Clin Chem Final

A toxicology screen is set up using thin layer chromatographic plates. Four positive controls/standards are used with the following distance of migration from application point results: Std A = 8 cm; Std B = 15 cm; Std C = 22. The acetone solvent front moved 35 cm. After processing an unknown sample, a solute had a migration distance of 16 cm. (Rf = distance moved by solvent/ distance moved by a given sample). What are the retention factors (Rf) of standards A, B, and C?

0.23, 0.43, 0.63

he desired resolution for good quantitative or qualitative chromatographic analysis is .............. or greater.

1.25

Given the following data, calculate the resolution between the two solutes. The equation to calculate resolution is R = d2 - d1/ [(w1 + w2)] Peak A: peak begins at 1.40 minutes peak maximum occurs at 1.45 minutes (d1) peak returns to baseline at 1.50 minutes absorbance at peak maximum is 1.200 Peak B: peak begins at 1.55 minutes peak maximum occurs at 1.65 minutes (d2) peak returns to baseline at 1.75 minutes absorbance at peak maximum is 0.475

1.33

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...

150 mg/dL

which of the following set of wavelengths is most representative of the visible region?

350-750 nm

which wavelength would be absorbed strongly by a red-colored solution?

450 nm

Calculate the enzyme activity in IU/L, given the following information. Change in absorbance over 7 minutes = 0.350 Molar 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

allosteric proteins

A and B (contain distinct regulatory sites and have multiple functional sites/ always consist of several identical subunits)

multiple substrate enzyme reactions are divided into 2 classes:

A and C (sequential displacement and double displacement / sequential displacement and ping-pong)

in regard to absorption photometry, absorbance is calculated from transmittance by which one of the following formulae?

A= -logT

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.

which of the following is necessary for maximal enzyme velocity? A: The enzyme concentration must be in excess of the substrate concentration B: the substrate concentration must be in excess of the enzyme concentration C: the substrate and enzyme concentrations must be equal D: the enzyme and substrate reaction must be reversible

B: the substrate concentration must be in excess of the enzyme concentration

The fragments typically produced and analyzed in methods employing mass spectroscopy are typically:

Cations caused by electron loss or proton attachment

The most commonly used detector for clinical gas-liquid chromatography (GLC) is based on:

Flame ionization

In regard to mass spectrometry, what is a molecular ion?

It is the unfragmented ion of the original molecule being studied.

Which of the following enzymes has multiple molecular forms (isoenzymes) whose clinical significance is used in diagnosis?

Lactate dehydrogenase, creatine kinase, and alkaline phosphatase

The term isocratic is used in high-performance liquid chromatography (HPLC) to mean that the:

Mobile phase consists of a constant solvent composition

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 term reverse phase is used in HPLC to indicate that the mobile phase is:

More polar than the stationary phase

light scattering when the wavelength is greater than 10 times the particle diameter is described by:

Rayleigh's law

which substance is used to generate the light signal in electrochemiluminescence?

Ruthenium

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.

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.

SITUATION: A GC-MS analysis using nitrogen as the carrier gas shows an extensively noisy baseline. A sample of the solvent (ethyl acetate) used for the extraction procedure was injected and showed the same noise. Results of an Autotune test showed the appearance of a base peak at 16 with two smaller peaks at 17 and 18. These results indicate that:

The carrier gas is contaminated

In MS/MS, the first mass filter performs the same function as:

The chromatography column

Which one of the following statements best describes Beer law?

The concentration of a substance is inversely proportional to the logarithm of transmitted light.

What is the purpose of an internal standard in HPLC and GC methods?

To compensate for variation in extraction and injection

How is trapping-type spectrometry different from typical beam-type mass spectrometry?

Trapping-type mass spectrometry uses an ion trap designed to collect ions in three dimensions instead of two dimensions as in a typical beam-type mass spectrometer.

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.

in absorption spectrophotometry:

absorbance is proportional to concentration

select the chemical that is used in most HPLC procedures to decrease solvent polarity

acetonitrile

the type of separation mechanism for chromatography that involves, as one example, use of immunologic principles is ________________ chromatography

affinity

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

Which one of the following enzymes catalyzes the transfer of an amino group to alpha- ketoglutarate with the formation of oxaloacetate and glutamate?

aspartate aminotransferase (AST)

A good transition-state analog:

binds to the enzyme more tightly than the substrate.

To calculate the turnover number of an enzyme, you need to know:

both A and B. (the enzyme concentration / the initial velocity of the catalyzed reaction at [S] >> Km.)

the polarization of light in a fluorescent polarization immunoassay allows the measurement of which of the following?

bound fraction in the presence of free fraction

in thin-layer chromatography, the solvent migrates up the sorbent (i.e. alumina, silica gel, cellulose) by which action:

capillary action

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.

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

in high performance thin-layer chromatography (HPTLC), developed bands are compared with reference standard concentrations, each band is measured using:

densitometer

the "spreading" of a white beam 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

what component is used in a GC-MS but not used in an LC-MS?

electron source

what process is most often used in LC-MS to introduce the sample into the mass filter?

electrospray ionization (ES)

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 analyze 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 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

in the clinical toxicology laboratory, it is common to use _____________ to measure drugs of abuse

gas chromatography mass spectrophotometer

what type of detector is used in high performance liquid chromatography with electrochemical detection (HPLC-ECD)?

glassy carbon electrode

In comparing nephelometry and turbidity, nephelometric measurements should demonstrate .............. sensitivity, and turbidimetric measurements should demonstrate ....................sensitivity. In practice, turbidimetric measurements have been found to demonstrate ................. sensitivity.

high, limited, high

the relaxed form of an allosteric enzyme has ------ affinity for the substrates

higher

which one of the following statements concerning nephelometry is correct?

in a nephelometric procedure, the measurement of scattered light that is not in the direct path of the transmitted light is made at right angles to the incident light

in which one of the following mass spectrometers does the fragmentation of ions take place after they have been separated by their M/Z value in a first stage?

in a tandem mass spectrophotometer

the role of an enzyme in an enzyme-catalyzed reaction is to:

increase the rate at which substrate is converted into produce

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

why is vacuum necessary in the mass filter of a GC-MS?

it prevents collision between fragments

When the kcat/KM ratio is at its upper limit, it is referred to as..

kinetic perfection

which two optical techniques are combined operationally in a flow cytometer?

laser-induced fluorometry and light scattering techniques

A linear relationship between concentration and fluorescence intensity is seen as long as solutions being quantified have an absorbance of:

less than 0.100

Mass spectrometry identifies analytes based on:

mass to charge ratio

______________ techniques measure light scattered by a particulate 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 is true? A: enzymes force reactions to proceed in only one direction B: enzymes alter the equilibrium of the reaction C: enzymes alter the standard free energy of the reaction D: all of the above E: none of the above

none of the above

In normal-phase chromatography, the mobile phase is relatively .............. _, and the stationary phase is relatively .............. _. .............. solute molecules are retained the longest in this type of chromatography.

nonpolar, polar, polar

there 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

tubidimetry is the measurement of the reduction in light transmission caused by

particle formation

a type of chromatography in which separation occurs by differential distribution of solutes between two immiscible liquids is known as

partition chromatography

which of the following is not among the six internationally accepted classes of enzymes? A: hydrolases B: ligases C: oxidoreductases D: polymerases E: transferases

polymerases

The major cellular origin of acid phosphatase 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

in thin layer chromatography procedure for drug screening, the retention factor (Rf) value for a compound is given by the:

ratio of distance moved by the unknown solute to distance moved by the solvent in the mobile phase

Transition-state analog:

resembles the transition-state structure of the normal enzyme-substrate complex.

if tandem mass spectrometry is combined with a chromatographic separation, what is added to the physical property characterization of the compound being analyzed?

retention time

an example of a clinical application of an HPLC coupled to a tandem mass spectrometer would be:

screening and confirming the presence of inborn errors of metabolism

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

what substrate concentration is typically utilized in enzymatic analyses to ensure zero order kinetics?

substrate concentration of 10-100 x Km

in clinical applications using gas chromatography which one of the following column temperatures techniques will cause the more volatile analytes to elute first and therefore produce the best separation of complex mixtures of analytes with a range of volatilities?

temperature programmed operation

in a fluorometric measurement, the difference between the maximum wavelength of the excitation light and the maximum wavelength of the emitted fluorescent light is a constant referred to as:

the Stokes shift

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 form an individual known to have 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

What is the relationship between the Michaelis-Menton plot and the Lineweaver-Burk plot?

the lineweaver-burk plot is a double reciprocal transformation of the Michaelis-menton plot

A blood specimen is obtained from an individual who is known to have elevated lipids and the serum appear milky. This individual's physician has ordered an estrogen immunoassay that your laboratory performs using 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

The recommended assay, because of its specificity and sensitivity for the measurement of the activity of the CK-MB isoenzyme, is the:

the monoclonal sandwich immunoassay

the partition coefficient in liquid-liquid extraction is:

the ratio of the concentration of the solute in two liquids

which one of the following statements is true of enzyme catalysts?

they lower the activation energy for the conversion of substrate to product

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

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

blood clotting cascades are controlled by...

zymogen activation