biochem exam questions
What is the net charge of asp when completely protonate? Assume the pKa of -NH3+ is 9.2 and pKa of -COOH is 2.1.
+1
Which of the following R groups below is valine?
-CH2(CH3)2
Which of the following R groups below is leucine?
-CH2CH(CH3)2
Which of the following correctly represents a protein backbone?
-Ca-C-N-Ca-C-N-
Which of the following peptide segments is most likely to form an α helix?
-Met-Glu-Ile-Val-Trp-Lys-Leu-Ala-
What is the net charge of glu at pH 3.9? Assume the pKa of -NH3+ is 9.2 and pKa of -COOH is 2.1.
0
What is the concentration of a protein that has an extinction coefficient of 66,000 M-1cm-1, a pathlength of 1 cm and an absorbance of 0.76
11.5uM
Consider that a hydrogen bond requires a weekly acidic donor and a weakly basic acceptor, how many donors and acceptors, respectively, does 1 water molecule have?
2 donors, 2 acceptors
IgG is one the of the five classes of antibodies. What is their subunit composition?
2 heavy chains and 2 light chains
What is the biochemical definition of steady state conditions?
25c and pH 7
How many PKA's does the tripeptide valine-histidine-tryptophan have
3
What is the pI of the dipeptide tyr-pro? Assume the pKa of -NH3+ is 9.2 and pKa of -COOH is 2.1.
5.97
Which pH is closest to neutral pH?
6.7
What is the pI of the dipeptide glu-val? Assume the pKa of -NH3+ is 9.2 and pKa of -COOH is 2.1.
7.98
How does fetal hemoglobin (Hb F) differ from normal adult hemoglobin (Hb A)?
A histidine residue in Hb A is replaced with a neutral amino acid in Hb F.
which of the following statements reaction spontaneity is false?
A reaction is said to be spontaneous when it can proceed in either the reverse or forward direction
Which of the following statements about conversion from T to R state is incorrect?
A smaller central cavity is formed when subunits displace
Which of the following is not part of the general structure of alpha amino acids?
Alpha amino group R group Hydrogen Carboxyl group Alpha carbon
Define primary structure
Amino acid sequence
Which of the following statements is incorrect?
BPG binding increases the oxygen affinity of hemoglobin.
There is a limited size of polypeptides that are observed in biological organism. Which of the following is not a reason why this is observed?
Characteristics of proteins are only dependent on amino acid composition favoring smaller polypeptides
Which of the following statements about secondary structures is true?
Coils are unique and irregular structures and are considered a type of secondary structure.
A peptide bond is formed by a ____ reaction between two amino acids.
Condensation
Which statement about 3° structure determination is false?
Cryo-EM is most suitable for measuring very small proteins.
What is denaturation
Disruption in the structure
Which of the following statements about heme properties is correct?
Fe has six coordination positions, four of which are occupied by the nitrogen atoms of the porphyrin ring.
Which of the following amino acids is not capable of forming an isopeptide bond?
Gln
Which of the following statements describes an important difference between hemoglobin (Hb) and myoglobin (Mb)?
Hb is a heterotetramer containing 2 alpha and 2 beta chains
Which amino acid has a side chain pKa of 6.04?
His
Which of the following interactions is most responsible for the maintenance of protein secondary structure?
Hydrogen bonds
The pH at which a polypeptide carries no charge is called:
Isoelectric point
Which stereochemical configuration of amino acids do proteins use?
L
Under which of the following conditions would hemoglobin have the highest affinity for oxygen?
Low bisphosphoglycerate and high pH
Which of the following amino acid combinations will have the least ability to stabilize tertiary structure?
Lys and Arg
In anion exchange chromatography, the resin is
Positively charged
In a protein, which amino acid is considered the most conformationally restricted?
Pro
Which of the following amino acids does not have absorbance in the UV range (280 nm)
Pro
Which of the following polypeptides is least likely to form a beta strand?
Ser-Glu-Asp-Asn-Phe-Gly-Ala-Pro-Lys-Ser-Ile-Leu-Trp
Which statement correctly describes oxygen binding to hemoglobin?
The binding of the first oxygen molecule enhances the binding of the other three oxygen molecules
Under which of the following conditions will hemoglobin bind less oxygen?
The concentration of carbon dioxide increases
What would be the result if a protein was treated with a chaotropic agent?
The protein would denature, and the nonpolar portions would become more soluble
Which of the following is not a type of chromatography used to separate proteins
Thin layer chromatography
Which amino acid has a side chain pKa of 10.46?
Tyr
Which of the following statements about water is false?
Water is a nonpolar molecule
Which of the options below is a naturally occurring constraint on the formation of a β-strand?
a Pro residue
Choose the correct definition of a Bronsted-Lowery base:
a proton acceptor
Which of the following answers correctly lists functional groups in the molecule shown below?
amide, hydroxyl
Proteins are made from which monomer?
amino acids
Micelles are formed from
amphiiphilic compounds with a single nonpolar tail
Hydronium ion is formed when
an additional proton is accepted by a water molecule
In an α-helix, the R groups on the amino acid residues:
are found on the outside of the helix spiral.
Which type of amino acids have absorbance that can be used to quantify them?
aromatic
A test that is highly specific for a target protein is called
assay
The first step in sequencing a protein is:
break the disulfide bonds bewteen polypeptide chains
Which one of the following functional groups has a negative formal charge?
carboxylate group
A strong acid ionizes __________________ while a weak acid ionized ________________.
completely, partially
The following reaction is nonspontaneous when it occurs at 300 K. The ΔS for the reaction is -75 J mol-1 K-1 and the ΔH is -15,000 J mol-1. Does the temperature need to be increased or decreased to make the reaction spontaneous?
decreased
Which of the following is not one of the four major levels of protein structure?
domain structure
Which of the following terms is defined as the heat exchanged in a reaction?
enthalpy
What type of cell has a membrane enclosed nucleus encapsulating DNA?
eukaryote
What two things provide efficiency in cellular functions (two answers need to be selected)?
evolved metabolic pathways, compartmentation
The amino acid composition is more important than the sequence of amino acids.
false
The _______________ law of thermodynamics states that energy is neither created nor destroyed
first
What is the function of protein disulfide isomerase?
form temporary disulfide bonds to stabilize intermediate forms
Which pair of amino acids below would interact through electrostatic interactions at pH 7.0?
glu and lys
Water organized around a substance is called a __________.
hydration shell
Which of the following forces does not contribute to protein stability.
hydrophilic affect
The center of globular proteins is composed of non-polar residues due to the
hydrophobic effect
The variable portion of the antibody sequence responsible for binding the antigens is found in the:
hypervariable loop
Which amino acid is least soluble in water?
ile
Met
interior
Which of the following statements about oxygen bound to myoglobin is correct?
is the sixth coordination link to the heme iron
Which of the statements about dialysis is true?
it is the movement of water and solutes across a a membrane
Which of the following statements about fibrous proteins is false?
keratin is a triple helix with individual right-handed helices and left-handed coiled helices.
Which statement best describes osmosis?
net movement of water across a membrane
Hypervariable region has the sequence Ala-Leu-Gly-Asn-Ile. What property would you expect an antigen to have for favorable binding at pH 7.
nonpolar
What is the net charge of gly at pH 7.0? Assume the pKa of -NH3+ is 9.2 and pKa of -COOH is 2.1.
o
Which of the following statements about structure is true?
only proteins with more than one subunit have quaternary structure
The pressure that must be applied to equalize the flow of water across a membrane in both directions is called
osmotic pressure
A protein is least soluble when:
pH = pI
monosaccharides are the monomers that make up which biological polymer?
polysaccharides
When △H is +, what must △S be for a reaction to be spontaneous. Choose all correct answers
positive if temperature is above deltaH/deltaS
When the pH is below the pKa, the functional group will always be
protonated
Which of the following statements about the protein backbone is false?
rotation occurs around the C-N and Ca-N bond
Which level of structure is defined as local spatial arrangements of the protein backbone?
secondary structure
Which of the following elements is not one of the four most abundant elements that makes up life
sulfur
His
surface
Asn
surface or interior
Which of the following statements about hemoglobin conformations is false?
the T stat of hemoglobin has a higher affinity for O2
As the concentration of {H+] in solution increases, which of the following statements are true? Select all that apply
the concentration of [OH-] decreases, the pH decreases
Which of the following is not a change in hemoglobin that occurs due to the binding of molecular oxygen?
the heme moves into the hydrophobic pocket of hemoglobin
Which of the following correctly describes why antiparallel B sheets are more stable than parallel B sheets?
the hydrogen bonding distance and angles are optimal
Mass spectrometry can help in protein sequencing by measuring:
the mass to charge ratio (m/z)
Consider a mutant hemoglobin that has a hill coefficient of 1 and p50 value that is lower than normal hemoglobin. Choose the statement below that best describes the two proteins.
the oxygen binding curve for the hypothetical hemoglobin is hyperbolic, and the curve for the normal hemoglobin is sigmoidal.
Which of the following statements correctly describes the β-sheet?
the sheets have a pleated edge on appearance (zigzag like)
What is the correct definition of the hydrophobic effect?
the tendency of water to minimize its contacts with hydrophobic molecules
Which of the following statements about molecular chaperones is false?
they can help shuttle proteins across membranes and prevent improper aggregation.
Which of the following statements about motifs is false?
β barrels can be made from a combination of β-strands and α-helices
