BIOCHEM Chp.2 Enzymes

Question 1

What are the key features of an enzyme/catalyst?

Answer 1

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

Question 2

What do oxidoreductases catalyze?

Answer 2

oxidation-reactions/ Electron donor is known as reductant, and electron acceptor the oxidant

Question 3

What do transferases catalyze?

Answer 3

the movement of function groups from one molecule to another such as kinases

Question 3

What do hydrolases catalyze?

Answer 3

the breaking of a compound into 2 molecules using the addition of water

Question 3

What do lyases catalyze?

Answer 3

the cleavage of a single molecule into 2 products

Question 4

What do isomerases catalyze?

Answer 4

the rearrangement of bonds within a stereoisomer and constitutional isomers

Question 4

What do ligases catalyze?

Answer 4

addition or synthesis reactions, generally b/w large similar molecules like nucleic acids and often require ATP

Question 5

Give an example of oxidoreductase.

Answer 5

enzymes with dehydrogenases or reductase

Question 6

Give an example of transferases

Answer 6

aminotransferase, kinases

Question 7

Give an example of hydrolases

Answer 7

phosphatase, peptidase, nuclease, lipases

Question 8

What is the diff b/w endergonic and exergonic reactions?

Answer 8

endergonic - requires energy input - change in G > 0
exergonic - energy is given off - change in G < 0

Question 9

Give an example of lyases

Answer 9

synthases

Question 10

What is the diff b/w apo and holoenzymes?

Answer 10

apoenzymes - enzymes w/o their cofactor
haloenzyme - enzymes with their cofactor

Question 11

What are the water-soluble vitamins?

Answer 11

B complex, vitamin C

Question 11

What are the fat-soluble vitamins?

Answer 11

vitamin A, D, E, and K

Question 12

What is the diff b/w coenzyme and cofactors?

Answer 12

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)

Question 13

How can you increase the Vmax of an enzyme?

Answer 13

by increasing the enzyme concentration

Question 13

What is Km?

Answer 13

the substrate concentration at which half of the enzyme’s active sites are full

Question 14

What does a high Km and low Km mean?

Answer 14

a low Km reflects a high affinity for the substrate, conversely, a high Km reflects a slow affinity of the enzyme for the substrate

Question 15

What is the graph of cooperative binding enzymes?

Answer 15

the binding curve is sigmoidal

Question 15

What is catalytic efficiency?

Answer 15

a large Kcat (high turnover) or small Km (high substrate affinity) will result in a higher catalytic efficiency, which indicates a more efficient enzyme

Question 16

What is the plot of michaelis-menten?

Answer 16

the graph is a hyperbola

Question 17

What is the plot of Lineweaver-burk?

Answer 17

the plot is a double reciprocal graph of the Michaelis-mente equation and is thus linear in graphing

Question 18

What is the cooperativity if the Hill’s coefficient > 1?

Answer 18

positively cooperative binding is occurring such that after 1 ligand is bound, the affinity of the enzyme for further ligands increases

Question 19

What is the cooperativity if the Hill’s coefficient < 1?

Answer 19

negatively cooperative binding is occurring such that after 1 ligand is bound, the affinity of the enzyme for further ligands decreases

Question 20

What is the cooperativity if Hill’s coefficient = 1?

Answer 20

the enzyme does not exhibit cooperative binding

Question 21

What are the y and x intercepts of lineweaver-burk plots?

Answer 21

y-intercept gives the value of 1/Vmax, and the x-axis shows the value of -1/Km

Question 22

What happens to enzyme velocity when temperature increases?

Answer 22

enzyme catalytic activities double in velocity for every 10 degrees Celsius increase in temp until the optimum temp is reached

Question 23

What happens to enzyme catalytic activities when pH increases?

Answer 23

pH affects ionization of the active site, and changes in pH can lead to denaturation of the enzyme

Question 24

What happens to enzyme catalytic activities when salinity increases?

Answer 24

increasing salt levels can disrupt hydrogen and ionic bonds, causing a partial change in the conformation of the enzyme, and in some cases, denaturation.

Question 25

What is feedback inhibition/negative feedback?

Answer 25

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

Question 26

What happens in competitive inhibition?

Answer 26

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

Question 27

What happens in Noncompetitive inhibition?

Answer 27

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

Question 28

What happens to Km and Vmax in noncompetitive inhibition?

Answer 28

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

Question 28

What happens to Km and Vmax in competitive ihibition?

Answer 28

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.

Question 29

What happens in mixed inhibition?

Answer 29

the inhibitor can bind the allosteric site of the enzyme or the enzyme-substrate complex but has a different affinity for each

Question 30

What happens in uncompetitive inhibition?

Answer 30

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

Question 31

What happens to Km and Vmax in uncompetitive inhibition?

Answer 31

Both Km and Vmax are lowered

Question 32

What happens to Km and Vmax in mixed inhibition?

Answer 32

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

Question 33

What is irreversible inhibition?

Answer 33

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

Question 34

What are allosteric enzymes?

Answer 34

enzymes with multiple binding sites that alternate between active and inactive forms, causing a conformational shift in the protein

Question 35

What results from an allosteric activator?

Answer 35

in a shift that makes the active site more available for binding to the substrate

Question 36

What are the 3 types of covalent enzyme modifications?

Answer 36

phosphorylation, dephosphorylation, and glycosylation

Question 37

What is a zymogen?

Answer 37

an inactive enzyme