ANDREY K LECTURE ON ACTIVE SITE ETC.

What is an active site on an enzyme?

3D region on enzyme that contains amino acids responsible for substrate binding and catalytic groups responsible for catalyzing rxns.

What does it mean to stabilize and lower the energy of the transition state?

Catalytic groups in active site stimulate forming & breaking of bonds and ­ increase rxn rate

Lowering the energy of the transition state does what to the speed of the reaction?

decrease E of transition state, increase­ rxn rate

Is there a role for water in the active site?

water is only in the active site when water is a reactant

The microenvironment of the active site is ?

nonpolar

Why is an enzyme large overall but the active site is small?Where are the catalytic amino acid residues that comprise the active site actually located -together on the polypeptide chain, or distant from one another? How do they meet up to form an active site?

• Small microenvironment in active site brings reactants closer together, decrease likelihood of other rxns & decrease unwanted products

• Residues in active site are found far away from each other on primary sequence of Polypeptide chain. Large enzyme must fold and form 3D shape to bring residues in active site closer together

• Large enzyme supports/stabilizes small active site

What are the non-covalent interactions that bind an enzyme to its substrate?

Hydrogen bonds, hydrophobic interactions, Van der Waals forces

Which bonds are stronger, covalent or non-covalent?

Covalent bonds are stronger

Why are weak bonds used in the enzyme-substrate interaction?

Non-covalent bonds, the weaker ones are more easily reversible between active site & substrate

Why does this binding interaction need to be reversible?

• New product releases from active site

• cycle can repeat since enzymes are reusable

Enzymes and substrates work this way, but so do certain other types of biological interactions, like antibody-antigen, and hormone-receptor. Why do you think these need to have weak chemical bonds? What do you think would happen if interactions like these were covalently bonded?

If these interactions were covalently bonded, rxns would not be as reversible. Would need to create more enzymes for rxns to repeat or also generate significant energy to break bonds between substrate and enzyme.