Enzymes Flashcards
What are enzymes
Biological catalysts made of globular proteins
Their active site is specific and unique in shape due to the folding and bonding in the tertiary structure of the protein
Due to this specific active site shape, enzymes can only attach to substances that are complementary in shape.
Enzymes catalyse both intercellular and extra cellular reactions
(EXAMPLES)
Catalase is an intracellular enzyme inside liver cells that breaks down hydrogen peroxide into oxygen and water
Trypsin is an extra cellular enzyme in the small intestine that hydrolyses proteins
How do enzymes catalyse reactions
They lower the activation energy after attaching to the substrate
Activation energy is the amount of energy needed before the reaction can occur
Describe the Lock and Key model hypothesis
The enzyme is like a lock and that the substrate is like a key that fits into it due to the enzymes specific tertiary structure resulting in a complimentary shape
The charged groups within the active site distort the substrate and therefore lower the activation energy
Describe the Induced fit hypothesis
The enzyme is like a glove and the substrate is like your hand
They are not perfectly complementary however the active site changes shape to mould around the substrate
This puts strain on the bonds and lowers activation energy
Factors affecting enzymes
Temperature
pH
Enzyme concentration
Substrate concentration
Describe how temperature affects enzymes
If the temperature is too low, there is insufficient kinetic energy for successful collisions
If the temperature is too high, enzymes will denature so the active site changes shape and enzyme substrate complexes cannot form
High temperatures cause bonds to break and the tertiary structure to alter which causes a change in the active site shape
What is the Q10 temperature coefficient?
A measure of the rate of change of an enzyme controlled reaction as a result of increasing the temperature by 10degrees
formula
Q10 = rate of reaction at (X+10degrees) /
rate of reaction at X degrees
Q10 = R2/R1
Describe how pH affects enzymes
If the pH is too high or too low, it will interfere with the charges in the amino acids in the active site
This will cause ionic/hydrogen bonds to break which alters the tertiary structure and therefore changes the shape of the active site (the enzyme denatures)
Enzymes have different optimal pH values
Describe how substrate concentration affects enzyme activity
Low concentration of substrates means the reaction will be lower due to less collisions between enzyme and substrate
Increased substrate concentration will increase rate of reaction
At high concentration of substrates, the rate of reaction will plateau because all enzyme active sites are in use
Describe how enzyme concentration affects enzyme activity
At low enzyme concentrations, there will be a lower rate of reaction
Increasing enzyme concentration will increase the rate of reaction as enzyme substrate complexes will be more likely to form
At high enzyme concentrations, unless unlimited substrate is added, the rate of reaction plateaus as there is insufficient substrate to bind
What are competitive inhibitors
Same shape as the substrate (complementary to the active site) therefore bind to the active site and prevent substrate from binding therefore rate of reaction is lowered
Most competitive inhibitors are reversible (if high enough substrate concentration, the inhibitor can be knocked out)
What are non competitive inhibitors
Inhibitors bind to the enzyme away from the active site at a location called the allosteric site, this causes the active site to change shape so the substrate can no longer bind.
Rate of reaction is much lower
What is end product inhibition
The products of some reactions are reversible inhibitors for the enzymes involved
This enables the reactions to be controlled (can turn reactions on and off)
If there is a lot of product present, enzymes will be inhibited and the reaction will slow or stop
This prevents resources from being wasted
What are the 3 non protein molecules sometimes required to catalyse a reaction
Cofactors (inorganic molecules)
Coenzymes (organic molecules)
-Some enzymes require cofactors/coenzymes to bind to the active site to make it complementary to the substrate
Prosthetic groups
-Type of cofactor but they are permanently attached by covalent or non covalent forces
What is precursor activation
Enzymes often occur in an inactive form and require activation by a cofactor
This prevents enzymes from causing damage within cells by ensuring they are only used when needed
An enzyme is activated by the binding of a cofactor as this causes a change in the tertiary structure so that the active site is complimentary in shape to its substrate
The precursor protein (the inorganic enzyme) is known as the apoenzyme when it is activated by the binding of the cofactor it is known as the holoenzyme.
