Enzymes Mechanisms Of Action Flashcards
Name four reasons enzymes are preferred over inorganic catalysts for biological reactions
Greater reaction specificity
Mild reaction conditions
Higher reaction rates
Capacity for regulation
What type of reaction is catalyzes by oxidoreductase?
Transfer of electrons
What type of reaction is catalyzes by transferases?
Group transfer reactions
What type of reaction is catalyzes by hydrolases?
Hydrolysis reactions (transfer of functional groups to water)
What type of reaction is catalyzed by lyases?
Cleavage of C-C, C-O, or C-N, or other bonds by elimation, leaving double bonds or rings
What type of reactions are catalyzed by isomerases?
Transfer of groups within molecules to yield isomeric forms
What types of reactions are catalyzed by ligases?
Formation of C-C, C-S, C-O, and C-N bonds by condensation reactions coupled to cleavage of ATP or similar cofactor.
What is a prosthetic group?
Compound that is tightly and stably incorporated into a protein’s structure by covalent or noncovalent forces
What is a cofactor?
Compound that binds in a transient, dissociable manner either to the enzyme or to a substrate such as ATP
What is a coenzyme?
Group transfer agents that transport many substrates from one point within the cell to another
What is the difference between an Apoenzyme and a Holoenzyme?
Apoenzyme - enzyme without the cofactor or prosthetic group
Holoenzyme - complete enzyme with cofactor or prosthetic group
What three enzymes make up Pyruvate Dehydrogenase?
Pyruvate Dehydorgenase
Dihydrolipoyl transacetylase
Dihydrolipoyl dehydrogenase
What coenzyme is utilized by pyruvate dehydrogenase?
Tiamin pyrophosphate (TPP)
It is bound to the enzyme
What coenzymes are utilized by Dihydrolipoyl transacetylase?
Lipoate - covalently linked
Coenzyme A - substrate
What coenzymes are utilized by Dihydrolipoyl Dehydrogenase?
FAD - bound to the enzyme
NAD - substrate for the enzyme (reduced by FADH2)
What type of reactions are NAD and NADP involved in?
Redox reactions
NAD+ is an oxidizing agent (accepts electrons and becomes reduced)
What is Pellagra and what causes it?
Pellegra is a skin disorder that can later cause neurological problems
Results from a dietary deficiency of Niacin
What amino acid can Niacin be derived from?
Tryptophan
What is the role of tetrahydrofolate?
Dontaes a Carbon in the form of -CH3, -CH2OH, or -CHO in amino acid and nucleic acid synthesis.
What results from tetrahydrofolate deficiency?
Folic Acid Deficiency
Low-birth weight infant and spina bifida
Describe the Lock and Key Model of Enzyme-substrate Interaction
A substrate fits perfectly into the shape of the active site, enzyme doesn’t change conformation.
Active site compliments shape and ionic properties
E.g. dihydrofolate reductase
Describe the Induced-Fit Model of Enzyme-substrate interaction
Binding of substrate induces conformational change in the enzyme.
E.g. binding of D-glucose in hexokinase and Citrate Synthase
Explain Catalysis by Proximity
Effective molarity and orientation of substrate molecules in the active site of enzymes will enhance the rate of reactions
E.g. substrate channeling by multi-enzyme complexes
(Pyruvate dehydrogenase)
Explain Acid-Base Catalysis
Ionizable functional groups of amino acid side chains and prosthetic groups contribute to catalysis by acting as acids or bases
Explain Catalysis by strain
Enzymes bind their substrates in an unfavorable conformation to waken the bond that will undergo cleavage
E.g. stickase model
Explain Covalent Catalysis
Formation of a covalent bond between the enzyme and one or more substrates to create a more reactive enzyme
E.g. group transfer reactions
Usually a serine residue in the active site
What type of catalysis is utilized by aspartic portease family enzymes?
Acid-Base, utilize two conserved aspartic acid residues.
E.g. Pepsin, lysosomal cathepsins, HIV protease
What type of catalysis does Chymotrypsin utilize?
Type of Serine Protease
Covalent Catalysis, formation of acyl-enzyme intermediate
Acid-Base Catalysis, Asp102-His57-Ser195 at active site act as proton shuttle
What type of Catalysis is utilized by Fructose-2,6-Bisphosphatase?
Covalent and Acid-Base
Why are catalytic residues evolutionarily conserved?
Critical to the structure and function of proteins
Majority of disease causing mutations are mutations of these conserved catalytic residues
What are isozymes?
Enzymes that catalyze the same reaction.
May differ in reaction rate, inhibition properties, electrophoretic mobility, or immunologic properties
How are NAD+(P)-dependent dehydrogenases utilized in enzyme assays?
They can be coupled to other enzymatic reactions and assessed via absorbance to measure enzymatic activity.
E.g. Measurement of Hexokinase activity by coupling with G6P dehydrogenase.
What are Enzyme-linked immunosorbent assays (ELISAs) utilized for?
Measure relative enzyme/protein expression.
Does not measure activity
