Ch 6 Enzymes

Question 1

What significant discovery did NASA announce on Jan. 29, 2025?

Answer 1

NASA discovered amino acids on asteroid Bennu

Question 2

What are the ways to increase the rate of chemical reactions?

Answer 2

• Increasing the temperature
• Increasing the concentrations of the reacting substances
• Adding a catalyst

Question 3

What is a catalyst?

Answer 3

A substance that participates in the reaction yet returns to its original form

Question 4

What are enzymes?

Answer 4

Catalysts used by living systems to increase the rates of chemical reactions

Question 5

What is the active site of an enzyme?

Answer 5

A specific fraction of the structure where reactions take place

Question 6

Most enzymes work under what conditions?

Answer 6

Mild conditions

Question 7

True or False: Enzymes can operate under extreme temperatures and pressures.

Answer 7

False

Question 8

What is activation energy (ΔG‡)?

Answer 8

Energy input needed to start the reaction

Question 9

How do enzymes affect activation energy?

Answer 9

Enzymes lower the activation energy

Question 10

What does a negative ΔG° indicate?

Answer 10

The reaction is spontaneous

Question 11

What are the seven major classifications of enzymes?

Answer 11

• Oxidoreductases
• Transferases
• Hydrolases
• Lyases
• Isomerases
• Ligases
• Translocases

Question 12

What is the difference between kinetics and thermodynamics?

Answer 12

Kinetics refers to the speed of a reaction, while thermodynamics refers to the direction and likelihood of a reaction

Question 13

What is stereospecificity in enzymes?

Answer 13

Most enzymes are very specific with respect to the stereochemistry of substrates

Question 14

What is the lock-and-key model?

Answer 14

A model where the substrate binds to a portion of the enzyme with a complementary shape

Question 15

What is the induced fit model?

Answer 15

Binding of the substrate induces a change in the conformation of the enzyme for a complementary fit

Question 16

What are cofactors?

Answer 16

Substances that aid in catalysis, including metal ions and organic molecules

Question 17

What are coenzymes?

Answer 17

Organic molecules that act as cofactors, often derived from vitamins

Question 18

What is acid-base catalysis?

Answer 18

A mechanism where a proton is transferred between the enzyme and the substrate

Question 19

What is covalent catalysis?

Answer 19

A mechanism where a covalent bond forms between the catalyst and the substrate during the transition state

Question 20

What is metal ion catalysis?

Answer 20

A mechanism where metal ions mediate oxidation-reduction reactions or promote reactivity

Question 21

What is the catalytic triad?

Answer 21

The hydrogen-bonded arrangement of Asp, His, and Ser residues in enzymes like chymotrypsin

Question 22

In the context of enzyme kinetics, what does [S] represent?

Answer 22

Substrate concentration

Question 23

What analogy is used to describe enzyme activity and velocity?

Answer 23

A monkey is like an enzyme and a peanut is like a substrate

Question 24

Fill in the blank: Enzymes often use _______ to aid in catalysis.

Answer 24

cofactors

Question 25

What is enzyme kinetics?

Answer 25

How fast an enzyme catalyzes a reaction under a given set of conditions.

Question 26

How are rates of enzyme reactions measured?

Answer 26

In units of product produced or substrate consumed per time period, e.g., moles/unit time.

Question 27

What does Chymotrypsin catalyze?

Answer 27

The selective hydrolysis of peptide bonds, particularly at Phe and Tyr residues.

Question 28

What is the significance of color change in measuring chymotrypsin activity?

Answer 28

It indicates the rate of colored product formation.

Question 29

What is Vmax?

Answer 29

The maximum processing speed of the enzyme when it is saturated with substrate.

Question 30

Is Vmax a constant value?

Answer 30

No, it is dependent on the amount and type of enzyme.

Question 31

What describes the relationship between initial rate of an enzyme-catalyzed reaction and substrate concentration?

Answer 31

Many enzymes obey Michaelis–Menten kinetics.

Question 32

What characterizes a unimolecular reaction?

Answer 32

It has a velocity dependent on the concentration of only one substrate.

Question 33

What is the rate equation for a unimolecular reaction?

Answer 33

𝜈 = k [A], where k has units of sec–1.

Question 34

What characterizes a bimolecular reaction?

Answer 34

It has a velocity dependent on two substrate concentrations.

Question 35

What is the rate equation for a bimolecular reaction?

Answer 35

𝜈 = k [A] [B] or k [A]² or k [B]², where k has units of M–1 ⋅ sec–1.

Question 36

What does 'steady state' mean in enzyme kinetics?

Answer 36

It refers to a constant value of the enzyme-substrate complex (E∙S).

Question 37

Who developed enzyme kinetics?

Answer 37

Maud Menten, MD/PhD, around 1913 in Berlin.

Question 38

What does KM represent in enzyme kinetics?

Answer 38

The concentration of substrate at which half of the enzyme’s active sites are bound to substrate (½ Vmax).

Question 39

What does a high KM value indicate?

Answer 39

A low substrate affinity.

Question 40

What does a low KM value indicate?

Answer 40

A high substrate affinity.

Question 41

Fill in the blank: The maximum rate when the enzyme is saturated with substrate is called _______.

Answer 41

Vmax

Question 42

If two enzymes have the same Vmax, how is the enzyme with a higher affinity for substrate determined?

Answer 42

The enzyme with the lower KM value has the higher affinity.