Questions and Answers of Fundamentals Of Biochemistry

A child suffering from severe abdominal pain is admitted to the hospital several hours after eating a meal consisting of hamburgers, fried potatoes, and ice cream. Her blood has the appearance of
Identify the products generated by the action of pancreatic lipase on the lipid shown Below. HC-0-cl HC-0- || || HC-0-C 9 9 1-Palmitoyl-2,3-dioleoyl-glycerol 16 18 18
(a) What is the charge of bile acids in the small intestine, where the pH is 7–8?(b) According to one hypothesis, bile acids are toxic to VetBooks bacteria and so could help limit their growth in
Bacteria that live in the large intestine metabolize glycocholic acid using amidases and hydroxylases.(a) Draw the reaction product.(b) Compare the solubility of the product and glycocholic acid.(c)
Two lipoproteins have the following characteristics:Which lipoprotein has a higher density? Lipoprotein A Lipoprotein B Diameter () 200 100 % Triacylglycerol 10 5 % Protein 20 55
Which fatty acids were used to build the molecule shown here, which functions as a signaling molecule? 0-C-(CH) 14CH3 CH(CH),CH(CH)10 COO
Why are the symptoms of carnitine palmitoyl transferase II deficiency more severe during fasting?
The first three steps of β oxidation chemically resemble three successive steps of the citric acid cycle. Which steps are these?
The structure of E. coli ACP includes an extensive hydrophobic pocket. What is its purpose?
The surface of E. coli ACP has a patch of Glu side chains. What can you conclude about the side chains likely to be located on the surface of the E. coli β-hydoxyacyl-ACP dehydrase?
Intestinal microbes produce butyrate, which helps regulate the immune system. How many rounds of β oxidation of palmitate are required to produce butyrate?
Short-chain fatty acids such as butyrate are absorbed by the mammalian intestine and used as metabolic fuels. How many ATP can be derived from the complete oxidation of butyrate?
Why is it important that liver cells lack 3-ketoacyl-CoA transferase?
The compound triclosan inhibits bacterial enoyl-ACP reductase. Explain why triclosan is useful as a microbicide. Cl Cl Triclosan OH Cl
An animal is fed palmitate with a 14C-labeled carboxyl group. Under ketogenic conditions, where would the label appear in acetoacetate?
On what carbon atoms does the 14CO2 used to synthesize malonyl- CoA from acetyl-CoA appear in palmitate?
Explain why adipocytes need glucose as well as fatty acids in order to synthesize triacylglycerols.
The antidiabetes drugs known as thiazolidinediones induce the production of glycerol kinase in adipocytes. Explain why this would decrease the concentration of serum fatty acids, which are often
Intestinal bacteria convert choline to trimethylamine, and the liver converts this gas to trimethylamine N-oxide (TMAO). TMAO promotes atherosclerosis, possibly by stimulating macrophages to take up
Which fatty acids were used to build the molecule shown here, which is synthesized by intestinal cells following a meal? ZH N O
Is the fatty acid shown below likely to be synthesized in animals? Explain. CH3CH-CH=CH3 CH7 C 0
One strategy for converting biomass to conventional hydrocarbon fuels involves the use of naturally occurring bacterial enzymes. In certain cyanobacteria, a fatty acyl-ACP undergoes conversion to a
The tricarboxylate transport system supplies cytosolic acetyl-CoA for palmitate synthesis. What percentage of the NADPH required for palmitate synthesis is thereby provided?
Atorvastatin, which is administered orally, has limited solubility in aqueous solutions. Is it more soluble in the stomach or in the small intestine?
Explain why cellular stressors such as high temperatures or oxidative damage would trigger the production of proteasomes.
Ritonavir, an inhibitor of HIV protease (Box 12-3), also inhibits the chymotrypsin-like activity of the proteasome. Explain why this dual inhibitory effect could contribute to the neurotoxic side
An L-amino acid oxidase in mammalian peroxisomes requires H2O and O2 as substrates and catalyzes amino acid deamination, producing H2O2 as a product. Write a balanced equation for the reaction.
Which of the 20 “standard” amino acids are(a) Purely glucogenic,(b) Purely ketogenic,(c) Both glucogenic and ketogenic?
Alanine, cysteine, glycine, serine, and threonine are amino acids whose breakdown yields pyruvate. Which, if any, of the remaining 15 amino acids also do so?
Explain why traditional diets from different parts of the world often include combinations of a grain and a legume, such as rice and beans or couscous and lentils.
Which three mammalian enzymes can potentially react with and thereby decrease the concentration of free NH+4?
E. coli can convert glutamate to ornithine. Describe the two reactions that do so.
Sarcosine dehydrogenase catalyzes N-demethylation of the nonstandard amino acid sarcosine. Name the reaction product. HC H N. 0 Sarcosine -0
Explain the chemical change that occurs in converting kynurenine (a product of tryptophan degradation) to kynurenate, a reaction in which α-ketoglutarate is transformed to glutamate. N. OH
Many of the most widely used herbicides inhibit the synthesis of aromatic amino acids. Explain why the compounds are safe to use near animals.
Describe the reactions that convert epinephrine to the compound shown here. CH3 O OH 0
From which amino acid is 2-phenylethanol derived and what chemical changes take place in the conversion? OH 2-Phenylethanol
From what amino acid is the signaling molecule tyramine derived? HO Tyramine NH
The compound shown here is used to treat trypanosome infection. What amino acid does the compound resemble? HN O | || +HN-(CH)3-C-C-0- H-C-F F
From which amino acid is the compound agmatine derived? NH T *HgN(CH,)4NH-C=NH Agmatine
From what amino acid is melatonin derived? Describe the modifications that have occurred. H3C-0 HN HN Melatonin CH3
PLP is a cofactor for a number of enzymes involved in amino acid metabolism. Give an example of reaction in which PLP participates in cleavage of the a, b, and c bonds of an amino acid, as diagrammed
Explain why inhibitors of monoamine oxidase (MAO), the enzyme that catalyzes one of the reactions in epinephrine breakdown, are often used as drugs to treat mood disorders.
Some diazotrophs produce a vanadium-containing VFe protein in addition to the MoFe protein. The vanadium-containing nitrogenase converts N2 to NH3 and also converts CO to compounds such as ethane and
Nitrosomonas is a photophobic (light-avoiding) chemoautotrophic bacterium that converts ammonia into nitrite. Explain how the organism can fix CO2 via the Calvin cycle in the absence of sunlight.
The nucleotide deoxyuridylate (dUMP) is converted to deoxythymidylate (dTMP) by methylation. Could this explain why rapidly dividing cancer cells consume large quantities of glycine?
Proliferating cells require NADPH for biosynthetic processes. Much of the NADPH is provided by the pentose phosphate pathway, but 10-formyl tetrahydrofolate is also a source of reducing power.
Mouse embryonic stem cells produce high levels of threonine dehydrogenase, whose activity appears to be essential for maintaining high levels of S-adenosylmethionine. Explain the link between
Rice plants that have been engineered to overexpress alanine aminotransferase need about two-thirds less fertilizer than control plants. What does this information reveal about the process of
Heterozygotes for erythropoietic protoporphyria show only 20 to 30% residual ferrochelatase activity rather than the 50% that is normally expected for an autosomal dominant inherited disease. Provide
Toxins that occur in certain mushrooms block β oxidation in humans. Explain why ingesting the mushrooms leads to heart palpitations and severe hypoglycemia (low blood sugar).
Growth factor stimulation of cells leads to inhibition of pyruvate kinase. As a result, glycolytic intermediates are redirected to the pentose phosphate pathway. Explain why this would help promote
The Bacteroides and Firmicutes, the most abundant organisms colonizing the human colon (large intestine), are obligate anaerobes that rely exclusively on fermentation rather than respiration. In
Some foods containing live microorganisms, known as probiotics, are advertised for their health benefits. Offer a reason why consuming such foods in most cases has no perceptible effect on the
Explain why insulin is required for adipocytes to synthesize triacylglycerols from fatty acids.
Predict the effect of an overdose of insulin on brain function in a normal person.
Stimulation of a certain Gs protein–coupled receptor activates protein kinase A (PKA). Predict the effect of PKA activation on the following substrates of PKA:(a) Acetyl-CoA carboxylase,(b)
Why can adipose tissue be considered to be an endocrine organ?
If the circulatory system of an ob/ob mouse is surgically joined to that of a normal mouse, what will be the effect on the appetite and weight of the ob/ob mouse?
In experiments to test the appetite-suppressing effects of PYY3–36, why must the hormone be administered intravenously rather than orally?
When administered intravenously, the peptide hormone PYY3–36 sometimes triggers nausea in humans. Is this consistent with its biological function?
In addition to regulating AMPK activity, adiponectin has antiinflammatory activity, which makes it attractive as a potential drug for treating inflammatory diseases. Explain why researchers are
Explain why mice deficient in UCP1 become obese when raised at 28°C but not at 20°C.
Explain why a common diagnostic test for diabetes involves orally administering a glucose solution to an individual and then measuring the concentration of blood glucose two hours later.
Explain why the probability of death as a function of body mass index (a measure of obesity) is a U-shaped curve.
High concentrations of 3-phosphoglycerate inhibit 6-phosphogluconate dehydrogenase. How does this regulatory mechanism help control the growth of a cancer cell?
What is the advantage for some tumors to stop expressing the genes for glucose-6-phosphatase, phosphoenolpyruvate carboxykinase, and fructose bisphosphatase?
Pancreatic β cells express a receptor for fatty acids. Fatty acid binding to the protein appears to stimulate insulin secretion. Does this phenomenon make metabolic sense?
Substances derived from food can act as hormones when they enter the circulation. Explain why it is advantageous for leucine to act on the central nervous system to reduce food intake.
Explain why it makes metabolic sense for adipocytes to release leptin in response to circulating short-chain fatty acids.
High concentrations of free fatty acids in the blood are known to cause insulin resistance in muscle, but only after 5 hours. This suggests that a metabolite of the fatty acids may be responsible for
Pancreatic β cells release a peptide hormone, amylin, along with insulin. Amylin acts on the brain to slow gastric emptying and inhibit the release of digestive enzymes from the pancreas.(a) Explain
Discuss, in terms of AMPK activity and GLUT4, how physical inactivity might lead to insulin resistance.
In acute lymphoblastic leukemia, the cancerous white blood cells typically lack the enzyme asparagine synthetase. Why is the administration of asparaginase an effective therapy for this type of
Describe the metabolic effects of liver failure.
From which purine is caffeine derived? HC. N -Z N CH3 Caffeine N N CH3
Among the many eat-all-you-want-and-lose-weight diets that have been popular for a time is one that eliminates all carbohydrates but permits the consumption of all the protein and fat desired. Would
How does 2-azahypoxanthine, a fungal product that stimulates plant growth, differ from guanine? H H N Z-Z N N. N N 2-Axahypoxanthine
Which reaction of the IMP → AMP pathway resembles a reaction of the urea cycle?
When starved, bacteria produce the intracellular signaling molecule ppGpp (guanosine-3′,5′-bisdiphosphate). Draw its structure.
List all the enzymes of nucleotide biosynthesis that use glutamine as an amino group donor.
Calculate the cost, in ATP equivalents, of synthesizing de novo(a) IMP(b) AMP(c) CTP. Assume all substrates (e.g., ribose-5-phosphate and glutamine) and cofactors are available.
The compound shown here is being tested as an anticancer agent.(a) Explain why it inhibits CTP production.(b) Explain why it also inhibits phospholipid synthesis. - 0= OH N H OH OH
Why is dATP toxic to mammalian cells?
The purine and pyrimidine rings are built from the amino acids aspartate, glutamine, and glycine. Why is serine required for the synthesis of deoxyribonucleotides?
Why do individuals who are undergoing chemotherapy with FdUMP or methotrexate often temporarily go bald?
Explain why methotrexate inhibits the synthesis of histidine and methionine.
p-Aminosalicylate is used to treat infections with Mycobacterium tuberculosis. Explain how this compound blocks the production of thymidylate. HN 0 OH p-Aminosalicylate
Is trimethoprim a mechanism-based inhibitor of bacterial dihydrofolate reductase?
6-Mercaptopurine (Box 23-2), after its conversion to the corresponding nucleotide through salvage reactions, is a potent competitive inhibitor of IMP in the pathways for AMP and GMP biosynthesis. It
Is allopurinol a mechanism-based inhibitor of xanthine oxidase?
Individuals with a complete deficiency of dihydropyrimidine dehydrogenase exhibit a variety of symptoms. What compounds are likely to be present at high levels in the urine of these patients?
A nucleotide derivative that may have intracellular signaling activity is synthesized from NAD+ by the removal of the nicotinamide group and addition of an acetyl group at the 2′ position of the
Why is gout more prevalent in populations that eat relatively large amounts of meat?
Gout resulting from the de novo overproduction of purines can be distinguished from gout caused by impaired excretion of uric acid by feeding a patient 15N-labeled glycine and determining the
Calculate the contour length for the gene in in Problem 3 if it assumed an A-DNA conformation.Problem 3Amino acid residues in proteins are each specified by three contiguous bases. What is the
Virus-infected cells produce the intracellular messenger cGAMP, a cyclic dinucleotide in which the GMP 2′-OH group is linked to the 5′-phosphate of AMP. Draw its structure.
How is the melting curve of duplex DNA affected by adding a small amount of ethanol?
How is the melting curve of duplex DNA affected by decreasing the ionic strength of the solution?
You have discovered an enzyme secreted by a particularly virulent bacterium that cleaves the C2′—C3′ bond in the deoxyribose residues of duplex DNA. What is the effect of this enzyme on

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