Bacteria have a (negative?) feedback loop that can inhibit metabolism (raise
activation energy somehow)
o!Irreversible inhibition: covalently bond to side chains in active site -
permanently inactivates enzyme
!!Example, nerve gas - once it goes in it never comes out
o!Reversible inhibition: bonds noncovalently, prevents substrate from bonding
temporarily
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