Chapter 4: Enzymes Flashcards
What are enzymes?
Proteins or RNA which act as biological catalysts
Why are enzymes necessary?
Reactions within the cell may be spontaneous however they require too much time or heat to occur
How do enzymes make metabolic pathways happen?
Each step in the pathway is catalyzed by a specific Enzyme
What does ase imply?
enzyme
How do enzymes work?
They speed up rxn rate by lowering activation energy
Are enzymes consumed in the reaction?
No
What is the substrate?
The reactant that binds to the enzyme’s active site
Are enzymes substrate-specific?
Yes
What does induced fit mean?
binding of substrate
causes a change in the
shape of the enzyme to
bring amino acid side
chains in position to
catalyze the reaction
How does the substrate bind in the active site?
The substrate binds to the active site of enzyme via non-covalent interactions such
as H-bonds and ionic bonds (weak interactions).
How do enzymes lower activation energy?
i. Hold substrates in correct orientation
ii. Induced fit may stress the substrate’s chemical bonds (making
them easier to break) and stabilize the transition state
iii. Active site may provide a microenvironment for a specific
reaction (ex. acidic and basic side amino acids can change pH)
iv. Amino acid side chains in active site may participate directly in
the reaction
What are the factors that affect biological reaction rates?
(1) Substrate concentration
(2) Enzyme concentration
(3) Environmental conditions
* Temperature
* pH
(4) Cofactors or coenzymes
If the temperature is increased what is the effect on the rxn rate?
rxn rate also increases
Why does pH affect rxn rate?
- Enzymes are usually most active within a specific pH range
o Extreme pHs affect the ionization of amino acid side chains and cause the
enzyme to denature - The optimal pH range for most enzymes is 6-8
o Some enzymes can function at extreme pHs (ex: pepsin in the stomach
How does irreversible enzyme inhibition work?
Inhibitor attaches by a covalent linkage
How does reversible enzyme inhibition work?
- Inhibitor attaches by weak, non-covalent bonds
- Important part of regulating metabolism in our bodies
What is a competitive inhibitor?
The inhibitor binds to the active site and competes with
substrate for binding.
What is a non-competitive inhibitor?
- Inhibitor binds somewhere else on the enzyme
(not the active site!) - Causes enzyme to change shape so the active
site can no longer bind to substrate.
How can you overcome competitive inhibition?
Increase substrate concentration
Can increasing substrate concentration overcome non-competitive inhibitors?
No, because they bond to a secondary site which changes the shape of the enzyme
What are allosteric enzymes?
- Involved in regulation of metabolic pathways
- Have 2 conformations: Active and inactive.
What is the allosteric site?
- location where a regulator binds to the enzyme
- Not at the active site!
- Usually located where the polypeptides join
What is the regulator?
- Molecule that binds weakly to allosteric site
- Can be inhibitor or activator of the enzyme
What do allosteric activators do?
stabilize the active form of the enzyme
