Question 1

What is the relationship between the Michaelis-Menten plot and the Lineweaver-Burk plot?&#10;A)The Lineweaver-Burk plot is a double reciprocal transformation of the Michaelis-Menten plot.&#10;B)The Lineweaver-Burk plot is a logarithmic transformation of the Michaelis-Menten plot.&#10;C)The Lineweaver-Burk plot is a semilogarithmic transformation of the Michaelis-Menten plot.&#10;D)The Lineweaver-Burk plot is an inverse logarithmic transformation of the Michaelis-Menten plot.

Accepted Answer

The Michaelis-Menten plot is a plot of substrate concentration versus reaction velocity.The curvature of this plot makes it difficult to determine values such as Km.The Lineweaver-Burk plot is a double reciprocal transformation of the Michaelis-Menten plot.The Lineweaver-Burk plot is a plot of 1/substrate concentration versus 1/reaction velocity.This transformation converts the curve of the Michaelis-Menten plot into a straight line from which it is easier to determine values such as Km.

Question 2

An enzyme activity of 50 IU/L is equal to _____ nK/L.&#10;A)3.0&#10;B)16.7&#10;C)416&#10;D)835

Accepted Answer

$ 1 \mathrm{IU} / \mathrm{L} $ is equal to $ 16.7 \mathrm{nK} / \mathrm{L} $. Thus:
$$
50 \mathrm{IU} / \mathrm{L} \times \frac{16.7 \mathrm{nK} / \mathrm{L}}{1 \mathrm{IU} / \mathrm{L}}=835 \mathrm{nK} / \mathrm{L}
$$

Question 3

Which type of enzyme inhibitor is associated with an increased Km in order to maintain maximal velocity?&#10;A)competitive inhibitor&#10;B)noncompetitive inhibitor&#10;C)uncompetitive inhibitor&#10;D)allosteric inhibitor

Accepted Answer

Competitive inhibitors bind to the active site of an enzyme, preventing substrate binding. This increases the Km (the substrate concentration at which the reaction rate is half of Vmax) because more substrate is needed to outcompete the inhibitor and achieve the same reaction rate. However, the maximal velocity (Vmax) remains unchanged because the inhibitor can be outcompeted by a high substrate concentration.

Question 4

Enzymes that are of diagnostic utility are primarily located ______, and changes in plasma concentration of these enzymes are indicative of ______.&#10;A)in plasma, the cause of the disease leading to the change&#10;B)within cells, the cause of the disease leading to the change&#10;C)in plasma, the location and nature of the pathological change&#10;D)within cells, the location and nature of the pathological change

Accepted Answer

Most diagnostically useful enzymes are found in high concentration within cells.The concentration of these enzymes in plasma under normal conditions is significantly less.When disease develops within a particular cell or tissue in which a specific enzyme is concentrated, there will be a significant increase in plasma level of the enzyme.This significant increase serves as a valuable indicator of the cell or tissue from which the enzyme was derived.

Question 5

What is the purpose of transforming the Michaelis-Menten plot into a Lineweaver-Burk plot?&#10;A)to establish a linear relationship that allows for the conversion of enzyme activity into enzyme concentration&#10;B)to establish a linear relationship that allows for the conversion of measured absorbance into enzyme activity&#10;C)to establish a linear relationship that allows for the conversion of measured absorbance into enzyme concentration&#10;D)to establish a straight-line relationship from which Km and the maximal velocity can be determined with accuracy

Accepted Answer

The Lineweaver-Burk transformation takes a curve that is difficult to work with and transforms the curve into a straight line.The purpose for this transformation is to allow the determination of Km and Vmₐₓ with greater accuracy than could be achieved using a curve.

Question 6

A convenient method for assaying enzyme activity is based on measuring the conversion between the oxidized and reduced forms of nicotinamide adenine dinucleotide (NAD/NADH).Which form of nicotinamide adenine dinucleotide has a unique wavelength of absorption, and what is the wavelength at which is unique absorption is at its maximum?

A)oxidized, 260 nm
B)oxidized, 340 nm
C)reduced, 260 nm
D)reduced, 340 nm

Accepted Answer

The oxidized form of nicotinamide adenine dinucleotide is abbreviated NAD, and the reduced form is abbreviated NADH.Both NAD and NADH show significant absorbance at 260 nm.These two forms differ in their absorbance at 340 nm.NADH shows significant absorbance at 340 nm, whereas NAD does not absorb at this wavelength.

Question 7

Considering the active site of an enzyme, which of the following statements is not correct?&#10;A)The active site of an enzyme involves a relatively small percentage of the total number of amino acids in the enzyme.&#10;B)The active site of an enzyme is the location where allosteric inhibitors bind to the enzyme.&#10;C)The attraction between enzyme and substrate is typically non-covalent.&#10;D)The active site of an enzyme takes on a three-dimensional orientation for specific binding with the substrate.

Accepted Answer

The active site of an enzyme typically involves a relatively small percentage of the total number of amino acids in the enzyme.For example, active sites may involve only 5 to 10 amino acids out of a total of 200 to 300 amino acids in the entire enzyme.These 5 to 10 amino acids are typically spaced far apart in the primary sequence.However, as a result of the folding of the tertiary structure, these amino acids are located spatially in close proximity, forming a three-dimensional conformation that is specific for the substrate.The attraction between the active site and substrate typically involves hydrogen bonding, electrostatic and hydrophobic interactions, and van der Waals forces.

Question 8

Which of the following is necessary for maximal enzyme velocity?&#10;A)The enzyme concentration must be in excess of the substrate concentration.&#10;B)The substrate concentration must be in excess of the enzyme concentration.&#10;C)The substrate and enzyme concentrations must be equal.&#10;D)The enzyme and substrate reaction must be reversible.

Accepted Answer

To measure the maximum velocity of an enzymatic reaction, substrate concentration must be in excess of enzyme concentration.Because the total number of active binding sites on the enzyme are limited and the amount of enzyme is constant, as the amount of substrate increases, the sites on the enzyme will become increasingly saturated.Beyond this point, with further increases in substrate concentration, as soon as the enzyme converts one substrate molecule to product, another substrate molecule will be available to take its place.At this level of substrate excess, the reaction becomes independent of substrate concentration, and the enzymatic reaction will proceed at its maximal velocity.

Question 9

A/An ______ is a non-protein organic material that is one type of cofactor that may be needed for the ______form of the enzyme being measured.&#10;A)activator, apoenzyme&#10;B)coenzyme, holoenzyme&#10;C)activator, holoenzyme&#10;D)coenzyme, apoenzyme

Accepted Answer

A coenzyme is a non-protein organic material that is an example of a cofactor that may be needed to ensure that the holoenzyme is the enzyme form being measured.A holoenzyme is the complete enzyme-cofactor complex needed for full catalytic activity of the enzyme.

Question 10

Which of the following factors that influence enzymatic activity demonstrate a bell-shaped curve when relating the factor to enzyme activity?&#10;A)pH&#10;B)temperature&#10;C)noncompetitive inhibitors&#10;D)both a and b

Accepted Answer

Enzymatic reactions have a select pH and temperature at which maximal velocity can be achieved.As the pH and the temperature move away from these select values in either direction, enzyme activity declines

Question 11

What substrate concentration is typically utilized in enzymatic analyses to ensure zero-order kinetics?&#10;A)substrate concentration equal to &#189; Km&#10;B)substrate concentration equal to Km&#10;C)substrate concentration of less than 10 &#215; Km&#10;D)substrate concentration of 10 - 100 &#215; Km

Accepted Answer

The answer of What substrate concentration is typically utilized in...

Question 12

Which type of enzyme inhibitor binds to the active site and is considered to be a reversible inhibitor?&#10;A)competitive inhibitor&#10;B)noncompetitive inhibitor&#10;C)uncompetitive inhibitor&#10;D)allosteric inhibitor

Accepted Answer

The answer of Which type of enzyme inhibitor binds to...

Question 13

Enzymes are a subgroup of ______ that can be distinguished from other members of the group by the enzyme's ______.&#10;A)carbohydrates, catalytic activity&#10;B)lipids, lipid solubility&#10;C)proteins, catalytic activity&#10;D)nucleic acids, lipid solubility

Accepted Answer

The answer of Enzymes are a subgroup of ______ that...

Question 14

Most clinical laboratory assays measure concentration of analyte in the blood stream.Why do most enzyme analyses measure enzyme activity instead of enzyme concentration?&#10;A)The assays utilized to measure enzymes involve equilibrium reactions where the reaction can proceed in both directions during the assay.&#10;B)The enzyme being analyzed may be present in such a large concentration that it is difficult to maintain linearity, causing activity measurements to be more suitable.&#10;C)Enzymes are not consumed during the reactions in which they are involved, requiring analysis by activity instead of concentration.&#10;D)The products formed by enzymatic reactions are not sufficiently chromophoric to be measured by traditional spectrophotometric techniques.

Accepted Answer

The answer of Most clinical laboratory assays measure concentration of...

Question 15

The purpose of an enzyme is to:&#10;A)alter the energy difference between the substrate and product&#10;B)increase the rate of a chemical reaction&#10;C)prevent the reversal of chemical reactions&#10;D)protect the substrate during the addition of heat or energy

Accepted Answer

The answer of The purpose of an enzyme is to:&#10;A)alter...

Question 16

Calculate the enzyme activity in IU/L, given the following information.
Change in absorbance over 7 minutes = 0.350
Molar absorptivity = 6.22 × 10³ L/mol•cm
Light path = 1 cm
Total assay volume = 3.0 mL
Total sample volume = 0.5 mL

A)0.3 IU/L
B)1.3 IU/L
C)48 IU/L
D)338 IU/L

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Accepted Answer

The answer of Calculate the enzyme activity in IU/L, given...

Question 17

The loss of enzyme activity is known as ______ and is typically a result of changes in the enzyme's _____ structure.&#10;A)inactivation, secondary&#10;B)denaturation, primary&#10;C)inactivation, primary&#10;D)denaturation, tertiary

Accepted Answer

The answer of The loss of enzyme activity is known...

Deck 15: Clinical Enzymology