bch 3025 exam 1 modules 1-5

In a bacterial cell, the DNA is in the:
A) cell envelope.
B) cell membrane.
C) nucleoid.
D) nucleus.
E) ribosomes.

nucleoid

A major change occurring in the evolution of eukaryotes from prokaryotes was the development of:
A) DNA.
B) photosynthetic capability.
C) plasma membranes.
D) ribosomes.
E) the nucleus.

the nucleus.

In eukaryotes, the nucleus is enclosed by a double membrane called the:

A) cell membrane.
B) nuclear envelope.
C) nucleolus.
D) nucleoplasm.
E) nucleosome

nuclear envelope

The dimensions of living cells are limited, on the lower end by the minimum number of biomolecules necessary for function, and on the upper end by the rate of diffusion of solutes such as oxygen. Except for highly elongated cells, they usually have lengths and diameters in the range of:
A) 0.1 m to 10 m.
B) 0.3 m to 30 m.
C) 0.3 m to 100 m.
D) 1 m to 100 m.
E) 1 m to 300 m.

0.3 micro meters to 100 micro meters

The bacterium E. coli requires simple organic molecules for growth and energy—it is therefore a
A) chemoautotroph.
B) chemoheterotroph.
C) lithotroph.
D) photoautotroph.
E) photoheterotroph.

chemo heterotroph.

Which one of the following has the cellular components arranged in order of increasing size?
A) Amino acid < protein < mitochondrion < ribosome
B) Amino acid < protein < ribosome < mitochondrion
C) Amino acid < ribosome < protein < mitochondrion
D) Protein < amino acid < mitochondrion < ribosome
E) Protein < ribosome < mitochondrion < amino acid

Amino acid < protein < ribosome < mitochondrion

The three-dimensional structure of macromolecules is formed and maintained primarily through noncovalent interactions. Which one of the following is not considered a noncovalent interaction?

A) carbon-carbon bonds
B) hydrogen bonds
C) hydrophobic interactions
D) ionic interactions
E) van der Waals interactions

carbon-carbon bonds

Which one of the following is not among the four most abundant elements in living organisms?
A) Carbon
B) Hydrogen
C) Nitrogen
D) Oxygen
E) Phosphorus

Phosphorus

The four covalent bonds in methane (CH4) are arranged around carbon to give which one of the following geometries?
A) linear
B) tetrahedral
C) trigonal bipyramidal
D) trigonal planar
E) trigonal pyramidal

tetrahedral

What functional groups are present on this molecule?
A) ether and aldehyde
B) hydroxyl and aldehyde
C) hydroxyl and carboxylic acid
D) hydroxyl and ester
E) hydroxyl and ketone

hydroxyl and aldehyde

The macromolecules that serve in the storage and transmission of genetic information are:
A) carbohydrates.
B) lipids.
C) membranes.
D) nucleic acids.
E) proteins.

nucleic acids.

Stereoisomers that are nonsuperimposable mirror images of each other are known as
A) anomers.
B) cis-trans isomers.
C) diastereoisomers.
D) enantiomers.
E) geometric isomers

enantiomers.

The enzyme fumarase catalyzes the reversible hydration of fumaric acid to l-malate, but it will not catalyze the hydration of maleic acid, the cis isomer of fumaric acid. This is an example of:
A) biological activity.
B) chiral activity.
C) racemization.
D) stereoisomerization.
E) stereospecificity.

stereo specificity.

Humans maintain a nearly constant level of hemoglobin by continually synthesizing and degrading it. This is an example of a(n):
A) dynamic steady state.
B) equilibrium state.
C) exergonic change.
D) free-energy change.
E) waste of energy.

dynamic steady state

If heat energy is absorbed by the system during a chemical reaction, the reaction is said to be
A) at equilibrium.
B) endergonic.
C) endothermic.
D) exergonic.
E) exothermic.

Endothermic

If the free energy change delta G for a reaction is -46.11 kJ/mol, the reaction is:

A) at equilibrium.
B) endergonic.
C) endothermic.
D) exergonic.
E) exothermic.

Exergonic.

The major carrier of chemical energy in all cells is
A) acetyl triphosphate.
B) adenosine monophosphate.
C) adenosine triphosphate.
D) cytosine tetraphosphate.
E) uridine diphosphate

adenosine triphosphate

Enzymes are biological catalysts that enhance the rate of a reaction by:
A) decreasing the activation energy.
B) decreasing the amount of free energy released.
C) increasing the activation energy.
D) increasing the amount of free energy released.
E) increasing the energy of the transition state.

decreasing the activation energy.

Energy requiring metabolic pathways that yield complex molecules from simpler precursors are:
A) amphibolic.
B) anabolic.
C) autotrophic.
D) catabolic.
E) heterotrophic.

Anabolic

Hereditary information (with the exception of some viruses) is preserved in
A) deoxyribonucleic acid.
B) membrane structures.
C) nuclei.
D) polysaccharides.
E) ribonucleic acid.

deoxyribonucleic acid

When a region of DNA must be repaired by removing and replacing some of the nucleotides, what ensures that the new nucleotides are in the correct sequence?
A) DNA cannot be repaired and this explains why mutations occur.
B) Specific enzymes bind the correct nucleotides.
C) The new nucleotides basepair accurately with those on the complementary strand.
D) The repair enzyme recognizes the removed nucleotide and brings in an identical one to replace it.
E) The three-dimensional structure determines the order of nucleotides.

The new nucleotides basepair accurately with those on the complementary strand.

The three-dimensional structure of a protein is determined primarily by:
A) electrostatic guidance from nucleic acid structure.
B) how many amino acids are in the protein.
C) hydrophobic interaction with lipids that provide a folding framework.
D) modification during interactions with ribosomes.
E) the sequence of amino acids in the protein.

the sequence of amino acids in the protein.

According to Oparin’s theory for the origin of life, the prebiotic atmosphere
A) already contained some primitive RNA molecules.
B) basically was very similar to the atmosphere of today.
C) contained many amino acids.
D) had an abundance of methane, ammonia, and water.
E) was rich in oxygen.

had an abundance of methane, ammonia, and water

The chirality of an amino acid results from the fact that its alpha carbon:
A) has no net charge.
B) is a carboxylic acid.
C) is bonded to four different chemical groups.
D) is in the L absolute configuration in naturally occurring proteins.
E) is symmetric

is bonded to four different chemical groups

Of the 20 standard amino acids, only ___________ is not optically active. The reason is that its side chain ___________.
A) alanine; is a simple methyl group
B) glycine; is a hydrogen atom
C) glycine; is unbranched
D) lysine; contains only nitrogen
E) proline; forms a covalent bond with the amino group

glycine; is a hydrogen atom

Two amino acids of the standard 20 contain sulfur atoms. They are
A) cysteine and serine.
B) cysteine and threonine.
C) methionine and cysteine
D) methionine and serine
E) threonine and serine.

methionine and cysteine

All of the amino acids that are found in proteins, except for proline, contain a(n)
A) amino group.
B) carbonyl group.
C) carboxyl group.
D) ester group.
E) thiol group

amino group.

Which of the following statements about aromatic amino acids is correct?
A) All are strongly hydrophilic.
B) Histidine’s ring structure results in its being categorized as aromatic or basic, depending on pH.
C) On a molar basis, tryptophan absorbs more ultraviolet light than tyrosine.
D) The major contribution to the characteristic absorption of light at 280 nm by proteins is the phenylalanine R group.
E) The presence of a ring structure in its R group determines whether or not an amino acid is aromatic.

On a molar basis, tryptophan absorbs more ultraviolet light than tyrosine

Which of the following statements about cystine is correct?
A) Cystine forms when the —CH2—SH R group is oxidized to form a —CH2—S—S—CH2— disulfide bridge between two cysteines.
B) Cystine is an example of a nonstandard amino acid, derived by linking two standard amino acids.
C) Cystine is formed by the oxidation of the carboxylic acid group on cysteine.
D) Cystine is formed through a peptide linkage between two cysteines.
E) Two cystines are released when a —CH2—S—S—CH2— disulfide bridge is reduced to —CH2—SH.

Cystine forms when the —CH2—SH R group is oxidized to form a —CH2—S—S—CH2— disulfide bridge between two cysteines.

The uncommon amino acid selenocysteine has an R group with the structure —CH2—SeH (pKa = 5). In an aqueous solution, pH = 7.0, selenocysteine would:
A) be a fully ionized zwitterion with no net charge.
B) be found in proteins as D-selenocysteine.
C) never be found in a protein.
D) be nonionic.
E) not be optically active

be a fully ionized zwitterion with no net charge.

Amino acids are ampholytes because they can function as either a(n):
A) acid or a base.
B) neutral molecule or an ion.
C) polar or a nonpolar molecule.
D) standard or a nonstandard monomer in proteins.
E) transparent or a light-absorbing compound.

acid or a base

Titration of valine by a strong base, for example NaOH, reveals two pK’s. The titration reaction occurring at pK2 (pK2 = 9.62) is:

A) —COOH + OH —COO + H2O.
B) —COOH + —NH2 —COO + —NH2+.
C) —COO + —NH2+ —COOH + —NH2.
D) —NH3+ + OH —NH2 + H2O.
E) —NH2 + OH —NH + H2O.

—NH3+ + OH- –> —NH2 + H2O.

In a highly basic solution, pH = 13, the dominant form of glycine is:

A) NH2—CH2—COOH.
B) NH2—CH2—COO-.
C) NH2—CH3+—COO-.
D) NH3+—CH2—COOH.
E) NH3+—CH2—COO-.

C) NH2—CH3+—COO-.

For amino acids with neutral R groups, at any pH below the pI of the amino acid, the population of amino acids in solution will have:
A) a net negative charge.
B) a net positive charge.
C) no charged groups.
D) no net charge.
E) positive and negative charges in equal concentration.

a net positive charge

What is the approximate charge difference between glutamic acid and alpha-ketoglutarate at pH 9.5?

A) 0
B) ½
C) 1
D) 1½
E) 2

½

The formation of a peptide bond between two amino acids is an example of a(n) ______________ reaction.
A) cleavage
B) condensation
C) group transfer
D) isomerization
E) oxidation reduction

condensation

The peptide alanylglutamylglycylalanylleucine has:
A) a disulfide bridge.
B) five peptide bonds.
C) four peptide bonds.
D) no free carboxyl group.
E) two free amino groups.

four peptide bonds.

An octapeptide composed of four repeating glycylalanyl units has
A) one free amino group on an alanyl residue.
B) one free amino group on an alanyl residue and one free carboxyl group on a glycyl residue.
C) one free amino group on a glycyl residue and one free carboxyl group on an alanyl residue.
D) two free amino and two free carboxyl groups.
E) two free carboxyl groups, both on glycyl residues

one free amino group on a glycyl residue and one free carboxyl group on an alanyl residue

At the isoelectric pH of a tetrapeptide:

A) only the amino and carboxyl termini contribute charge.
B) the amino and carboxyl termini are not charged.
C) the total net charge is zero.
D) there are four ionic charges.
E) two internal amino acids of the tetrapeptide cannot have ionizable R groups.

the total net charge is zero.

Which of the following is correct with respect to the amino acid composition of proteins?
A) Larger proteins have a more uniform distribution of amino acids than smaller proteins.
B) Proteins contain at least one each of the 20 different standard amino acids.
C) Proteins with different functions usually differ significantly in their amino acid composition.
D) Proteins with the same molecular weight have the same amino acid composition.
E) The average molecular weight of an amino acid in a protein increases with the size of the protein.

Proteins with different functions usually differ significantly in their amino acid composition

The average molecular weight of the 20 standard amino acids is 138, but biochemists use 110 when estimating the number of amino acids in a protein of known molecular weight. Why?
A) The number 110 is based on the fact that the average molecular weight of a protein is 110,000 with an average of 1,000 amino acids.
B) The number 110 reflects the higher proportion of small amino acids in proteins, as well as the loss of water when the peptide bond forms.
C) The number 110 reflects the number of amino acids found in the typical small protein, and only small proteins have their molecular weight estimated this way.
D) The number 110 takes into account the relatively small size of nonstandard amino acids.
E) The number 138 represents the molecular weight of conjugated amino acids.

The number 110 reflects the higher proportion of small amino acids in proteins, as well as the loss of water when the peptide bond forms.

In a conjugated protein, a prosthetic group is:
A) a fibrous region of a globular protein.
B) a nonidentical subunit of a protein with many identical subunits.
C) a part of the protein that is not composed of amino acids.
D) a subunit of an oligomeric protein.
E) synonymous with "protomer."

a part of the protein that is not composed of amino acids.

Prosthetic groups in the class of proteins known as glycoproteins are composed of:
A) carbohydrates.
B) flavin nucleotides.
C) lipids.
D) metals .
E) phosphates.

carbohydrates.

Which of the following refers to particularly stable arrangements of amino acid residues in a protein that give rise to recurring patterns?
A) Primary structure
B) Secondary structure
C) Tertiary structure
D) Quaternary structure
E) None of the above

Secondary structure

Which of the following describes the overall three-dimensional folding of a polypeptide?
A) Primary structure
B) Secondary structure
C) Tertiary structure
D) Quaternary structure
E) None of the above

Quaternary structure

For the study of a protein in detail, an effort is usually made to first:
A) conjugate the protein to a known molecule.
B) determine its amino acid composition.
C) determine its amino acid sequence.
D) determine its molecular weight.
E) purify the protein.

purify the protein.

In a mixture of the five proteins listed below, which should elute second in size-exclusion (gel- filtration) chromatography?
A) cytochrome c Mr = 13,000
B) immunoglobulin G Mr = 145,000
C) ribonuclease A Mr = 13,700
D) RNA polymerase Mr = 450,000
E) serum albumin Mr = 68,500

immunoglobulin G Mr = 145,000

By adding SDS (sodium dodecyl sulfate) during the electrophoresis of proteins, it is possible to:
A) determine a protein’s isoelectric point.
B) determine an enzyme’s specific activity.
C) determine the amino acid composition of the protein.
D) preserve a protein’s native structure and biological activity.
E) separate proteins exclusively on the basis of molecular weight

separate proteins exclusively on the basis of molecular weight.

To determine the isoelectric point of a protein, first establish that a gel:
A) contains a denaturing detergent that can distribute uniform negative charges over the protein’s surface.
B) exhibits a stable pH gradient when ampholytes become distributed in an electric field.
C) is washed with an antibody specific to the protein of interest.
D) neutralizes all ionic groups on a protein by titrating them with strong bases.
E) relates the unknown protein to a series of protein markers with known molecular weights, Mr.

exhibits a stable pH gradient when ampholytes become distributed in an electric field.

The first step in two-dimensional gel electrophoresis generates a series of protein bands by isoelectric focusing. In a second step, a strip of this gel is turned 90 degrees, placed on another gel containing SDS, and electric current is again applied. In this second step:

A) proteins with similar isoelectric points become further separated according to their molecular weights.
B) the individual bands become stained so that the isoelectric focus pattern can be visualized.
C) the individual bands become visualized by interacting with protein-specific antibodies in the second gel.
D) the individual bands undergo a second, more intense isoelectric focusing.
E) the proteins in the bands separate more completely because the second electric current is in the opposite polarity to the first current.

proteins with similar isoelectric points become further separated according to their molecular weights.

The term specific activity differs from the term activity in that specific activity
A) is measured only under optimal conditions.
B) is the activity (enzyme units) in a milligram of protein.
C) is the activity (enzyme units) of a specific protein.
D) refers only to a purified protein.

is the activity (enzyme units) in a milligram of protein.

The functional differences, as well as differences in three-dimensional structures, between two different enzymes from E. coli result directly from their different:

A) affinities for ATP.
B) amino acid sequences.
C) roles in DNA metabolism.
D) roles in the metabolism of E. coli.
E) secondary structures.

amino acid sequences

One method used to prevent disulfide bond interference with protein sequencing procedures is:

A) cleaving proteins with proteases that specifically recognize disulfide bonds.
B) protecting the disulfide bridge against spontaneous reduction to cysteinyl sulfhydryl groups.
C) reducing disulfide bridges and preventing their re-formation by further modifying the —SH groups.
D) removing cystines from protein sequences by proteolytic cleavage.
E) sequencing proteins that do not contain cysteinyl residues.

reducing disulfide bridges and preventing their re-formation by further modifying the —SH groups.

Even when a gene is available and its sequence of nucleotides is known, chemical studies of the protein are still required to determine:

A) molecular weight of the protein.
B) the amino-terminal amino acid.
C) the location of disulfide bonds.
D) the number of amino acids in the protein.
E) whether the protein has the amino acid methionine in its sequence.

the location of disulfide bonds

The term "proteome" has been used to describe:

A) regions (domains) within proteins.
B) regularities in protein structures.
C) the complement of proteins encoded by an organism’s DNA.
D) the structure of a protein-synthesizing ribosome.
E) the tertiary structure of a protein.

the complement of proteins encoded by an organism’s DNA

A major advance in the application of mass spectrometry to macromolecules came with the development of techniques to overcome which of the following problems?

A) Macromolecules were insoluble in the solvents used in mass spectrometry.
B) Mass spectrometric analyses of macromolecules were too complex to interpret.
C) Mass spectrometric analysis involved molecules in the gas phase.
D) Most macromolecules could not be purified to the degree required for mass spectrometric analysis.
E) The specialized instruments required were prohibitively expensive.

Mass spectrometric analysis involved molecules in the gas phase.

Compare the following sequences taken from four different proteins, and select the answer that best characterizes their relationships

A) Based only on sequences in column B, protein 4 reveals the greatest evolutionary divergence.
B) Comparing proteins 1 and 2 in column A reveals that these two proteins have diverged the most throughout evolution.
C) Protein 4 is the protein that shows the greatest overall homology to protein 1.
D) Proteins 2 and 3 show a greater evolutionary distance than proteins 1 and 4.
E) The portions of amino acid sequence shown suggest that these proteins are completely unrelated.

Based only on sequences in column B, protein 4 reveals the greatest evolutionary divergence

The interactions of ligands with proteins:

A) are relatively nonspecific.
B) are relatively rare in biological systems.
C) are usually irreversible.
D) are usually transient.
E) usually result in the inactivation of the proteins.

are usually transient

A prosthetic group of a protein is a non-protein structure that is

A) a ligand of the protein.
B) a part of the secondary structure of the protein.
C) a substrate of the protein.
D) permanently associated with the protein.
E) transiently bound to the protein.

permanently associated with the protein

When oxygen binds to a heme-containing protein, the two open coordination bonds of Fe2+ are occupied by:

A) one O atom and one amino acid atom.
B) one O2 molecule and one amino acid atom.
C) one O2 molecule and one heme atom.
D) two O atoms.
E) two O2 molecules.

one O2 molecule and one amino acid atom

In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as:

A) hyperbolic.
B) linear with a negative slope.
C) linear with a positive slope.
D) random.
E) sigmoidal.

hyperbolic.

Which of the following statements about protein-ligand binding is correct?

A) The Ka is equal to the concentration of ligand when all of the binding sites are occupied.
B) The Ka is independent of such conditions as salt concentration and pH.
C) The larger the Ka (association constant), the weaker the affinity.
D) The larger the Ka, the faster is the binding.
E) The larger the Ka, the smaller the Kd (dissociation constant).

The larger the Ka, the smaller the Kd (dissociation constant)

Myoglobin and the subunits of hemoglobin have:

A) no obvious structural relationship.
B) very different primary and tertiary structures.
C) very similar primary and tertiary structures.
D) very similar primary structures, but different tertiary structures.
E) very similar tertiary structures, but different primary structures.

very similar tertiary structures, but different primary structures

An allosteric interaction between a ligand and a protein is one in which:
A) binding of a molecule to a binding site affects binding of additional molecules to the same site.
B) binding of a molecule to a binding site affects binding properties of another site on the protein.
C) binding of the ligand to the protein is covalent.
D) multiple molecules of the same ligand can bind to the same binding site.
E) two different ligands can bind to the same binding site.

binding of a molecule to a binding site affects binding properties of another site on the protein.

In hemoglobin, the transition from T state to R state (low to high affinity) is triggered by

A) Fe2+ binding.
B) heme binding.
C) oxygen binding.
D) subunit association.
E) subunit dissociation

oxygen binding.

Which of the following is not correct concerning 2,3-bisphosphoglycerate (BPG)?

A) It binds at a distance from the heme groups of hemoglobin.
B) It binds with lower affinity to fetal hemoglobin than to adult hemoglobin.
C) It increases the affinity of hemoglobin for oxygen.
D) It is an allosteric modulator.
E) It is normally found associated with the hemoglobin extracted from red blood cells.

It increases the affinity of hemoglobin for oxygen

Which of the following is not correct concerning cooperative binding of a ligand to a protein?

A) It is usually a form of allosteric interaction.
B) It is usually associated with proteins with multiple subunits.
C) It rarely occurs in enzymes.
D) It results in a nonlinear Hill Plot.
E) It results in a sigmoidal binding curve.

It rarely occurs in enzymes

The amino acid substitution of Val for Glu in Hemoglobin S results in aggregation of the protein because of ___________ interactions between molecules.

A) covalent
B) disulfide
C) hydrogen bonding
D) hydrophobic
E) ionic

hydrophobic

The fundamental cause of sickle-cell disease is a change in the structure of:
A) blood.
B) capillaries.
C) hemoglobin.
D) red cells.
E) the heart.

hemoglobin.

An individual molecular structure within an antigen to which an individual antibody binds is as a(n):
A) antigen.
B) epitope.
C) Fab region.
D) Fc region
E) MHC site

epitope.

The proteins of the Major Histocompatibility Complex (MHC) bind and display:
A) antigen fragments.
B) B cell fragments.
C) immunoglobin fragments.
D) macrophage fragments.
E) T cell fragments.

antigen fragments

Which of the following parts of the IgG molecule are not involved in binding to an antigen?

A) Fab
B) Fc
C) Heavy chain
D) Light chain
E) Variable domain

Fc

A monoclonal antibody differs from a polyclonal antibody in that monoclonal antibodies:

A) are labeled with chemicals that can be visualized.
B) are produced by cells from the same organism that produced the antigen.
C) are synthesized by a population of identical, or "cloned," cells.
D) are synthesized only in living organisms.
E) have only a single polypeptide chain that can recognize an antigen.

are synthesized by a population of identical, or "cloned," cells.

Which of the following generalizations concerning motor proteins is correct?
A) They convert chemical energy into kinetic energy.
B) They convert chemical energy into potential energy.
C) They convert kinetic energy into chemical energy.
D) They convert kinetic energy into rotational energy.
E) They convert potential energy into chemical energy.

They convert chemical energy into kinetic energy.

The predominant structural feature in myosin molecules is:
A) a beta structure.
B) an alpha helix.
C) the Fab domain.
D) the light chain.
E) the meromyosin domain.

an alpha helix

The energy that is released by the hydrolysis of ATP by actin is used for:
A) actin filament assembly.
B) actin filament disassembly.
C) actin-myosin assembly.
D) actin-myosin disassembly.
E) muscle contraction.

actin filament assembly

During muscle contraction, hydrolysis of ATP results in a change in the:

A) conformation of actin.
B) conformation of myosin.
C) structure of the myofibrils.
D) structure of the sarcoplasmic reticulum.
E) structure of the Z disk.

conformation of myosin.

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:

A) Apo enzyme.
B) coenzyme.
C) holoenzyme.
D) prosthetic group.
E) substrate.

Apoenzyme

Which one of the following is not among the six internationally accepted classes of enzymes?

A) Hydrolases
B) Ligases
C) Oxidoreductases
D) Polymerases
E) Transferases

Polymerases

Enzymes are potent catalysts because they
A) are consumed in the reactions they catalyze.
B) are very specific and can prevent the conversion of products back to substrates.
C) drive reactions to completion while other catalysts drive reactions to equilibrium.
D) increase the equilibrium constants for the reactions they catalyze.
E) lower the activation energy for the reactions they catalyze.

lower the activation energy for the reactions they catalyze

The role of an enzyme in an enzyme-catalyzed reaction is to:
A) bind a transition state intermediate, such that it cannot be converted back to substrate.
B) ensure that all of the substrate is converted to product.
C) ensure that the product is more stable than the substrate.
D) increase the rate at which substrate is converted into product.
E) make the free-energy change for the reaction more favorable.

increase the rate at which substrate is converted into product

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

A) Their catalytic activity is independent of pH.
B) They are generally equally active on D and L isomers of a given substrate.
C) They can increase the equilibrium constant for a given reaction by a thousand fold or more.
D) They can increase the reaction rate for a given reaction by a thousand fold or more.
E) To be effective, they must be present at the same concentration as their substrate.

They can increase the reaction rate for a given reaction by a thousand fold or more

Which one of the following statements is true of enzyme catalysts?
A) They bind to substrates, but are never covalently attached to substrate or product.
B) They increase the equilibrium constant for a reaction, thus favoring product formation.
C) They increase the stability of the product of a desired reaction by allowing ionizations, resonance, and isomerizations not normally available to substrates.
D) They lower the activation energy for the conversion of substrate to product.
E) To be effective they must be present at the same concentration as their substrates.

They lower the activation energy for the conversion of substrate to product.

Which of the following statements is false?
A) A reaction may not occur at a detectable rate even though it has a favorable equilibrium.
B) After a reaction, the enzyme involved becomes available to catalyze the reaction again.
C) For S -&gt; P, a catalyst shifts the reaction equilibrium to the right.
D) Lowering the temperature of a reaction will lower the reaction rate.
E) Substrate binds to an enzyme’s active site.

For S –> P, a catalyst shifts the reaction equilibrium to the right.

Enzymes differ from other catalysts in that only enzymes
A) are not consumed in the reaction.
B) display specificity toward a single reactant.
C) fail to influence the equilibrium point of the reaction.
D) form an activated complex with the reactants.
E) lower the activation energy of the reaction catalyzed.

display specificity toward a single reactant.

Compare the two reaction coordinate diagrams below and select the answer that correctly describes their relationship. In each case, the single intermediate is the ES complex.

A) (a) describes a strict "lock and key" model, whereas (b) describes a transition-state complementarity model.
B) The activation energy for the catalyzed reaction is #5 in (a) and is #7 in (b).
C) The activation energy for the uncatalyzed reaction is given by #5 + #6 in (a) and by #7 + #4 in (b).
D) The contribution of binding energy is given by #5 in (a) and by #7 in (b).

(a) describes a strict "lock and key" model, whereas (b) describes a transition-state complementarity model.

Which of the following is true of the binding energy derived from enzyme-substrate interactions?
A) It cannot provide enough energy to explain the large rate accelerations brought about by enzymes.
B) It is sometimes used to hold two substrates in the optimal orientation for reaction.
C) It is the result of covalent bonds formed between enzyme and substrate.
D) Most of it is derived from covalent bonds between enzyme and substrate.
E) Most of it is used up simply binding the substrate to the enzyme.

It is sometimes used to hold two substrates in the optimal orientation for reaction.

The concept of "induced fit" refers to the fact that:
A) enzyme specificity is induced by enzyme-substrate binding.
B) enzyme-substrate binding induces an increase in the reaction entropy, thereby catalyzing the reaction.
C) enzyme-substrate binding induces movement along the reaction coordinate to the transition state.
D) substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation.
E) when a substrate binds to an enzyme, the enzyme induces a loss of water (desolvation) from the substrate.

substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation

In the following diagram of the first step in the reaction catalyzed by the protease chymotrypsin, the process of general base catalysis is illustrated by the number ________, and the process of covalent catalysis is illustrated by the number _________.

A) 1; 2
B) 1; 3
C) 2; 3
D) 2; 3
E) 3; 2

1; 2

The benefit of measuring the initial rate of a reaction V0 is that at the beginning of a reaction:
A) [ES] can be measured accurately.
B) changes in [S] are negligible, so [S] can be treated as a constant.
C) changes in Km are negligible, so Km can be treated as a constant.
D) V0 = Vmax.
E) varying [S] has no effect on V0.

changes in [S] are negligible, so [S] can be treated as a constant.

Which of the following statements about a plot of V0 vs. [S] for an enzyme that follows Michaelis-Menten kinetics is false?

A) As [S] increases, the initial velocity of reaction V0 also increases.
B) At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km.
C) Km is the [S] at which V0 = 1/2 Vmax.
D) The shape of the curve is a hyperbola.
E) The y-axis is a rate term with units of m/min.

At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km.

Michaelis and Menten assumed that the overall reaction for an enzyme-catalyzed reaction could be written as
k1 k2
E + S ES E + P
k-1

Using this reaction, the rate of breakdown of the enzyme-substrate complex can be described by the expression:
A) k1 ([Et] – [ES]).
B) k1 ([Et] – [ES])[S].
C) k2 [ES].
D) k-1 [ES] + k2 [ES].
E) k-1 [ES].

k-1 [ES] + k2 [ES].

The steady state assumption, as applied to enzyme kinetics, implies

A) Km = Ks.
B) the enzyme is regulated.
C) the ES complex is formed and broken down at equivalent rates.
D) the Km is equivalent to the cellular substrate concentration.
E) the maximum velocity occurs when the enzyme is saturated.

the ES complex is formed and broken down at equivalent rates.

An enzyme-catalyzed reaction was carried out with the substrate concentration initially a thousand times greater than the Km for that substrate. After 9 minutes, 1% of the substrate had been converted to product, and the amount of product formed in the reaction mixture was 12 micromol. If, in a separate experiment, one-third as much enzyme and twice as much substrate had been combined, how long would it take for the same amount (12 micromol) of product to be formed?
A) 1.5 min
B) 13.5 min
C) 27 min
D) 3 min
E) 6 min

27 min

Which of these statements about enzyme-catalyzed reactions is false?
A) At saturating levels of substrate, the rate of an enzyme-catalyzed reaction is proportional to the enzyme concentration.
B) If enough substrate is added, the normal Vmax of a reaction can be attained even in the presence of a competitive inhibitor.
C) The rate of a reaction decreases steadily with time as substrate is depleted.
D) 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.
E) The Michaelis-Menten constant Km equals the [S] at which V = 1/2 Vmax.

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.

The following data were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics:
V0 Substrate added
(micromol/min) (mmol/L)
—————————————
217 0.8
325 2
433 4
488 6
647 1,000
—————————————
A) 1 mM.
B) 1,000 mM.
C) 2 mM.
D) 4 mM.
E) 6 mM.

2 mM

For enzymes in which the slowest (rate-limiting) step is the reaction
k2
ES –&gt; P

Km becomes equivalent to:
A) kcat.
B) the [S] where V0 = Vmax.
C) the dissociation constant, Kd, for the ES complex.
D) the maximal velocity.
E) the turnover number.

the dissociation constant, Kd, for the ES complex.

The Lineweaver-Burk plot is used to

A) determine the equilibrium constant for an enzymatic reaction.
B) extrapolate for the value of reaction rate at infinite enzyme concentration.
C) illustrate the effect of temperature on an enzymatic reaction.
D) solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration.
E) solve, graphically, for the ratio of products to reactants for any starting substrate concentration.

solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration

The double-reciprocal transformation of the Michaelis-Menten equation, also called the Lineweaver-Burk plot, is given by
1/V0 = Km /(Vmax[S]) + 1/Vmax.
To determine Km from a double-reciprocal plot, you would

A) multiply the reciprocal of the x-axis intercept by -1.
B) multiply the reciprocal of the y-axis intercept by -1.
C) take the reciprocal of the x-axis intercept.
D) take the reciprocal of the y-axis intercept.
E) take the x-axis intercept where V0 = 1/2 Vmax.

multiply the reciprocal of the x-axis intercept by -1.

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

A) the enzyme concentration.
B) the initial velocity of the catalyzed reaction at [S] &gt;&gt; Km.
C) the initial velocity of the catalyzed reaction at low [S].
D) the Km for the substrate.
E) both A and B.

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

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 the:
A) dissociation constant.
B) half-saturation constant.
C) maximum velocity.
D) Michaelis-Menten number.
E) turnover number.

turnover number.

In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction, the presence of a competitive inhibitor will alter the:
A) curvature of the plot.
B) intercept on the l/[S] axis.
C) intercept on the l/V axis.
D) pK of the plot.
E) Vmax.

intercept on the l/[S] axis.

In competitive inhibition, an inhibitor
A) binds at several different sites on an enzyme.
B) binds covalently to the enzyme.
C) binds only to the ES complex.
D) binds reversibly at the active site.
E) lowers the characteristic Vmax of the enzyme

binds reversibly at the active site

Vmax for an enzyme-catalyzed reaction:
A) generally increases when pH increases.
B) increases in the presence of a competitive inhibitor.
C) is limited only by the amount of substrate supplied.
D) is twice the rate observed when the concentration of substrate is equal to the Km.
E) is unchanged in the presence of a uncompetitive inhibitor.

is twice the rate observed when the concentration of substrate is equal to the Km.

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) a Glu residue on the enzyme is involved in the reaction.
B) a His residue on the enzyme is involved in the reaction.
C) the enzyme has a metallic cofactor.
D) the enzyme is found in gastric secretions.
E) the reaction relies on specific acid-base catalysis.

a His residue on the enzyme is involved in the reaction.

Both water and glucose share an —OH that can serve as a substrate for a reaction with the terminal phosphate of ATP catalyzed by hexokinase. Glucose, however, is about a million times more reactive as a substrate than water. The best explanation is that:

A) glucose has more —OH groups per molecule than does water.
B) the larger glucose binds better to the enzyme; it induces a conformational change in hexokinase that brings active-site amino acids into position for catalysis.
C) the —OH group of water is attached to an inhibitory H atom, while the glucose —OH group is attached to C.
D) water and the second substrate, ATP, compete for the active site resulting in a competitive inhibition of the enzyme.
E) water normally will not reach the active site because it is hydrophobic.

the larger glucose binds better to the enzyme; it induces a conformational change in hexokinase that brings active-site amino acids into position for catalysis.

A good transition-state analog:
A) binds covalently to the enzyme.
B) binds to the enzyme more tightly than the substrate.
C) binds very weakly to the enzyme.
D) is too unstable to isolate.
E) must be almost identical to the substrate.

binds to the enzyme more tightly than the substrate.

A transition-state analog:
A) is less stable when binding to an enzyme than the normal substrate.
B) resembles the active site of general acid-base enzymes.
C) resembles the transition-state structure of the normal enzyme-substrate complex.
D) stabilizes the transition state for the normal enzyme-substrate complex.
E) typically reacts more rapidly with an enzyme than the normal substrate.

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

The role of the metal ion (Mg2+) in catalysis by enolase is to
A) act as a general acid catalyst
B) act as a general base catalyst
C) facilitate general acid catalysis
D) facilitate general base catalysis
E) stabilize protein conformation

facilitate general base catalysis

Which of the following statements about allosteric control of enzymatic activity is false?
A) Allosteric effectors give rise to sigmoidal V0 vs. [S] kinetic plots.
B) Allosteric proteins are generally composed of several subunits.
C) An effector may either inhibit or activate an enzyme.
D) Binding of the effector changes the conformation of the enzyme molecule.
E) Heterotropic allosteric effectors compete with substrate for binding sites.

Heterotropic allosteric effectors compete with substrate for binding sites.

A small molecule that decreases the activity of an enzyme by binding to a site other than the catalytic site is termed a(n):
A) allosteric inhibitor.
B) alternative inhibitor.
C) competitive inhibitor.
D) stereospecific agent.
E) transition-state analog.

allosteric inhibitor.

Allosteric enzymes:
A) are regulated primarily by covalent modification.
B) usually catalyze several different reactions within a metabolic pathway.
C) usually have more than one polypeptide chain.
D) usually have only one active site.
E) usually show strict Michaelis-Menten kinetics.

usually have more than one polypeptide chain.

A metabolic pathway proceeds according to the scheme, R –&gt; S -&gt; T -&gt; U -&gt; V -&gt; W. A regulatory enzyme, X, catalyzes the first reaction in the pathway. Which of the following is most likely correct for this pathway?

A) Either metabolite U or V is likely to be a positive modulator, increasing the activity of X.
B) The first product S, is probably the primary negative modulator of X, leading to feedback inhibition.
C) The last product, W, is likely to be a negative modulator of X, leading to feedback inhibition.
D) The last product, W, is likely to be a positive modulator, increasing the activity of X.
E) The last reaction will be catalyzed by a second regulatory enzyme.

The last product, W, is likely to be a negative modulator of X, leading to feedback inhibition.

Which of the following has not been shown to play a role in determining the specificity of protein kinases?
A) Disulfide bonds near the phosphorylation site
B) Primary sequence at phosphorylation site
C) Protein quaternary structure
D) Protein tertiary structure
E) Residues near the phosphorylation site

Disulfide bonds near the phosphorylation site

How is trypsinogen converted to trypsin?
A) A protein kinase-catalyzed phosphorylation converts trypsinogen to trypsin.
B) An increase in Ca2+ concentration promotes the conversion.
C) Proteolysis of trypsinogen forms trypsin.
D) Trypsinogen dimers bind an allosteric modulator, cAMP, causing dissociation into active trypsin monomers.
E) Two inactive trypsinogen dimers pair to form an active trypsin tetramer.

Proteolysis of trypsinogen forms trypsin

To possess optical activity, a compound must be:
A) a carbohydrate.
B) a hexose.
C) asymmetric.
D) colored.
E) D-glucose.

asymmetric.

Which of the following monosaccharides is not an aldose?
A) erythrose
B) fructose
C) glucose
D) glyceraldehyde
E) ribose

fructose

The reference compound for naming D and L isomers of sugars is
A) fructose.
B) glucose.
C) glyceraldehyde.
D) ribose.
E) sucrose.

glyceraldehyde.

When two carbohydrates are epimers:
A) one is a pyranose, the other a furanose.
B) one is an aldose, the other a ketose.
C) they differ in length by one carbon.
D) they differ only in the configuration around one carbon atom.
E) they rotate plane-polarized light in the same direction.

they differ only in the configuration around one carbon atom.

Which of the following is an epimeric pair?
A) D-glucose and D-glucosamine
B) D-glucose and D-mannose
C) D-glucose and L-glucose
D) D-lactose and D-sucrose
E) L-mannose and L-fructose

D-glucose and D-mannose

Which of following is an anomeric pair
A) D-glucose and D-fructose
B) D-glucose and L-fructose
C) D-glucose and L-glucose
D) alpha-D-glucose and beta-D-glucose
E) alpha-D-glucose and beta-L-glucose

alpha-D-glucose and beta-D-glucose

When the linear form of glucose cyclizes, the product is a(n):
A) anhydride.
B) glycoside.
C) hemiacetal.
D) lactone.
E) oligosaccharide.

hemiacetal.

Which of the following pairs is interconverted in the process of mutarotation?
A) D-glucose and D-fructose
B) D-glucose and D-galactose
C) D-glucose and D-glucosamine
D) D-glucose and L-glucose
E) alpha-D-glucose and beta-D-glucose

alpha-D-glucose and beta-D-glucose

Which of the following is not a reducing sugar?
A) Fructose
B) Glucose
C) Glyceraldehyde
D) Ribose
E) Sucrose

Sucrose

Which of the following monosaccharides is not a carboxylic acid?
A) 6-phospho-gluconate
B) gluconate
C) glucose
D) glucuronate
E) muramic acid

glucose

D-Glucose is called a reducing sugar because it undergoes an oxidation-reduction reaction at the anomeric carbon. One of the products of this reaction is:

A) D-galactose.
B) D-gluconate.
C) D-glucuronate.
D) D-ribose.
E) muramic acid.

D-gluconate

From the abbreviated name of the compound Gal(betA1 –&gt; 4)Glc, we know that:

A) C-4 of glucose is joined to C-1 of galactose by a glycosidic bond.
B) the compound is a D-enantiomer.
C) the galactose residue is at the reducing end.
D) the glucose is in its pyranose form.
E) the glucose residue is the anomer.

C-4 of glucose is joined to C-1 of galactose by a glycosidic bond

Starch and glycogen are both polymers of:
A) fructose.
B) glucose1-phosphate.
C) sucrose.
D) alpha-D-glucose.
E) beta-D-glucose.

ALPHA-D-glucose

Which of the following statements about starch and glycogen is false?
A) Amylose is unbranched; amylopectin and glycogen contain many (alpha 1 -&gt; beta 6) branches.
B) Both are homopolymers of glucose.
C) Both serve primarily as structural elements in cell walls.
D) Both starch and glycogen are stored intracellularly as insoluble granules.
E) Glycogen is more extensively branched than starch.

Both serve primarily as structural elements in cell walls.

Which of the following is a heteropolysaccharide?

A) Cellulose
B) Chitin
C) Glycogen
D) Hyaluronate
E) Starch

Hyaluronate

The basic structure of a proteoglycan consists of a core protein and a:
A) glycolipid.
B) glycosaminoglycan.
C) lectin.
D) lipopolysaccharide.
E) peptidoglycan.

glycosaminoglycan.

In glycoproteins, the carbohydrate moiety is always attached through the amino acid residues:
A) asparagine, serine, or threonine.
B) aspartate or glutamate.
C) glutamine or arginine.
D) glycine, alanine, or aspartate.
E) tryptophan, aspartate, or cysteine

asparagine, serine, or threonine.

Which of the following is a dominant feature of the outer membrane of the cell wall of gram negative bacteria?
A) Amylose
B) Cellulose
C) Glycoproteins
D) Lipopolysaccharides
E) Lipoproteins

Lipopolysaccharides

The biochemical property of lectins that is the basis for most of their biological effects is their ability to bind to:
A) amphipathic molecules.
B) hydrophobic molecules.
C) specific lipids.
D) specific oligosaccharides.
E) specific peptides.

specific oligosaccharides.

Hemoglobin glycation is a process where ________ is ________ attached to hemoglobin.

a: glycerol; covalently
b: glucose; enzymatically
c: glucose; non-enzymatically
d: N-acetyl-galactosamine; enzymatically
e: galactose; non-enzymatically

glucose; non-enzymatically

Enthalpy is defined as

A: a spontaneous reaction.
B: the entropy of the system.
C: the heat content of a system.
D: entropy and heat content of system.
E: None of the available answers.

the heat content of a system.

List atoms commonly found in biological molecules that are often hydrogen-bond acceptors.

A: carbon
B: oxygen
C: nitrogen
D:oxygen and nitrogen
E: carbon, oxygen, and nitrogen.

oxygen and nitrogen

What gives proteins such a dominant role in biochemistry?

A: the variation in protein sizes
B: the ability to act as a blueprint
C: their ability to self-replicate
D: their ability to spontaneously fold into complex three-dimensional structures
E: All of the available answers

their ability to spontaneously fold into complex three-dimensional structures

In what pH range is zwitterionic Alanine the predominate structure?
A: 0-2
B: 9-14
C: 8-10
D: 2-4
E: 2-9

2-9

The relaxed form of an allosteric protein has _________ affinity for its ligand or substrate

A: higher
B: equal
C: lower
D: no
E: None of the available answers.

higher

Allosteric proteins

A:contain distinct regulatory sites and have multiple functional sites.

B: display cooperativity.

C: always consist of several identical subunits.

D: contain distinct regulatory sites, have multiple functional sites, and display cooperativity

E: All the available answers

contain distinct regulatory sites, have multiple functional sites, and display cooperativity

What is the common strategy by which catalysis occurs?

A: increasing the probability of product formation
B:shifting the reaction equilibrium
C:stabilization of transition state
D: All of the available answers.
E: maintaining the reaction equilibrium

stabilization of transition state

Fructose can cyclize to (a)
A: pyranose ring.
B: furanose ring.
C:both pyranose and furanose ring forms.
D: All of the available answers.
E: sucrose.

both pyranose and furanose ring forms.

Glycoproteins are normally

A: found on membranes.
B: secreted as extracellular proteins.
C:found inside organelles.
D: found on membranes and secreted as extracellular proteins.
E: All of the available answers.

found on membranes and secreted as extracellular proteins.

At pH 7.0, converting a glutamic acid to gamma-carboxyglutamate will have what effect on the overall charge of the protein containing it?

A: It will become more negative
B: It will become more positive.
C: It will stay the same.
D: There is not enough information to answer the question.
E: The answer depends on the salt concentration.

It will become more negative