WEEK 1: PROTEINS AS ENZYMES Flashcards
What are Enzymes?
Enzymes are biological catalysts that speed up chemical
reactions in living organisms.
State the 2 properties displayed by enzymes in a reaction.
*Enzymes do not change equilibrium of a reaction.
*Enzymes are not consumed at the end of a chemical
reaction
Define the following terms:
*Ribozymes
*Abyzymes
RNA molecules that act as enzyme.
Abzymes(man made) are antibodies that act
as enzymes.
State the properties of enzymes.
● Enzymes are globular proteins
● Enzymes are made up of amino acids (AA) ranging
from a few AA to thousands AA in length.
● Enzymes are substrate specific
● Enzymes are water soluble
● Enzymes are temperature sensitive
How do Enzymes Work?
(Explain with an equation)
Substrate + Enzyme Substrate—–Enzyme complex ——Product + Enzyme
How does the Substrate-Enzyme complex make the conversion of the Substrate to the Product easier?
By modifying reaction kinetics
What is activation energy?
AE stands for Activation energy: This is the minimum energy needed to start a chemical reaction.
What is the effect of enzymes on activation energy?
Activation Energy (AE) is lowered by enzymes.
Where does enzyme catalysis occurs?
Enzyme catalysis occurs at the active site on the enzyme.
The active site in most enzymes is a cleft or pocket on the enzyme’s surface.
Why does the substrate-enzyme complex require higher temperatures to denature than the enzyme alone?
The substrate-enzyme complex has a higher thermal stability than the enzyme itself.
The complex requires higher temperatures to denature than the enzyme alone.
State the functions of an enzyme active site.
*It is a recognition site for substrates.
*The 3D structure of the enzyme active site also protects substrates from solvent and facilitates catalysis.
*The active site also binds to co-factors, prosthetic groups and co-enzymes.
State the 2 parts of the enzyme active site.
A binding site for the substrate
A catalysis site, it reduces the activation energy.
What is a cofactor of an enzyme?
State the cofactor for ACE2.
A cofactor is a non-protein molecule that supports a biochemical reaction.
Cofactors can take the form of metal ions, organic substances or other molecules with beneficial characteristics not typically present in amino acids.
Zinc here is an enzyme cofactor. Without zinc, ACE2 won’t function as an enzyme.
Describe the 4 ways of facilitating catalysis by an enzyme.
Catalysis by Proximity:
*Enzymes align reactants on the surface but align the correct reactants in the correct orientation and at the correct distance from each other, so they form bonds with each other.
Acid-Base Catalysis:
Enzymes may act as acids or bases via donating protons or accepting them to balance development of charges during
transition state (using their amino acid side chain groups or prosthetic groups.
Covalent Catalysis:
This involves the enzyme forming a covalent bond with the substrate, enabling the enzyme to become a reactant and
lowering the activation energy of the reaction. The enzyme returns to its original unchanged state at the end of the reaction.
Catalysis by Strain:
Enzymes may strain the reactant (substrate) when they bind it, making an unfavorable transition state easier to reach.
This conformational change weakens the bonds making cleaving of bond.
How is the ‘‘lock and key model” of enzyme catalysis different from the ‘‘induced fit” model?
*The ‘‘lock and key’’ model gives a good picture of the specificity of the interaction between enzyme and substrate, but it is essentially a static picture.
*The ‘‘induced fit’’ model states that when the substrate binds to the enzyme, the enzyme changes shape and wraps around the substrate, bringing reactive groups
close to the substrate molecule
After the reaction has taken place, the shape opens up again allowing the product to be released.
-Some enzymes can even change the shape of the substrate molecule when it binds to the active site.
