Enzyme Catalysis Flashcards
Enzymes are biological catalysts. Describe what a catalyst does
increases rate of reaction but does not effect the equilibrium constant
A catalyst decreases activation energy. True or false?
true
Does an enzyme effect the free energy of a reaction?
no
Reaction rates of enzymatically catalyzed reactions are generally how much greater than non-catalyzed reactions? non-enzymatically catalyzed reactions?
10^6 - 10^12; 10^3
Enzymatic reactions have milder reaction conditions. Describe some of these conditions
occur at atmospheric pressure, neutral pH, and temperatures less than 100 degrees celsius
Enzymatic reactions have tremendous reaction specificity that results in what?
very rarely occurring side products
True or false?
Enzyme activity can vary in response to biological molecules other than the enzyme’s substrates or products
true
What is a unit of enzyme activity?
the amount of substrate converted to product in a given amount of time
What is a specific activity of an enzyme?
the number of units per mg protein
Most human enzymes have a temperature optimum of about ___ degrees celsius
37
Pepsin is an enzyme in the stomach and has a pH optimum of about ___. Trypsin is an enzyme active in the small intestine and has a pH optimum of about ___
2; 8
What type of reaction does an oxidoreductase enzyme catalyze? give some examples of oxidoreductase enzymes
oxidation-reduction reactions; dehydrogenases, oxidases, reductases, peroxidases, catalase, oxygenase, hydroxylase
What type of reaction does a transferase enzyme catalyze? give some examples of transferase enzymes
catalyze transfer of a group such as glycosyl, methyl, or phosphoryl; transaldolase, transketolase, acyl transferase, kinases, phosphomutases
What type of reaction do hydrolases catalyze? give some examples of hydrolase enzymes
catalyze hydrolytic cleavage of C-C, C-O, C-N, and other bonds; esterase’s, glycosides, peptidases, phosphotases, etc
What type of reaction do lyases catalyze? give some examples of lyase enzymes
catalyze cleavage of C-C, C-O, C-N, and other bonds by atom elimination, leaving double bonds; decarboxylases, aldolases, hydratases, dehydratases, synthases
What type of reaction do isomerases catalyze? give some examples of isomerase enzymes
catalyze geometric or structural changes within a molecule; racemases, epimerases, isomerases, some mutases
What type of reaction do ligases catalyze? give some examples of ligase enzymes
catalyze the joining together of two molecules coupled to the hydrolysis of ATP; synthetases and carboxylases
Define active site
a specific region on the enzyme where the reaction occurs
The ___ of the enzyme is critical for the appropriate structure of the active site
structure
note: lock and key - enzyme has to fit
Changes in the enzyme structure (due to AA composition) may or may not have major effects on the activity of the enzyme. True or false?
true
In regards to catalysis by proximity, in order for molecules to react, they must come within ____ ____ distance of each other
bond forming
In regards to catalysis by proximity, the active site of an enzyme binds substrates creating a ___ local concentration
high
In regards to catalysis by proximity, the substrates are also bound in a ___ ___ conducive to reaction
specific orientation
In regards to acid-base catalysis, ____ functional groups of AA side chains may participate in catalysis by acting as acids and/or bases
ionizable
In regards to catalysis by strain, enzymes which catalyze reactions which break bonds may bind substrates in what type of manner?
in such a way to destabilize the bond to be broken
In regards to covalent catalysis, a ___ bond is established between substrate and enzyme
covalent
In regards to covalent catalysis, the covalently modified enzyme essentially then becomes a ___ for the reaction
substrate
In regards to covalent catalysis, the reaction of covalently modified enzyme to product is more ___ ____ than the reaction of substrate to product
energetically favorable
What are cofactors, coenzymes, and prosthetic groups? (in general as a group)
small, non-protein molecules and metal ions which participate directly in the enzymatic process
Many cofactors, coenzymes, and prosthetic groups are derived from what?
vitamins
Prosthetic groups are tightly and stably incorporated into the protein, sometimes by ___ bonds
covalent
metal ions are the most common prosthetic groups. give some examples
Co, Cu, Mg, Mn, and Zn
enzymes containing a metal prosthetic group are called _____
metalloenzymes
Pyroxial phosphate is a prosthetic group derived from what?
vitamin pyrodoxine, B6
Thiamine pyrophosphate is a prosthetic group derived from what?
thiamine, B1
FMN and FAD are prosthetic groups derived from what?
riboflavin, vitamin B2
Cofactors bind _____ to either the substrate or the enzyme but are nonetheless required for activity
transiently
What is the most common cofactor?
Mg2+
note: it is required for enzymes which involve ATP
Coenzymes serve as “___”, accepting a group from one reaction and supplying the group in other reactions
shuttles
Coenzyme A transfers what?
acyl groups
Folates transfer what?
one carbon groups
Isoenzymes are physically distinct enzymes, meaning they are different proteins with different AA sequences which catalyze what?
the same reaction
What are some of the different properties between isoenzymes?
kinetic differences (substrate affinities), differences in activity regulation
Isoenzymes may be differentially expressed by different tissues. Give an example
the heart isoenzymes of creatine kinase may be distinguished form the skeletal muscle isoenzymes of creatine kinase
