Enzymes Flashcards
What type of protein are enzymes?
globular proteins?
how do enzymes catalyse a reaction?
lower activation energy
what is activation energy?
minimum amount of energy needed to start a reaction
what is free energy?
energy of a system that is available to perform work
list three conditions that must be satisfied for a reaction to take place
- molecules collide with sufficient energy
- products have less free energy than reactants
- activation energy
what is the active site?
specific region where enzyme is functional and substrate binds
why are enzymes highly specific?
due to tertiary structure
name two types of reactions involving enzymes
- degradation - break down of food into nutrients
- synthesis - formation of products (condensation)
what is the compound formed from an enzyme and substrate?
enzyme-substrate complex
what are the two models of enzyme action?
- lock and key model
- induced fit model
explain lock and key model
substrate is complementary to enzyme because it is specific
explain induced fit model
substrate has similar shape but not exact shape needed so the enzyme moulds itself around the substrate and puts strain on particular bond/s in substrate which lowers activation energy
why is induced fit model a better explanation?
explains how other molecules which bind to enzyme not on its active site affect the enzyme active site - enzyme structure is flexible whereas lock and key model suggests the structure is rigid
how does increase in temperature affect enzyme action?
- increase in temp - lead to higher KE - more ES complex formed up to optimum
- after this high KE will break bonds in tertiary structure (hydrogen bonds/ ionic bonds/ disulphide bridges)
- shape of active site is altered so no ES complexes can be formed
how does a cold temperature affect enzyme action?
enzymes have a lower KE therefore less collisions and less ES complex so less product formed - this means there is a lower rate of reaction
how does change in pH affect enzyme action?
- disruption of attraction of hydrogen bonds alters the secondary protein structure
- also alters tertiary structure as ionic bonds also affected so active site changes
how does enzyme concentration affect enzyme action ?
with an excess of substrate, as enzyme concentration increases, rate of reaction increases because more active sites to bind with substrates
how does substrate concentration affect enzyme action?
as you increase substrate concentration, rate of reaction increases because more active sites are occupied
- after a while it has no effect because all active sites occupied
what are cofactors?
substances that are present in a enzyme-catalysed reaction to ensure reaction occurs at appropriate rate
- bind temporarily to enzyme or substrate
what are prosthetic groups?
cofactors which bind permanently to active site e.g. zinc ion for carbonic anhydrase
what are coenzymes?
enzymes that bind temporarily to active site before or whilst substrate binds
- usually vitamins
- chemically changed by process
what is competitive inhibition?
molecule similar shape to substrate so fits in active site
when is inhibitors most successful?
at a low concentration of substrate because fewer substrate are converted
how can competitive inhibition be reversed?
by adding more substrate
what is non-competitive inhibition?
binds to another part of enzyme which disrupts tertiary structure (hydrogen bonds/ ionic bonds/ disulphide bridges) so alters active site
how do non-competitive inhibitors affect rate of reaction at a low substrate concentration?
less substrate converted to product so lower rate of reaction
what is end-product inhibition?
form of negative feedback where high concentration of end-product inhibits enzyme to prevent further production (e.g. insulin/glucose)
