BIOCHEM Chp.2 Enzymes Flashcards
What are the key features of an enzyme/catalyst?
lower the activation energy by stabilizing the transition state
increases the kinetic rate of RXN
does not alter the equilibrium constant
does not change or become consumed in the RXN
pH and temperature-sensitive
do not affect the overall change in G
enzyme specificity for a certain substrate
What do oxidoreductases catalyze?
oxidation-reactions/ Electron donor is known as reductant, and electron acceptor the oxidant
What do transferases catalyze?
the movement of functional groups from one molecule to another such as kinases
What do hydrolases catalyze?
the breaking of a compound into 2 molecules using the addition of water
What do lyases catalyze?
the cleavage of a single molecule into 2 products
What do isomerases catalyze?
the rearrangement of bonds within a stereoisomer and constitutional isomers
What do ligases catalyze?
addition or synthesis reactions, generally b/w large similar molecules like nucleic acids and often require ATP
Give an example of oxidoreductase.
enzymes with dehydrogenases or reductase
Give an example of transferases
aminotransferase, kinases
Give an example of hydrolases
phosphatase, peptidase, nuclease, lipases
What is the diff b/w endergonic and exergonic reactions?
endergonic - requires energy input - change in G > 0
exergonic - energy is given off - change in G < 0
Give an example of lyases
synthases
What is the diff b/w apo and holoenzymes?
apoenzymes - enzymes w/o their cofactor
haloenzyme - enzymes with their cofactor
What are the water-soluble vitamins?
B complex, vitamin C
What are the fat-soluble vitamins?
vitamin A, D, E, and K
What is the diff b/w coenzyme and cofactors?
cofactors are inorganic molecules or metal ions that are often ingested as dietary minerals
coenzymes are small organic groups such as vitamins and their derivatives (NAD+, FAD, coenzyme A)
How can you increase the Vmax of an enzyme?
by increasing the enzyme concentration
What is Km?
the substrate concentration at which half of the enzyme’s active sites are full
What does a high Km and low Km mean?
a low Km reflects a high affinity for the substrate, conversely, a high Km reflects a low affinity of the enzyme for the substrate
What is the graph of cooperative binding enzymes?
the binding curve is sigmoidal
What is catalytic efficiency?
a large Kcat (high turnover) or small Km (high substrate affinity) will result in a higher catalytic efficiency, which indicates a more efficient enzyme
What is the plot of michaelis-menten?
the graph is a hyperbola
What is the plot of Lineweaver-burk?
the plot is a double reciprocal graph of the Michaelis-mente equation and is thus linear in graphing
What is the cooperativity if the Hill’s coefficient > 1?
positively cooperative binding is occurring such that after 1 ligand is bound, the affinity of the enzyme for further ligands increases
What is the cooperativity if the Hill’s coefficient < 1?
negatively cooperative binding is occurring such that after 1 ligand is bound, the affinity of the enzyme for further ligands decreases
What is the cooperativity if Hill’s coefficient = 1?
the enzyme does not exhibit cooperative binding
What are the y and x intercepts of lineweaver-burk plots?
y-intercept gives the value of 1/Vmax, and the x-axis shows the value of -1/Km
What happens to enzyme velocity when temperature increases?
enzyme catalytic activities double in velocity for every 10 degrees Celsius increase in temp until the optimum temp is reached
What happens to enzyme catalytic activities when pH increases?
pH affects ionization of the active site, and changes in pH can lead to denaturation of the enzyme
What happens to enzyme catalytic activities when salinity increases?
increasing salt levels can disrupt hydrogen and ionic bonds, causing a partial change in the conformation of the enzyme, and in some cases, denaturation.
What is feedback inhibition/negative feedback?
a regulatory mechanism where the catalytic activity of an enzyme is inhibited by the presence of high levels of a product later in the same pathway
What happens in competitive inhibition?
inhibitor binds to the binding site of the enzyme. Can be overcome by adding more substrate so that the substrate-to-inhibitor ratio is higher
What happens in Noncompetitive inhibition?
inhibitor binds to an allosteric site instead of the active site which induces a change in enzyme conformation, and thus Cannot be overcome by adding more substrate
What happens to Km and Vmax in noncompetitive inhibition?
Vmax is decreased because there is less enzyme available to react but it does not alter the Km because the remaining active enzymes maintain the same affinity for their substrates
What happens to Km and Vmax in competitive ihibition?
Km is increased. The Vmax is not altered because if enough substrates are added, it will outcompete the inhibitor to run the reaction at maximum velocity.
What happens in mixed inhibition?
the inhibitor can bind the allosteric site of the enzyme or the enzyme-substrate complex but has a different affinity for each
What happens in uncompetitive inhibition?
inhibitor binds only to the enzyme-substrate complex and locks the substrate in the enzyme, preventing its release. The formation of the enzyme-substrate complex creates conformational change that allows the uncompetitive inhibitor to bind
What happens to Km and Vmax in uncompetitive inhibition?
Both Km and Vmax are lowered
What happens to Km and Vmax in mixed inhibition?
if the inhibitor binds to the enzyme, it increases the Km (lowers the affinity), and Vmax is decreased
If the inhibitor binds to the enzyme-substrate complex, it lowers the Km (increases infinity), and Vmax is decreased
What is irreversible inhibition?
a type of inhibition in which the active site is made unavailable for a prolonged period or the enzyme is permanently altered. this type of inhibition is not easily overcome or reversed
What are allosteric enzymes?
enzymes with multiple binding sites that alternate between active and inactive forms, causing a conformational shift in the protein
What results from an allosteric activator?
in a shift that makes the active site more available for binding to the substrate
What are the 3 types of covalent enzyme modifications?
phosphorylation, dephosphorylation, and glycosylation
What is a zymogen?
an inactive enzyme
