Bishop Chapter 13 Enzymes

Question 1

Define active site.

Answer 1

A region on an enzyme that binds to a protein or other substance during a reaction.

Question 2

Define substrate.

Answer 2

The substance on which an enzyme acts.

Question 3

Define allosteric site.

Answer 3

A site that allows molecules to either activate or inhibit (or turn off) enzyme activity.

Question 4

Define isoenzyme.

Answer 4

A group of enzymes that catalyze the same reaction but have different enzyme forms and catalytic efficiencies.

Isozymes are usually distinguished by their electrophoretic mobilities.

Question 5

Define isoform.

Answer 5

When an enzyme is subject to posttranslational modifications.

Question 6

Define cofactor.

Answer 6

A non-protein chemical compound or metallic ion that is required for an enzyme’s role as a catalyst.

Question 7

Define activators.

Answer 7

Inorganic cofactors, such as chloride or magnesium ions.

Question 8

Define coenzyme.

Answer 8

An organic cofactor, such as nicotinamide adenine dinucleotide (NAD).

Question 9

Define zymogen.

Answer 9

Enzymes that are secreted from an organ of production in a structurally inactive form.

Question 10

Define oxidoreductases.

Answer 10

Catalyze an oxidation-reduction reaction between two substrates.

Question 11

Define transferases.

Answer 11

Catalyze the transfer of a group other than hydrogen from one substrate to another.

Question 12

Define hydrolases.

Answer 12

Catalyze hydrolysis of various bonds.

Question 13

Define lyases.

Answer 13

Catalyze removal of groups from substrates without hydrolysis; the product contains double bonds.

Question 14

Define isomerases.

Answer 14

Catalyze the interconversion of geometric, optical, or positional isomers.

Question 15

Define ligases.

Answer 15

Catalyze the joining of two substrate molecules, coupled with breaking of the pyrophosphate bond in ATP or a similar compound.

Question 16

Define activation energy.

Answer 16

The energy required to raise all molecules in 1 mole of a compound at a certain temperature to the transition state at the peak of the energy barrier.

Question 17

What is a way to provide more energy for a reaction?

Answer 17

Increase temperature.

Question 18

Define absolute specificity.

Answer 18

The enzyme combines with only one substrate and catalyzes only the one corresponding reaction.

Question 19

Define group specific.

Answer 19

Enzymes that combine with all substrates containing a particular chemical group (i.e. phosphate ester).

Question 20

Define bond specificity.

Answer 20

Enzymes that are specific to chemical bonds.

Question 21

Define stereoisomeric specificity.

Answer 21

Enzymes that predominantly combine with only one optical isomer of a certain compound.

Question 22

What is a major influence at which an enzymatic reaction proceeds, whether forward or reverse?

Answer 22

Substrate concentration.

Question 23

Define first-order kinetics.

Answer 23

When the reaction rate is directly proportional to substrate concentration.

Question 24

Define zero-order kinetics.

Answer 24

When the reaction rate only depends on enzyme concentration.

Question 25

Define the Michaelis-Menten constant (Km).

Answer 25

A constant for a specific enzyme and substrate under defined reaction conditions and is an expression of the relationship between the velocity of the enzymatic reaction and substrate concentration.

Question 26

The higher the ___ level, the faster the reaction will proceed.

Answer 26

enzyme

Question 27

How would changing the pH of a solution effect the enzymes?

Answer 27

May denature an enzyme or influence its ionic state.

Question 28

How does low temperatures affect enzymes?

Answer 28

Renders them reversibly inactive; freezing prevents activity loss until analysis.

Question 29

Define competitive inhibitors.

Answer 29

Inhibitors that physically bind to the active site of an enzyme and compete with the substrate for the active site.

Question 30

Define noncompetitive inhibitors.

Answer 30

Inhibitors that bind an enzyme at a place other than the active site and may be reversible.

Question 31

Define uncompetitive inhibition.

Answer 31

The inhibitor binds to the ES complex - increasing substrate concentration results in more ES complexes to which the inhibitor binds and, thereby, increases the inhibition.

Question 32

During uncompetitive inhibition, how would the reaction be affected if you increased substrate concentration?

Answer 32

Increases inhibition.

Question 33

What is the common method for enzyme quantitation?

Answer 33

Measurement of catalytic activity; activity is related to concentration.

Question 34

What kind of precautions should you take when doing enzyme quantitation in zero-order kinetics?

Answer 34

Ensure the absence of inhibitors, and other variables that may influence the rate of the reaction are controlled.

Question 35

For measurement of enzymatic reactions, describe the methodology of the fixed-time method.

Answer 35

The reactants are combined, the reaction proceeds for a designate time, the reaction is stopped (usually by inactivating the enzyme with a weak acid), and a measurement is made of the amount of reaction that has occurred.

Question 36

For measurement of enzymatic reactions, describe the methodology of the continuous-monitoring (or kinetic assays).

Answer 36

Multiple measurements, usually of absorbance change, are made during the reaction, either at specific time intervals or continuously by a continuous-recording spectrophotometer.