Carbohydrates – amino acid

Undergraduate Questions (50 Pts) 1. (4 pts) A chemist working in a pharmaceutical lab synthesized a new drug as a racemic mixture. Why is it important that she separates the two enantiomers and test each for its biological activity? 2. (6 pts) Phosphoric acid (H3PO4) has three dissociable protons, with the pKa’s shown below. Which form of phosphoric acid predominates in a solution at pH 4? Explain your answer. AcidpKa H3PO42. 14 H2PO4–6. 86 HPO42–12. 4 3.

(4 pts) Mutations may arise during DNA replication when mispairing occurs as a result of the transient formation of a rare tautomeric from of a base, such as the imino tautomer of adenine shown below. Draw the structure of a base pair with proper Watson-Crick geometry that contains a rare imino tautomer of adenine (see the structure below). What base sequence change such a mispairing would cause? [pic] 4. (4 pts) Methanol (wood alcohol) is highly toxic because it is converted to formaldehyde in a reaction catalyzed by the enzyme alcohol dehydrogenase: NAD+ + methanol > NADH + H+ + formaldehyde.

Part of the medical treatment for methanol poisoning is to administer ethanol (ethyl alcohol) in amounts large enough to cause intoxication under normal circumstances. Explain this treatment in terms of what you know about examples of enzymatic reactions. 5. (4 pts) The number of structurally different polysaccharides that can be made with 20 different monosaccharides is far greater than the number of different polypeptides that can be made with 20 different amino acids even though both polymers contain an equal number of 100 total residues. Is the statement true or false? Explain your reasoning. 6.

(4 pts) A plant breeder has developed a new frost-resistant variety of tomato that contains higher levels of unsaturated fatty acids in membrane lipids than those found in standard tomato varieties. However, when temperatures climb above 95 °F, this frost-resistant variety dies, whereas the standard variety continues to grow. Provide a likely explanation of the biochemical basis of increased tolerance to cold and increased susceptibility to heat of this new tomato variety. 7. (4 pts) Why is the mobility of H+ in ice only about an order of magnitude less than that in liquid water, whereas, the moblility of Na+ in solid NaCl is zero?

8. (6 pts) The amino acid histidine has a side chain for which the pKa is 6. 0. Calculate what fraction of the histidine side chains will carry a positive charge at pH 5. 4. Be sure to show your work. 9. (4 pts) When a polypeptide is in its native conformation, there are weak interactions between its R groups and when it is denatured there are similar interactions between the protein groups and water. What then accounts for the greater stability of the native conformation? 10. (2 pts) A polypeptide is subjected to the following degradative techniques resulting in polypeptide fragments with the indicated amino acid sequences.

What is the amino acid sequence of the entire polypeptide? I. Cyanogen Bromide treatment: i. Asp-Ile-Lys-Gln-Met ii. Lys iii. Lys-Phe-Ala-Met iv. Tyr-Arg-Gly-Met II. Trypsin Hydrolysis: i. Gln-Met-Lys ii. Gly-Met-Asp-Ile-Lys iii. Phe-Ala-Met-Lys iv. Tyr-Arg 11. ( 6 pts) A biochemist obtains the following set of data for an enzyme that is known to follow Michaelis-Menten kinetics. SubstrateInitial concentrationvelocity (? M)(? mol/min) ————————————— 149 296 8349 50621 100676 1,000698 5,000699 ————————————— A. Vmax for the enzyme is __________. Explain in one sentence how you determined Vmax. B. Km for the enzyme is _________.

Explain in one sentence how you determined Km. 12. (2 pts) Describe one biological advantage of storing glucose units in branched polymers (glycogen, amylopectin) rather than in linear polymers. Graduate Questions (50 Pts) A patient has been admitted to the emergency room and is disoriented, having trouble speaking and suffering from nausea and vomiting. The patient is also hyperventilating and has admitted to taking an entire bottle of aspirin. She was admitted at 9 PM two hours after taking the tablets. Blood work analysis results are shown in Table 1 and suggest the patient is also experiencing mild respiratory alkylosis.

Table 1 – Arterial blood gas concentration in patient | |2 hours after aspirin |10 hours after aspirin ingestion|Normal values | | |ingestion | | | |pCO2 |26 mm Hg |19 mm Hg |35 – 45 mm Hg | |HCO3- |18 mM |21 mM |22 – 26 mM | |pO2 |113 mm Hg |143 mm Hg |75-100 mm Hg | |pH |7. 44 |7. 55 |7. 35 – 7. 45 | |Blood saliclylate concentration, |57 |117 | | |mg/dL | | | | The patient is given a stomach lavage with saline and two doses of activated charcoal to absorb the aspirin. Eight hour later, nausea and vomiting become severe and the respiratory rate has increase. The patient is now in severe respiratory alkylosis.

Further treatment involves a gastric lavage at ph 8. 5 as well as further activated charcoal treatments every 30 minutes. A bicarbonate drip is also administered to prevent blood bicarbonate levels from dropping below 15mM. Over the next four hours, blood salicylate concentrations decrease and the patient’s blood pH begins to drop finally returning to normal after 60 hours. 13. (2 pts) Aspirin, or acetylsalicylic acid (structure shown in Figure 1), is hydrolyzed in the presence of aqueous acid and stomach esterases to salicylic acid (the pharmacologically active form of the drug) and acetic acid.

Write the balanced chemical reaction for this transformation. 14. (8 pts) Since the patient was brought into the emergency room only two hours after the overdose, you suspect that her stomach might contain undissolved aspirin that is continuing to be absorbed. You decide to use a gastric lavage at pH 8. 5 to effectively remove any undissolved aspirin. This treatment solubilizes the aspirin so that it can easily be removed from the stomach. A. Calculate the percentage of protonated and unprotonated forms of salicylic acid at the pH of the stomach, which is usually around 2. 0. B.

Calculate the percentage of protonated and unprotonated forms of salicylic acid at the pH of the gastric lavage. (Note: Assume that the pK values for the carboxylate group in salicylic acid and acetylsalicylic acid are the same. ) C. Why does the gastric lavage result in increased solubility of the drug? 15. (8 pts) It has been shown that salicylates act directly on the nervous system to stimulate respiration. Thus, our patient is hyperventilating due to her salicylate overdose. A. Explain how the salicylate-induced hyperventilation leads to the values of pO2 and pCO2 symptoms seen in the patient.

B. Explain how the salicylate-induced hyperventilation causes the pH of the patient’s blood to increase. Illustrate your answer with the appropriate equations. C. Why was the bicarbonate drip necessary? D. Sixty hours after aspirin ingestion, the patient’s blood pH has returned to normal (pH = 7. 4). Describe how the carbonic/bicarbonate buffering system responded to bring the patient’s blood Diabetics lack the protein insulin, which is produced by the pancreatic (-cells of the islets of Langerhans. Insulin stimulates uptake of glucose from the blood into the tissues.

Diabetes is treated by replacing the missing insulin. Human insulin is produced industrially by recombinant bacteria, but before this method was available, animal insulin was used instead. Insulin consists of two polypeptide chains, an A chain and a B chain, joined together by disulfide bonds. The smaller of the two chains is referred to as the A chain and is 21 amino acids long in humans. The second chain is referred to as the B chain and is 30 amino acids long in humans. Insulin from various animals is similar to, but not identical to human insulin, as illustrated in Table 2.

A schematic diagram of the structure of insulin is shown in Figure 2. Table 2: Variation in positions A8, A9, A10, B1, B2, B27 and B30 of insulin. (All other amino acids are the same. ) |Species |A8 |A9 |A10 |B1 |B2 |B27 |B30 | |Human |Thr |Ser |Ile |Phe |Val |Thr |Thr | |Cow |Ala |Ser |Val |Phe |Val |Thr |Ala | |Pig |Thr |Ser |Ile |Phe |Val |Thr |Ala | |Horse |Thr |Gly |Ile |Phe |Val |Thr |Ala | |Rabbit |Thr |Ser |Ile |Phe |Val |Thr |Ser | |Dog |Thr |Ser |Ile |Phe |Val |Thr |Ala | |Chicken |His |Asn |Thr |Ala |Ala |Ser |Ala | |Duck |Glu |Asn |Pro |Ala |Ala |Ser |Thr.

| Figure 2. Structure of proinsulin. (From Voet and Voet, 1995, p. 193) [pic] 16. (2 pts) What animals would serve as the best sources of insulin to be used for treating diabetics? Explain your answer. 17. (3 pts) Would the pI values of the animal insulins be the same as, greater than, or less than human insulin? 18. (2 pts) An SDS-PAGE gel is run of proinsulin and insulin. Samples were treated with B-mercaptoethanol prior to electrophoresis. Draw a picture of the predicted results.

Procedure a. Weigh accurately a definite number of aspirin tablets (two or three tablets weighing no more than 1. 5 g) into a 250 cm3 conical flask. Initiate the hydrolysis of the aspirin by adding 25 cm3 of 1. 0 …

Acetylsalicylic acid is an acetyl derivative of salicylic acid which appears as a white and crystalline and a weakly acidic substance with a melting point of 135°C and is also known to be aspirin. It is one of the most …

Standardization of dilute sulphuric acid 1. 1. 32g of the sodium carbonate was weighted accurately in a beaker. 2. 120cm3 of deionised water was added to the beaker containing sodium carbonate. 3. The mixture was stirred gently to let the …

Standardization of dilute sulphuric acid 1. 32g of the sodium carbonate was weighted accurately in a beaker. 120cm3 of deionised water was added to the beaker containing sodium carbonate. The mixture was stirred gently to let the sodium carbonate to …

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