exam 1 (B) Flashcards
What statements are correct about cysteine?
i. It is aromatic non-polar amino acid
ii. Cysteine has “C” one-letter abbreviation
iii. N-terminus pKa is 8.5, while R group pKa is 8
iv. C-terminus pKa is 2, while R group pKa is 6
v. Cysteines make disulfide bonds
a) ii, iv, v
b) ii, v
c) i, iii, iv
d) ii, iv, v
e) iii, iv
b) ii, v
What statement correctly describes the difference between Phe and Tyr?
a) At physiological pH, Phe is a zwitterion, while Tye has net negative one charge
b) Phe is aromatic, while Tyr is not
c) One OH group
d) These two amino acids have different C and N termini pKa.
e) Phe is commonly found in a-helix, while Tyr has a high propensity presence of b-sheets
c) One OH group
Select two peptide pairs that would have the net charge of -3 at pH 11
a) STRA and VDEA
b) KHCF and PARS
c) CKSA and KCTG
d) AVAR and ERTA
e) None of the above
c) CKSA and KCTG
A titration curve shown above can be used to explain protonation-deprotonation of which pairs of compounds?
i. Histidine
ii. Proline
iii. Cysteine
iv. Phenylalanine
v. H3PO4
a. i, ii
b. ii, iv
c. iv, v
d. i, iii, v
e. ii, iii, v
d. i, iii, v
In the case of Thr, Point A would be equal to ?
a. 12
b. 9
c. 8.5
d. 13
e. 10
d. 13
What is the pH of a solution containing 1.8 x 10-3M HCl?
a. 2.5
b. -2.5
c. 2.7
d. 5.8
e. 3.0
c. 2.7
At what pH range, His has net +2 charge?
a) Below pH 2
b) From pH 2 to pH 6
c) From pH 6 to pH 9
d) From pH 8 to pH 9
e) Above pH 9
a) Below pH 2
Which pair of amino acids will have opposite absolute chiral configuration?
a) His and Ala
b) Lys and Arg
c) Arg and Cys
d) Val and Phe
e) Phe and Tyr
c) Arg and Cys
AHAS, FPFIGQQG, and VVWTPPHCDNNR peptides are loaded in the column with carbohydrate polymer beads (gel filtration). What is the expected elution sequence of these peptides?
a) AHAS, FPFIGQQG, and VVWTPPHCDNNR
b) FPFIGQQG, AHAS, and VVWTPPHCDNNR
c) VVWTPPHCDNNR, AHAS, and FPFIGQQG
d) VVWTPPHCDNNR, FPFIGQQG, and AHAS
e) AHAS, VVWTPPHCDNNR, and FPFIGQQG
d) VVWTPPHCDNNR, FPFIGQQG, and AHAS
What is the protein concentration if the solution of protein has an absorption of 0.5? The extinction coefficient is 1000 cm-1/M and measurements were done in the cell with 0.5 cm pathway.
a) 0.1 mM
b) 1 mM
c) 0.05 µM
d) 0.1 µM
e) 8 µM
b) 1 mM
What secondary structure can the protein adopt if Ψ=60 and Φ=60?
a) Antiparallel β-sheet
b) Parallel β-sheet
c) Collagen triple helix
d) Closed ring
e) Left-handed alpha-helix
e) Left-handed alpha-helix
α helix has 30 amino acid residues. Calculate how many Angstroms the α helix would cover.
a) 45
b) 20
c) 22.7
d) 50
e) 21
a) 45
Which statement incorrectly describes α helix?
a) In α helix, the peptide C=O bond of the nth residue hydrogen bonds with the peptide N-H group of the (n+4)th residue
b) α helix is primarily stabilized by hydrogen bonding
c) Ala or Asp destabilizes a-helix
d) String of Asp, Glu, Lys or Arg at neutral pH destabilizes α helix
e) All statements are correct
c) Ala or Asp destabilizes a-helix
What statement correctly describes both keratin and collagen?
a) Both keratin and collagen are globular proteins
b) Prolines in keratin can be hydroxylated to 4-hydroxyprolines, whereas collagen possess a high amount of disulfide bonds
c) Keratin has around 33% Gly, whereas collagen is dominated by Phe
d) Collagen is a triple helix; Hard keratins have high sulfur content and can be found in hair, horn, and nail
e) None of the statements is correct
d) Collagen is a triple helix; Hard keratins have high sulfur content and can be found in hair, horn, and nail
What chemical modifications lead to the transformation of His to histamine?
a) Hydroxylation and deamination
b) Esterification and protonation
c) Decarboxylation
d) Decarboxylation and dihydroxylation
e) Dopamine cannot be formed from Tyr
c) Decarboxylation
What is pI for the following peptide at physiological pH: Val-Ser-Cys-Phe?
a) 5.5
b) 9.5
c) 2.85
d) 6.1
e) 3.8
a) 5.5
What separation technique would you prefer to use to purify KKRHPPVAKR from DDEPADADV and PFYYAAGVCC?
a) Ion exchange with CM-modified cellulose
b) Ion exchange with DEAE-modified cellulose
c) Gel filtration
d) Affinity chromatography
e) Salting out
a) Ion exchange with CM-modified cellulose
what is the phenotypic appearance of Ehlers-Danlos Syndrome?
a) Hyperextensibility of the joints and skin
b) Defects in Type I collagen
c) Formation of spots on the skin, spongy gums, and bleeding from the mucous membranes
d) Memory loss
e) Anemia
a) Hyperextensibility of the joints and skin
What is the major physiological function of Hsp70?
a) ion transport
b) protein folding
c) peptide bond hydrolysis
d) posttranslational modification of proteins
e) this molecule does not exist
b) protein folding
what posttranslational modifications are found in proteins?
i) hydroxylation and methylation
ii) deamination and esterification
iii) phosphorylation and adenylylation
iv) acetylation and acylation
a) i, ii, iii
b) i, iii, iv
c) iii
d) iii, iv
e) ii
b) i, iii, iv
What is the expected function of a protein domain shown in yellow?
a) protein anchoring in membranes
b) regulatory function
c) catalytic function
d) protein binding
e) all of the above
c) catalytic function
Which of the following physical factors can cause protein denaturation?
a) high temperature
b) pH
c) detergents
d) chaotropic agents
e) all of the above
e) all of the above
What statement correctly describes Protein Disulfide Isomerase (PDI)?
a) it is a protein that catalyzes the rearrangement of a polypeptide’s non-native disulfide bonds
b) PDI is involved in protein folding
c) PDI can exist in two states: oxidized and reduced
d) oxidized form of PDI catalyzes the initial formation of a polypeptide’s disulfide bonds
e) all of the above
e) all of the above
The temperature at which the reaction given below is at equilibrium is
Ag2O(s)⟶2Ag(s)+1/2O2(g).
Given that ΔHo=40 kJ mol−1 and ΔSo=0.1 kJ K−1 mol−1.
a) 410K
b) 400K
c) 0.00025K
d) 40K
e) 4K
b) 400K
Identify homo-peptides from all listed below
i. 4-Lys
ii. His-His-His
iii. P-A-P-A
iv. His-Ala
v. AGGAT
a) i, iii
b) iii, iv, v
c) i, ii, iii
d) i, ii
e) iii, v
d) i, ii
Ka of acetic acid is 1.8 x 10-5 . What is pKa?
a) 4.74
b) 7.44
c) -4.4
d) -4.74
e) 0
a) 4.74
Calculate the pH of a formic buffer containing 100 mM acetic acid and 0.2 M sodium acetate. The pKa of formic acid is 2.76.
a) 4.46
b) 1.46
c) 1.06
d) 3.06
e) 5.11
d) 3.06
The formation of nitrogen monoxide is under equilibrium at 25°C.
N2(g)+O2(g)⇄2NO(g)
ΔG∘ of the reaction is 173.4 kJ/mol. Considering R=8.314 J/K · mol, what is Keq?
a) 4.0 x 10-31
b) 4.0 x 1031
c) 2.1 x 10-3
d) 1.88 x 10-25
e) 1.8 x 10-31
a) 4.0 x 10-31
The peptide with the following sequence was exposed to first to trypsin and then to chymotrypsin: AFARPSKAS. What fragments of these peptide can be found in solution?
a) AF, ARPSK, and AS
b) AF, AR, PSK, and AS
c) AFAR, PSK and AS
d) AFAR and PSKAS
e) none of the above
a) AF, ARPSK, and AS
Name molecular interactions that help stabilizing tertiary structure of proteins
a) hydrogen bonding
b) disulfide bonds
c) ionic bonds
d) hydrophobic interactions
e) all of the above
e) all of the above
Proline is typically not found in the following structural elements
a. β-sheets
b. β-turns
c. α-helices
d. all of the above
e. a and c
e. a and c
What is an estimate number of amino acid residues in the protein with MW=59.4 kDa?
a. 540
b. 440
c. 250
d. 601
e. 20
a. 540
A solution of the following peptide was subjected to elastase. Next, the resulting product interacted with dansyl chloride. Finally, the solution was heated in the presence of a strong acid until the complete hydrolysis of all amino acids. Which amino acids in this solution were dansylamino acids?
SMV FPTA PAETYCA HYY
a) S, F, P and H
b) S, F, P, E and H
c) S and H
d) S, F, and H
e) S, Y, and H
a) S, F, P and H
A solution that contains one peptide was hydrolyzed and analyzed by HPLC. Two amino acid standards (His and Tyr) were also injected. It was found that their retention time matches the peaks observed in the peptide hydrolysate. What conclusions can be made about the amino acid composition of the peptide?
i. It is a homopeptide that consists of His amino acid residues.
ii. The peptide consists of both His and Tyr amino acid residues.
iii. The peptide has equal concentrations of His and Tyr
iv. The peptide has ~2 times higher amount of His than Tyr
v. The peptide has ~2 times higher amount of Tyr than His.
a) ii. Iii
b) ii, iv
c) ii, v
d) i
e) none of the above.
b) ii, iv
Consider the reaction: Glucose 1-phosphate -> Glucose 6-phosphate
The concentration of G 1-P is 10 mM and G 6-P is 20 mM at equilibrium. Calculate Keq?
a. 2
b. 0.5
c. 20
d. 0.05
e. 1
a. 2
