W3 Enzymes and Catalysis/Lec 5 Flashcards
What are enzymes?
Biologival catalysts that speed up specific enzymatic reactions
What are enzymes made of?
Protein
What is enzyme specificity?
- Ability of the enzyme to specifically recognise the proper substrate (reactant)
- It is a molecular recognition mechanism
- Recognition and specificity is based on structural complementarity (3D fit)
What is the lock and key theory?
(nutshell)
- The active site and substrate are perfectly complementary for each other (like a key fits into a lock)
What is the induced fit hypothesis?
- Substrate is not exactly complementary to the active site. After binding, a conformational change occurs to allow a better fit between the active site and substrate
What is the active site? What are the key features? (important)
A 3D pocket located in a small region of the enzyme:
Substrate binding site:
- Amino acids side chains interact with the substrate (the reactant of the reaction)
- These interactions orientate the substrate within the active site
Catalytic site:
- Amino acids that performs/catalyses the reaction
The correct folding of the enzyme is required
Substrate-enzyme binding alters the structure of the substrate to promote the formation of the transition state.
How do enzymes have catalytic power?
- They increase the rate of a reaction by lowering the activation energy
What is a holoenzyme?
What is an apoenzyme?
A complete catalytically-active enzyme together with its cofactor
The protein part of the enzyme on its own without its cofactor
What are enzyme cofactors?
They are additional chemical components that provide active site reactive groups.
What are competitive inhibitors?
They compete with the substrate to bind to the active site and block it.
Can be reversed by adding more substrate
Can be irreversible
What are noncompetitive inhibitors?
They bind to an allosteric site which causes a conformational change in the enzyme and the block of the catalytic activity. Their effect is usually reversible
What are the different conditions that affect enzyme function?
Temperature
pH
Ionic conditions
Substrate concentration
Presence of inhibitors
How are enzymes efficient and reusable?
Efficient- They are active at very low concentrations
Reusable- They are not altered or consumed during or after the reaction
What is an inactive enzyme called in the absence of its essential cofactor?
Apoenzyme
What is the enzyme called when it is linked to its cofactor(s) and is able to act as a catalyst?
Holoenzyme
