Enzymes and Enzyme Kinetics Flashcards
What are the characteristics of enzymes?
1) Enzymes increase the rate(s) of a reaction; enzymes can accelerate rxn’s as much as 1016 over uncatalyzed rxn’s
2) Enzymes are not consumed / destroyed during a chemical rxn
3) Enzymes may be localized to specific areas
4) Enzymes do NOT change the energetics of a reaction. That is, they do not change the delta G of a reaction.
5) Enzymes are present at low concentrations
6) Enzymes increase the probablity of a rxn occuring and therefore increase the rate of a rxn
7) Enzyme activity can be regulated
Describe the physical appearance of an enzyme.
Enzymes are large, multi-subunit proteins. Their structure is vital to maintaining the integrity of he active site of the enzyme.
Describe the active site of the enzyme.
The structure of an enzyme may serve to channel the substrate to the active sites binding residues.
The active site may contain cofactors or coenzymes that are essential for catalytic action.
What is a cofactor?
A cofactor is a non-protein molecule that binds to an enzyme and is required for its biological activity.
What are some common cofactors?
Fe2+
Cu2+
K+
Se
Zn2+
What is a coenzyme?
A nonprotein organic substance that usually contains a vitamin or mineral and combines with a specific protein, the apoenzyme, to form an active enzyme system.
What is a prosthetic group?
The nonprotein component of a protein. For example, the heme group in hemoglobin.
The nonprotein portion of the overall protein is usually covalently bound to the protein.
True or False: Enzymes are specific.
True. Enzymes display a high degree of specificity and selectivetity for their substrate.
What controls the specficity of an enzyme?
The structure of an enzyme controls its specificity.
How may one get a clue to what reaction an enzyme catalyzes?
The enzyme name gives clues as to the reactions that are catalyzed by a particular enzyme.
What are hydrolases?
Hydrolases are enzymes that catalyze hydrolytic cleavage reactions.
What are nucleases?
Nucleases are enzymes that break down nucleic acids.
What are proteases?
Proteases are enzymes that break down proteins.
What are synthases?
Synthases are enzymes that are used in anabolic reactions that polymerize two smaller molecules.
What are polymerases?
Polymerases are enzymes that catalyze the polymerization of nucleic acids.
What are kinases?
Kinases are enzymes that catalyze the addition of a phosphate group to a molecule.
Protein kinases add a PO4 to a protein.
What are phosphatases?
Phosphatases catalyze the removal of a phosphate group.
What are ATPases?
ATPases are enzymes that hydrolyze ATP.
What are the six major classes of enzymes and what do they catalyze?
1) Oxidoreductases - Oxidation & Reduction rxn’s
2) Transferases - Group transfer
3) Hydrolases - Hydrolysis rxn’s (Transfers functional groups to water)
4) Lyases - Addition or removal of groups to form double bonds
5) Isomerases - Isomerization (intramolecular group transfer)
6) Ligases - Ligation of two substrates at the expense of ATP hydrolysis
What is a nucleophile?
Nucleophiles are molecules that have relatively rich pi bonds or lone pairs that act as electron sources in the making of new bonds.
What is an electrophile?
Electrophiles are molecules with relatively electron poor atoms and they serve as acceptors (or sinks) for electrons from nucleophiles.
What are examples of nucleophiles?

What are some common enzymatic reactions?
1) Make a bond between a nucleophile and an electrophile.
2) Break a bond so that stable molecules/ions are created
3) Add protons - The molecule has a strongly basic functional group or there is a strong acid present
4) Take a proton away - The molecule has a strongly acidic proton (amino acids) or there is a strong base present.
How do enzymes work?
Enzymes work by lowering the activation enegry (Kinetic barrier) that a molecule needs to “become” a product.
Before a substarte can become a product, it must have a certain minimum energy to pass through a transition state.


















