Questions and Answers of Biochemistry Concepts And Connections

Sketch the structure of folic acid. Also sketch how it serves as a carrier of one-carbon groups.
MicroRNAs play a role in physical nerve damage. What other neurological diseases are they associated with?
What enzymes are involved in production of both miRNA and siRNA?
What is the metabolic basis for the observation that many adults cannot ingest large quantities of milk without developing gastric difficulties?
A friend asks you why some parents at her child’s school want a choice of beverages served at lunch, rather than milk alone. What do you tell your friend?
Show that the reaction Glucose → 2 Glyceraldehyde-3-phosphate is slightly endergonic (ΔG°' = 2.2 kJ mol-1 = 0.53 kcal mol-1); that is, it is not too far from equilibrium. Use the data in Table
What are some of the main differences between the cell walls of plants and those of bacteria?
How does the presence of α-bonds versus α-bonds influence the digestibility of glucose polymers by humans?
According to Table 17.1, four reactions have positive ΔG values. How can this be explained? Table 17.1 Step Reaction 1 Glucose + ATP → Glucose-6-phosphate + ADP 2 Glucose-6-phosphate
According to Table 17.1, several reactions have very positive ΔG°' values. How can this be explained, given that these reactions do occur in the cell? Table 17.1 Step Reaction 1 Glucose + ATP →
Why are all the reactions in Table 20.1 written as reduction reactions? Table 20.1 Standard Reduction Potentials for Several Biological Reduction Half Reactions Reduction Half Reaction O₂ + 2H+ +
Would you expect ΔG°' for the hydrolysis of a thioester to be(a) Large and negative,(b) Large and positive, (c) Small and negative, or(d) Small and positive? Give the reason for your answer.
How are lipases activated hormonally?
What is the metabolic purpose of linking a fatty acid to coenzyme A?
Outline the role of carnitine in the transport of acyl-CoA molecules into the mitochondrion. How many enzymes are involved? What are they called?
What is the difference between the type of oxidation catalyzed by acyl-CoA dehydrogenase and that catalyzed by β-hydroxy-CoA dehydrogenase?
Why does the degradation of palmitic acid to eight molecules of acetyl-CoA require seven, rather than eight, rounds of the β-oxidation process?
Given the nature of the hormonal activation of lipases, what carbohydrate pathways would be activated or inhibited under the same conditions?
Compare the energy yields from the oxidative metabolism of glucose and of stearic acid. To be fair, calculate it on the basis of ATP equivalents per carbon and also ATP equivalents per gram.
Which generates more ATP—the processing of the reduced electron equivalents formed during β-oxidation through the electron transport chain, or the processing of the acetyl-CoA generated from
It is frequently said that camels store water in their humps for long desert journeys. How would you modify this statement on the basis of information in this chapter?
You hear a fellow student say that the oxidation of unsaturated fatty acids requires exactly the same group of enzymes as the oxidation of saturated fatty acids. Is the statement true or false? Why?
What are the unique enzymes needed to β-oxidize a monounsaturated fatty acid?
What are the unique enzymes needed to β-oxidize a polyunsaturated fatty acid?
Calculate the net ATP yield from oleic acid (18:1 Δ9).
How many cycles of β-oxidation are required to process a fatty acid with 17 carbons?
Briefly outline the reactions involved in ketone production.
Why might a doctor smell the breath of a person known to have diabetes who has just passed out?
Why might a person who is an alcoholic have a “fatty liver”?
What is the metabolic importance of malonyl-CoA?
In fatty acid degradation, we encounter coenzyme A, mitochondrial matrix, trans double bonds, L-alcohols, β-oxidation, NAD+ and FAD, acetyl-CoA, and separate enzymes. What are the counterparts in
How is ACP similar to coenzyme A? How is it different?
What is the purpose of having ACP as a distinct activating group for fatty acid synthesis?
Why are linoleate and linolenate considered essential fatty acids? What step in production of polyunsaturated fatty acids are mammals unable to perform?
Is it possible to convert fatty acids to other lipids without acyl-CoA intermediates?
What is the role of citrate in the transport of acetyl groups from the mitochondrion to the cytosol?
In the mitochondrion is a short-chain carnitine acyltransferase that can take acetyl groups from acetyl-CoA and transfer them to carnitine. How might this be related to lipid biosynthesis?
What is the source of the glycerol in triacylglycerol synthesis?
What is the activating group used in the formation of phosphoacylglycerols?
What are the differences between synthesis of phosphatidylethanolamine in prokaryotes and eukaryotes?
A cholesterol sample is prepared using acetyl-CoA labeled with 14C at the carboxyl group as precursor. Which carbon atoms of cholesterol are labeled?
Which molecules have cholesterol as a precursor?
What structural feature do all steroids have in common? What are the biosynthetic implications of this common feature?
In steroid synthesis, squalene is oxidized to squalene epoxide. This reaction is somewhat unusual, in that both a reducing agent (NADPH) and an oxidizing agent (O2) are required. Why are both needed?
Why must cholesterol be packaged for transport rather than occurring freely in the bloodstream?
A drug that reduces blood cholesterol has the effect of stimulating the production of bile salts. How might this result in lower blood cholesterol?
What role does neuropeptide Y play in control of appetite? Where do its effects take place?
What is the role of melanocortins in control of appetite?
What is ghrelin? What is its effect on appetite? Is there any substance that has an opposite effect?
How does leptin affect the metabolism of lipids?
What is the connection between insulin and leptin production?
Chlorophyll is green because it absorbs green light less than it absorbs light of other wavelengths. The accessory pigments in the leaves of deciduous trees tend to be red and yellow, but their color
The bean sprouts available at the grocery store are white or colorless, not green. Why?
What are the principal metal ions used in electron transfer in chloroplasts? Compare them to the ions found in mitochondria.
How is the structure of chloroplasts similar to that of mitochondria?How does it differ?
Suggest a reason why plants contain light-absorbing pigments in addition to chlorophylls a and b.
The first amino acid in protein synthesis in the chloroplast is N-formylmethionine. What is the significance of this fact?
Is it fair to say that the synthesis of NADPH in chloroplasts is merely the reverse of NADH oxidation in mitochondria? Explain your answer.
Do all the chlorophyll molecules in a photosynthetic reaction center play the same roles in the light reactions of photosynthesis?
Which is likely to have evolved first, the electron transport chain in chloroplasts or in mitochondria? Explain your answer.
A larger proton gradient is required to form a single ATP in chloroplasts than in mitochondria. Suggest a reason why.
What is implied about the energy requirements of photosystems I and II by the fact that there is a difference in the minimum wavelength of light needed for them to operate (700 nm for photosystem I
Is it reasonable to list standard reduction potentials for the reactions of photosynthesis? Why or why not?
Why is a photosynthetic reaction center comparable to a battery?
It has taken considerable amounts of research to establish the number of protons pumped across the mitochondrial membrane at the various stages of electron transport.Would you expect to encounter
Why does a loosely bound cytochrome play a unique role in the reaction-center events in Rhodopseudomonas
What are the evolutionary implications of the similarity in structure and function of ATP synthase in chloroplasts and mitochondria?
In cyclic photophosphorylation in photosystem I, ATP is produced, even though water is not split. Explain how the process takes place.
What are the major similarities and differences between ATP synthesis in chloroplasts, as compared with mitochondria?
How can a proton gradient be created in cyclic photophosphorylation in photosystem I?
Can ATP production take place in chloroplasts in the absence of light? Give the reason for your answer.
What is the advantage to plants to have the option of both cyclic and noncyclic pathways for photophosphorylation
Suppose that a prokaryotic organism that contains both chlorophyll a and chlorophyll b has been discovered.Comment on the evolutionary implications of such a discovery.
Why is rubisco likely to be the most abundant protein in nature?
Is the sequence of amino acids in rubisco encoded by nuclear genes or not? Explain.
Name some other metabolic pathways that have reactions similar to those of the dark reactions of photosynthesis.
If photosynthesizing plants are grown in the presence of 14CO2, is every carbon atom of the glucose that is produced labeled with the radioactive carbon? Why or why not?
Why would nature evolve a key enzyme, rubisco, that is so sensitive to oxygen, resulting in photorespiration?
Does the whole Calvin cycle represent carbon dioxide fixation? Why or why not?
What is the evolutionary advantage to organisms that the Calvin cycle has a number of reactions in common with other pathways?
Why do we refer to the conversion of six molecules of carbon dioxide (six carbon atoms) to one molecule of glucose (also six carbon atoms) as a net reaction?
How does the production of sugars by tropical plants differ from the same reactions in the Calvin cycle?
What kinds of organisms can fix nitrogen? Which ones cannot?
What is the Haber process?
How are nitrogen-utilizing pathways controlled by feedback inhibition?
Comment briefly on the usefulness to organisms of feedback control mechanisms in long biosynthetic pathways.
Metabolic cycles are rather common (Calvin cycle, citric acid cycle, urea cycle). Why are cycles so useful to organisms?
What is the relationship between α-ketoglutarate, glutamate, and glutamine in amino acid anabolism?
Draw the mechanism of transamination with pyridoxal phosphate.
What cofactors are involved in one-carbon transfer reactions of amino acid anabolism?
Why is there no net gain of methionine if homocysteine is converted to methionine with S-adenosylmethionine as the methyl donor?
Show, by the equation for a typical reaction, why glutamate plays a central role in the biosynthesis of amino acids.
Sulfanilamide and related sulfa drugs were widely used to treat diseases of bacterial origin before penicillin and more advanced drugs were readily available. The inhibitory effect of sulfanilamide
By means of a structural formula, show how S-adenosylmethionine is a carrier of methyl groups.
Proteins contain methionine but not α-aminon-hexanoic acid. The only structural difference is the substitution of —CH2— for —S—. Both groups are similar in size and hydrophobic character.
In general, what categories of amino acids are essential in humans and which are nonessential?
List the essential amino acids for a phenylketonuric adult and compare them with the requirements for a normal adult.
How many α-amino acids participate directly in the urea cycle? Of these, how many can be used for protein synthesis?
Describe citrulline and ornithine based on their similarity to one of the 20 standard amino acids.
How many ATPs are required for one round of the urea cycle? Where do these ATPs get used?

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