Chem exam 1
Which of the following methods of measuring enzyme activity utilizes an increase in absorbance at 340nm as an indicator reaction?
"Forward" LD reaction
A nanometer is equivalent to
10^-9 meters
A standard calibrator solution of glucose has a concentration of 125 mg/dL and gives an absorbance of 0.20. Assuming a linear reaction, what is the concentration of glucose in a patient's serum that has an absorbance of 0.24?
150 mg/dL
Which of the following set of wavelengths is the most representative of the visible region?
350-750 nm
Calculate the enzyme activity in IU/L, given the following information. Change in absorbance over 7 minutes = 0.350Molar absorptivity = 6.22 x 103 L/mol•cm Light path = 1 cm Total assay volume = 3.0 mL Total sample volume = 0.5 mL
48 IU/L
A green-colored solution would show highest transmittance at:
525 nm
A manual stat protein analysis is performed on a patient sample. The patient's unknown sample had an absorbance reading of 0.6. The protein calibrator with an absorbance reading closest to the unknown's absorbance had a concentration of 6 g/dL and an absorbance reading of 0.5. Applying Beer law, calculate the unknown protein concentration in the patient sample.
7.2 g/dL
In regard to absorption photometry, absorbance is calculated from transmittance by which of the following formulae?
A = -log T
Enzyme X exhibits maximum activity at pH = 6.9. X shows a fairly sharp decrease in its activity when the pH goes much lower than 6.4. One likely interpretation of this pH activity is that :
A His residue on the enzyme is involved in the reaction.
Which one of the following enzymes catalyzes the transfer of an amino group to alpha-ketoglutarate with the formation of oxaloacetate and glutamate?
AST
In absorption spectrophotometry:
Absorbance is directly proportional to concentration
A reaction rate assay measures enzyme ________; an endpoint assay measures enzyme ________
Activity; activity
Of the following, the only clinically analyzed enzyme in the urine is:
Amylase
One extracellular enzyme whose serum activity measured clinically is:
Amylase
Which of the following enzymes requires chloride (Cl-) as an activator?
Amylase
At present, the major diagnostic usefulness of tartrate-resistant acid phosphatase type 5b is in its use as a marker of conditions with:
An osteolytic component
One of the enzymes involved in glycolysis, aldolase, requires Zn2+ for catalysis. Under conditions of zinc deficiency, when the enzyme may lack zinc, it would be referred to as the :
Apoenzyme
Which of the following statements about a plot of V0 vs. [S] for an enzyme that follows Michaelis-Menten kinetics is false?
At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km. SHOULD BE: At very high [S], the velocity curve becomes a plateau-like and is close to Vmax.
In competitive inhibition, an inhibitor :
Binds reversibly at the active site.
A good transition-state analog :
Binds to the enzyme more tightly than the substrate
Examples of cofactors are :
Biotin and thiamine pyrophosphateZn2+, Mg2+, Ni2+Pyridoxal phosphate and coenzyme A
A physician orders several laboratory tests on a 55-year-old-male patient who is complaining of generalized pain, stiffness, fatigue, and headaches. Based on the following serum test results, what is the most likely diagnosis: ALP-significantly increased, GGT-normal
Bone disease
Many allosteric enzymes have two types of subunits, termed :
Catalytic and regulatory
Which of the following is NOT a way in which enzymes stabilize a transition state?
Causing the temperature of the environment to increase
The benefit of measuring the initial rate of a reaction V0 is that at the beginning of a reaction :
Changes in [S] are negligible, so [S] can be treated as a constant
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.
Coenzyme, Holoenzyme
What type(s) of inhibition can be reversed?
Competitive Mixed Non-competitive
Which type of enzyme inhibitor binds to the active site and is considered to be a reversible inhibitor?
Competitive inhibitor
The loss of enzyme activity is known as ______ and is typically a result of changes in the enzyme's _____ structure.
Denaturation; Tertiary
The "spreading" of a white bean of light into a spectrum is called:
Dispersion
In a photomultiplier tube the intermediate electrode that amplifies the electrical signal is called a(n):
Dynode
Which of the following statements best illustrates the difference between photons from fluorescent emission and the excitation photons?
Emission photons are lower energy and longer wavelength
Most clinical laboratory assays measure concentration of analyte in the blood stream. Why do most enzyme analyses measure enzyme activity instead of enzyme concentration?
Enzymes are not consumed during the reactions in which they are involved, requiring analysis by activity instead of concentration
When a purified enzyme is used as a reagent, such as urease in the measurement of urea, the enzyme must be ____________ concentration so that the reaction follows _______________ kinetics
Excess; first
Riboflavin is a water-soluble organic substance that is not synthesized by humans. Metabolically, it is chemically converted into a substance called flavin adenine dinucleotide, which is required by succinate dehydrogenase. Which of the following statements is most correct?
Flavin adenine dinucleotide is a coenzyme.
When selecting a photometric technique that is more sensitive to a low concentration of analyte, a laboratory director compares absorbance measuring devices against those that measure fluorescence intensity. Which technique is considered more sensitive in its measurements and why?
Fluorescence intensity measurements are more sensitive because of the use of intense light sources, signal filtering, and sensitive light emission photometers.
Which instrument requires a primary and secondary monochromator?
Fluorometer
Which is the most sensitive enzyme for monitoring chronic alcoholic liver disease?
GGT
Which of the following enzymes detect very early changes in liver cell damage?
GGT
The relaxed form of an allosteric enzyme has _________ affinity for the substrates
HIGHER
In comparing nephelometry and turbidity, nephelometric measurements should demonstrate ___________ sensitivity, and turbiditic measurements should demonstrate _________ sensitivity, turbidimetric measurements have been found to demonstrate __________ sensitivity.
High, limited, high
The role of an enzyme in an enzyme-catalyzed reaction is to:
Increase the rate at which substrate is converted into product
The purpose of an enzyme is to :
Increase the rate of a chemical reaction
In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction, the presence of a competitive inhibitor will alter the :
Intercept on the l/[S] axis
Phenyl-methane-sulfonyl-fluoride (PMSF) inactivates serine proteases by binding covalently to the catalytic serine residue at the active site; this enzyme-inhibitor bond is not cleaved by the enzyme. This is an example of what kind of inhibition?
Irreversible
Vmax for an enzyme-catalyzed reaction :
Is twice the rate observed when the concentration of substrate is equal to the Km.
When the kcat / km ratio is at its upper limit it is referred to as :
Kinetic perfection (~108 - 109 s-1M-1 )
Which of the following enzymes tests is most affected by "hemolysis"?
Lactate dehydrogenase
Which of the following enzymes has multiple molecular forms (isoenzyme) whose clinical significance is used in diagnosis?
Lactate dehydrogenase, creatine kinase, and alkaline phosphate
Which two optical techniques are combined operationally in a flow cytometer?
Laser-induced fluorometry and light scattering techniques
The enzyme that is inhibited by hemoglobin is:
Lipase
Which one of the following statements concerning lipase is incorrect?
Lipase is a small enzyme that can be detected in urine
The principal source of serum cholinesterase (CHE) in blood is:
Liver
Enzymes are potent catalysts because they :
Lower the activation energy for the reactions they catalyze
Heart tissue contains which of the following CK enzyme?
MM and MB
Activators that are required for normal CK activity include:
Magnesium only
In spectrophotometric determinations, which of the following is the formula for calculating the absorbance of a solution?
Molar absorptivity × length of light path × concentration in mol/L
The recommended assay, because of its specificity and sensitivity for the measurement of the activity of the CK-MB isoenzyme, is the:
Monoclonal sandwich immunoassay
If you were asked by your laboratory director to set up an enzyme profile (group of tests) specifically to assess hepatobiliary (biliary obstruction) disease, which one of the following sets of enzymes would be most appropriate?
NTP, ALP, and gamma-glutamyltransferase (GGT)
These are several interferences that can affect or limit fluorescence measurements. For example, the inner filter effect:
Occurs when the solution absorbs greater than 2% of the exciting light, producing a nonlinear response between concentration and fluorescence emission.
Tartrate-resistant acid phosphatase (TR-ACP) that is present in unhemolyzed serum is synthesized mainly in:
Osteoclasts
Why is heparin the only acceptable anticoagulant to use when obtaining blood samples for ALP analysis?
Other anticoagulants contain inhibitors of magnesium, which is a required cofactor for ALP activation
Turbidimetry is the measurement of the reduction in light transmission caused by:
Particle formation
Which of the following is an example of a zymogen?
Pepsinogen & Procarboxypeptidase
Which one of the following is not among the six internationally accepted classes of enzymes?
Polymerases
The major cellular origin of acid phosphate activity in serum is:
Prostate
A regulatory mechanism that is not readily reversible :
Proteolytic cleavage
Which of the following products are formed from the forward reaction catalyzed by ALT?
Pyruvate and glutamate
Light scattering when the wavelength is greater than 10 times the particle diameter is described by:
Rayleigh's Law
A transition-state analog :
Resembles the transition-state structure of the normal enzyme-substrate complex
Which substance is used to generate the light signal in electrochemiluminescence?
Ruthenium
Multiple substrate enzyme reactions are divided into two classes :
Sequential displacement and double displacement&Sequential displacement and ping-pong
The Lineweaver-Burk plot is used to :
Solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration.
Which of the following components is not needed in a chemiluminescent immunoassay analyzer?
Source lamp
The concept of "induced fit" refers to the fact that :
Substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation.
What substrate concentration is typically utilized in enzymatic analyses to ensure zero-order kinetics?
Substrate concentration of 10 - 100 X Km
What is the relationship between the Michaelis-Menten plot and the Lineweaver-Burk plot?
The Lineweaver-Burk plot is a double reciprocal transformation of the Michaelis-Menten plot.
Which of these statements about enzyme-catalyzed reactions is false?
The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the enzyme-catalyzed reaction. ENZYMES DO NOT CHANGE EQUILIBRIUM, ONLY REACTION RATES!
Considering the active site of an enzyme, which of the following statements is not correct?
The active site of an enzyme is the location where allosteric inhibitors bind to the enzyme
Which one of the following statements best describes Beer law?
The concentration of a substance is inversely proportional to the logarithm of transmitted light.
Laboratory analysis of free thyroxine (fT4) in your chemistry laboratory is performed with a conventional fluorometric analyzer, which uses a laser light as the excitation source. You have received a sample from an individual known to have a very elevated fT4 level. For the sample's value to be within linear range of the assay, you dilute the sample by a factor of 10 and proceed with the analysis. Upon reviewing the results, you note that the value of the diluted sample is reported as "none detected." What is the likely reason for this result?
The dilution of the sample has lowered produced photobleaching by the intense light source and photodecomposition of the analyte.
To calculate the turnover number of an enzyme, you need to know :
The enzyme concentration & The initial velocity of the catalyzed reaction at [S] >> Km
Which of the following is true under the following conditions: The enzyme concentration is 5 nM, the substrate concentration is 5mM, and the Km is 5 μM.
The enzyme is saturated with substrate
A blood specimen is obtained from an individual who is known to have elevated lipids and the serum appears milky. This individual's physician has ordered an estrogen immunoassay that your laboratory performs using a nephelometric technique. Which one of the following statements is correct concerning the possible outcome of this assay?
The lipemic specimen will produce interfering background light intensity and excess light scatter in this type of assay.
Which of the following is necessary for maximal enzyme velocity?
The substrate concentration must be in excess of the enzyme concentration.
Which of the following statements is true of enzyme catalysts?
They can increase the reaction rate for a given reaction by a thousand fold or more.
What is the purpose of transforming the Michaelis-Menten plot into a Lineweaver-Burk plot?
To establish a straight-line relationship from which Km and the maximal velocity can be determined with accuracy
The number of substrate molecules converted to product in a given unit of time by a single enzyme molecule at saturation is referred to as:
Turnover number
Examples of covalent modification include :
Ubiquination Phosphoylation and dephosphoryation Acetylation
Which of the following statements about fluorometry is accurate?
Unsaturated cyclic molecules are often fluorescent.
The usefulness of analyzing lipoprotein-associated phospholipase A2 for the identification of individuals at risk for future cardiovascular events is because of its:
Upregulation in atherosclerotic lesions, particularly complex plaque.
When substrate concentration is much greater than KM, the rate of catalysis is almost equal to :
Vmax
Blood clotting cascades are controlled by :
Zymogen activation
Allosteric proteins :
contain distinct regulatory sites and have multiple functional sites display cooperativity
Increased enzymatic activity is typically observed in serum or plasma:
following injury or damage to tissue
A linear relationship between concentration and fluorescence intensity is seen as long as solutions being quantified have an absorbance of:
less than 0.100
________ technique measures light scattered by a particle solution, and _________ techniques measure a decrease in light transmission through a particulate solution, _______ measurements can be performed on a basic UV/Visible spectrophotometer.
nephelometric, turbidimetric, turbidimetric
Which of the following factors influence enzymatic activity demonstrate a bell-shaped curve when relating the factor to enzyme activity?
pH and Temperature
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?
reduced, 340nm
In a fluorometric measurement, the difference between the maximum wavelength of the excitation light and the maximum wavelength of the emitted fluorescence light is a constant referred to as:
the Stokes shift
