Chapter 4: Enzyme Kinetics

Question 1

Enzyme kinetics

Answer 1

• Investigation of rates of enzyme-catalyzed reactions

- Help determine substrate specificity and reaction mechanisms

Question 2

Establishes the initial rate of reaction

Answer 2

• Measuring either the disappearance of substrate or the appearance of product per unit time

Question 3

Progressive curve

Answer 3

• The time course of an enzyme-catalyzed reaction
• Concentration on y-axis
• Time on x-axis

Question 4

Maximum velocity of enzyme (Vmax)

Answer 4

• The point where the enzyme the enzyme is saturated with substrate (all enzyme in ES form) and very little free enzyme exists

Question 5

Initial reaction rates (Vo)

Answer 5

• Measured by drawing a tangent to the hyperbolic plot of [product] formed vs time when t = 0

Question 6

Progress cruve (Vo) is at maximum

Answer 6

• Substrate supplies are high and a minimal amount of product has been formed
• Makes reverse reaction insignificant

Question 7

High enzyme concentration effect on initial rate

Answer 7

• Initial rate will be higher at high enzyme concentration than at low enzyme concentration
• More product is formed as time increases for each enzyme when substrate is in excess

Question 8

Gradient of slope

Answer 8

• Calculates the amount of product formed per unit time

Question 9

Calculate initial rate (Vo)

Answer 9

• Can be determined by measuring the gradient at t = 0

Question 10

First order kinetics

Answer 10

• At low concentrations or substrate, a rapid increase in reaction velocity that is proportional to [S] is observed

Question 11

Zero order kinetics

Answer 11

• At high [S] the curve plateaus at a maximum value (Vmax)

- Reaction velocity is independent of changes in [S]

Question 12

Temperature

Answer 12

• Reaction rate initially increases when this increases as the enzyme is activated

Question 13

Denaturation of the enzyme

Answer 13

• Occurs when the non-covalent stabilizing factors of an enzyme are broken
• Reaction rate declines as the temperature is further increased
• Native conformation of the enzyme is disrupted

Question 14

pH

Answer 14

• Measure of [H+] of a solution

- (-) log [H+] = log 1/[H+]

Question 15

Functional groups

Answer 15

• Side chains of amino acids
• Can function as weak acids
• Perform acid/base interactions
• Degree of ionization changes as pH fluctuates

Question 16

Interstitial fluid buffer system

Answer 16

• Carbonic acid - Bicarbonate
• Hydrogen phosphate
• Proteins

Question 17

Intracellular fluid buffer system

Answer 17

• Carbonic acid - Bicarbonate
• Hydrogen phosphate
• Proteins

Question 18

Blood buffer system

Answer 18

• Carbonic acid - Bicarbonate
• Hemoglobin
• Hydrogen phosphate
• Plasma proteins

Question 19

Acidosis

Answer 19

• pH of blood falls

- Common in poorly controlled diabetes mellitus

Question 20

Protects against acidosis

Answer 20

• Carbonic acid - bicarbonate buffer system of the blood

Question 21

Alkalosis

Answer 21

• pH of the blood becomes elevated above 7.4

- May occur with extended periods of vomiting or from hyperventilation

Question 22

Hydrogen phosphate - dihydrogen phosphate buffer system

Answer 22

• Works in the cytoplasm of most cells

Question 23

Gastric pepsin

Answer 23

• Secreted from the chief cells in gastric glands

- Optimal pH of 1.5

Question 24

Michaelis constant (Km)

Answer 24

• The substrate concentration at which the initial velocity is 1/2 Vmax (half the enzyme active sites are occupied)

Question 25

Y-intercept of LWB

Answer 25

1/Vmax

Question 26

X-intercept of LWB

Answer 26

-1/Km

Question 27

Gradient/slope of LWB

Answer 27

Km/Vmax

Question 28

Enzyme Kinetics

Answer 28

- The study of the initial rates (Vo) of enzyme-catalyzed reactions

Question 29

Plotting of Vo vs [S] or an enzyme-catalyzed reaction yields:

Answer 29

- A classic hyperbolic plot for enzymes that exhibit M/M kinetics

Question 30

Michaelis constant (Km)

Answer 30

- The substrate concentration at which the reaction rate is half maximal

Question 31

Lower Km

Answer 31

- Higher enzyme's affinity for susbtrate

Question 32

Changes in temperature and pH

Answer 32

- Can alter enzyme activity