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All Textbook Solutions for Introduction to General, Organic and Biochemistry

21.97P 21.98P 21.99P 21-100 What are the functions of a cell membrane? To what extent is a bilayer that consists entirely of lipids able to carry out these functions?21-101 Glycerophospholipids tend to have both a positive charge and a negative charge in their hydrophilic portions. Does this fact help or hinder lipid packing in membranes? Explain.21.102P Problem 22-1 Show how to form the dipeptide valyiphenylalanine (Val—Phe).Problem 22-2 What is the oxidation number (the charge) on the platinum atom in cisplatin, [Pt(NH3)2Cl2]?22.3P 22.4P 22-5 What are the functions of (a) ovalbumin and (b) myosin?22-6 The members of which class of proteins are insoluble in water and can serve as structural materials?22-7 What is the function of an immunoglobulin?22.8P 22-9 What is the difference in structure between tyrosine and phenylalanine?22-10 Classify the following amino acids as nonpolar, polar but neutral, acidic, or basic. (a) Arginine (b) Leucine (c) Glutamic acid (d) Asparagine (e) Tyrosine (f) Phenylalamne (g) Glycine 22-11 Which amino acid has the highest percentage of nitrogen (g N/100 g amino acid)?22.12P 22.13P 22.14P 22.15P 22-16 Which amino acids in Table 22-1 have more than one stereocenter?22-17 What are the similarities and differences in the structures of alanine and phenylalanine?22-18 Draw the structures of L- and D-valine.22.19P 22-20 Show how alanine, in solution at its isoelectric point, acts as a buffer (write equations to show why the pH does not change much if we add an acid or a base).22-21 Explain why an amino acid cannot exist in an un-ionized form at any pH.22-22 Draw the structure of valine at pH 1 and at pH 12.22.23P 22-24 Draw the most predominant form of histidine at its isoelectric point.22-25 Draw the most predominant form of lysine at its isoelectric point.22.26P 22-27 Show by chemical equations how alanine and glutamine can be combined to give two different dipeptides.22-28 A tetrapeptide is abbreviated as DPKH. Which amino acid is at the N-terminus, and which is at the C-terminus?22-29 Draw the structure of a tripeptide made of threomne, arginine, and methionine.22-30 (a) Use the three-letter abbreviations to write a representation of the following tripeptide: (b) Which amino acid is at the C-terminal end, and which is at the N-terminal end?22-31 A polypeptide chain is made of alternating valine and phenylalanine. Which part of the polypeptide is polar (hydrophilic)?22.32P 22-33 Which of the three functional groups on histidine is the most unique?22.34P 22-35 Why is histidine considered a basic amino acid when the pKa of its side chain is 6.0?22.36P 22.37P 22-38 Why does proline not absorb light at 280 nm?22.39P 22.40P 22.41P 22-42 (a) How many atoms of the peptide bond lie in the same plane? (b) Which atoms are they?22-43 (a) Draw the structural formula of the tripeptide Met—Ser—Cys. (b) Draw the different ionic structures of this tripeptide at pH 2.0, 7.0, and 10.0.22-44 How can a protein act as a buffer?22-45 Proteins are least soluble at their isoelectric points. What would happen to a protein precipitated at its isoelectric point if a few drops of dilute HCl were added?22-46 How many different tripeptides can be made (a) using one, two, or three residues each of leucine, threonine, and valine and (b) using all 20 amino acids?22-47 How many different tetrapeptides can be made (a) if the peptides contain the residues of asparagine, proline, serine, and metbionine and (b) if all 20 amino acids can be used?22-48 How many amino acid residues in the A chain of insulin are the same in insulin from humans, cattle (bovine), hogs, and sheep?22-49 Based on your knowledge of the chemical properties of amino acid side chains, suggest a substitution for leucine in the primary structure of a protein that would probably not change the character of the protein very much.22-50 Is a random coil a (a) primary, (b) secondary, (c) tertiary or (d) quaternary structure? Explain.22-51 Decide whether the following structures that exist in collagen are primary, secondary tertiary, or quaternary (a) Tropocollagen (b) Collagen fibril (e) Collagen fiber (d) The proline—hydroxyproline——glycine repeating sequence 22.52P 22-53 Do iron and zinc ions play role in protein structure? If so, what is the role for either or both?22.54P 22-55 Consider the coordination compound Fe(CO)5 and show that in forming this compound, the 18-electron rule is satisfied for iron.22.56P 22-57 Consider the coordination compound [Zn(NH3)2Cl2], which contains Zn(NH3)22+ and Cl ions. Show that in forming this coordination compound, the 18-electron rule is satisfied for zinc.22.58P 22-59 What is the effect of salt bridges on the tertiary structure of proteins?22.60P 22-61 Polyglutamic acid (a polypeptide chain made only of glutamic acid residues) has an a-helix conformation below pH 6.0 and a random-coil conformation above pH 6.0. What is the reason for this conformational change?22-62 Distinguish between intermolecular and intramolecular hydrogen bonding between backbone groups. Where in protein structures do you find one, and where do you find the other?22-63 Identify the primary, secondary, and tertiary structures in the numbered boxes:22-64 If both cysteine residues on the B chain of insulin were changed to alanine residues, how would it affect the quaternary structure of insulin?22-65 (a) What is the difference in the quaternary structure between fetal hemoglobin and adult hemoglobin? (b) Which can carry more oxygen? (c) What would the oxygen saturation curve of fetal hemoglobin look like compared to that of myoglobin and regular adult hemoglobin?22.66P 22.67P 22.68P 22.69P 22.70P 22-71 Which amino acid side chain is most frequently involved in denaturation by reduction?22-72 What does the reducing agent do in straightening curly hair?22-73 Silver nitrate is sometimes put into the eyes of newborn infants as a preventive measure against gonorrhea. Silver is a heavy metal. Explain how this treatment may work against bacteria.22-74 Why do nurses and physicians use 70% alcohol to wipe the skin before giving injections?22-75 (Chemical Connections 22A) Why must some people avoid drinking diet sodas with Nutrasweet?22.76P 22.77P 22.78P 22.79P 22.80P 22.81P 22-82 (Chemical Connections 22H) How does the fiberscope help to heal bleeding ulcers?22.83P 22-84 How many different dipeptides can be made (a) using only alanine, tryptophan, glutamic acid, and arginine and (b) using all 20 amino acids?22-85 Denaturation is usually associated with transitions from helical structures to random coils. If an imaginary process were to transform the keratin in your hair from an (-helix to a (-pleated sheet structure, would you call the process denaturation? Explain.22.86P 22.87P 22.88P 22-89 What kind of noncovalent interaction occurs between the following amino acids? (a) Valine and isoleucine (b) Glutamic acid and lysine (c) Tyrosine and threonine (d) Alanine and alanine 22.90P 22-91 Which amino acid does not rotate the plane of polarized light?22-92 Write the expected products of the acid hydrolysis of the following tetrapeptide:22-93 What charges are on aspartic acid at pH 2.0?22.94P 22.95P 22.96P 22-97 Gelatin is derived from collagen by denaturation. Is a gelatin dessert likely to be a good source of dietary protein?22.98P 22.99P 22.100P 22-101 Using what you know about protein denaturation, what is one reason you must maintain a body temperature in a strict range?22.102P 22.103P 22-104 Why is collagen not a very good source of dietary protein?22.105P What is the difference between a catalyst and an enzyme?What are ribozymes made of?Would a lipase hydrolyze two triglycerides, one containing only oleic acid and the other containing only palmitic acid, with equal ease?Compare the activation energy in uncatalyzed reactions and in enzyme-catalyzed reactions.23.5P 23.6P 23.7P Monoamine oxidases are important enzymes in brain chemistry. Judging from the name, which of the following would be a suitable substrate for this class of enzymes:23.9P 0 What kind of reaction does each of the following enzymes catalyze? (a) Deaminases (b) Hydrolases (c) Dehydrogenases (d) Isomerases 23.11P 23.12P 3 What is the difference between reversible and ire-versible noncompetitive inhibition?23.14P 5 At a very low concentration of a certain substrate, we find that when the substrate concentration doubles, the rate of the enzyme-catalyzed reaction also doubles. Would you expect the same finding at a very high substrate concentration? Explain.6 If we wish to double the rate of an enzyme-catalyzed reaction, can we do so by increasing the temperature by 10°C? Explain.7 A bacterial enzyme has the following temperature-dependent activity. (a) Is this enzyme more or less active at normal body temperature than when a person has a fever? (b) What happens to the enzyme activity if the patient’s temperature is lowered to 35°C?8 The optimal temperature for the action of lactate dehydrogenase is 36°C. It is irreversibly inactivated at 85°C, but a yeast containing this enzyme can survive for months at —10°C. Explain how this can happen.9 The activity of pepsin was measured at various pH values. When the temperature and the concentrations of pepsin and substrate were held constant, the following activities were obtained: (a) Plot the pH dependence of pepsin activity. (b) What is the optimal pH? (c) Predict the activity of pepsin in the blood at pH 7.4.23.20P 23.21P 23.22P 23.23P 4 What kind of chemical reaction occurs most frequently at the active site?5 Which of the following is a correct statement describing the induced-fit model of enzyme action? Substrates fit into the active site: (a) because both are exactly the same size and shape. (b) by changing their size and shape to match those of the active site. (c) by changing the size and shape of the active site upon binding.23.26P 7 Enzymes are long protein chains, usually containing more than loo amino acid residues. Yet the active site contains only a few amino acids. Explain why the other amino acids of the chain are present and what would happen to the enzyme activity if the enzyme’s structure were changed significantly.23.28P 23.29P 0 Can the product of a reaction that is part of a sequence act as an inhibitor for another reaction in the sequence? Explain.1 What is the difference between a zymogen and a proenzyme?2 The enzyme trypsin is synthesized by the body in the form of a long polypeptide chain containing 235 amino acids (trypsinogen), from which a piece must be cut before the trypsin can be active. Why does the body not synthesize trypsin directly?23.33P 23.34P 23.35P 23.36P 23.37P 23.38P 9 The enzyme phosphofructokinase (PFK) (Chapter 28) has two types of subunits, M and L, for muscle and liver, respectively. These subunits combine to form a tetramer. How many isozymes of PFK exist? What are their designations?23.40P 1 After a heart attack, the levels of certain enzymes rise in the serum. Which enzyme would you monitor within 24 hours following a suspected heart attack?23.42P 23.43P 23.44P 5 Chemists who have been exposed for years to or ganic vapors usually show higher-than-normal activity when given the alkaline phosphatase test. Which organ in the body do organic vapors affect?6 Which enzyme preparation is given to patients after duodenal ulcer surgery?7 Chymotrypsm is secreted by the pancreas and passed into the intestine. The optimal pH for this enzyme is 7.8. If a patient’s pancreas cannot manufacture chymotrypsin, would it be possible to supply it orally? What happens to chymotrypsin’s activity during its passage through the gastrointestinal tract?8 Explain why transition-state analogs are potent inhibitors.23.49P 0 Explain the relationship between transition-state analogs and abzymes.1 (Chemical Connections 23A) Acetylcholine causes muscles to contract. Succinylcholine, a close relative, is a muscle relaxant. Explain the different effects of these related compounds.23.52P 23.53P 23.54P 23.55P 6 (Chemical Connections 23C) What role does Mn2+ play in anchoring the substrate in the active site of protein kinase?7 (Chemical Connections 23C) Which amino acids of the active site interact with the =CH2 group of the phosphoenol pyruvate? Do these amino acids provide the same surface environment? What is the nature of the interaction?8 (Chemical Connections 23D) What is the strategy in drug design to fight AIDS?9 (Chemical Connections 23D) Why did scientists want to create a drug to inhibit cGMF diesterases?23.60P 23.61P 23.62P 3 (Chemical Connections 23E) What is the relationship between protein modification and allosteric control of phosphofructokinase?23.64P 23.65P 23.66P 23.67P 23.68P 23.69P 23.70P 1 Food can be preserved by inactivation of enzymes that would cause spoilage—for example, by refrigeration. Give an example of food preservation in which the enzymes are inactivated (a) by heat and (b) by lowering the pH.23.72P 3 Would you expect to find active digestive enzymes in a cooked hot dog? What is the reason for your answer?23.74P 23.75P 23.76P 7 An enzyme has the following pH dependence: At what pH do you think this enzyme works best?23.78P 23.79P 0 Nerve gases operate by forming covalent bonds at the active site of cholinesterase. Is this an example of competitive inhibition? Can the nerve gas molecules be removed by simply adding more substrate (acetyl choline) to the enzyme?1 What would be the appropriate name for an enzyme that catalyzes each of the following reactions:23.82P 3 A liver enzyme is made of four subunits: 2A and 2B. The same enzyme, when isolated from the brain, has the following subunits: 3A and lB. What would you call these two enzymes?23.84P 23.85P 23.86P 23.87P 23.88P 23.89P 23.90P 23.91P Problem 24-1 What is the functional difference between G-protein and GTP?24-2 What kind of signal travels along the axon Of a neuron?24.3P 24.4P 24.5P 24.6P 24.7P 24.8P 24.9P 24-10 Which end of the acetylcholine molecule fits into the receptor site?24.11P 24.12P 24.13P 24.14P 24.15P 24-16 List two features by which taurine differs from the amino acids found in proteins.24.17P 24-18 What is unique in the structure Of GABA that distinguishes it from the amino acids that are present in proteins?24.19P 24.20P 24.21P 24-22 How is the catalytic unit of protein kinase activated in adrenergic neurotransmission?24.23P 24.24P 24.25P 24.26P 24.27P 24.28P 24.29P 24.30P 24.31P 24.32P 24.33P 24.34P 24.35P 24.36P 24.37P 24.38P 24.39P 24.40P 24-41 Describe the signaling pathway involving insulin.24-42 Does insulin use a G-protein signaling pathway? What is the nature of the insulin receptor?24.43P 24.44P 24.45P 24-46 Do steroid hormones always bind directly to DNA in their action to stimulate protein synthesis? If not, what do they do?24.47P 24.48P 24.49P 24.50P 24.51P 24.52P 24.53P 24.54P 24.55P 24.56P 24.57P 24.58P 24.59P 24.60P 24-61 (Chemical Connections 24C) What are the purposes Of the drugs that are used to fight Alzheimer's?24.62P 24.63P 24.64P 24.65P 24.66P 24.67P 24.68P 24.69P 24.70P 24.71P 24.72P 24.73P 24.74P 24.75P 24.76P 24.77P 24.78P 24.79P 24-80 (Chemical Connections 24G) What makes ketamine an attractive prospect for an antidepressant?24.81P 24.82P 24.83P 24.84P 24.85P 24.86P 24.87P 24.88P 24.89P 24.90P 24.91P 24.92P 24-93 Why are receptors proteins, rather than any Other kind of molecule?24.94P 24-95 What relationship do adrenergic messengers have to amino acid messengers, and what does this relation- ship say about the biochemical origin Of adrenergic messengers?24-96 What functional groups are found in the structures Of chemical messengers? What do these structural features imply about the active sites of the enzymes that process these messengers?24.97P 24.98P

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