12-06: Enzymes

biological catalyst

proteins that speed up metabolic reactions by lowering energy barriers

activation energy

minimum energy required to initiate a reaction

substrate

the substance an enzyme acts on and makes more reactive

substrate specific

enzymes depend on the enzymes 3d shape but they are flexible - they won't just bond to anything it has to be their specific substrate

how enzymes work

distort the substrate's chemical bonds so less energy is needed and provides a micro environment more ideal for the chemical rxn. side chains of amino acids can be positioned to participate in the rxn and help with the reactivity (breaks the bonds within the substrates which makes the rxn occur more readily)

rxn rates, concentration of substrate plays a role in rxn speed

more substrate = faster rxn, UNLESS it becomes saturated, in which case the rxn rate plateaus - if all active sites are occupied.

optimal conditions for enzymes

a cells physical and chemical environment impacts enzyme activity and each enzyme has optimal conditions that it favours (to obtain its most active enzyme conformation, favourite shape). temperature and pH impact the enzyme

optimal temperature for enzymes

allows the greatest # of collisions w/o denaturing the enzyme

e.g. heat makes collisions increase but if there is too much heat, it will denature the enzymes - the optimal temperature is 35-40ºC

optimal pH for enzymes

typically a pH of 6-8 but some will operate at the extremes of pH (like digestive enzymes - e.g. pepsin is lower and trypsin is higher in pH)

cofactors

small non protein helpers for enzymes (e.g. metal atoms of zinc, iron, copper)

some enzymes don't even work in optimal conditions & need help

coenzymes

organic molecules (e.g. vitamins)

some enzymes don't even work in optimal conditions & need help

inhibitors

molecules that bond to enzymes to make them less effective

competitive inhibitors

molecules that bind reversibly or irreversibly to the active site and compete with the substrate for space in the active site

reversible competitive inhibitors

looks similar and behaves similarly to the substrate, when the competitor is in high concentration to inactivates the enzyme by outcompeting the substrate - reversible as the competitor can be overwhelmed by high concentrations of substrate

irreversible competitive inhibitors

the competitor occupies the active site permanently and therefore deactivate the enzyme, e.g. carbon monoxide, more common

non competitive inhibition

The inhibitor reacts with the allosteric site (some other place on the enzyme that isn’t the active site), changing the shape of its active site If the shape is altered then the substrate can’t bond to it

reversible non competitive inhibitors

used to regulate metabolic pathways in the cell (series of chemical reactions required for a specific product)

irreversible non competitive inhibitors

bind irreversibly wth some other part of the enzyme and permanently denature/inactivate it

Permanently alter the native conformation of the protein

control of metabolism

Allosteric enzymes have 2 conformations - one catalytically active and the other inactive

Binding of an activator to an allosteric site stabilizes the active conformation

Binding of an inhibitor to an allosteric site stabilizes the inactive conformation

Enzyme activity changes continually in response to changes in the relative proportions of activators and inhibitors

enzyme saturation

all enzymes are being used, and rxn rate plateaus and if all active sites are occupied

optimal conditions

Each enzyme has optimal environmental conditions that favour the most active enzyme conformation (the enzyme works best when its in its favourite shape and environment)

optimal temperature

allows the greatest number of molecular collisions without denaturing the enzyme - heat makes collisions increase but if there is too much heat, it will denature the enzymes → for most human enzymes is 35ºC - 40ºC

optimal pH

for most enzymes is 6-8 but some will operate at more extremes of pH (like digestive enzymes; pepsin is lower and trypsin is higher in pH)

cofactors

small nonprotein (e.g. metal atoms of zinc, iron, copper) that help the enzymes to function

coenzymes

organic molecules (e.g. vitamins) that help the enzyme to function

inhibitors

molecules that