Biochemistry Lecture 10 - Enzymes as Catalysts Flashcards
Which residue on chymotrypsin becomes “unusually reactive?”
Serine-195
What molecule on Serine-195 attacks the carbonyl of the substrate? Why is it so reactive?
The hydroxyl oxygen attacks. It is extra electronegative due to hydrogen bonding with the lone pair of a nitrogen on the catalytic machinery.
What substrates does chymotrypsin bind?
Bulky hydrophobic residues.
What substrates does trypsin bind?
Positively charged residues.
What substrates does elastase bind?
Small, hydrophobic residues. Remember that elastin makes up lung tissue, which is obviously not water soluble.
What group of enzymes are chymotrypsin, trypsin, and elastase a part of?
The Serine Proteases.
What two residues sterically hinder substrate size on the elastase enzyme?
Valine, threonine.
What is the specificity binding pocket? Where are they located on an enzyme?
It is where the substrate binds. They are located in a small crevice on the surface on the enzyme.
What do enzymes do to the transition state of a reaction?
Stabilize them.
What stabilizes the oxyanion in the transition state found in the oxyanion hole of chymotrypsin?
Two hydrogen bonds stabilize the oxyanion.
What does removal of a product do for a reaction?
It helps drive the reaction toward the products.
Do enzymes change the free engergy (G) of the products or reactants?
No!
Do enzymes lower the activation barrier of a reaction?
Yes!
Do enzymes alter the equilibrium ratio of a reaction?
No!
How can enzymes promote unfavorable reactions such as peptide bond formation?
They couple ATP hydrolysis with these bond-forming reactions. If the sum total delta G is negative then the reactions will proceed.
