Daily Test- 2 (28th April 2015)- (Protein Part-C Question Discussion)

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Daily Test-2:

Daily Test-2 Protein Part-C Questions

Slide2:

Pepsin is the name given to a mix of several digestive enzymes secreted (as larger precursor proteins) by glands that line the stomach. These glands also secrete hydrochloric acid, which dissolves the particulate matter in food, allowing pepsin to enzymatically cleave individual protein molecules. The resulting mixture of food, HCl , and digestive enzymes is known as chyme and has a pH near 1.5. A. What pI would you predict for the pepsin proteins? 1 2 3 4 B. What functional groups must be present to confer this pI on pepsin? COOH NH3+ COO- NH2 C. Which amino acids in the proteins would contribute such groups? Asp, Glu His, Lys Arg , Leu Gly , Trp Question No 1

Question No 2:

Question No 2 A purified protein is in a Hepes (N-(2-hydroxyethyl) piperazine -N -(2-ethanesulfonic acid)) buffer at pH 7 with 500 mM NaCl . A sample (1 mL) of the protein solution is placed in a tube made of dialysis membrane and dialyzed against 1 L of the same Hepes buffer with 0 mM NaCl . Small molecules and ions (such as Na + , Cl - , and Hepes ) can diffuse across the dialysis membrane, but the protein cannot. (a) Once the dialysis has come to equilibrium, what is the concentration of NaCl in the protein sample? 0.5 mM 0.05 M 0.005 5 (b) If the original 1 mL sample were dialyzed twice, successively, against 100 mL of the same Hepes buffer with 0 mM NaCl , what would be the final NaCl concentration in the sample ? 0.05 mM . 0.5 mM 500 M 5 mM

Question No 3:

Question No 3 A sample (660 mg) of an oligomeric protein of Mr 132,000 was treated with an excess of 1-fluoro-2, 4-dinitrobenzene (Sanger’s reagent) under slightly alkaline conditions until the chemical reaction was complete. The peptide bonds of the protein were then completely hydrolyzed by heating it with concentrated HCl . The hydrolysate was found to contain 5.5 mg of a single type 2,4-Dinitrophenyl derivative. [Derivatives of the alpha-amino groups of other amino acids could not be found .] How many subunits are present in the protein 1 2 3 4 The protein obtained is a Dimer Homotetramer Heterotetramer Trime

Question No 4:

Question No 4 Protein A has a binding site for ligand X with a Kd of 10 -6 M. Protein B has a binding site for ligand X with a Kd of 10 -9 M. Which protein has a higher affinity for ligand X? Protein A Protein B Both will have similar affinity Data is inappropriate What is the Ka for protein B? 10^9 10^-9

Question No 5:

Question No 5 Which of the following situations would produce a Hill plot with nH = 1.0 ? (a) The protein with multiple subunits, each with a single ligand-binding site. Binding of ligand to one site decreases the binding affinity of other sites for the ligand. (b) The protein with a single polypeptide with two ligand-binding sites, each having a different affinity for the ligand. (c) The protein is a single polypeptide with a single ligand-binding site. As purified, the protein preparation is heterogeneous, containing some protein molecules that are partially denatured and thus have a lower binding affinity for the ligand . (d) None of the above

Slide7:

What is the effect of the following changes on the O 2 affinity of hemoglobin? (a) A drop in the pH of blood plasma from 7.4 to 7.2 . Increases the O 2 affinity of hemoglobin Decreases the O 2 affinity of hemoglobin ( b) A decrease in the partial pressure of CO 2 in the lungs from 6 kPa (holding one’s breath) to 2 kPa (normal ). Increases the O 2 affinity of hemoglobin Decreases the O 2 affinity of hemoglobin (c) An increase in the BPG level from 5 mM (normal altitudes) to 8 mM (high altitudes ). Increases the O 2 affinity of hemoglobin Decreases the O 2 affinity of hemoglobin (d) An increase in CO from 1.0 parts per million (ppm) in a normal indoor atmosphere to 30 ppm in a home that has a malfunctioning or leaking furnace. Increases the O 2 affinity of hemoglobin Decreases the O 2 affinity of hemoglobin Question No 6

Question No 7:

Question No 7 When all the BPG is carefully removed from samples of HbA and HbF , the measured O2-saturation curves (and consequently the O2 affinities) are displaced to the left. However, HbA now has a greater affinity for oxygen than does HbF . When BPG is reintroduced, the O2-saturation curves return to normal, as shown in the graph. What is the effect of BPG on the O2 affinity of hemoglobin? Binding of BPG to hemoglobin reduces the affinity of hemoglobin for O2 Binding of BPG to hemoglobin increases the affinity of hemoglobin for O2 Binding of BPG to hemoglobin doesn’t alter the affinity of hemoglobin for O2 All of the above

Question No 8:

Question No 8 An isotonic saline solution (one that has the same salt concentration as blood) is 0.9% NaCl . What is its ionic strength? 0.3076 M 3.076 mM 3.706 M 370.6 M

Answer Key:

Answer Key 1. a-1, b-3, c-1 2. a-1, b-1 3. a-4, b-2 4. a-2, b-1 5. d 6. a-2, b-1, c-2, d-2 7-a 8-a

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