Chapter 6 Reading Enzymes Flashcards
Q # 1 What components besides amino acid residues are sometimes necessary for an enzyme to be active?
Cofactors,
Q # 2 What are the functions of co-enzymes? Note that many are derivatives of vitamins.
organic or metalloorganic molecule that act as transient carriers of specific functional groups.
Cofactor
an additional chemical component that aids in enzymatic activity
Prosthetic group
a co-enzyme or metal ion that is bound tightly or covalently bound to the enzyme of a protein.
Holoenzyme
A complete catalytically active enzyme together with its bound co-enzyme and or metal ions.
Apoprotein
aka apopenzyme. The protein part of an enzyme
HOT LILY (International classes of enzymes)
312456; Hydrolyases, oxidoreductases; transferases; Lyases, isomerases, Ligases
Oxidoreductases
EC: 1, Transfer electrons (hydride ions or H atoms)
Transferase
EC 2; Group transfer reactions
Hydrolases
EC 3: Hydrolysis reactions (transfer of functional groups to water)
Lyases
EC4 ; Cleavage of C-C, C-O, C-N or other bonds by elimination, leaving double bonds or rings, or addition of groups to double bonds
Isomerases
EC 5; transfer of groups within molecules to yield isomeric forms
Ligases
EC 6: Formation of C-C, C-S, C-O and C-N bonds by condensation reactions coupled to cleavage of ATP or similar cofactor.
Q # 4 Why are catalysts necessary for reactions in living systems to proceed at a useful rate?
Many reactions that occur in cells would not occur (or would occur at incredibly low rates) without catalysts. Most biologically active molecules are stable at cellular pH, temperature, and environment.
Active site
Region of an enzyme where its substrate binds to. The active site provides and environment for reactions to occur.
Substrate
The molecule bound in the active site and acted upon by its substrate
Q # 5 What is the difference between a transition state and a reaction intermediate?
The transition state is not a chemical species. It is simply a point where decay to product or substrate is equally likely. A reaction intermediate is a chemical species other than the substrate and product individually.
Q # 6 What affects the reaction equilibrium between S and P? What affects the reaction rate of the conversion from S to P? Which aspect of a reaction can an enzyme alter?
a) The activation barrier b) Reaction rates can be increased or decreased by temperature and or pressure c) enzymes decrease the activation barrier for a reaction to occur
What do catalysts actually affect?
Catalysts increase the rate of a reaction, catalysts do NOT affect reaction equilibria. (A reaction is in equilibrium when there is no net change in the concentration of reactants or products)
Activation Energy
The energy difference between the transition state and the ground state of either the products or the reactants.
Rate limiting step
the reaction intermediate(s) that have the highest activation energy
Q # 7 What does a large, positive K’eq (e.g, K’eq = 1,000) for a reaction mean in terms of the final relative concentrations of products and reactants? What does a very small K’eq (e.g, K’eq = 0.001) mean?
A large positive value for K’eq means a large negative value for ∆G’˚ and a higher value of products to reactants. A small K’eq means a large positive value for ∆G’˚ which means a greater concentration of substrate.
Q # 9 In qualitative terms, what is the relationship between the rate constant K and the activation energy for an enzymatic reaction?
k relates to the amount of substrate that will be converted to product in a period of time.
What is K’eq?
K’eq is the equilibrium constant under standard conditions.
What is the relationship between ∆G’˚ and K’eq?
∆G’˚ = -RTlnK’eq; Large negative ∆G’˚ reflects a favorable reaction equilibrium. one in which there is much more product than substrate at equilibrium.
Q # 10 What is the specific source of energy for lowering the activation energy barriers in enzyme-catalyzed reactions?
(Binding energy)Most of the energy comes from weak, non covalent interactions between substrate and enzyme. Covalent interactions also play a role.
Binding energy
∆Gb; the major source of free energy used by enzymes to lower the activation energies of reactions. 1) Catalytic power comes from energy released in forming many weak bonds and interactions between enzyme and substrate. 2) enzymes are complementary to transition states. not to the substrates
Q # 11 Why is it important for an enzyme to be complementary to the reaction transition state rather than to the substrate?
If an enzyme was complementary to the substrate, it would actually stabilize the substrate and increase the activation energy of the reaction. ( lower activation energy arises from the sum of activation energy and binding energy)
Q # 12 What is one reason that some enzymes are very large molecules?
Enzymes must have multiple functional groups to provide multiple opportunities for weak interactions. Enzymes also need a larger structure to keep interacting groups properly positioned and to keep the cavity from collapsing.
Q # 13 How does binding energy contribute to the high degree of specificity shown by enzymes?
Each enzyme has functional groups which maximize the non covalent interactions. Specificity arises, because of the difference in interactions within the active site. Specificity arises from weak interactions in the active site.
