Exam 1: Quizzes and hw 8

What is the reason for the existence of the hydrophobic effect?

the tendency of polar molecules to self-associate in the presence of an aqueous solution

 

the inability of charged molecules to dissolve in water

 

the property of nucleic acids to dissolve in water

 

the tendency of water molecules to make a bond with hydrophobic proteins

 

the tendency of nonpolar molecules to self-associate in the presence of an aqueous solution

the tendency of nonpolar molecules to self-associate in the presence of an aqueous solution

Which statement about interactions in the formation of the DNA double helix is INCORRECT?

 

Van der Waals interactions are nearly optimal in a double-helical structure.

 

Surface complementarity maximizes the formation of hydrogen bonds and van der Waals interactions while minimizing the nonpolar surface area exposed to the aqueous environment.

 

Phosphate groups repel one another resulting in the helical shape of the DNA molecule.

 

Ionic bonds between oppositely charged functional groups are responsible for the formation of the double helix. 

 

Nonpolar surfaces of the bases are moved into contact with each other due to a more complete base stacking.

Ionic bonds between oppositely charged functional groups are responsible for the formation of the double helix. 

What is FALSE regarding the laws of thermodynamics?

 

Ordered structures can be formed within a system only if the entropy of the surroundings will proportionally increase.

 

The local decrease in enthalpy will increase the entropy of the surroundings.

 

Energy can be neither created nor destroyed.

 

Total entropy of the universe is always decreasing as continuous formation of ordered structures results in less disorder in the universe.

Heat is a manifestation of the kinetic energy associated with the random motion of molecules.

Total entropy of the universe is always decreasing as continuous formation of ordered structures results in less disorder in the universe.

How was the fact that formation of the double helix does not violate the second law of thermodynamics experimentally confirmed?

 

in a water bath monitoring the change in heat to sustain constant Gibbs energy in the bath

 

in a water bath monitoring the change in entropy to sustain a constant temperature in the bath

 

in a water bath monitoring the free energy to sustain constant heat content in the bath

 

in a water bath monitoring the change in entropy to check whether it remains constant

 

in a water bath monitoring the change in heat to sustain a constant temperature in the bath

in a water bath monitoring the change in heat to sustain a constant temperature in the bath

The structure of DNA described by Watson and Crick includes:

 

base pairs that are stacked on the outside of the triple helix.

 

a triple helix.

 

base pairs that are stacked on the inside of the double helix.

 

a triple helix composed of three intertwined strands.

 

a sugar-phosphate backbone that lies on the inside of the helix.

base pairs that are stacked on the inside of the double helix.

What did Watson and Crick suggest to be significant about the base-pairing found in the DNA helix?

 

The mechanism of copying genetic information was apparent from the structure of the double helix.

 

The DNA could be circular.

 

Only one of the strands could act as a template.

 

It allowed the DNA to twist in a helix.

 

The DNA sequence was determined by the sequence of RNA.

The mechanism of copying genetic information was apparent from the structure of the double helix.

What gives proteins such a dominant role in biochemistry?

 

ability to spontaneously fold into complex three-dimensional structures

 

rigidity of the peptide backbone

 

usage of 40 different building blocks

 

ability to act as a blueprint

 

ability to self-replicate

ability to spontaneously fold into complex three-dimensional structures

Order the type of interactions by the bond strength in descending value.

 

covalent bonds, van der Waals interactions, hydrogen bonds

 

hydrophobic interactions, hydrogen bonds, electrostatic interactions

 

hydrogen bonds, covalent bonds, van der Waals interactions

 

covalent bonds, hydrogen bonds, van der Waals interactions

 

van der Waals interactions, covalent bonds, hydrogen bonds

covalent bonds, hydrogen bonds, van der Waals interactions

In DNA replication, the new strand always grows in the _____ direction.

 

3 to 5

5 to 1

2 to 3

3 to 2

5 to 3

5 to 3

Under physiological conditions, most DNA is in the form of a _______ form helix.

 

B

 

Z

 

D

 

A

B

What is the technique on which the Watson–Crick model was based?

 

electron microscopy

 

absorbance spectrophotometry

 

radioactive labeling

 

X-ray diffraction

 

spectrofluorometry

X-ray diffraction

Although the right-handed double helix is the most well-known DNA structure, DNA can also form:

 

tight globules.

 

left-handed helices.

 

straight chains.

 

branched chains.

 

triple strands.

left-handed helices.

What is NOT a key property that enables proteins to participate in a wide range of functions?

 

Proteins contain different functional groups.

 

Proteins are linear polymers built of different amino acids.

 

Some proteins are quite rigid, whereas others display considerable flexibility.

 

Proteins have a high molecular weight.

 

Proteins can interact with one another and with other biological macromolecules to form complex assemblies.

Proteins have a high molecular weight.

What does an α-amino acid consist of?

 

carboxylic acid group, δ carbon, imine radical, hydrogen atom, distinctive R group

 

carbonyl group, α carbon, amino group, oxygen atom, distinctive R group

 

carboxylic acid group, α carbon, amino group, hydrogen atom, distinctive R group

 

carboxylic acid group, ε carbon, nitro group, hydrogen atom

 

alcohol group, α carbon, amino group, nitrogen atom, distinctive R group, hydrogen atom

carboxylic acid group, α carbon, amino group, hydrogen atom, distinctive R group

In an acidic solution (pH = 1), what is the ionization state of glycine?

 

The amino group is neutral; the carboxyl group is neutral.

 

The amino group is negatively charged; the carboxyl group is negatively charged.

 

The amino group is positively charged ; the carboxyl group is neutral.

 

The amino group is positively charged; the carboxyl group is negatively charged.

 

The amino group is positively charged; the carboxyl group is positively charged.

The amino group is positively charged ; the carboxyl group is neutral.

Which amino acid has the one-letter abbreviation K?

 

lysine

 

valine

 

histidine

 

alanine

 

asparagine

lysine

What is the amino-terminal residue and what is the carboxyl-terminal residue in the sequence of amino acids Gly-Tyr-Gly-Phe-Leu?

 

There are no N-terminal and C-terminal residues in the sequences of amino acids.

 

Tyrosine is N-terminal and leucine is C-terminal.

 

Leucine is N-terminal and glycine is C-terminal.

 

Glycine is N-terminal and leucine is C-terminal.

 

Phenylalanine is N-terminal and leucine is C-terminal.

Glycine is N-terminal and leucine is C-terminal.

Knowledge of the amino acid sequences is important for several reasons. What is NOT one of those reasons?

 

The sequence of a protein is necessary to determine its function.

 

Changes in the amino acid sequence can lead to abnormal protein functioning and disease.

 

Amino acid sequences determine the three-dimensional structures of proteins.

 

Knowledge of the sequence of a protein can help to prevent mutations.

 

The sequence of a protein reveals much about its evolutionary history.

Knowledge of the sequence of a protein can help to prevent mutations.

What is the configuration of peptide bonds in proteins?

 

Approximately one third are in the cis configuration and rest are in the trans configuration.

 

Almost all peptide bonds are in the cis configuration.

 

Almost all peptide bonds are in the trans configuration.

 

Approximately one third are in the trans configuration and rest are in the cis configuration.

 

Half of all peptide bonds are in the trans configuration and the other half are in the cis configuration.

Almost all peptide bonds are in the trans configuration.

Which amino acid forms disulfide bonds?

 

serine

 

proline

 

histidine

 

cysteine

 

methionine

cysteine

What amino acid residue would MOST likely be buried in the interior of a water soluble protein, rather than on the surface?

 

Trp

 

Arg

 

Asp

 

Ser

 

Lys

Trp

In lab you explored the structure of lysozyme using computational software. What insight could be gained about the function of lysozyme simply by observing its structure? (Choose all correct responses.)

 

location of the active site

 

rate of the enzyme-catalyzed reaction

 

amino acids that might be involved in binding the substrate or catalysis

 

catalytic efficiency of the enzyme

 

Delta G of the reaction

location of the active site

Amino acids that might be involved in binding the substrate or catalysis

The RNA world hypothesis states that life was based on RNA before DNA-based life evolved. Compare and contrast the structure/function of DNA and RNA. Based on your understanding of the structure/function of RNA compared to DNA, make an argument supporting the RNA world hypothesis. What evolutionary advantage does DNA give to modern living organisms?

DNA is a double helix structure whereas RNA is a single stranded molecule. RNA as well has intramolecular base pairing meaning that it can base pair with itself A-U and C-G and does not need that second strand like DNA does. Since RNA is able to do these things it allows for greater function as seen through mRNA, tRNA, and rRNA as well as greater mobility because it is smaller than DNA. 

 An evolutionary advantage that DNA gives modern living organisms was found by Watson and Crick and it contains genetic information templates that either side can be copied for self replication, and the building of proteins. 

Dna is more stable than RNA

It is commonly assumed by beginning science students that formation of hydrogen bonds between complementary bases drives the formation of the double helix. Explain why this is not the case. 

Single-stranded DNA molecules are hydrogen bonded ot water molecules, so these bonds must be broken in order to form new hydrogen bonds between complementary bases during formation of the double helix.

A proton exists in a solution as:

 

a water molecule.

 

a hydronium ion.

 

H⁺.

 

H₂O⁺.

 

a deprotonated water molecule.

a hydronium ion.

Which statement is INCORRECT if the buffer capacity is not consumed upon addition of a strong acid to the solution?

 

There are more protonated forms of the buffer compound than deprotonated ones.

 

The pH differs from the pK_a value of the buffer's base component.

 

There are more deprotonated forms of the buffer compound than protonated ones.

 

When hydrogen ions are added to this buffer solution they remain free.

 

Such a buffer is not actually a buffer and cannot mitigate the pH changes.

There are more deprotonated forms of the buffer compound than protonated ones.

What are the primary chemical components present in a phosphate buffer at pH = 7.4?

 

H₃PO₄ and HPO₄^2–

 

H₃PO₄ and PO₄^3–

 

H₂PO₄^– and HPO₄^2–

 

HPO₄^2– and PO₄^3–

 

H₂PO₄^– and PO₄^3–

H₂PO₄^– and HPO₄^2–

Choose the correct groups for Thr, Lys, Trp, respectively, on the basis of general chemical characteristics.

 

polar but uncharged; negatively charged; hydrophobic

 

positively charged; positively charged; polar but not charged

 

positively charged; hydrophobic; polar but not charged

 

negatively charged; hydrophobic; positively charged

 

polar but uncharged; positively charged; hydrophobic

polar but uncharged; positively charged; hydrophobic

What is the term for the combination helix-turn-helix?

 

globular protein

 

domain

 

supertetriary structure

 

motif

 

tertiary structure

motif

What is the simplest sort of quaternary structure?

 

a dimer consisting of two identical subunits

 

a tetramer consisting of two identical subunits and diverse subunits

 

a trimer consisting of two identical subunits and one diverse subunit

 

a monomer

 

a dimer consisting of two different subunits

a dimer consisting of two identical subunits

In the ribonuclease experiments performed by Anfinsen, β-mercaptoethanol reduced:

 

all charged residues, and the protein was unable to take part in signaling.

 

all incorrectly paired bonds and stabilized the protein structure.

 

all bonds, and the unfolded protein molecules became tangled up with one another to form aggregates.

 

all bonds and destroyed the protein structure.

 

incorrectly paired disulfide bonds, allowing them to reform with the correct pairing until the most stable conformation of the protein had been obtained.

incorrectly paired disulfide bonds, allowing them to reform with the correct pairing until the most stable conformation of the protein had been obtained.

The overall three-dimensional structure of a single polypeptide is referred to as _____ structure.

 

quaternary

 

supersecondary

 

secondary

 

primary

 

tertiary

tertiary

The amino acids Tyrosine, Asparagine, and Serine:

 

are negatively charged at pH = 7.0.

 

are polar.

 

have double bonds in side chains.

 

have aromatic rings.

 

are positively charged at pH = 7.0.

are polar

The term quaternary with respect to protein structure stands for:

 

a repeating structure stabilized by intrachain hydrogen bonds.

 

a multisubunit structure.

 

the only four amino acids that can form hydrogen bonds.

 

a linear sequence of four amino acids.

 

the ability to form all four kinds of noncovalent bonds.

a multisubunit structure.

What pair of amino acids is positively charged at a neutral pH?

 

Asp, Glu

 

Cys, Met

 

Leu, Pro

 

Lys, Arg

 

Tyr, Arg

Lys, Arg

What amino acid residue would MOST likely be buried in the interior of a water-soluble globular protein?

 

Ser

 

Gln

 

Lys

 

Phe

 

Asp

Phe

Protein concentration can be determined using a spectrophotometer due to protein's absorbance of light at 280 nm.

 

True

False

True

What is another name for molecular exclusion chromatography?

 

gel electrophoresis

 

high-performance liquid chromatography

 

ion-exchange chromatography

 

affinity chromatography

 

gel-filtration chromatography

gel-filtration chromatography

What method can be used to separate proteins only by their charge?

 

ion-exchange chromatography

 

affinity chromatography

 

dialysis

 

gel electrophoresis

 

gel-filtration chromatography

ion-exchange chromatography

Which technique is used to determine the amino acid sequence of proteins?

 

electrophoresis.

 

ion-exchange chromatography.

 

gel-filtration chromatography.

 

tandem mass spectrometry.

 

affinity chromatography.

tandem mass spectrometry.

Knowledge of the amino acid sequences is important for several reasons. What is NOT one of those reasons?

Knowledge of the sequence of a protein can help to prevent mutations.

An α helix is a coil stabilized by:

 

extrachain hydrogen bonds between the carbonyl hydrogen of a residue and the amide oxygen of the third residue away.

 

intrachain nitrogen bonds between the carbonyl nitrogen of a residue and the amide nitrogen of the second residue away.

 

intrachain nitrogen bonds between the carbonyl nitrogen of a residue and the amide nitrogen of the sixth residue away.

 

extrachain oxygen bonds between the carbonyl oxygen of a residue and the amide nitrogen of the fifth residue away.

 

intrachain hydrogen bonds between the carbonyl oxygen of a residue and the amide hydrogen of the fourth residue away.

  intrachain hydrogen bonds between the carbonyl oxygen of a residue and the amide hydrogen of the fourth residue away.

A β sheet is formed by linking two or more β strands lying next to one another through:

 

ionic bonds.

 

disulfide bridges.

 

nitrogen bonds.

 

hydrogen bonds.

 

oxygen bonds.

hydrogen bonds.

What level of protein structure is composed of α helices, β sheets, and turns?

 

supersecondary

 

primary

 

tertiary

 

secondary

 

quaternary

secondary

Which of the following have an influence on the tertiary structure of a protein? (Choose all correct responses.)

 

solvent

 

primary structure

 

rotation of the peptide bonds

 

interaction with other molecules

primary structure

 

rotation of the peptide bonds

 

interaction with other molecules

What amino acid residue would MOST likely be buried in the interior of a water-soluble globular protein?

 

Ser

 

Asp

 

Lys

 

Trp

 

Arg

Trp

Suppose you have grown a culture of bacteria that have been engineered to express a protein that binds glucose. You would like to purify this protein. List in order a sequence of three techniques that you might employ to purify this protein. Briefly, explain what is accomplished with each technique.

centifugation to seperate the the solids and salts, size exclusion for the smaller molecules to go through, then affinity such as glucose binding protein to see if that protein binds

Explain how comparing the amino acid sequence of a protein like lysozyme from several different species can provide insight into the nature of the functional regions of the protein, such as the active site, for example.

Comparing amino acid sequences from several different species allows us to know what amino acids are essential for the function of the protein. When looking at the active site specifically and the amino acids present there we can compare what amino acids are similar between various species to see what type of substrate would bind. This would give us insight into the function of the protein between all species and if a hydrophobic, charged, polar, etc substrate binds to the active site of the lysozyme and how the amino acid structure effects the function. 

What molecule stores oxygen in muscle cells?

 

myoglobin

 

individual β subunits of hemoglobin

 

individual α subunits of hemoglobin

 

hemoglobin

 

metmyoglobin

myoglobin

As the partial pressure of carbon dioxide increases, the affinity of oxygen binding to hemoglobin:

 

increases.

 

decreases.

 

increases then decreases.

 

stays the same.

 

decreases then increases.

decreases.

Select all that apply. The binding of 2-3-bisphosphogycerate to the T state of hemoglobin:

 

stabilizes the equilibrium between T and R states.

 

increases its affinity for oxygen binding.

 

pushes the equilibrium between T and R states toward the T state.

 

displaces oxygen from hemoglobin.

 

decreases its affinity for oxygen binding.

pushes the equilibrium between T and R states toward the T state

decreases the affinity for oxygen binding

What is the Bohr effect?

 

the ability of myoglobin to retain oxygen when competing for a substrate with hemoglobin

 

the regulation of oxygen binding by hydrogen ions and carbon dioxide

 

the alteration of hemoglobin conformation in the presence of carbon monoxide

 

the ability of hemoglobin to retain oxygen when competing for a substrate with myoglobin

 

the regulation of oxygen binding by 2,3-BPG

the regulation of oxygen binding by hydrogen ions and carbon dioxide

The Bohr effect influences the oxygen-binding curve by:

 

making the oxygen-binding curve sharper.

 

shifting the oxygen-binding curve to the left.

 

shifting the oxygen-binding curve to the right.

 

shifting the oxygen-binding curve up and to the right.

 

making the oxygen-binding curve smoother.

shifting the oxygen-binding curve to the right.

What type of binding is indicated by a sigmoidal-shaped binding curve?

 

uncooperative

 

cooperative

 

competitive

 

noncompetitive

 

reversible

 

cooperative

What statement is CORRECT concerning the oxygenation plot of proteins X and Y shown below?

 

Proteins X and Y contain a single binding site.

 

Protein X corresponds to myoglobin, and protein Y corresponds to hemoglobin.

 

Protein X exhibits tighter oxygen binding than protein Y.

 

Protein Y exhibits tighter oxygen binding than protein X.

 

Protein X corresponds to hemoglobin, and protein Y corresponds to myoglobin.

Protein X exhibits tighter oxygen binding than protein Y.

Consider the oxygen-binding profile at three different pH values of 7.6, 7.4, and 7.2. Which statement is MOST accurate?

 

Hb has a higher affinity for oxygen at the pH of curve Z.

 

Curve Y most likely corresponds to pH 7.4.

 

pH has no effect on oxygenation of hemoglobin.

 

Curve X most likely corresponds to pH 7.2.

 

Curve Z most likely corresponds to pH 7.6.

Curve Y most likely corresponds to pH 7.4.

A reason hemoglobin is sensitive to changes in pH is that the T state of hemoglobin is stabilized by a salt bridge between β1 Asp 94 and the C-terminal _____ of the β1 chain.

 

proline

 

lysine

 

serine

 

tyrosine

 

histidine

histidine

What is the structure of the hemoglobin molecule?

 

α₁β₂ trimer

 

α₂β₁ trimer

 

α₂ dimer

 

β₂ dimer

 

α₂β₂ tetramer

 

α₂β₂ tetramer

How does oxygen binding change the quaternary structure of hemoglobin?

 

After oxygen binding, one αβ dimer of hemoglobin shifts with respect to the other by a rotation of 15 degrees. It increases the binding affinity of other sites.

 

After oxygen binding, one αβ dimer of hemoglobin shifts with respect to the other by a rotation of 180 degrees. It decreases the binding affinity of other sites.

 

After oxygen binding, the hemoglobin protein denatures, which increases the binding affinity of other sites.

 

After oxygen binding, one αβ dimer of hemoglobin shifts with respect to the other by a rotation of 15 degrees. It decreases the binding affinity of other sites.

 

After oxygen binding, the iron atom pulls on the proximal lysine residue.

After oxygen binding, one αβ dimer of hemoglobin shifts with respect to the other by a rotation of 15 degrees. It increases the binding affinity of other sites.

Oxygen binding at the coordination site causes:

 

release of the iron atom from the heme prosthetic group

 

the iron atom to move from the plane of the porphyrin towards the outside.

 

the iron atom to rearrange the electrons to become effectively larger.

 

formation of the hemoglobin tetramer

 

the iron atom to move from outside the plane of the porphyrin into the plane.

the iron atom to move from outside the plane of the porphyrin into the plane.

Oxygen binding to hemoglobin is dependent on the partial pressure of oxygen. From a physiological perspective, why is this important?

Aside from partial pressure of oxygen, there are other mechanisms that influence hemoglobin's affinity for oxygen. From a physiological perspective what is the value of having all of these different ways of fine-tuning the affinity of hemoglobin for oxygen?

Having hemoglobin depend on the partial pressure of oxygen for oxygen binding allows for oxygen to be delivered properly to its respective place. For example, hemoglobin has a lower binding affinity in tissues compared to myoglobin because hemoglobin does most of its oxygen delivery to the tissues. If hemoglobin had a high affinity at the partial pressure where tissues were then oxygen would not be released from hemoglobin and be delivered to the tissues. 

Another mechanism that influences hemoglobin's affinity could be pH which is important for the physiological pH of blood is around 7.4. If it becomes too acidic or basic for example: CO2 becoming carbonic acid then the oxygen affinity to hemoglobin would change to adjust to that discrepancy. Or the binding of 2,3 BPG to stabilize the T state occurs less frequently in the fetus so that hemoglobin has a higher affinity for oxygen compared to adults were the affinity foroxygen is less. 

A system is at equilibrium when

 

ΔG for the system is zero.

 

ΔG for the system is positive.

 

ΔG for the system is negative.

 

ΔH for the system is zero.

 

ΔH for the system is negative.

ΔG for the system is zero.

The ΔG of a reaction depends on the:

 

free energy of activation.

 

nature of the reactants alone.

 

difference in free energy between the reactants and the products.

 

nature of the products alone.

 

molecular mechanism of the transformation.

 

difference in free energy between the reactants and the products.

When ΔG° for a reaction is positive:

 

the reaction is exergonic and can take place spontaneously regardless of concentrations of reactants and products.

 

the reaction's spontaneity depends on the concentrations of the reactants and products.

 

the reaction is endergonic and cannot take place spontaneously regardless of concentrations of reactants and products.

 

the reaction is endergonic and can take place spontaneously.

 

the reaction is exergonic and cannot take place spontaneously.

the reaction's spontaneity depends on the concentrations of the reactants and products.

A reaction can occur spontaneously only if ΔG is:

positive.

lower than ΔG°

higher than ΔG°

zero.

negative.

 

negative.

What statement about enzymes is CORRECT?

 

Enzymes alter the standard free energy of the reaction.

 

All known enzymes are proteins.

 

They accelerate reactions by factors of as much as a million or more.

 

These molecules alter the equilibrium of the reaction.

 

Enzymes force reactions to proceed in only one direction.

They accelerate reactions by factors of as much as a million or more.

Select all that apply. Examples of cofactors include:

 

subunits

 

proteins

 

polypeptides

 

vitamins

 

Zn²⁺, Mg²⁺, and Ni²⁺.

vitamins

 

Zn²⁺, Mg²⁺, and Ni²⁺.

What term describes an enzyme with its cofactor?

 

holoenzyme

 

coenzyme

 

ligase

 

apoenzyme

 

inactive enzyme

holoenzyme

Prosthetic groups are referred to as:

 

apoenzymes.

 

holoenzymes.

 

coenzymes.

 

active sites.

 

inhibitors.

coenzymes.

A system is at equilibrium when

 

ΔG for the system is zero.

 

ΔG for the system is negative.

 

ΔG for the system is positive.

 

ΔH for the system is zero.

 

ΔH for the system is negative.

ΔG for the system is zero.

The standard conditions for ΔGº are:

 

100 kPa, [reactants] 1.0 M, [OH^–] 10^–5, 25ºC.

 

100 kPa, [reactants] 1.0 M, [H⁺] 10^–7, 25ºC.

 

100 kPa, [products] 1.0 M, [OH^–] 10^–1, 20ºC.

 

100 kPa, [reactants] 1.0 M, [OH^–] 10^–7, 0ºC.

 

100 kPa, [products] 1.0 M, [H⁺] 10^–1, 25ºC

100 kPa, [reactants] 1.0 M, [H⁺] 10^–7, 25ºC.

Which type of reaction requires an input of energy to proceed?

 

reversible reaction

 

irreversible reaction

 

catalyzed reaction

 

exergonic reaction

 

endergonic reaction

endergonic reaction

The ΔG of a reaction depends only on the:

 

free energy of activation.

 

molecular mechanism of the transformation.

 

difference in free energy between the final and initial states.

 

nature of the reactants.

 

nature of the products.

difference in free energy between the final and initial states.

Choose the CORRECT statement about enzymes.

 

Enzymes shift the equilibrium of a chemical reaction.

 

Enzymes increase the number of products of a chemical reaction.

 

Enzymes increase the rate of a chemical reaction.

 

Enzymes decrease the free energy of reactants.

 

Enzymes decrease the rate of a chemical reaction.

Enzymes increase the rate of a chemical reaction.

The Gibbs free energy of activation is the difference between the:

 

substrate and the transition state.

 

substrate and the product.

 

product and the transition state.

 

substrate and the final state.

 

final and initial states.

substrate and the transition state.

What is the main difference in the lock-and-key and induced-fit models of enzyme–substrate binding?

 

According to the lock-and-key model, the active site has a free structure. According to the induced-fit model, the active site has a rigid structure.

 

According to the lock-and-key model, the active site forms a shape complementary to the substrate only after the substrate has been bound. According to the induced-fit model, the active site is complementary in shape to the substrate.

 

According to the lock-and-key model, the active site binds to the substrate to form a transition state. According to the induced-fit model, the active site binds to the substrate to form a final state.

 

According to the lock-and-key model, the only certain conformation of the active site is complementary to the substrate. According to the induced-fit model, several conformations of the active site are complementary to the substrate.

 

According to the lock-and-key model, an enzyme increases a reaction by decreasing the activation energy. According to the induced-fit model, an enzyme increases a reaction by facilitating the formation of the transition state.

According to the lock-and-key model, the only certain conformation of the active site is complementary to the substrate. According to the induced-fit model, several conformations of the active site are complementary to the substrate.

Which type of the multiple substrate reaction is shown?

 

ordered sequential reaction

 

random sequential reaction

 

double-displacement reaction

 

ordered displacement reaction

 

double sequential reaction

ordered sequential reaction

According to the Michaelis–Menten model, K_M equals the substrate concentration at which the reaction rate is:

 

minimal.

 

at half of its maximal value.

 

maximal.

 

twice its maximal value.

 

a third of its maximal value.

at half of its maximal value.

The turnover number per second of carbonic anhydrase is 600,000. The total number of resulting ions of bicarbonate per 1 minute is:

 

600,000.

 

300,000.

 

36,000,000.

 

3,600,000.

 

18,000,000.

36,000,000.

What shape does the curve of initial velocity versus substrate concentration for allosteric enzymes have?

 

sigmoidal

 

hyperbolic

 

parabolic

 

linear

 

logarithmic

sigmoidal

When substrate concentration is much greater than K_M, the reaction is:

 

first order with a maximum rate.

 

zero order with a maximum rate.

 

second order, independent of the substrate concentration.

 

zero order with a minimal rate.

 

pseudo-first order, independent of the substrate concentration.

zero order with a maximum rate.

A substituted enzyme intermediate is a modified enzyme in a _____ reaction.

 

double-displacement

 

random sequential

 

ordered sequential

 

allosteric

 

concerted displacement

double-displacement

When the k_cat:K_M ratio is at its upper limit, it is referred to as:

 

Circe limit.

 

Michaelis rate.

 

kinetic perfection.

 

turnover number.

 

kinetic deficiency.

kinetic perfection.

The active site of an enzyme:

 

is a three-dimensional cavity, formed by a coenzyme.

 

occupies a significant part of an enzyme.

 

consists of unique microenvironments formed by water molecules.

 

binds to the substrate by multiple weak attractions.

 

binds to the substrate after a prolonged contact.

 

binds to the substrate by multiple weak attractions.

What compound mimics the structure of the transition state of an enzyme?

 

transition-state analog

 

affinity label

 

mechanism-based inhibitor

 

suicide inhibitor

 

reactive substrate analog

 

transition-state analog

In a Lineweaver–Burk plot, the presence of a competitive inhibitor will alter:

 

V_max.

 

[S].

 

the intercept on 1/V_max.

 

the intercept on 1/[S].

 

the slope of the curve.

the intercept on 1/[S].

 

the slope of the curve.

Carbonic anhydrase is reported to:

 

catalyze the hydration of carbonic acid.

 

add a water molecule to carbonic acid.

 

catalyze the hydration of carbonic dioxide.

 

catalyze carbonic acid synthesis.

 

add a phosphate group to carbonic dioxide.

 

catalyze the hydration of carbonic dioxide.

 

catalyze carbonic acid synthesis.

What can reduce the effect of a competitive inhibitor of an enzyme?

 

increased substrate concentration

 

decreased reaction temperature

 

increased reaction temperature

 

increased coenzyme concentration

 

increased enzyme concentration

increased substrate concentration

What possesses the highest free energy?

 

reactant

 

product

 

transition state

 

final state

 

initial state

transition state

When ΔG for a reaction is positive:

 

the reaction is endergonic and can take place spontaneously.

 

the reaction is exergonic and can take place spontaneously at preceding concentrations.

 

the reaction is endergonic and cannot take place spontaneously at preceding concentrations.

 

the reaction is exergonic and cannot take place spontaneously.

 

the reaction's spontaneity depends on the concentrations of the reactants and products.

the reaction's spontaneity depends on the concentrations of the reactants and products.

What allows comparing an enzyme's preference for different substrates?

 

specificity constant

 

dissociation constant

 

Michaelis constant

 

rate constant

 

turnover number

dissociation constant

A reaction can occur spontaneously only if ΔG is:

 

negative.

positive.

zero.

lower than ΔG°

higher than ΔG°.

negative.

What type of inhibitor binds to a site other than the catalytic site? Select all that apply.

 

alternative inhibitor

 

allosteric inhibitor

 

transition-state analog

 

competitive inhibitor

 

group-specific inhibitor

allosteric inhibitor

What macromolecules possess catalytic activity? Select all that apply.

 

proteins

 

nucleic acids

 

lipids

 

carbohydrates

 

vitamins

proteins

 

nucleic acids

What types of inhibition are reversible? Select all that apply.

 

competitive

 

noncompetitive

 

mixed

 

uncompetitive

 

suicide

 

competitive

 

noncompetitive

 

mixed

 

uncompetitive

The site on an enzyme where the reaction that is catalyzed by the enzyme occurs is the _____ site.

 

binding

 

substrate

 

allosteric

 

regulatory

 

active

active

What statement about enzymes is CORRECT?

 

Enzymes force reactions to proceed in only one direction.

 

These molecules alter the equilibrium of the reaction.

 

Enzymes alter the standard free energy of the reaction.

 

All known enzymes are proteins.

 

They accelerate reactions by factors of as much as a million or more.

They accelerate reactions by factors of as much as a million or more.

If a reaction is exergonic at specific reactant concentrations, it is considered:

 

to be at equilibrium.

 

nonspontaneous.

 

spontaneous.

 

irreversible.

 

that ΔG is positive.

spontaneous.

Five K_M values are given for the binding of substrates to a particular enzyme. Which has the strongest affinity when k_–1 is greater than k₂?

 

150 mM

 

0.15 mM

 

150 µM

 

1.5 nM

 

15 000 pM

1.5 nM

Which of the following is TRUE under the following conditions: the enzyme concentration is 5nM, the substrate concentration is 5 mM, and the K_M is 5 µM? Select all that apply.

 

The enzyme is saturated with the substrate.

 

Most of the enzyme does not have substrate bound.

 

There is more enzyme than substrate.

 

There is more substrate than enzyme.

 

Concentration of the ES complex is higher than substrate concentration.

The enzyme is saturated with the substrate.

There is more substrate than enzyme.