Homework Questions: Exam 1 Flashcards
In a reaction, H = -81 kj*mol^-1
highly exothermic
What term is used to describe the exclusion of non polar substances from an aqueous solution?
hydrophobic effect
Which of the following functional groups could NOT act as a hydrogen bond donor?
a) ester
b) an aldehyde
c) both ester and aldehyde
d) amino
e) hydroxyl
c) both an ester and aldehyde
molecules such as methanol and ethanol are very soluble in water because _____________.
they contain O-H groups that can form multiple H-bonds with water
Which of the following is an example of hydrophobic effect?
a) the lipid membrane of cells and organelles
b) protein folding that places hydrophobic AA is the interior of the proton
c) separation of salad dressing
d) oil sheens seen on the ocean following an oil spill
e) all of the above
e) all of the above
in a water molecule, hydrogen are partially _______; oxygens are partially ________.
positive; negative
a molecule that has both a polar and non polar region called _____________.
amphiphilic
What is the pH of a solution made by mixing equal volumes of 1 M sodium acetate and 0.1 M acetic acid? (pK of acetic acid is 4.76)
5.76
If we desire to make a buffer solution with a pH=5, which of the following acids can be used
a) acetic acid (Ka=1.810^-5)
b) HCN (Ka=6.210^-10)
c) HF (Ka=4.2*10^-4)
d) H2SO4 (Ka=10^3)
a) acetic acid (Ka=1.8*10^-5)
Considering a 0.1 M formic acid buffer, what is the concentration of formic acid present in a solution of pH 4.25 if the pK of formic acid is 3.75?
HA = 0.024 M
a buffer solution has the following characteristic:
a) pH=pKa + 2 is the buffer capacity
b) it is a solution of any acid and its conjugate base
c) pH is unaffected by dilution
d) pH=pKa + log (weak acid/conjugate base)
c) pH is unaffected by dilution
Which statement best explains why buffers are best made when the desired pH is within one unit of the corresponding weak acid’s pK?
a solutions typically resist changes in pH up to the point where the molar concentrations of weak acid and conjugate base are within a factor of 10
in the equation H2PO4- + H2O === HPO4^2- + H3O+ , what is the acid and conjugate base
- H2PO4- (ACID)
- HPO4^2- (conjugate base)
50 ml of 0.18 M solution of a HNO2 (Ka=4.5*10^-4) is added to a 35 ml of 0.16 M solution of KNO2. What is the pH of the resulting solution?
3.14
If we desire to make a buffer solution with a pH=3 using HNO2 and NaNO2, what should be the concentration ratio of weak acid to conjugate base? (pKa=3.35)
2.2
What is the pH pf a buffer solution consisting of 0.093 M acetic acid and 0.12 M sodium acetate? for acetic acid, pKa=4.76
4.87
The buffer compound has a pK of 8.3. What is its useful buffering range?
pH 7.3-9.3
Which of the following best describes the side chains of the non polar amino acids (glycine is not included)?
they are primarily neutral hydrocarbon structures
What amino acid has a side chain containing a sulfhydryl group?
cysteine
three of the 20 AA that are incorporated into proteins are aromatic they are:
tyrosine, phenylalanine, tryptophan
Why is Gly considered achiral?
because guy’s side chain is a H atom
Which amino acid side chain cannot form a hydrogen bond:
a) tyrosine
b) valine
c) tryptophan
d) glutamine
b) valine
Which AA side chain is aromatic?
a) threonine
b) phenylalanine
c) alanine
d) glutamic acid
b) phenylalanine
How many charged groups do ALL isolated AA have at physiological pH?
more than 1
What is the net charge at 7 PH on a peptide with the sequence: Ala-Thr-Leu-Asp-Ala-Lys-Pro-Glu
-1
What is the net overall charge on glutamic acid at pH 12?
-2
There are several AA side chains which are always charged at physiological pH. These are:
glu, asp, lys, and arg
T/F: The condensation of 2 AA yield a peptide bond and a molecule of water
True
Which of the following statements about peptide bonds is FALSE. Peptide bonds are:
a) involved in forming the primary structure of proteins
b) amides
c) regid and planar, with partial double bond character
d) charged
e) covalent
d) charged
Which of the following statements is FALSE?
a) both a-helices and B-sheets form adjacent (sequential) amino acid residues in the polypeptide
b) both a-helices and B-sheets have R groups that are oriented away from the core structure
c) both a-helices and B-sheets have conformations that minimize steric strain in the polypeptide backbone
d) both a-helices and B sheets are stabilized by hydrogen bonds in the polypeptide
a) both a-helices and B-sheets form adjacent (sequential) amino acid residues in the polypeptide
Which functional groups of a peptide bond can form h-bonds with water?
a) only the amino group
b) only the carbonyl group
c) both the amino group and the carbonyl group
c) both the amino group and the carbonyl group
What stabilizes the polypeptide backbone into regular secondary structure?
hydrogen bonds
What is the major factor that “drives” the folding of proteins into their tertiary structures?
placement of hydrophobic amino acid residues within the interior of the protein
Which one of the following sequences of 5 amino acids would most likely be located in the interior of a globular soluble protein?
a) Glu-Asn-Ser-Thr-Gln
b) Met-Cys-Pro-His-Tyr
c) Met-Phe-Pro-Ile-Leu
d) Val-Ala-Val-Glu-Val
c) Met-Phe-Pro-Ile-Leu
Which of the following series of amino acids is most likely to be buried in the center of a water-soluble globular protein?
a) Glu-Asp-Leu
b) Gly-Asn-Ser
c) Ala-Leu-Phe
d) Pro-Gln-His
c) Ala-Leu-Phe
A protein with a quaternary structure…
a) contains more than one subunit
b) has twice the normal amount of secondary structure
c) contains only 4 types of amino acids
d) is not stabilized by the hydrophilic effect
a) contains more than one subunit
Which of the following diseases has been linked to protein misfolding?
a) shingles
b) diabetes
c) aids
d) tuberculoses
e) malarian
f) Creutzfeldt-Jakob disease
f) creutzfeldt-Jakob disease
The aggregation of a misfiled protein may lead to…
a) a neurodegeneration disease
b) nerve cell degeneration
c) the accumulation of starch
d) a bacterial infection
a) a neurodegeneration disease
Which of the following statements about hemoglobin is TRUE?
a) in the Bohr effect the binding of oxygen to hemoglobin is increased by the presence of H+ ions
b) the affinity of fetal hemoglobin for oxygen is higher than that of maternal hemoglobin
c) variations in the primary structure of hemoglobin always results in genetic diseases
d) hemoglobin differs from myoglobin because it contains more B-pleated sheet structure
b) the affinity of fetal hemoglobin for oxygen is higher than that of maternal hemoglobin
What are the 2 conformations of hemoglobin?
- T state (confirmation of deoxyhemoglobin)
- R state (conformation of oxyhemoglobin)
The C-terminal His 146 on the B chain of hemoglobin also forms an interaction with Lys residue on the neighboring a-chain in the T form. What is the nature of the interaction?
a) H bonding
b) ion pairing
c) dipole-dipole forces
d) London dispersion forces
b) ion pairing
Collagen has an unusual amino acid composition because…
a) collagen genes are highly prone to mutations
b) some amino acids are unstable in the extracellular matrix
c) certain residues must interact with vitamin C
d) only certain residues can form triple helix
d) only certain residues can form triple helix
During the initial synthesis of collagen molecule ___________ and ____________ are most often incorporated into the growing protein.
Gly, Pro
The ability for an enzyme to pick out one particular substrate from the myriad of molecules floating around its environment is an example of ________________.
a) natural selection
b) specificity
c) high affinity
d) processivity
e) none of the above
b) specificity
Which of the following is FALSE with respect to an enzyme catalyzed reaction?
a) enzyme catalyzed reactions are superior to chemically catalyzed reactions because they are more specific and they lack side products
b) enzymes increase a reaction rate by binding the transition state more highly than the substrate (s).
c) enzymes increase the kinetic an thermodynamic favorability of a reaction
d) enzymes lower the activation energy of a reaction to increase the reaction rate
c) enzymes increase the kinetic an thermodynamic favorability of a reaction
How does a catalyst increase the rate of a reaction?
a) it makes the reaction more exergonic
b)it increases the temperature of the reaction
c) it allows molecules to more easily from the transition state
d) it causes a localized increase in the concentration of reactants
e) non of the above
c) it allows molecules to more easily from the transition state
What represents the overall free energy change of the catalyzed reaction?
(triangle) G
Which statement expresses the correct relationship between cosubstrates, coenzymes, and cofactors?
___________ are __________ that transiently bind to enzymes, while ___________ are ___________ that are organic compounds
cosubstrates are coenzymes that transiently bind to enzymes, while coenzymes are cofactors that are organic compounds
To catalyze a reaction, an enzyme must do which of the following?
a) raise the free energy of activation to a value above that of the uncatalyzed reaction
b) raise the free energy of activation to a value above the free energy of the reactants and products
c) lower the free energy of activation to a value below that of the uncatalyzed reaction
d) lower the free energy of activation to a value below the free energy of the reactants and products
c) lower the free energy of activation to a value below that of the uncatalyzed reaction
Which of the following is one way in which metal ions participate in the catalytic process?
a) by shielding positive charge
b) by mediating oxidation-reductase through irreversible changes in the metal’s oxidation state
c) by binding to substrates to orient them properly for reaction
d) by making water molecules more basic
c) by binding to substrates to orient them properly for reaction
The difference in free energy between the substrate and product of reaction catalyzed by Enzyme A is negative and small. What conclusions can be drawn about this reaction?
a) the reaction is not spontaneous and is slow
b) the reaction is spontaneous and its speed is unknown from these data
c) the reaction is spontaneous but slow
d) the reaction is spontaneous and fast
b) the reaction is spontaneous and its speed is unknown from these data
The ability for an enzyme to change its shape upon substrate binding represents the concept of ___________
induced fit
what model does this description fit? “enzyme-substrate binding induces a conformational change in the enzyme, such that the binding site better conforms to the shape of the substrate”
induced fit
The molecule chymotrypsinogen is known as a(n) ____________.
a) apoenzym
b) holoenzyme
c) protease inhibitor
d) zymogen
e) none of the above
d) zymogen
Which of the following is the BEST explanation for the frequent appearance of His side chains in enzyme active sites?
a) the His side chain is negatively charged
b) the His side chain is able to act as both an acid and base under physiological conditions
c) the His side chain is non-polar an therefore typically located away from the surface of globular proteins
d) the His side chain plays a major role in non-covalent binding interactions with substrates
b) the His side chain is able to act as both an acid and base under physiological changes
…..manufacturers of tofu treat it to eliminate serine protease inhibitors. Why is the treatment necessary?
a) serine protease inhibitors would interfere with digestion of proteins
b) serine protease inhibitors would increase the pH of the small intestine
c) serine protease inhibitors would decrease the pH of the small intestine
d) none of the above
a) serine protease inhibitors would interfere with digestion of proteins
Chymotrypsin has large specificity pocket to bind the aromatic amino acids while elastase has a very small specificity pocket meant to bind to Ala or Gly. Which of the following AA substitutions changes the specificity pocket of chymotrypsin to that of elastase?
Gly—>Val
A molecule decreases the activity of an enzyme by binding to a site other than the active site. What is the name of this molecule?
an allosteric inhibitor
The graph illustrates the activity of various enzymes, where the rate of the reaction (v) is plotted as a function of substrate concentration. Which curve represents the activity of a non-allosteric enzyme?
1
When a substrate and enzyme interact, the first chemical species formed is __________________.
enzyme-substrate complex
In the graph shown which of the following statements is TRUE concerning the “plateau” region of the curve?
the enzymes active site is saturated
For an enzyme that displays Michaelis-Menton kinetics, what is the effect of a competitive inhibitor on Vmax?
a) it may increase or decrease
b) it increases
c) there is no effect
d) it decreases
c) there is no effect
A line weaver-birk plot is a _________.
a) double reciprocal plot
b) sigmoidal plot
d) Michaelis-Menton plot
c) logarithmic plot
d) hyperbolic plot
a) double reciprocal plot
Which of the following statements is INCORRECT with respect to allosteric enzymes?
a)allosteric enzymes must have quaternary structure
b) allosteric enzymes have two states, one that has low activity and one that has high activity
c) allosteric enzymes bind molecules that cause a change in the tertiary structure on the protein
d) allosteric enzymes always have hyperbolic reaction kinetics
d) allosteric enzymes always have hyperbolic reaction kinetics
For an enzyme that displays Michaelis-Menton kinetics, what is the effect of a competitive inhibitor on Km?
a) it may increase or decrease
b) there is no effect
c) it decreases
d) it increases
d) it increases
The catalytic constant, kcat, is also known as the __________.
turnover number
some irreversible inhibitors are called _________________ because they bind to the active site of the enzyme and begin the catalytic process, just like a normal substrate.
suicide substances
Which of the following statements about the enzyme whose activity is illustrated in curve 5 is TRUE?
a) this enzyme does not have quaternary structure
b) this enzyme most likely catalyses a metabolically reversible (equilibrium) reaction
c) the substrate of this enzyme inhibits its activity
d) this enzyme undergoes a change in shape via process termed cooperativity
d) this enzyme undergoes a change in shape via process termed cooperativity
In the figure, Curve C represents a graph of reaction rate vs substrate concentration for an allosteric enzyme. Which of the remaining curves in this figure would represent the same enzyme in the presence of a heteroallosteric inhibitor?
curve D
A reversible inhibitor that binds to a site other than the active site regardless of whether or not the substrate is bound is a _____________.
noncompetitive inhibitor
Which two curves, of the combinations listed, most accurately illustrate how the activity of an allosteric enzyme differs in the absence and presence of Ann allosteric activator?
absence of activator curve ___; presence of activator curve ___
absence of activator curve 3; presence of activator curve 2
In which clinical trial phase is the prospective drug tested on healthy volunteers to identify a safe dosage range?
Phase 1
