2.4 Enzymes Flashcards
What are enzymes ?
Proteins that act as biological catalysts for metabolic reactions
The formation of enzyme-substrate complexes lowers the activation energy of a reaction.
What properties do enzymes have ?
Specific tertiary structure to form an active site complementary to a specific substrate
Give an example of an enzyme that catalyses intracellular reactions.
DNA replicase - formation of phosphodiester bonds in DNA replication
Give an example of an enzyme that catalyses extracellular reactions.
Amylase - hydrolysis of carbohydrates into maltose
Explain the induced fit model of enzyme action.
The shape of the active site is not exactly complementary to the substrate
When the substrate is being adsorbed to the enzyme, the tertiary structure of the enzyme changes and enables it to be tightly moulded to the substrate
The change in shape puts strain on the bonds within the substrate, lowering Ea.
Explain the lock and key model of enzyme action.
Suggests that the active site has a rigid shape determined by tertiary structure and binds to only one substrate
Formation of ES lowers Ea.
Name the 5 factors affecting enzyme rate of reaction.
Enzyme concentration
Substrate concentration
Inhibitor concentration
pH
Temperature
How does substrate concentration affect rate of reaction (fixed enzyme conc.) ?
The rate increases then plateaus
The plateau indicates the point in which the maximum number of ES complexes are formed at any given time.
How does the enzyme concentration affect rate of reaction (substrate in excess) ?
The rate increases then plateaus
The plateau indicates the point in which the maximum number of ES complexes are formed at any given time.
How does temperature affect the rate of enzyme controlled reactions ?
The rate increases until it reaches its optimum temperature then drops
The drop occurs as the ionic and hydrogen bonds holding the active site in its shape are broken, leaving the site unsuitable for the substrate.
What is the temperature coefficient (Q10) ?
Q10 is the measure of the difference in rate of reaction per 10 C temperature increase
Q10 = R2 / R1 where R represents rate.
How does pH affect rate of reaction in enzyme controlled reactions ?
Enzymes have a narrow pH where they can function optimally
As the pH gets further from this optimum, OH- and H+ ions begin to interact with ionic and hydrogen bonds, changing the structure of the active site
This lowers rate
How do competitive inhibitors work ?
They have a similar shape to the substrate and so bind to the site
This prevents ES complexes from forming for a short time
How do non competitive inhibitors work ?
They bind to the allosteric site of an enzyme
When they bind to an enzyme, they cause a conformational change to the active site.
This renders the enzyme unable to form ES complexes anymore
How will increasing substrate concentration affect rate in competitive and non competitive inhibitors ?
Competitive - decreases the effect of inhibitor
Non competitive - no effect
