Enzymes Flashcards
What is enzyme specificity?
A given enzyme will only catalyze a single reaction or class of reactions with these substrates
Oxidoreductases
Enzymes that catalyze oxidation-reduction reactions - transfer of electrons between biological molecules
What cofactor do many oxidoreductases have?
One that acts as an electron carrier - NAD+ or NADP+
Reductant
Electron donor
Oxidant
Electron acceptor
What class of enzymes does a dehydrogenase fall within?
Oxidoreductase
What class of enzymes does a reductase fall within?
Oxidoreductase
Transferases
Enzymes that catalyze the movement of a functional group from one molecule to another
What class of enzymes does a kinase fall within?
Transferase
What do kinases do?
Catalyze the transfer of a phosphate group (usually from ATP) to another molecule
Hydrolases
Enzymes that catalyze the breaking of a compound into two molecules using the addition of water
What class of enzymes does a nuclease fall within?
Hydrolase
What class of enzymes does a phosphatase fall within?
Hydrolase
Lysases
Enzymes that catalyze the cleavage of a single molecule into two products WITHOUT the use of water as a substrate
What is a lysase often called when catalyzing its reverse reaction?
Synthase
Isomerase
Enzyme that catalyzes the rearrangement of bonds within a molecule
Ligases
Enzyme that catalyzes addition or synthesis reactions, generally between large, similar molecules, often requiring ATP
What class of enzymes would catalyze the synthesis of small molecules?
Lysase
What class of enzymes would catalyze the synthesis of large molecules?
Ligase
What type of molecules are cofactors typically?
Inorganic or metal ions
How does the body obtain cofactors?
Diet
What type of molecules are coenzymes typically?
Small organic groups
How does the body obtain coenzymes?
Vitamins
Prosthetic groups
Cofactors or coenzymes that are tightly bound to an enzyme and are necessary for enzyme function
Apoenzymes
Enzyme without its cofactor
Holoenzymes
Enzyme with its cofactor
Enzyme saturation
No active sites are left and reaction cannot go any faster
How can Vmax be increased?
Adding more enzyme
Describe Michaelis-Menten Plot
x axis has substrate concentration
y axis has reaction velocity
Km is the substrate concentration at half of Vmax
Slope increases and then reaches Vmax
Michaelis-Menten Equation
v=(Vmax[S])/(Km+[S])
When comparing two enzymes, does a higher Km suggest a higher or lower enzyme affinity?
Lower - requires more substrate to reach half-saturated
Describe Lineweaver-Burk Polot
Double reciprocal of Michaelis-Menten Plot x axis is 1/[S] y axis is 1/v x-intercept is 1/Km y-intercept is 1/Vmax
How does enzyme cooperativity affect the Michaelis-Menten Plot?
Becomes sigmoidal - Substrate binding encourages change in shape from tense to relax, further improving enzyme affinity for substrate
Hill’s coefficient
Numerical quantification of cooperativity
Hill coefficient >1
Positive cooperation - binding of substrate improves enzyme affinity for more substrate
Hill coefficient <1
Negative cooperation - binding of substrate decreases enzyme affinity for more substrate
Hill coefficient =1
Enzyme does not exhibit cooperative binding
What are the four types of reversible enzyme inhibition?
Competitive
Non-competitive
Mixed
Uncompetitive
What occurs to the enzyme in competitive inhibition?
Inhibitor binds to the active site
How is competitive inhibition overcome?
Add more substrate
Does competitive inhibition change Vmax and why?
No - if enough substrate is added it will still run at maximum velocity
Does competitive inhibition change Km and why?
Yes - more substrate will be needed to reach half of Vmax
What occurs to the enzyme in noncompetitive inhibition?
Inhibitor binds to an allosteric site and induces a change in enzyme conformation (can bind either enzyme or enzyme-substrate complex with same affinity)
Does noncompetitive inhibition change Vmax and why?
Yes - lowers it because there is less enzyme available to react
Does noncompetitive inhibition change Km and why?
No - the noncompetitive inhibitor does not change the affinity for substrate and adding more will not change the reaction
Allosteric site of an enzyme
Non-catalytic site that binds regulators
What occurs to the enzyme in mixed inhibition?
Inhibitor can bind either the enzyme or enzyme-substrate complex with different affinities
Does mixed inhibition change Vmax and why?
Yes - lowers it because there is less enzyme available to react
Does mixed inhibition change Km and why?
Yes - it raises Km if it preferentially binds to the enzyme and it lowers Km if it preferentially binds to the enzyme-substrate complex
What is similar and different about noncompetitive and mixed inhibitors?
Both can bind to both the enzyme alone and the enzyme-substrate complex. Noncompetitive have the same affinity for both while mixed have different affinities
What occurs to the enzyme in uncompetitive inhibition?
Inhibitor binds to allosteric site only to enzyme-substrate complex and locks the substrate into the enzyme
Does uncompetitive inhibition change Vmax and why?
Yes - lowers it because reaction cannot reach full speed
Does uncompetitive inhibition change Km and why?
Yes - lowers it because technically increases enzyme affinity by keeping substrate locked into enzyme
When is irreversible inhibition most applicable?
Drugs / medications - irreversibly bind to enzymes that modulate pain or inflammatory pathways, for example
Allosteric enzymes
Have multiple binding sites and alternate between an active and inactive form
What are examples of covalent enzyme modifications?
Phosphorylation, glycosylation
Zymogens
Inactive forms of very dangerous enzymes such as apoptotic or strong digestive enzymes that contain an active and regulatory domain - the regulatory domain must be altered to expose the active site
