Enzymes

structure, function, factors affecting activity, enzyme inhibition, models of enzyme action

what is an enzyme?

what is an enzyme?

a globular protein that acts as a biological catalyst

what is the active site?

a short chain of amino acids

are enzymes soluble in water? why?

yes, because the side chains of the amino acids are hydrophilic

what is the active site made up of?

a short chain of amino acids

what are the rest of the amino acids apart from the active site responsible for?

maintain the enzyme’s shape

does the substrate have the same shape as the active site?

no, they are complementary

how do enzymes speed up the rate of reaction?

by lowering the activation energy

where do enzymes work?

extracellularly and intracellularly

what are co-factors and co-enzymes?

non-protein molecules that bind to an enzyme before it catalyses a reaction

what is a coenzyme?

an organic molecule that temporarily bonds to the enzyme and transfers a chemical group required for that specific reaction

what are co-factors (activators)?

an inorganic group that permanently bonds to the enzyme and is a type of prosthetic groups

which factors affect enzyme action?

temperature, pH, inhibitors, concentration of enzyme, concentration of substrate

how does temperature affect rate of enzyme action?

as temp increases, rate increases until a point after which it decreases because the enzyme is denatured

why does increasing temperature cause the rate of reaction to decrease?

increasing temp increases the kinetic energy of the molecules so there are more frequent collisions, resulting in more frequent formations of enzyme-substrate complexes

why does increasing temperature cause rate of reaction to decrease?

after a certain temperature, hydrogen bonds between the tertiary structure break, causing the shape of the protein to change

why does changing pH affect rate of enzyme action?

if the pH becomes too high or low, hydrogen and ionic bonds between the tertiary structure break so it becomes denatured

how does increasing the concentration of the enzyme affect rate of enzyme action?

rate increases then plateaus

why does increasing the concentration of the enzyme cause the rate of reaction to increase?

because a higher concentration causes more collisions and makes it more likely that an enzyme-substrate complex will form

why does increasing the concentration of enzymes stop having an effect after a while?

because the substrate becomes the limiting reactant as there are more enzymes than substrates

how does increasing the concentration of the substrate cause the rate of reaction to change?

it increases until the point of saturation after which it doesn’t change

why does increasing the concentration of the substrate cause the rate of reaction to increase?

because a higher concentration means more enzyme-substrate complexes will form

why does increasing the concentration of the substrate stop having an effect after the point of saturation?

because there are no longer enough enzymes to bind to

what is an inhibitor?

a substance that interferes with the active site, reducing its activity

how do competitive inhibitors affect the enzyme?

they have a similar shape to the substrate so bind to the active site and prevent the enzyme-substrate complex from forming

what happens if substrate concentration is increased in the presence of a competitive inhibitor?

the effect of the inhibitor is reduced

how do non-competitive inhibitors affect the enzyme?

they bind to an allosteric site and cause the active site to change shape, preventing the formation of an enzyme-substrate complex

what are the two models of enzyme action?

lock and key theory, induced fit model

what does the induced fit model suggest?

the active site changes shape slightly as the substrate bonds with the active site. as it changes shape, this distorts bonds in the substrate and lowers activation energy

what happens to the shape of the active site once the substrate molecule leaves? (induced fit model)

it reverts back to its original shape

what does the lock and key theory suggest?

each substrate will only fit the active site of one particular enzyme

which model came first?

lock and key