Biochemistry - Question

QUesiton

3

Question: An acid is a compound that in aqueous solution will readily: A.Shed a proton. B.Shed an electron. C.Gain a proton. ● D.Gain an electron. ● None of the above.

A

Question

A From the book "Road Map Biochemistry" •The answer is A. •The ratio of conjugate base to its acid for a physiologic buffer helps determine the pH of a solution according to the terms of the Henderson-Hasselbalch equation. When the concentration of base equals that of the acid form, the ratio is 1.0 and the pH = pKa. In this case, a ratio of acid to base of 100:1 inverts to a base to acid ratio of 1:100 and calculates pH = 1.86.

A 2-day-old neonate becomes lethargic and uninterested in breast-feeding. Physical examination reveals tachypnea (rapid breathing) with a normal heartbeat and breath sounds. Initial blood chemistry values include normal glucose, sodium, potassium, chloride, and bicarbonate (HCO3−) levels; initial blood gas values reveal a pH of 7.53, partial pressure of oxygen (pO2) normal at 103 mmHg, and partial pressure of carbon dioxide (pCO2) decreased at 27 mmHg. The pH of body fluids is stabilized by buffer systems. Which of the following compounds is the most effective buffer at physiologic pH? A.Na2HPO4, pKa 12.32 B.NH4OH, pKa 9.24 C.NaH2PO4, pKa 7.41 D.CH3CO2H, pKa 4.74 E.Citric acid, pKa 3.09

D

Question: In an aqueous solution where the H+ concentration is 1x10-6 M, the OH- concentration must be: A. 14 x 10-6 M B. 1 x 10-6 M C. 1 x 10-7 M D. 1 x 10-8 M ● 14 x 10-8 M

D

The diagram below plots the percentage of drugs A, B, and C excreted at two pH levels. Using the diagram, determine which of the following statements is the most correct: A.Drug A could be a nonelectrolyte B.Drug A could be a weak base C.Drug B could be a nonelectrolyte D.Drug B could be a weak base E.Drug C could be a weak acid

D

L Amino Acids (Humans Have it)

L Amino Acids (Humans) A Amino Acids (Microrganisms)

§An 11-year-old female presents to the emergency department with a history of 2 days of vague abdominal pain, nausea, polyuria, polydipsia, and vomiting. The parents state that the child has lost weight in the past few months. During physical examination, it is noted that the patient has a deep, sighing breathing, orthostatic hypotension, and dry mucosa. What is the acid-base disorder of this patient? Laboratory:Na+: 130K+: 6.01Cl-: 93HCO3​-:11glucose: 760BUN: 38Cr: 2.5pH 7.26HCO3-: 10PCO2: 24

Metabolic acidosis with adequate respiratory compensation

Questions (PKU Issue)

Primary Structure A 10-year-old child, who was incontinent, unable to feed himself, and spoke incoherently was referred for investigations. He presented a picture of severe mental retardation with an I.Q. of 65. Detailed biochemical investigations with the plasma and the urine samples, and with the cell free extract* prepared from the hepatocytes (obtained by liver biopsy), led to the conclusion that the child had an impaired ability to convert phenylalanine to tyrosine. This is due to a defect in the enzyme, phenylalanine hydroxylase. The gene for this enzyme was identified and sequenced. Sequences of the complementary mRNA and the corresponding amino acid segment were determined, both for the patient as well as for a normal subject. It may be observed that a point mutation caused a proline residue to be present at a certain position in polypeptide chain of the patient; the corresponding position was occupied by leucine in the normal subject. PKU issue

•Henderson - Hasselbalch equation (H-H equation)

describes the relationship between pH, pKa and buffer concentrations of protons, acid/base, which is important for understanding buffer action and acid-base balance in the blood and tissues. •For the dissociation of a weak acid [HA] into H+ and A−, the H-H equation can be derived as follows:

•Substitute into Henderson-Hasselbalch equation: •7.03 = 6.10 + log [HCO3-]/1.1 mM, or •0.93 = log [HCO3-]/1.1 mM •The anti-log of 0.93 = 8.5, thus: •

•8.5 = [HCO3-]/1.1 mM, or [HCO3-] = 9.4 mM • •Since normal [HCO3-] equals 24 mM, there was a decrease of 14.6 mmol of [HCO3-] per liter of blood in this patient. •This would be approaching the point where, if left untreated, the HCO3- buffering capacity would be no longer effective in this patient.

•The blood values of a patient were pH = 7.03 and [CO2] = 1.1 mM. What is the patient's blood [HCO3-] and how much of the normal [HCO3-] has been used in buffering the acid causing the condition? •

•The pK' for [HCO3-]/[CO2] = 6.10