Harpers Flashcards
Biologic polymers that catalyze the chemical reactions
Enzymes
Characteristics of enzymes
Catalytic activity
Substrate specificity
Stereospecificity
Enzymes are classified by reaction type. Name the six classes of enzymes.
Oxidoreductases Transferases Hydrolases Lyases Isomerases Ligases
Naming enzymes may use modifiers to indicate the:
Substrate
Source of the enzymes
Regulation
Feature of its mechanism of action
Enzymes that catalyze oxidations and reductions
Oxidoreductases
Enzymes that catalyze transfer of moieties such as glycosyl, methyl, or phosphoryl groups
Transferases
Enzymes that catalyze hydrolytic cleavage of C-C, C-O, C-N and other covalent bonds
Hydrolases
Enzymes that catalyze cleavage of C-C, C-O, C-N and other covalent bonds by atom elimination, generating double bonds
Lyases
Enzymes that catalyze geometric or structural changes within a molecule
Isomerases
Enzymes that catalyze the joining together of two molecules in reactions coupled to the hydrolysis of ATP
Ligases
Tightly and stably incorporated into a protein’s structure by covalent or noncovalent forces
Prosthetic group
Examples are pyridoxal phosphate, flavin mononucleotide, flavin adenine dinucleotide, thiamin pyrophosphate, biotin, metal ions of cobalt, copper, magnesium, manganese, zinc
Prosthetic group
Enzymes that contain tightly bound metal ions
Metalloenzymes
Serve functions similar to those of prosthetic groups but bind in transient, dissociable manner either to the enzyme or to a substrate such as ATP
Cofactors
Must be present in the medium surrounding the enzymes for catalysis to occur
Cofactors
Enzymes that require a metal ion cofactor
Metal-activated enzyme
Serve as recyclable shuttle-or group transfer agents-that transport many substrates from one point within the cell to another
Coenzymes
Stabilize species such as hydrogen atoms or hydride ions that are too reactive to persist for any significant time period in the presence of the water or organic molecules that permeate the cell interior
Coenzymes
Adaptor or handle that facilitates the recognition and binding of small chemical groups
Coenzymes
Many coenzymes, cofactors and prosthetic groups are derivatives of ____
B vitamins
Component of the redox coenzymes NAD and NADP
Nicotamide
Component of the redox coenzymes FMN and FAD
Riboflavin
Component of the acyl group carrier coenzyme A
Pantothenic acid
Participates in decarboxylation of alpha-keto acids
Thiamin
Function in one-carbon metabolism
Folic acid
Cobamide
Enzymes and substrates interact to form ES complex whose thermal stability was ___ than that of enzyme itself
Greater
Recognition site for binding substrates
Active site
The higher the concentration of enzyme and substrate, the ___ frequently they will encounter one another, and the ___ will be the rate of the reaction.
More
Greater
True or false
In specific acid catalysis or specific base, the rate of reaction is sensitive to changes in the concentration of protons and dependent of the concentrations of other acids or bases present in the solution or at the active site.
False
Independent of the concentration of other acids or bases present in the solution
Reactions whose rates are responsive to all the acids or bases present are said to be subject to ____
General acid/base catalysis
Enzymes that catalyze ___ reactions that involve breaking a covalent bond typically bind their substrate in a conformation that is somewhat unfavorable for the bond that will undergo cleavage
Lytic
A transient species that represents the transition state in the transformation of substrates to products
Transition state intermediates
The process of ____ involves the formation of a covalent bond between the enzyme and one or more substrates
Covalent catalysis
Covalent catalysis introduces a new reaction pathway whose activation energy is ___ than the reaction pathway in homogenous solution.
Lower
When substrates approach and bind to an enzyme they induce a conformational change analogous to placing a hand into a glove
Induced fit model
Exquisitely high specificity with which enzymes discriminate their substrates when forming an ES complex
Lock and key model
Several physically distinct versions of a given enzyme, each of which catalyzes the same reaction
Isoenzyme
Field of biochemistry concerned with the quantitative measurement of the rates of enzyme-catalyzed reactions and the systematic study of factors that affect these rates
Enzyme kinetics
Anything that increases the frequency or energy of collision between substrates will ___ the rate of the reaction in which they participate
Increase
Two factors that increase the frequency of collision between substrate
Temperature
Reactant concentration
True or false
The presence of an enzyme alters the equilibrium constant of the reaction.
False
It only lowers the activation energy. Since they emerge unchanged at the completion of the reaction, they do not affect the free energy for the overall reaction.
In Michaelis-Menten equation, when [S] is considerably below Km, v is proportionate to k[S]. Therefore, the initial reaction velocity is ____ to [S].
Directly proportional
In Michaelis-Menten equation, when [S] = Km, the initial velocity is ___.
Half-maximal
The linear form of Michaelis-Menten equation
Double reciprocal plot
Lineweaver-Burk plot
When further increases in substrate concentration do not further increase velocity, the enzyme is said to be ___ with the substrate
Saturated
An exclusive property of multimeric enzymes that bind substrate at multiple sites
Cooperative behavior
Inhibitor binds to the substrate-binding portion of the active site thereby blocking access by the substrate
Competitive inhibition
Can be overcome by raising the concentration of substrate
Competitive inhibition
Acts by decreasing the number of free enzyme molecules available to bind the substrate to form ES and thus eventually to form product
Competitive inhibitor
Competitive inhibitor has no effect on ____ but raises the ___
Vmax
Km apparent
Binding of the inhibitor does not affect binding of the substrate
Noncompetitive inhibition
Formation of both EI and EIS complexes is possible
Noncompetitive inhibition
True or false
Competitive and noncompetitive inhibitors are reversible inhibitors, meaning the inhibitors form a dissociable, dynamic complex with the enzyme
True
Modifications of enzyme involving making or breaking covalent bonds essential for substrate binding, catalysis or maintenance of the enzyme’s conformation
Irreversible inhibitors
