Studied by 58 people
Which statement about DNA structure is INCORRECT?
It is a branched polymer with a flexible backbone.
The DNA backbone is built of repeating sugar–phosphate units.
Each DNA strand has directionality due to identical orientation of the sugar–phosphate units.
Each sugar is connected to two phosphate groups through different linkages.
Its structure is a double helix composed of two intertwined strands.
it is a branched polymer with a flexible backbone
What makes water a versatile solvent?
stabilization of large molecular complexes
ease of breaking different bonds
irreversible breakage of different bonds
simultaneous formation of a large number of hydrogen bonds
stabilization by large molecular complexes
simulataneous formation of a large number of hydrogen bonds
Which statement about covalent bonds is INCORRECT?
A covalent bond is formed by the sharing of a pair of electrons between adjacent atoms.
If more than one electron pair is shared, then a covalent bond becomes stronger.
Existence of several resonance structures of nearly equal energies decreases stability of a compound.
Some molecules possess several patterns of covalent bonding.
The key properties of a bond are length and energy.
existence of several resonance structures of nearly equal energies decreases stability of a compound
What is the energy of an ionic interaction?
the product of a proportionality constant and charges of two atoms divided by the product of the dielectric constant and the distance between atoms
the product of the dielectric constant and a sum of two charges divided by the product of the proportionality constant and the distance between charges
the product of the dielectric constant and the distance between atoms divided by the product of the proportionality constant and charges of two atoms
the product of the dielectric constant and two charges subtracted from the product of the proportionality constant and the distance between charges
the difference between the proportionality constant and charges of two atoms multiplied by the dielectric constant
the product of a proportionality constant and charges of two atoms divided by the product of the dielectric constant and the distance between atoms
What is the reason for the existence of the hydrophobic effect?
the tendency of water molecules to make a bond with hydrophobic proteins
the tendency of polar 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
the inability of charged molecules to dissolve in water
the property of nucleic acids to dissolve in water
the tendency of nonpolar molecules to self-associate in the prescence of an aqueous solution
Which statement about noncovalent bonds is CORRECT?
Five fundamental noncovalent bonds differ in their geometry, strength, and specificity.
In the strongest hydrogen bonds, all their components lie along a straight line.
The transient asymmetry in the electronic charge distribution of one atom can induce a complementary asymmetry in the neighboring atoms due to hydrophobic interactions.
The release of water from more ordered structures is unfavorable.
Very strong repulsive forces become dominant at distances greater than the van der Waals contact distance.
in the strongest hydrogen bonds, all their components lie along a straight line
Which statement about ionic interactions in the formation of the DNA double helix is CORRECT?
Separation of negatively charged phosphate groups with distances greater than 10 Å prevents unfavorable interactions.
Only favorable ionic interactions take place when two strands of DNA come together.
Ionic interactions cause the formation of the double helix.
Disposition of negatively charged phosphate groups with distances greater than 10 Å provides only favorable interactions.
Some unfavorable ionic interactions take place when two strands of DNA come together.
some unfavorable ionic interactions take place when two strands of DNA come together
Which statement about the role of hydrogen bonds in DNA double helix formation is INCORRECT?
The hydrophobic effect contributes to the favorability of base stacking.
Hydrogen bonds contribute greatly to the overall process of double helix formation.
There are more hydrogen bonds with water than bonds between the bases in single-stranded DNA.
When two single strands come together, hydrogen bonds with water are broken and new hydrogen bonds between the bases of two DNA strands are formed.
Hydrogen bonds contribute greatly to the specificity of bases binding.
Hydrogen bonds contribute greatly to the overall process of double helix formation.
Which statement about nonpolar interactions in the formation of the DNA double helix is INCORRECT?
Van der Waals interactions are nearly optimal in a double-helical structure.
Nonpolar surfaces of the bases are moved into contact with each other due to a more complete base stacking.
Nucleotide bases tend to stack even in single-stranded DNA molecules.
The separation distance of the planes of adjacent bases needs to be adjusted for the favorable van der Waals contacts.
Surface complementarity maximizes the formation of hydrogen bonds and van der Waals interactions while minimizing the nonpolar surface area exposed to the aqueous environment.
The separation distance of the planes of adjacent bases needs to be adjusted for the favorable van der Waals contacts.
What is FALSE regarding the laws of thermodynamics?
Energy can be neither created nor destroyed.
The local decrease in enthalpy will increase the entropy of the surroundings.
Heat is a manifestation of the kinetic energy associated with the random motion of molecules.
Within chemical systems, potential energy is related to the likelihood that atoms will store energy in some form.
Ordered structures can be formed within a system only if the entropy of the surroundings will proportionally increase.
Within chemical systems, potential energy is related to the likelihood that atoms will store energy in some form.
The heat content of a system is called:
entropy.
enthalpy.
kinetic energy.
potential enthalpy.
kinetic entropy.
enthalpy
Why does a spontaneous chemical process always increase the entropy of the universe?
The system entropy will increase if and only if the entropy of surroundings is greater than the ratio of the heat transferred to the surroundings and their temperature.
The total entropy will increase if and only if the product of temperature and the change in system entropy is lower than zero.
The total entropy will increase if and only if the change in enthalpy is lower than zero.
The system enthalpy will increase only when the change in temperature is greater than zero.
The total entropy will increase if and only if the entropy of a system is greater than the ratio of the heat transferred to surroundings and their temperature.
The total entropy will increase if and only if the entropy of a system is greater than the ratio of the heat transferred to surroundings and their temperature.
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 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 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 heat to sustain constant Gibbs energy in the bath
in a water bath monitoring the change in heat to sustain a constant temperature in the bath
A proton exists in a solution as:
H+.
a water molecule.
a deprotonated water molecule.
a hydronium ion.
H2O+
a hydronium ion
What is the direct consequence of the bent shape of a water molecule?
Water is highly cohesive.
Distribution of charge is asymmetric.
Hydrogen atoms possess a net negative charge.
The oxygen atom possesses a net positive charge.
The water molecule is able to form hydrogen bonds.
distribution of charge is asymmetric
Why are free interactions of water molecules in bulk water more favorable than more ordered interactions with nonpolar compounds?
The total entropy in such interactions increases because the Gibbs free energy is positive.
The total entropy in such interactions decreases because the Gibbs free energy is negative.
The enthalpy of the ordered state is lower than the enthalpy of the bulk state.
The total entropy in such interactions increases because the Gibbs free energy is negative.
The total entropy in such interactions decreases because the Gibbs free energy is positive.
the total entropy in such interactions increases because the gibbs free energy is negative
What is the concentration of hydroxide ions [OH–] in an aqueous solution with pH 9?
10–9 M
10–14 M
105 M
9 M
10–5 M
10-5
Which statement about acid–base relations is CORRECT?
If [H+] is higher than 10–3, pH is above 3.
If [OH–] is 10–9, pH is 7.
If [H+] is lower than 10–9, pH is below 9.
If [OH–] is higher than 10–3, pH is below 3.
If [OH–] is 10–7, pH is 7.
if [OH-] is 10-7 , pH is 7
Which component of DNA bases is the most susceptible to hydroxide ions?
proton of N-1 atom of guanine base
proton of O atom of guanine base
proton of N-3 atom of thymine base
proton of O atom of adenine base
proton of N-1 atom of adenine base
proton of N-1 atom of guanine base
What is a pKa value in an acid–base reaction?
the equilibrium constant for proton dissociation
concentration of hydrogen ions in the solution
a quantitative measure of the strength of an acid in the solution
the equilibrium constant for the dissociation of water
concentration of hydroxide ions in the solution
a quantitative measure of the strenth of an acid in the solution
What is pKa of a buffer solution (pH = 5.05) containing 0.2 M sodium acetate and 0.1 M acetic acid?
4.75
0.2
0.3
4.45
1.58
4.75
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.
When hydrogen ions are added to this buffer solution they remain free.
The pH differs from the pKa value of the buffer's base component.
There are more deprotonated forms of the buffer compound than protonated ones.
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.
By which factor will the 1 M buffer sodium acetate (pKa = 4.75) increase the amount of acid required to produce a drop of pH from 7.4 to 7.3 in comparison with pure water where a respective change in [H+] is equal to 1 × 10–8 M?
5,600
60
60,000
1
600
60,000
Consider the conventional description of bonds in a Fischer projection. What is the CORRECT statement about the bonds in a Fischer projection?
Horizontal bonds project behind the page away from the viewer.
A solid wedge with the broad end away from the carbon atom denotes a bond coming away from the viewer.
The bonds to the central atom are represented by lines from that atom to the substituents.
Vertical bonds project behind the page away from the viewer.
A dashed wedge with its broad end at the carbon atom represents a bond going toward the viewer.
vertical bonds project behind the page away from the viewer
The structure of DNA described by Watson and Crick includes:
a triple helix.
a triple helix composed of three intertwined strands.
base pairs that are stacked on the inside of the double helix.
a sugar-phosphate backbone that lies on the inside of the helix.
base pairs that are stacked on the outside of the triple 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?
It allowed the DNA to twist in a helix.
The DNA could be circular.
It was a good base for the mechanism of copying genetic information.
Only one of the strands could act as a template.
The DNA sequence was determined by the sequence of RNA.
It was a good base for the mechanism of copying genetic information.
What gives proteins such a dominant role in biochemistry?
rigidity of the peptide backbone
ability to act as a blueprint
ability to self-replicate
ability to spontaneously fold into complex three-dimensional structures
usage of 40 different building blocks
ability to spontaneously fold into complex three-dimensional structures
What is the concentration of hydrogen ions in a urine sample that has a pH of 6?
10–6 M
10–8 M
106 M
10–14 M
6 M
10-6
Order the type of interactions by the bond strength in descending value.
hydrogen bonds, covalent bonds, van der Waals interactions
covalent bonds, van der Waals interactions, hydrogen bonds
van der Waals interactions, covalent bonds, hydrogen bonds
covalent bonds, hydrogen bonds, van der Waals interactions
hydrophobic interactions, hydrogen bonds, electrostatic interactions
covalent bonds, hydrogen bonds, van der Waals interactions
Which of the following is a hydrogen bond donor?
the N in H- - -N—HD
the S in S—H- - -O
the O and P in P—O- - -H
the H in O—H- - -O
the O in O—H- - -NN
the H in O-H---O
hat is the [A–]:[HA] ratio when a weak acid is in a solution one pH unit below its pKa?
1:1
1:10
10:1
2:1
1:2
1:10
Using the Henderson–Hasselbalch equation, calculate the pH of a buffer solution made from 0.20 M CH3COOH and 0.05 M CH3COO– that has pKa = 4.7.
5.3
4.1
2.5
0.4
5.0
4.1
What are the primary chemical components present in a phosphate buffer at pH = 7.4?
H3PO4 and PO43–
H2PO4– and PO43–
HPO42– and PO43–
H2PO4– and HPO42–
H3PO4 and HPO42–
H2PO4– and HPO42–
The chemical forces that contribute to the stability of the DNA due to the base stacking present in the DNA helix are:
hydrogen bonds.
van der Waals interactions.
hydrophobic interactions.
salt bridges.
charge repulsive forces.
van der Waals Interactions
Single-stranded nucleic acids can adopt complex structures through long-range interactions such as
Watson–Crick base pairing.
nonstandard hydrogen bonding.
hydrophobic effect.
hypochromic effect.
van der Waals interactions.
nonstandard hydrogen bonding
What group (or atom) of the nucleotide base is esterified to a phosphate group to bind that nucleotide to the next one?
the 3-hydroxyl (3-OH) group
the 5-hydroxyl (5-OH) group
N-1 in purines and N-9 in pyrimidines
N-9 in purines and N-1 in pyrimidines
none
none
What bonds link bases to sugars in nucleotides?
ester
α-glycosidic
β-glycosidic
phosphodiester
ether
β-glycosidic
Approximately how many base pairs are in the human genome?
about 3 × 1011
about 3 × 107
about 3 × 108
about 3 × 109
about 3 × 1010
3 x 109
Under physiological conditions, most DNA is in the form of a _______ form helix
B
What is the technique on which the Watson–Crick model was based?
absorbance spectrophotometry
electron microscopy
X-ray diffraction
radioactive labeling
spectrofluorometry
x-ray diffraction
How can the helix diameter for DNA in the A form be described as compared to other DNA forms?
broadest
narrowest
intermediate
broader than the Z form but narrower than the B form
broader than the B form but narrower than the Z form
broadest
Ribosomes are composed of:
DNA.
rRNA.
proteins.
DNA and rRNA.
rRNA and proteins.
rRNA and proteins
The temperature at which half of the DNA helical character is lost is referred to as:
Th.
Tm.
T0.5.
TDNA.
T50.
Tm
The difference in RNA bases compared with DNA bases is that RNA contains:
A instead of T.
U instead of G.
U instead of T.
A instead of U.
C instead of T.
U instead of T
Although the right-handed double helix is the most well-known DNA structure, DNA can also form:
triple strands.
straight chains.
branched chains.
left-handed helices.
tight globules.
left-handed helices
What is NOT a key property that enable proteins to participate in a wide range of functions?
Proteins have a high molecular weight.
Proteins contain different functional groups.
Some proteins are quite rigid, whereas others display considerable flexibility.
Proteins are linear polymers built of different amino acids.
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?
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, δ carbon, imine radical, hydrogen atom, distinctive R group
carboxylic acid group, α carbon, amino group, hydrogen atom, distinctive R group
What isomers of amino acids are found in proteins and what absolute configuration do they have?
L isomer; R absolute configuration
D and L isomers; R absolute configuration
L isomer; S absolute configuration
D isomer; S absolute configuration
L and D isomers; S absolute configuration
L isomer; S absolute configuration
In an acidic solution (pH = 1), what is the ionization state of an amino acid?
The amino group is deprotonated; the carboxyl group is protonated.
The amino group is not dissociated; the carboxyl group is not dissociated.
The amino group is protonated; the carboxyl group is deprotonated.
The amino group is protonated; the carboxyl group is not dissociated.
The amino group is deprotonated; the carboxyl group is not dissociated.
The amino group is protonated; the carboxyl group is not dissociated.
Choose the correct groups for Thr, Lys, His, Met, respectively, on the basis of general chemical characteristics.
polar but uncharged; negatively charged; positively charged; hydrophobic
polar but uncharged; positively charged; positively charged; hydrophobic
positively charged; hydrophobic; polar but not charged; positively charged
negatively charged; hydrophobic; positively charged; polar but not charged
positively charged; positively charged; polar but not charged; negatively charged
polar but uncharged; positively charged; positively charged; hydrophobic
Which amino acid has the one-letter abbreviation K?
histidine
asparagine
alanine
valine
lysine
lysine
The amide bond is a linkage between the:
β-amino group of one amino acid and the α-amino group of another amino acid.
β-carboxyl group of one amino acid and the β-amino group of another amino acid.
δ-carboxyl group of one amino acid and the α-carboxyl group of another amino acid.
α-amino group of one amino acid and the ε-amino group of another amino acid.
α-carboxyl group of one amino acid and the α-amino group of another amino acid.
α-carboxyl group of one amino acid and the α-amino group of another amino acid.
What is the amino-terminal residue and what is the carboxyl-terminal residue in the sequence of amino acids Gly-Tyr-Gly-Phe-Leu?
Leucine is N-terminal and glycine is C-terminal.
Glycine is N-terminal and leucine is C-terminal.
Tyrosine is N-terminal and leucine is C-terminal.
Phenylalanine is N-terminal and leucine is C-terminal.
There are no N-terminal and C-terminal residues in the sequences of amino acids.
Glycine is N-terminal and leucine is C-terminal.
A protein with a molecular weight of 75 550 g mol–1 has a mass of:
75,550 Da or 755.5 kDa.
7555 Da or 75.55 kDa.
75,550 Da or 75.55 kDa.
755,500 Da or 7.555 kDa.
7,555,000 Da or 75550 kDa.
75,550 Da or 75.55 kDa.
Knowledge of the amino acid sequences is important for several reasons. What is NOT one of those reasons?
Amino acid sequences determine the three-dimensional structures of proteins.
The sequence of a protein reveals much about its evolutionary history.
Knowledge of the sequence of a protein can help to prevent mutations.
Changes in the amino acid sequence can lead to abnormal protein functioning and disease.
The sequence of a protein is necessary to determine its function.
Knowledge of the sequence of a protein can help to prevent mutations.
What is the configuration of peptide bonds in proteins?
Almost all peptide bonds are in the cis configuration.
Almost all peptide bonds are in the trans configuration.
Half of all peptide bonds are in the trans configuration and the other half are in the cis configuration.
Approximately one third are in the trans configuration and rest are in the cis configuration.
Approximately one third are in the cis configuration and rest are in the trans configuration.
Almost all peptide bonds are in the trans configuration.
An α helix is a coil stabilized by:
intrachain hydrogen bonds between the carbonyl oxygen of a residue and the amide hydrogen of the fourth residue away.
intrachain nitrogen bonds between the carbonyl nitrogen of a residue and the amide nitrogen of the second residue away.
extrachain oxygen bonds between the carbonyl oxygen of a residue and the amide nitrogen of the fifth residue away.
intrachain nitrogen bonds between the carbonyl nitrogen of a residue and the amide nitrogen of the sixth residue away.
extrachain hydrogen bonds between the carbonyl hydrogen of a residue and the amide oxygen of the third 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:
nitrogen bonds.
oxygen bonds.
ionic bonds.
disulfide bridges.
hydrogen bonds.
hydrogen bonds
Why are porins considered to be "inside out" relatives to proteins that function in aqueous solution?
Porins are positively charged while usual proteins are negatively charged.
Porins interact with the neighboring alkane chains while usual proteins interact with alkene chains.
Porins function in outer membranes while usual proteins function in inner membranes.
Porins function only in bacteria while usual proteins function in all organisms.
Porins have a reverse distribution of hydrophobic and hydrophilic amino acids.
Porins have a reverse distribution of hydrophobic and hydrophilic amino acids.
What are the interactions that associate the two helices in α-keratin?
hydrogen bonds and electrostatic forces
van der Waals forces and covalent interactions
electrostatic forces and metallic bonds
van der Waals forces and ionic interactions
metallic bonds and van der Waals forces
van der Waals forces and ionic interactions
What is the simplest sort of quaternary structure?
a monomer
a dimer consisting of two different subunits
a dimer consisting of two identical subunits
a trimer consisting of two identical subunits and one diverse subunit
a tetramer consisting of two identical subunits and diverse subunits
a dimer consisting of two identical subunits
What is a structure of the hemoglobin molecule?
α2 dimer
β2 dimer
α2β1 trimer
α1β2 trimer
α2β2 tetramer
α2β2 tetramer
What disrupts the noncovalent interactions in proteins?
guanidinium sulfide
β-mercaptoethanol
uric acid
urea
ammonia
urea
In the ribonuclease experiments performed by Anfinsen, β-mercaptoethanol reduced:
all incorrectly paired bonds and stabilized the protein structure.
all bonds and destroyed the protein structure.
all charged residues, and the protein was unable to take part in signaling.
all bonds, and the unfolded protein molecules became tangled up with one another to form aggregates.
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.
What is the term for a molecule that contains both positive and negative charges but overall has a neutral charge?
enantiomer
amino acid
racemate
zwitterion
amphipath
zwitterion
Which amino acid forms disulfide bonds?
histidine
methionine
proline
serine
cysteine
cysteine
What amino acid has an ionizable R group with a pKa near neutral pH?
histidine
serine
aspartic acid
lysine
tyrosine
histidine
What plot type allows one to investigate the likely ϕ and ψ angles of the peptide backbone?
Hill
Lineweaver–Burk
Hanes–Woolf
Ramachandran
Michaelis–Menten
Ramachandran
What level of protein structure is composed of α helices, β sheets, and turns?
primary
secondary
tertiary
quaternary
supersecondary
secondary
The overall three-dimensional structure of a single polypeptide is referred to as _____ structure.
primary
secondary
tertiary
quaternary
supersecondary
tertiary
At a pH of 12, what is the charged groups present in glycine?
–NH3+
–COO–
–NH2+
–NH+
–CO–
-COO-
The amino acids Tyr, Asn, and Thr:
have aromatic rings.
are negatively charged at pH = 7.0.
are positively charged at pH = 7.0.
have double bonds in side chains.
are polar.
are polar
Which individual won a Nobel Prize for his or her landmark work in sequencing the protein insulin?
Pauling
McClintock
Gilbert
Maxam
Sanger
sanger
The term quaternary with respect to protein structure stands for:
a repeating structure stabilized by intrachain hydrogen bonds.
the ability to form all four kinds of noncovalent bonds.
a multisubunit structure.
a linear sequence of four amino acids.
the only four amino acids that can form hydrogen bonds.
multisubunit structure
What pair of amino acids is positively charged at a neutral pH?
Lys, Arg
Tyr, Arg
Cys, Met
Leu, Pro
Asp, Glu
lys, arg
What is NOT a modification acquired by proteins?
cleavage and trimming of the protein
addition of carbohydrate groups
phosphorylation of certain groups
hydrolysis of all protein
addition of acetyl groups
hydrolysis of all protein
What amino acid residue would MOST likely be buried in the interior of a water-soluble globular protein?
Asp
Ser
Phe
Lys
Gln
Phe
Note 
Flashcard (52)