Lehninger Principles of Biochemistry 5th Edition by David L. Nelson -Test Bank

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Lehninger Principles of Biochemistry 5th Edition by David L. Nelson -Test Bank

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Lehninger Principles of Biochemistry 5th Edition by David L. Nelson -Test Bank

Chapter 5   Protein Function

 

 

 

 

Multiple Choice Questions

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 153  Difficulty: 2     Ans: D

The interactions of ligands with proteins:

 

  1. are relatively nonspecific.
  2. are relatively rare in biological systems.
  3. are usually irreversible.
  4. are usually transient.
  5. usually result in the inactivation of the proteins.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 154  Difficulty: 1     Ans: D

A prosthetic group of a protein is a non-protein structure that is:

 

  1. a ligand of the protein.
  2. a part of the secondary structure of the protein.
  3. a substrate of the protein.
  4. permanently associated with the protein.
  5. transiently bound to the protein.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Pages: 154155    Difficulty: 2     Ans: B

When oxygen binds to a heme-containing protein, the two open coordination bonds of Fe2+ are occupied by:

 

  1. one O atom and one amino acid atom.
  2. one O2 molecule and one amino acid atom.
  3. one O2 molecule and one heme atom.
  4. two O atoms.
  5. two O2

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 156  Difficulty: 2     Ans: A

In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as:

 

  1. linear with a negative slope.
  2. linear with a positive slope.

 

 

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Pages: 155-156     Difficulty: 2     Ans: E

Which of the following statements about protein-ligand binding is correct?

 

  1. The Ka is equal to the concentration of ligand when all of the binding sites are occupied.
  2. The Ka is independent of such conditions as salt concentration and pH.
  3. The larger the Ka (association constant), the weaker the affinity.
  4. The larger the Ka, the faster is the binding.
  5. The larger the Ka, the smaller the Kd (dissociation constant).

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 159  Difficulty: 2     Ans: E

Myoglobin and the subunits of hemoglobin have:

 

  1. no obvious structural relationship.
  2. very different primary and tertiary structures.
  3. very similar primary and tertiary structures.
  4. very similar primary structures, but different tertiary structures.
  5. very similar tertiary structures, but different primary structures.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Pages: 161-162     Difficulty: 2     Ans: B

An allosteric interaction between a ligand and a protein is one in which:

 

  1. binding of a molecule to a binding site affects binding of additional molecules to the same site.
  2. binding of a molecule to a binding site affects binding properties of another site on the protein.
  3. binding of the ligand to the protein is covalent.
  4. multiple molecules of the same ligand can bind to the same binding site.
  5. two different ligands can bind to the same binding site.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 161  Difficulty: 1     Ans: C

In hemoglobin, the transition from T state to R state (low to high affinity) is triggered by:

 

  1. Fe2+
  2. heme binding.
  3. oxygen binding.
  4. subunit association.
  5. subunit dissociation.

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Pages: 167            Difficulty: 2     Ans: C

Which of the following is not correct concerning 2,3-bisphosphoglycerate (BPG)?

 

  1. It binds at a distance from the heme groups of hemoglobin.
  2. It binds with lower affinity to fetal hemoglobin than to adult hemoglobin.
  3. It increases the affinity of hemoglobin for oxygen.
  4. It is an allosteric modulator.
  5. It is normally found associated with the hemoglobin extracted from red blood cells.

 

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 165  Difficulty: 2     Ans: C

Which of the following is not correct concerning cooperative binding of a ligand to a protein?

 

  1. It is usually a form of allosteric interaction.
  2. It is usually associated with proteins with multiple subunits.
  3. It rarely occurs in enzymes.
  4. It results in a nonlinear Hill Plot.
  5. It results in a sigmoidal binding curve.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 168-169       Difficulty: 1     Ans: D

Carbon monoxide (CO) is toxic to humans because:

 

  1. it binds to myoglobin and causes it to denature.
  2. it is rapidly converted to toxic CO2.
  3. it binds to the globin portion of hemoglobin and prevents the binding of O2.
  4. it binds to the Fe in hemoglobin and prevents the binding of O2.
  5. it binds to the heme portion of hemoglobin and causes heme to unbind from hemoglobin.

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Pages: 168-169     Difficulty: 1     Ans: D

The amino acid substitution of Val for Glu in Hemoglobin S results in aggregation of the protein because of ___________ interactions between molecules.

 

  1. covalent
  2. disulfide
  3. hydrogen bonding
  4. hydrophobic
  5. ionic

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Pages: 168-169     Difficulty: 2     Ans: C

The fundamental cause of sickle-cell disease is a change in the structure of:

 

  1. red cells.
  2. the heart.

  1. Complementary interactions between proteins and ligands: the immune system and immunoglobulins

Pages: 170-171     Difficulty: 2     Ans: B

An individual molecular structure within an antigen to which an individual antibody binds is as a(n):

 

  1. Fab region.
  2. Fc region
  3. MHC site.

 

  1. Complementary interactions between proteins and ligands: the immune system and immunoglobulins

Page: 171-172       Difficulty: 3     Ans: B

Which of the following parts of the IgG molecule are not involved in binding to an antigen?

 

  1. Fab
  2. Fc
  3. Heavy chain
  4. Light chain
  5. Variable domain

 

  1. Complementary interactions between proteins and ligands: the immune system and immunoglobulins

Page: 173  Difficulty: 3     Ans: C

A monoclonal antibody differs from a polyclonal antibody in that monoclonal antibodies:

 

  1. are labeled with chemicals that can be visualized.
  2. are produced by cells from the same organism that produced the antigen.
  3. are synthesized by a population of identical, or cloned, cells.
  4. are synthesized only in living organisms.
  5. have only a single polypeptide chain that can recognize an antigen.

 

  1. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors

Page: 175  Difficulty: 2     Ans: A

Which of the following generalizations concerning motor proteins is correct?

 

  1. They convert chemical energy into kinetic energy.
  2. They convert chemical energy into potential energy.
  3. They convert kinetic energy into chemical energy.
  4. They convert kinetic energy into rotational energy.
  5. They convert potential energy into chemical energy.

 

  1. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors

Page: 175  Difficulty: 2     Ans: B

The predominant structural feature in myosin molecules is:

 

  1. a b
  2. an a
  3. the Fab domain.
  4. the light chain.
  5. the meromyosin domain.

 


  1. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors

Page: 177  Difficulty: 1     Ans: A

The energy that is released by the hydrolysis of ATP by actin is used for:

 

  1. actin filament assembly.
  2. actin filament disassembly.
  3. actin-myosin assembly.
  4. actin-myosin disassembly.
  5. muscle contraction.

 

  1. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors

Pages: 177-178     Difficulty: 1     Ans: B

During muscle contraction, hydrolysis of ATP results in a change in the:

 

  1. conformation of actin.
  2. conformation of myosin.
  3. structure of the myofibrils.
  4. structure of the sarcoplasmic reticulum.
  5. structure of the Z disk.

 

 

Short Answer Questions

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 153  Difficulty: 1

Describe the concept of induced fit in ligand-protein binding.

 

Ans: Induced fit refers to the structural adaptations that occur when a ligand binds to a protein.  This often involves a conformational change in the protein that alters the binding site to make it more complementary to the ligand.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 154  Difficulty: 2

Explain why most multicellular organisms use an iron-containing protein for oxygen binding rather than free Fe2+.  Your answer should include an explanation of (a) the role of heme and (b) the role of the protein itself.

 

Ans: (a) Binding of free Fe2+ to oxygen would result in the formation of reactive oxygen species that can damage biological structures.  Heme-bound iron is less reactive in this regard.  (b) Binding of oxygen to free heme can result in irreversible oxidation of the Fe2+ to Fe3+ that does not bind oxygen.  The environment of the heme group in proteins helps to prevent this from occurring.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Pages: 155157    Difficulty: 2

Describe how you would determine the Ka (association constant) for a ligand and a protein.

 

Ans: An experiment would be carried out in which a fixed amount of the protein is incubated with varying amounts of ligand (long enough to reach equilibrium).  The fraction of protein molecules that have a molecule of ligand bound is then determined.  A plot of this fraction (q) vs. ligand concentration [L] should yield a hyperbola.  The value of [L] when q = 0.5 is equal to 1/Ka.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins
Page: 163-164       Difficulty: 1

Why is carbon monoxide (CO) toxic to aerobic organisms?

 

Ans: It binds to heme with a higher affinity than oxygen, and thus prevents oxygen from binding to hemoglobin.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 156  Difficulty: 2

For the binding of a ligand to a protein, what is the relationship between the Ka (association constant), the Kd (dissociation constant), and the affinity of the protein for the ligand?

 

Ans: Ka = 1/Kd.  The larger the Ka (and hence the smaller the Kd), the higher the affinity of the protein for the ligand.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 156  Difficulty: 2

What fraction of ligand binding sites are occupied (q) when [ligand] = Kd?  Show your work.

 

Ans:

 

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 158  Difficulty: 2

Explain briefly why the relative affinity of heme for oxygen and carbon monoxide is changed by the presence of the myoglobin protein.

 

Ans: The geometry of binding O2 and CO to heme is slightly different.  In myoglobin there is a histidine residue that does not interact with the heme iron, but can interact with a ligand that is bound to the heme.  It does not affect O2 binding but because of steric hindrance, it may prevent CO binding.  As a result the relative affinity of protein-bound heme for CO and O2 is only 200, compared to 20,000 for free heme.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Pages: 156, 161    Difficulty: 3

Explain why the structure of myoglobin makes it function well as an oxygen-storage protein whereas the structure of hemoglobin makes it function well as an oxygen-transport protein.

 

Ans: The hyperbolic binding of oxygen to the single binding site of myoglobin results in a high affinity even at the relatively low partial pressures of O2 that occur in tissues.  In contrast, the cooperative (sigmoidal) binding of O2 to the multiple binding sites of hemoglobin results in high affinity at high partial pressures such as occur in the lungs, but lower affinity in the tissues.  This permits hemoglobin to bind O2 in the lungs and release it in the tissues.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Pages: 162165    Difficulty: 2

Describe briefly the two principal models for the cooperative binding of ligands to proteins with multiple binding sites

 

Ans: In the concerted model, binding of a ligand to one site on one subunit results in an allosteric effect that converts all of the remaining subunits to the high-affinity conformation.  As a result, all of the subunits are either in the low- or high-affinity conformation.  In the sequential model, each subunit is changed individually to the high affinity conformation.  As a result, there are many possible combinations of low- and high-affinity subunits.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Page: 167  Difficulty: 2

How does BPG binding to hemoglobin decrease its affinity for oxygen?

 

Ans: BPG binds to a cavity between the b subunits.  It binds preferentially to molecules in the low-affinity T state, thereby stabilizing that conformation.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins
Page: 166  Difficulty: 2
  1. a) What is the effect of pH on the binding of oxygen to hemoglobin (the Bohr Effect)? (b) Briefly describe the mechanism of this effect.

Ans: (a) The affinity decreases with decreasing pH.  (b)  At lower pH (i.e., higher H+ concentration) there is increasing protonation of protein residues such as histidine, which stabilizes the low affinity conformation of the protein subunits.

 

  1. Reversible binding of a protein to a ligand: oxygen-binding proteins

Pages: 168-169     Difficulty: 2

Explain how the effects of sickle cell disease demonstrate that hemoblobin undergoes a conformational change upon releasing oxygen.

 

Ans:  In Hemoglobin S, the wild-type glutamate at residue 6 of the B-chain is replaced by valine.  When oxygen is bound, both Hemoglobin A and Hemoglobin S are soluble, but in the deoxy- form. Hemoglobin S (but not Hemoglobin A) becomes very insoluble, due to exposure of the hydrophobic valine residue.  This exposed patch causes aggregation of deoxy-Hemoglobin S into long insoluble fibrous aggregates, resulting in distorted shapes of the red blood cells (and leading to the symptoms of the disease).  (See p. 168-169 and Fig. 5-20.)

 

  1. Complementary interactions between proteins and ligands: the immune system and immunoglobulins
Page: 170  Difficulty: 1

Why is it likely that the immune system can produce a specific antibody that can recognize and bind to any specific chemical structure?

 

Ans: As a result of genetic recombination mechanisms, antibody-producing B cells are capable of producing millions of different antibodies with different binding specificities.

 

 


  1. Complementary interactions between proteins and ligands: the immune system and immunoglobulins

Page: 171  Difficulty: 2

Describe briefly the basic structure of an IgG protein molecule.

 

Ans: An IgG protein contains two copies of a large polypeptide (heavy chain) and two copies of a small polypeptide (light chain).  b structure contributes significantly to the tertiary structure of domains of both chains.  Disulfide bonds link the heavy chains to one another and to the light chains.  The chains are arranged in a Y-shaped structure where the two arms are linked to the base by a protease sensitive (hinge) region.

 

  1. Complementary interactions between proteins and ligands: the immune system and immunoglobulins

Page: 173  Difficulty: 2

What is the chemical basis for the specificity of binding of an immunoglobin antibody to a particular antigen?

 

Ans: Specific binding results from complementarity between the chemical properties (such as size, charge, and hydrophobicity) of the antigen and the antigen-binding site of the antibody.

 

  1. Complementary interactions between proteins and ligands: the immune system and immunoglobulins

Page: 173  Difficulty: 2

What is the concept of induced fit as it applies to antigen-antibody binding?

 

Ans: The conformations of the antigen and antigen-binding site of the antibody are influenced by each other and change as binding occurs.  These conformational changes increase the chemical complementarity of the sites and result in tighter binding.

 

  1. Complementary interactions between proteins and ligands: the immune system and immunoglobulins

Page: 173  Difficulty: 2

Describe how immunoaffinity chromatography is performed.

 

Ans: The specific antibody is covalently attached to an inert supporting material, which is then packed into a chromatography column.  The protein solution is passed through the column slowly; most proteins pass directly through, but those for which the antibody has specific affinity are adsorbed.  They can subsequently be eluted by a buffer of low pH, a salt solution, or some other agent that breaks the antibody-antigen association.

 

  1. Complementary interactions between proteins and ligands: the immune system and immunoglobulins

Pages: 173175    Difficulty: 2

What properties of antibodies make them useful biochemical reagents?  Describe one biochemical application of antibodies (with more than just the name of the technique).

 

Ans: The important properties are the high specificity of protein recognition, and the high affinity of the antibody-antigen association.  These make possible immunoaffinity chromatography, immunocytochemistry, enzyme-linked immunosorbent assay (ELISA), and immunoblotting, all of which are described on pp. 173-175.

 

  1. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors

Page: 175  Difficulty: 2

Describe briefly the structure of myosin.

 

Ans: Myosin contains two copies of a large polypeptide (heavy chain) and four copies of a small polypeptide (light chain).  The a helix contributes significantly to the structure of the heavy chains.  At their carboxyl termini, the heavy chains are wrapped around each other in a fibrous left-handed coil.  At their amino termini, they each have a globular domain with which the light chains are associated.

 

  1. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors

Page: 176  Difficulty: 1

What is the relationship between G-actin and F-actin?

 

Ans: G-actin is a monomeric protein that can polymerize to form a long polymeric filament known as F-actin.

 

  1. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors

Page: 178  Difficulty: 2

What is the role of ATP and ATP hydrolysis in the cycle of actin-myosin association and disassociation that leads to muscle contraction?

 

Ans: ATP binding to myosin results in a conformational change that causes dissociation of actin from the myosin.  ATP hydrolysis results in a change of orientation of the myosin relative to the actin filament, which allows movement to the next actin subunit.  This is followed initially by release of the phosphate hydrolysis product and weak binding of the myosin to this actin subunit, and, subsequently, by tight binding and release of the ADP hydrolysis product.

 

  1. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors

Page: 178  Difficulty: 2

Describe the cycle of actin-myosin association and disassociation that leads to muscle contraction.

 

Ans: First, ATP binds to myosin and a cleft in the myosin molecule opens, disrupting the actin-myosin interaction so that the bound actin is released.  Second, ATP is hydrolyzed, causing a conformational change in the protein to a high-energy state that moves the myosin head and changes its orientation in relation to the actin thin filament.  Myosin then binds weakly to an F-actin subunit closer to the Z disk than the one just released.  Third, as the phosphate product of ATP hydrolysis is released from myosin, another conformational change occurs in which the myosin cleft closes, strengthening the myosin-actin binding.  Fourth, this is followed quickly by a power stroke during which the conformation of the myosin head returns to the original resting state, its orientation relative to the bound actin changing so as to pull the tail of the myosin toward the Z disk.  ADP is then released to complete the cycle.  (See Fig. 5-31, p. 178.)

 


  1. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors

Page: 177-179       Difficulty: 2

Although the myosin molecule walks along actin in discrete steps, you are aboe to make smooth motions using your muscles.  Explain how this is possible.

 

Ans: A given muscle consists of many bundled muscle fibers, each of which contains many myofibrils, each of which contains many thick and thin filaments.  Furthermore when a muscle contracts, the myosin molecules move asynchronously. Thus, the individual steps of individual myosin molecules are masked by the millions of other myosin molecules taking steps at different times.

Chapter 17   Fatty Acid Catabolism

 

 

 

 

Multiple Choice Questions

 

  1. Digestion, mobilization, and transport of fats

Pages: 648-649     Difficulty: 2     Ans: A

Lipoprotein lipase acts in:

 

  1. hydrolysis of triacylglycerols of plasma lipoproteins to supply fatty acids to various tissues.
  2. intestinal uptake of dietary fat.
  3. intracellular lipid breakdown of lipoproteins.
  4. lipoprotein breakdown to supply needed amino acids.
  5. none of the above.

 

  1. Digestion, mobilization, and transport of fats

Pages: 649-650     Difficulty: 2     Ans: B

Free fatty acids in the bloodstream are:

 

  1. bound to hemoglobin.
  2. carried by the protein serum albumin.
  3. freely soluble in the aqueous phase of the blood.
  4. nonexistent; the blood does not contain free fatty acids.
  5. present at levels that are independent of epinephrine.

 

  1. Digestion, mobilization, and transport of fats

Pages: 649-650     Difficulty: 2     Ans: C

The role of hormone-sensitive triacylglycerol lipase is to:

 

  1. hydrolyze lipids stored in the liver.
  2. hydrolyze membrane phospholipids in hormone-producing cells.
  3. hydrolyze triacylglycerols stored in adipose tissue.
  4. synthesize lipids in adipose tissue.
  5. synthesize triacylglycerols in the liver.

 

  1. Digestion, mobilization, and transport of fats

Pages: 650            Difficulty: 2     Ans: C

The glycerol produced from the hydrolysis of triacylglycerides enters glycolysis as:

 

  1. glucose-6-phosphate.
  2. dihydroxyacetone phosphate.
  3. glyceryl CoA.

 


  1. Digestion, mobilization, and transport of fats

Pages: 650-652     Difficulty: 1     Ans: A

Transport of fatty acids from the cytoplasm to the mitochondrial matrix requires:

 

  1. ATP, carnitine, and coenzyme A.
  2. ATP, carnitine, and pyruvate dehydrogenase.
  3. ATP, coenzyme A, and hexokinase.
  4. ATP, coenzyme A, and pyruvate dehydrogenase.
  5. carnitine, coenzyme A, and hexokinase.

 

  1. Digestion, mobilization, and transport of fats

Page: 652  Difficulty: 2     Ans: A

Fatty acids are activated to acyl-CoAs and the acyl group is further transferred to carnitine because:

 

  1. acyl-carnitines readily cross the mitochondrial inner membrane, but acyl-CoAs do not.
  2. acyl-CoAs easily cross the mitochondrial membrane, but the fatty acids themselves will not.
  3. carnitine is required to oxidize NAD+to NADH.
  4. fatty acids cannot be oxidized by FAD unless they are in the acyl-carnitine form.
  5. None of the above is true.

 

  1. Digestion, mobilization, and transport of fats

Pages: 651-652     Difficulty: 2     Ans: C

Carnitine is:

 

  1. a 15-carbon fatty acid.
  2. an essential cofactor for the citric acid cycle.
  3. essential for intracellular transport of fatty acids.
  4. one of the amino acids commonly found in protein.
  5. present only in carnivorous animals.

 

  1. Digestion, mobilization, and transport of fats

Page: 652  Difficulty: 2     Ans: B

Which of these is able to cross the inner mitochondrial membrane?

 

  1. AcetylCoA
  2. Fatty acylcarnitine
  3. Fatty acylCoA
  4. MalonylCoA
  5. None of the above can cross.

 


  1. Oxidation of fatty acids

Pages: 652-653     Difficulty: 2     Ans: C

What is the correct order of function of the following enzymes of b oxidation?

  1. b-Hydroxyacyl-CoA dehydrogenase
  2. Thiolase
  3. Enoyl-CoA hydratase
  4. Acyl-CoA dehydrogenase

 

  1. 1, 2, 3, 4
  2. 3, 1, 4, 2
  3. 4, 3, 1, 2
  4. 1, 4, 3, 2
  5. 4, 2, 3, 1

 

  1. Oxidation of fatty acids

Pages: 654-656     Difficulty: 2     Ans: D

If the 16-carbon saturated fatty acid palmitate is oxidized completely to carbon dioxide and water (via the b-oxidation pathway and the citric acid cycle), and all of the energy-conserving products are used to drive ATP synthesis in the mitochondrion, the net yield of ATP per molecule of palmitate is:

 

  1. 1,000.

 

  1. Oxidation of fatty acids

Pages: 654-656     Difficulty: 2     Ans: C

Saturated fatty acids are degraded by the stepwise  reactions of b oxidation, producing acetyl-CoA. Under aerobic conditions, how many ATP molecules would be produced as a consequence of removal of each acetyl-CoA?

 

  1. 2
  2. 3
  3. 4
  4. 5
  5. 6

 


  1. Oxidation of fatty acids

Pages: 650-656     Difficulty: 2     Ans: B

Which of the following is (are) true of the oxidation of 1 mol of palmitate (a 16-carbon saturated fatty acid; 16:0) by the b-oxidation pathway, beginning with the free fatty acid in the cytoplasm?

 

  1. Activation of the free fatty acid requires the equivalent of two ATPs.
  2. Inorganic pyrophosphate (PPi) is produced.
  3. Carnitine functions as an electron acceptor.
  4. 8 mol of FADH2are formed.
  5. 8 mol of acetyl-CoA are formed.
  6. There is no direct involvement of NAD+.

 

  1. 1 and 5 only
  2. 1, 2, and 5
  3. 1, 2, and 6
  4. 1, 3, and 5
  5. 5 only

 

  1. Oxidation of fatty acids

Pages: 650-658     Difficulty: 2     Ans: B

Complete oxidation of 1 mole of which fatty acid would yield the most ATP?

 

  1. 16-carbon saturated fatty acid
  2. 18-carbon mono-unsaturated fatty acid
  3. 16-carbon mono-unsaturated fatty acid
  4. 16-carbon poly-unsaturated fatty acid
  5. 14-carbon saturated fatty acid

 

  1. Oxidation of fatty acids

Pages: 650-656     Difficulty: 1     Ans: D

Which of the following statements apply (applies) to the b oxidation of fatty acids?

  1. The process takes place in the cytosol of mammalian cells.
  2. Carbon atoms are removed from the acyl chain one at a time.
  3. Before oxidation, fatty acids must be converted to their CoA derivatives.
  4. NADP+is the electron acceptor.
  5. The products of b oxidation can directly enter the citric acid cycle for further oxidation.

 

  1. 1 and 3 only
  2. 1, 2, and 3
  3. 1, 2, and 5
  4. 3 and 5 only
  5. 4 only

 


  1. Oxidation of fatty acids

Pages: 650-652     Difficulty: 3     Ans: D

Which of the following statements concerning the b oxidation of fatty acids is true?

 

  1. About 1,200 ATP molecules are ultimately produced per 20-carbon fatty acid oxidized.
  2. One FADH2 and two NADH are produced for each acetyl-CoA.
  3. The free fatty acid must be carboxylated in the b position by a biotin-dependent reaction before the process of b oxidation commences.
  4. The free fatty acid must be converted to a thioester before the process of b oxidation commences.
  5. Two NADH are produced for each acetyl-CoA.

 

  1. Oxidation of fatty acids

Pages: 650-656     Difficulty: 3     Ans: A

The balanced equation for the degradation of CH3(CH2)10COOH via the b-oxidation pathway is:

 

  1. A) CH3(CH2)10COOH + 5FAD + 5NAD+ + 6CoASH + 5H2O + ATP

6 Acetyl-CoA + 5FADH2 + 5NADH + 5H+ + AMP + PPi

  1. B) CH3(CH2)10COOH + 5FAD + 5NAD+ + 6CoASH + 5H2O

6 Acetyl-CoA + 5FADH2 + 5NADH + 5H+

  1. C) CH3(CH2)10COOH + 6FAD + 6NAD+ + 6CoASH + 6H2O + ATP

6 Acetyl-CoA + 6FADH2 + 6NADH + 6H+ + AMP + PPi

  1. D) CH3(CH2)10COOH + 6FAD + 6NAD+ + 6CoASH + 6H2O

6 Acetyl-CoA + 6FADH2 + 6NADH + 6H+

 

  1. Oxidation of fatty acids

Page: 653  Difficulty: 1     Ans: E

Which compound is an intermediate of the b oxidation of fatty acids?

 

  1. CH3(CH2)20COCOOH
  2. CH3CH2COCH2COOPO32
  3. CH3CH2COCH2OH
  4. CH3CH2COCOSCoA
  5. CH3COCH2COSCoA

 

  1. Oxidation of fatty acids

Page: 653  Difficulty: 2     Ans: A

The conversion of palmitoyl-CoA (16:0) to myristoyl-CoA (14:0) and 1 mol of acetyl-CoA by the b-oxidation pathway results in the net formation of:

 

  1. 1 FADH2and 1 NADH.
  2. 1 FADH2and 1 NADPH.
  3. 1 FADH2, 1 NADH, and 1 ATP.
  4. 2 FADH2and 2 NADH.
  5. 2 FADH2, 2 NADH, and 1 ATP.

 


  1. Oxidation of fatty acids

Pages: 654-656     Difficulty: 2     Ans: C

Which of the following is not true regarding the oxidation of 1 mol of palmitate (16:0) by the b-oxidation pathway?

 

  1. 1 mol of ATP is needed.
  2. 8 mol of acetyl-CoA are formed.
  3. 8 mol of FADH2are formed.
  4. AMP and PPiare formed.
  5. The reactions occur in the mitochondria.

 

  1. Oxidation of fatty acids

Pages: 654-656     Difficulty: 3     Ans: E

If an aerobic organism (e.g., the bacterium E. coli) were fed each of the following four compounds as a source of energy, the energy yield per mole from these molecules would be in the order:

 

  1. alanine > glucose > palmitate (16:0)
  2. glucose > alanine > palmitate
  3. glucose > palmitate > alanine
  4. palmitate > alanine > glucose
  5. palmitate > glucose > alanine

 

  1. Oxidation of fatty acids

Pages: 654-656, 657-660  Difficulty: 2     Ans: D

Which of the following is (are) true of the b oxidation of long-chain fatty acids?

 

  1. The enzyme complex that catalyzes the reaction contains biotin.
  2. FADH2serves as an electron carrier.
  3. NADH serves as an electron carrier.
  4. Oxidation of an 18-carbon fatty acid produces six molecules of propionyl-CoA.
  5. Oxidation of a 15-carbon fatty acid produces at least one propionyl-CoA.

 

  1. 1, 2, and 3
  2. 1, 2, and 5
  3. 2, 3, and 4
  4. 2, 3, and 5
  5. 3 and 5 only

 

  1. Oxidation of fatty acids

Pages: 657-660     Difficulty: 2     Ans: E

The following fatty acid, in which the indicated carbon is labeled with 14C, is fed to an animal:

14CH3(CH2)9COOH

After allowing 30 minutes for fatty acid b oxidation, the label would most likely be recovered in:

 

  1. acetyl-CoA.
  2. beta-hydroxy butyryl-CoA.
  3. both acetyl-CoA and propionyl-CoA.
  4. palmitoyl-CoA.
  5. propionyl-CoA.

 

  1. Oxidation of fatty acids

Pages: 657-660     Difficulty: 2     Ans: D

The carbon atoms from a fatty acid with an odd number of carbons will enter the citric acid cycle as acetyl-CoA and:

 

  1. succinyl-CoA.
  2. a-ketoglutarate.

 

  1. Oxidation of fatty acids

Pages: 657-660     Difficulty: 2     Ans: B

In the disease sprue, vitamin B12 (cobalamin) is poorly absorbed in the intestine, resulting in B12 deficiency. If each of the following fatty acids were in the diet, for which one would the process of fatty acid oxidation be most affected in a patient with sprue?

 

  1. CH3(CH2)10COOH
  2. CH3(CH2)11COOH
  3. CH3(CH2)12COOH
  4. CH3(CH2)14COOH
  5. CH3(CH2)18COOH

 

  1. Oxidation of fatty acids

Pages: 661            Difficulty: 2     Ans: B

Which enzyme is the major regulatory control point for b-oxidation?

 

  1. pyruvate carboxylase
  2. carnitine acyl transferase I
  3. acetyl CoA dehydrogenase
  4. enoyl CoA isomerase
  5. methylmalonyl CoA mutase

 

  1. Oxidation of fatty acids

Page: 662  Difficulty: 2     Ans: D

During b oxidation of fatty acids, ___________ is produced in peroxisomes but not in mitochondria.

 

  1. acetyl-CoA
  2. FADH2
  3. H2O
  4. H2O2
  5. NADH

 


  1. Oxidation of fatty acids

Pages: 664-665     Difficulty: 2     Ans: B

When comparing the b-oxidation and w-oxidation pathways, which one of the following statements is correct?

 

  1. b-oxidation and w-oxidation occur in the cytoplasm.
  2. b oxidation occurs at the carboxyl end of the fatty acid whereas w oxidation occurs at the methyl end.
  3. b oxidation occurs at the methyl end of the fatty acid whereas w oxidation occurs at the carboxyl end.
  4. b oxidation occurs mainly in the cytoplasm whereas w oxidation occurs mainly in the mitochondria.
  5. b oxidation occurs mainly in the mitochondria whereas w oxidation occurs mainly in the cytoplasm.

 

  1. Ketone bodies

Page: 666  Difficulty: 2     Ans: C

Ketone bodies are formed in the liver and transported to the extrahepatic tissues mainly as:

 

  1. acetoacetyl-CoA.
  2. beta-hydroxybutyric acid.
  3. beta-hydroxybutyryl-CoA.
  4. lactic acid.

 

 

 

  1. Ketone bodies

Page: 666  Difficulty: 1     Ans: D

The major site of formation of acetoacetate from fatty acids is the:

 

  1. adipose tissue.
  2. intestinal mucosa.

 

 


Short Answer Questions

 

  1. Digestion, mobilization, and transport of fats

Page: 647  Difficulty: 1

Why is it more efficient to store energy as lipid rather than as glycogen?

 

Ans: First, the energy yield per gram of lipid (about 38 kJ/g) is more than twice that for carbohydrate (about 17 kJ/g).  Second, lipid is stored as anhydrous lipid droplets, but carbohydrates such as glycogen and starch are stored hydrated, and the water of hydration roughly triples the effective weight of the carbohydrate, reducing the energy yield to about 6 kJ/g.

 

  1. Digestion, mobilization, and transport of fats

Page: 651  Difficulty: 2

In the first step of fatty acid oxidation, the fatty acid (RCOOH) is converted to its coenzyme A derivative in the following reaction:

 

RCOOH + ATP + CoASH RCOSCoA + AMP + PPi

 

The standard free-energy change (DG) for this reaction is 15 kJ/mol

What will tend to make the reaction more favorable when it takes place within a cell?

 

Ans: The hydrolysis of PPi by inorganic pyrophosphatase, for which DG is 19 kJ/mol, makes the overall DG more negative.

 

  1. Digestion, mobilization, and transport of fats

Pages: 651-652     Difficulty: 1

The oxidation of acetyl-CoA added to isolated, intact mitochondria is stimulated strongly by carnitine.  Why?

 

Ans: Carnitine is essential in the transport of fatty acyl groups into the mitochondrial matrix, where fatty acid oxidation occurs.

 

  1. Oxidation of fatty acids

Page: 653  Difficulty: 2

The b oxidation of fatty acids begins with this activation reaction:

 

RCH2CH2CH2COOH + ATP + CoASH

 

RCH2CH2CH2COSCoA + AMP + PPi

 

What are the next two steps (after transport into the mitochondria)?  Show structures and indicate where any cofactors participate.

 

Ans: The reactions are those catalyzed by fatty acylCoA dehydrogenase and enoyl hydratase.  See Fig. 17-8a, p. 653.

 


  1. Oxidation of fatty acids

Page: 653  Difficulty: 3

Draw the four basic steps in the oxidation of a saturated fatty acid (the b-oxidation pathway). Show structures, name enzymes, and indicate where any cofactors participate.

 

Ans: See Fig. 17-8a, p. 653.

 

  1. Oxidation of fatty acids

Page: 653  Difficulty: 2

Show the last step in the sequence of the four reactions in the b-oxidation pathway for fatty acid degradation.  Include the structures of reactant and product, the enzyme name, and indicate where any cofactors participate.

 

Ans: See the thiolase reaction, Fig. 17-8a, p. 653.

 

  1. Oxidation of fatty acids

Page: 653  Difficulty: 3

One of the steps in fatty acid oxidation in mitochondria involves the addition of water across a double bond. What is the next step in the process?  Show structures and indicate where any cofactor(s) participate(s).

 

Ans: The reaction is that catalyzed by b-hydroxyacyl-CoA dehydrogenase, for which NAD+ is cofactor.  See Fig. 17-8a, p. 653.

 

  1. Oxidation of fatty acids

Page: 653  Difficulty: 2

In the citric acid cycle, a double bond is introduced into a four-carbon compound containing the CH2CH2 group, producing fumarate. Show a similar reaction that occurs in the b-oxidation pathway.

 

Ans: See Fig. 17-8a, p. 653.

 

  1. Oxidation of fatty acids

Pages: 653-656     Difficulty: 3

Write a balanced equation for  the b oxidation of palmitoyl-CoA, a 16-carbon, fully saturated fatty acid, and indicate how much of each product is formed.

Ans: The overall reaction is:

Palmitoyl-CoA + 7CoA-SH + 7FAD + 7NAD+ + 7H2O

 

8 acetyl-CoA + 7FADH2 + 7NADH + 7H+

 


  1. Oxidation of fatty acids

Pages: 653-656     Difficulty: 3

For each two-carbon increase in the length of a saturated fatty acid chain, how many additional moles of ATP can be formed upon complete oxidation of one mole of the fatty acid to CO2 and H2O?

 

Ans: Each CH2CH2 unit yields 14 extra ATP molecules.  The two oxidations of the b-oxidation pathway produce 1 FADH2 and 1 NADH, which yield 1.5 and 2.5 ATP, respectively, by oxidative phosphorylation.  The extra acetyl-CoA, when oxidized via the citric acid cycle, yields another 10 ATP equivalents: 3 NADH, 1 FADH2, and 1 ATP or GTP.

 

  1. Oxidation of fatty acids

Pages: 653-656, 660         Difficulty: 3

Write a balanced equation for the complete oxidation (to acetyl-CoA and any other products that might be formed) of pelargonic acid, CH3(CH2)7COOH.

 

Ans: The odd-chain fatty acid is first activated to the CoA derivative, then oxidized to 3 acetyl-CoA and 1 propionyl-CoA by b oxidation.  The propionyl-CoA is converted to succinyl-CoA through the sequence of reactions shown on p. 660, Fig. 17-11.  The overall reaction is therefore:

 

Pelargonic acid + HCO3 + ATP + 4CoASH + 3FAD + 3NAD+ 

 

3 acetyl-CoA + succinyl-CoA + 3FADH2 + 3NADH + AMP + PPi

 

  1. Oxidation of fatty acids

Pages: 653-656, 660         Difficulty: 3

(a)  Describe the steps in the metabolic pathway in which cells oxidize a four-carbon, straight-chain, saturated fatty acid (butyrate; 4:0) to the fragments that enter the citric acid cycle.  Show the structures of intermediates and products, and indicate where any cofactor(s) participate(s).  (b)  In what way would you change or add to your answer if the starting fatty acid had been five carbons long (also straight-chain and saturated)?

 

Ans: (a)  Butyrate is first activated:

Butyrate + ATP + CoASH butyryl-CoA + AMP + PPi

Then, the butyryl group is transferred to carnitine and transported into the mitochondrial matrix, where it is reconverted to the butyryl-CoA derivative.  This passes through the four steps of b oxidation. (See Fig. 17-8a, p. 653.)  (b)  A five-carbon chain would undergo activation and one cycle of b oxidation, producing acetyl-CoA and propionyl-CoA.  Propionyl-CoA would be converted to succinyl-CoA by the reaction sequence in Fig. 17-11, p. 660.

 


  1. Oxidation of fatty acids

Pages: 653-656, 660         Difficulty: 3

An experimenter studying the oxidation of fatty acids in extracts of liver found that when palmitate (16:0) was provided as substrate, it was completely oxidized to CO2.  However, when undecanoic acid (11:0) was added as substrate, incomplete oxidation occurred unless he bubbled CO2 through the reaction mixture.  The addition of the protein avidin, which binds tightly to biotin, prevented the complete oxidation of undecanoic acid even in the presence of CO2, although it had no effect on palmitate oxidation.  Explain these observations in light of what you know of fatty acid oxidation reactions.

 

Ans: Oxidation of odd-chain fatty acid yields acetyl-CoA + propionyl-CoA.  The reaction CO2 + propionyl-CoA methylmalonyl-CoA is catalyzed by propionyl-CoA carboxylase, a biotin-containing enzyme, which is therefore inhibited by avidin.

 

  1. Oxidation of fatty acids

Page: 660  Difficulty: 3

Two vitamins, biotin and vitamin B12, play crucial roles in the metabolism of propionic acid (propionate). Explain this by showing the steps in which each is essential in propionate metabolism.

 

Ans: Biotin and vitamin B12 act as cofactors for propionyl-CoA carboxylase and methylmalonyl-CoA mutase, respectively; see Fig. 17-11, p. 660, for the complete sequence of reactions.

 

  1. Oxidation of fatty acids

Page: 660  Difficulty: 3

The total degradation of a fatty acid with an odd number of carbons yields acetyl-CoA and another compound, X.  Show the structure of X, and describe the pathway by which it is converted into a citric acid cycle intermediate, including where any cofactors participate.

 

Ans: X is propionyl-CoA, and its conversion into succinyl-CoA is accomplished by the reactions in Fig. 17-11, p. 660.

 

  1. Oxidation of fatty acids

Page: 660  Difficulty: 3

Show the shortest pathway by which propionyl-CoA can be converted into a citric acid cycle intermediate. Indicate where any cofactors participate.

 

Ans: See Fig. 17-11, p. 660.

 

  1. Ketone bodies

Pages: 666-667     Difficulty: 1

If you received a laboratory report showing the presence of a high concentration of ketone bodies in the urine of a patient, what disease would you suspect?  Why do ketone bodies accumulate in such patients?

 

Ans: The patient is probably an untreated diabetic, but the condition might also result from fasting.  In either case, the unavailability of glucose from the blood stimulates gluconeogenesis in the liver.  As the substrate for glucose formation, oxaloacetate is withdrawn from the citric acid cycle, bringing that cycle to a near halt.  The fatty acids being oxidized in the liver yield acetyl-CoA, which now cannot be oxidized via the citric acid cycle.  Reversal of the thiolase reaction produces acetoacetyl-CoA, which is then converted into ketone bodies and exported from the liver. See Fig. 17-18, p. 666.

 

  1. Ketone bodies

Pages: 666-667     Difficulty: 2

Draw the structure of one ketone body, and describe circumstances under which you would expect to find high concentrations of this compound in the urine of a human.

 

Ans: The ketone bodies, acetoacetate, b-hydroxybutyrate, and acetone (p. 666), are overproduced in untreated diabetes mellitus and during prolonged fasting, when fatty acids become the principle energy source.

 

  1. Ketone bodies

Pages: 666-667     Difficulty: 2

What are ketone bodies and why do they form during fasting?

 

Ans: The ketone bodies, acetoacetate, b-hydroxybutyrate, and acetone, are overproduced during fasting, when fatty acids from stored triacylglycerols become the principle oxidizable fuel.  Accumulation of acetyl-CoA and its precursor acetoacetyl-CoA favors ketone body formation.  Because oxaloacetate is used for gluconeogenesis, it is withdrawn from the citric acid cycle, bringing that cycle to a near halt.  The acetyl-CoA that is produced by b oxidation can no longer be oxidized via the citric acid cycle so it accumulates.

Chapter 27   Protein Metabolism

 

 

 

 

Multiple Choice Questions

 

  1. The genetic code

Page: 1069                        Difficulty: 2     Ans: C

A certain bacterial mRNA is known to represent only one gene and to contain about 800 nucleotides.  If you assume that the average amino acid residue contributes 110 to the peptide molecular weight, the largest polypeptide that this mRNA could code for would have a molecular weight of about:

 

  1. 5,000.
  2. 30,000.
  3. 80,000.
  4. An upper limit cannot be determined from the data given.

 

  1. The genetic code

Page: 1038                        Difficulty: 2     Ans: C

Assuming that the average amino acid residue contributes 110 to the peptide molecular weight, what will be the minimum length of the mRNA encoding a protein of molecular weight 50,000?

 

  1. 133 nucleotides
  2. 460 nucleotides
  3. 1,400 nucleotides
  4. 5,000 nucleotides
  5. A minimum length cannot be determined from the data given.

 

  1. The genetic code

Pages: 1070-1074 Difficulty: 3     Ans: D

Which of the following are features of the wobble hypothesis?

 

  1. A naturally occurring tRNA exists in yeast that can read both arginine and lysine codons.
  2. A tRNA can recognize only one codon.
  3. Some tRNAs can recognize codons that specify two different amino acids, if both are nonpolar.
  4. The wobble occurs only in the first base of the anticodon.
  5. The third base in a codon always forms a normal Watson-Crick base pair.

 

  1. The genetic code

Page: 1069                        Difficulty: 2     Ans: C

Which one of the following is true about the genetic code?

 

  1. All codons recognized by a given tRNA encode different amino acids.
  2. It is absolutely identical in all living things.
  3. Several different codons may encode the same amino acid.
  4. The base in the middle position of the tRNA anticodon sometimes permits wobble base pairing with 2 or 3 different codons.
  5. The first position of the tRNA anticodon is always adenosine.

 

  1. Protein synthesis

Pages: 1076-1077             Difficulty: 1     Ans: D

Which one of the following statements about ribosomes is true?

 

  1. The large subunit contains rRNA molecules, the small subunit does not.
  2. The RNA in ribosomes plays a structural, not catalytic, role.
  3. There are about 25 of them in an coli cell.
  4. There are two major subunits, each with multiple proteins.
  5. They are relatively small, with molecular weights less than 10,000.

 

  1. Protein synthesis

Pages: 1079-1080             Difficulty: 2     Ans: A

Which of the following statements about tRNA molecules is false?

 

  1. A, C, G, and U are the only bases present in the molecule.
  2. Although composed of a single strand of RNA, each molecule contains several short, double-helical regions.
  3. Any given tRNA will accept only one specific amino acid.
  4. The amino acid attachment is always to an A nucleotide at the 3 end of the molecule.
  5. There is at least one tRNA for each of the 20 amino acids.

 

  1. Protein synthesis

Page: 1080   &

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