Test Bank For Biochemistry 6th Edition Reginald Garrett

$25.00

Description

INSTANT DOWNLOAD COMPLETE TEST BANK WITH ANSWERS

 

Test Bank  For Biochemistry 6th Edition Reginald Garrett

 

Sample  Questions

 

1. Properties of water that render it so suited to its role as a medium of life include all EXCEPT:

  a. Unrivaled ability to form hydrogen bonds.
  b. Unusually high dielectric constant of water explains water’s ability to surround ions and increase the ions’ attraction for one another.
  c. Unparalleled ability to orient around nonpolar solutes to promote hydrophobic interactions.
  d. The small, but significant, tendency to form H+ and OH− ions.
  e. None, all are true.

 

ANSWER:   b

 

2. All are true for water for a substance of its molecular weight that is neither metallic nor ionic EXCEPT:

  a. a high surface tension.
  b. a chemically inert solvent, which has a great capacity to dissolve a diverse spectrum of molecules and ions.
  c. a positive volume of melting.
  d. a high dielectric constant.
  e. a high capacity to form hydrogen bonds

 

ANSWER:   c

 

3. The unrivaled ability to form ____ hydrogen bonds per liquid water molecule is the source of the strong intermolecular attractions unique to water.

  a. 1
  b. 2
  c. 3
  d. 4
  e. 5

 

ANSWER:   d

 

4. Because of its highly polar nature, water is an excellent solvent for polar substances, but NOT for:

  a. salts.
  b. sugars.
  c. aldehydes and ketones.
  d. hydrocarbons.
  e. alcohols and amines.

 

ANSWER:   d

 

5. The solvent with the highest dielectric constant in this group is:

  a. water.
  b. acetic acid.
  c. ethanol.
  d. hexane.
  e. benzene.

 

ANSWER:   a

 

6. Hydrogen bonds in ice are all EXCEPT:

  a. directional.
  b. straight.
  c. weak.
  d. responsible for the lower density of ice over liquid water.
  e. holding water molecules in ice apart.

 

ANSWER:   c

 

7. Pure liquid water consists of H2O molecules:

  a. held in a rigid three-dimentional network.
  b. with local preference for linear geometry.
  c. with large numbers of strained or broken hydrogen bonds.
  d. which do not switch H-bonds readily.
  e. all are true.

 

ANSWER:   c

 

8. The average lifetime of a hydrogen bond connection in water is on the order of 10:

  a. picoseconds.
  b. microseconds.
  c. milliseconds.
  d. seconds.
  e. nanoseconds.

 

ANSWER:   a

 

9. The ____ bonding of water with the polar functional groups on nonionic polar solutes such as sugars are ____ than the intermolecular attractions between solute molecules allowing solute molecules to readily dissolve in water.

  a. ionic, stronger
  b. hydrogen, weaker
  c. hydrophobic, stronger
  d. hydrogen, stronger
  e. ionic, weaker

 

ANSWER:   d

 

10. The H-bonded water around an ionic substance tends to ____; and the H-bonded water around nonpolar solutes tends to ____.

  a. inhibit ionization, promote hydrophobic interactions
  b. inhibit ionization, inhibit hydrophobic interactions
  c. not impact ionization, inhibit hydrophobic interactions
  d. promote ionization, not impact hydrophobic interactions
  e. promote ionization, promote hydrophobic interactions

 

ANSWER:   e

 

11. Amphiphilic (amphipathic) molecules include:

  a. sugars.
  b. acidic amino acids.
  c. inorganic salts.
  d. water.
  e. salts of fatty acids.

 

ANSWER:   e

 

12. In micelles:

  a. polar ends form hydrophobic interactions with water.
  b. nonpolar ends form hydrophilic interactions with water.
  c. hydrocarbon tails form hydrophobic interactions with water.
  d. polar ends are hydrophobic and nonpolar ends are hydrophilic.
  e. hydrocarbon tails are excluded from the water into hydrophobic domains.

 

ANSWER:   e

 

13. By limiting the orientation that neighboring water molecules can assume, solutes give ____ to the solvent and ____ the dynamic interplay among H2O molecules that occurs in pure water.

  a. pressure, disrupt
  b. disorder, increase
  c. disorder, decrease
  d. order, diminish
  e. order, increase

 

ANSWER:   d

 

14. To ____ the osmotic pressure created by the contents of their cytosol, cells tend to store substances such as amino acids and sugars in ____ form.

  a. increase, monomeric
  b. minimize, polymeric
  c. minimize, monomeric
  d. maximize, polymeric
  e. increase, polymeric

 

ANSWER:   b

 

15. Water ionizes because:

  a. the smaller electronegative oxygen atom strips the electron from one of its hydrogen atoms, leaving the proton to dissociate.
  b. the larger electronegative oxygen atom strips the electron from one of its hydrogen atoms, leaving the proton to dissociate.
  c. the smaller electropositive oxygen atom strips the electron from one of its hydrogen atoms, leaving the proton to dissociate.
  d. the larger electropositive oxygen atom strips the electron from one of its hydrogen atoms, leaving the proton to dissociate.
  e. None of the above

 

ANSWER:   b

 

16. Grapefruit juice at pH 3.2 contains about ____ times as much H+ as orange juice at pH 4.3.

  a. 0.9
  b. 10−7.5
  c. 10−2
  d. 12
  e. 101

 

ANSWER:   d

 

17. All are examples of weak electrolytes EXCEPT:

  a. hydrochloric acid.
  b. acetic acid.
  c. lactic acid.
  d. phosphoric acid.
  e. carbonic acid.

 

ANSWER:   a

 

18. If 0.1 moles of Na2HPO4 and 0.1 moles of NaH2PO4 are mixed in water, what is the resulting pH? The pKa values for phosphoric acid are 2.1, 7.2, 12.4.

  a. 2.1
  b. 4.65
  c. 7.2
  d. 9.8
  e. 12.4

 

ANSWER:   c

 

19. Estimate the pH of the resulting solution prepared by mixing 1.0 mole of solid disodium phosphate (Na2HPO4) and 1.25 mole of hydrochloric acid. The pKa values for phosphoric acid are 2.1, 7.2, 12.4.

  a. pH < 2.1
  b. pH = 2.1
  c. 2.1 < pH < 7.2
  d. pH = 7.2
  e. 7.2 < pH < 12.4

 

ANSWER:   c

 

20. Which of the following pairs would be the best buffer at pH 10.0?

  a. Acetic acid and sodium acetate (pKa = 4.76)
  b. H2CO3 and NaHCO3 (pKa values are 3.77 and 10.4)
  c. Lactic acid and sodium lactate (pKa = 3.86)
  d. NaH2PO4 and Na2HPO4 (pKa values are 2.1, 7.2, 12.4)
  e. Sodium succinate and succinic acid (pKa = 4.21)

 

ANSWER:   b

 

21. What ionic form(s) is/are most prevalent at pH 7.0? The pKa values of phosphoric acid are 2.1, 7.2, and 12.4.

  a. HPO42
  b. H2PO4
  c. HPO42 and PO43
  d. H2PO4− and HPO42
  e. All are correct

 

ANSWER:   b

 

22. A plasma pH of 6.8 doesn’t seem too far away from a normal pH of 7.4, but at pH 6.8 the H+ concentration is ____ times greater than at pH 7.4 and results in severe acidosis.

  a. 0.1
  b. 0.6
  c. 4
  d. 10
  e. 20

 

ANSWER:   c

 

23. pH = pKa when:

  a. [A−]/[HA] = 0
  b. log ([A−]/[HA]) = 1
  c. [A−] >> [HA]
  d. [A−] = [HA]
  e. log ([HA]/[A−]) = 1

 

ANSWER:   d

 

24. Buffers have all of the following characteristics EXCEPT:

  a. they have relatively flat titration curves at the pH(s) where they buffer.
  b. they resist changes in their pH as acid or base is added.
  c. they are typically composed of a weak acid and its conjugate base.
  d. they buffer best for polyprotic acids half-way between the two pKa values.
  e. buffer where the amounts of conjugate base are nearly equivalent to the amounts of weak acid.

 

ANSWER:   d

 

25. Buffer systems are effective when the pH values are within ____ pH unit(s) of the pKa value.

  a. 1
  b. 2
  c. 3
  d. 4
  e. 5

 

ANSWER:   a

 

26. Intracellular pH is maintained primarily by the ____ and ____ buffer systems, and the extracellular pH by the ____ buffer system.

  a. HPO42/H2PO4−; HCO3−/H2CO3; histidine
  b. H3PO4/H2PO4−; histidine; HCO3−/H2CO3
  c. HCO3−/H2CO3; H3PO4/H2PO4−; histidine
  d. HPO42/H2PO4−; histidine; HCO3−/H2CO3
  e. HCO3−/H2CO3; histidine; H3PO4/H2PO4

 

ANSWER:   d

 

27. Hyperventilation is a physiological mechanism to:

  a. lower [CO2 (g)] in the blood and increase blood pH.
  b. raise [CO2 (g)] in the blood and increase blood pH.
  c. lower [CO2 (g)] in the blood and decrease blood pH.
  d. raise [CO2 (g)] in the blood and decrease blood pH.
  e. lower [CO2 (g)] in the blood and increase [HCO3−].

 

ANSWER:   a

 

28. Water is particularly suited as a solvent for biosystems because it has all of the following characteristics EXCEPT:

  a. Water is a medium for ionization enhancing the variety of chemical species.
  b. Water is innocuous, yet a powerful solvent.
  c. Water is an excellent solvent for nonpolar substances.
  d. Water is relatively chemically inert, yet dissolves a variety of solutes.
  e. Through hydrophobic interactions, lipids coalesce into membranes in water.

 

ANSWER:   c

 

29. Which of the following weak acids would make the best buffer at pH = 5.0?

  a. acetic acid (Ka = 1.74 × 10−5, pKa = 4.76)
  b. H2PO4− (Ka = 1.38 × 10−7, pKa = 7.20)
  c. bicarbonate (Ka = 6.3 × 10−11, pKa = 10.24)
  d. tris-hydroxymethyl aminomethane (Ka = 8.32 × 10−9, pKa = 8.07)
  e. lactic acid (Ka = 1.38 × 10−4, pKa = 3.86)

 

ANSWER:   a

 

30. The enzyme fumarase has a pH optimum of about 7.6. What would be the buffer of choice to study this enzyme?

  a. lactic acid (Ka = 1.38 × 10−4, pKa = 3.86)
  b. bicarbonate (Ka = 6.3 × 10−11, pKa = 10.24)
  c. acetic acid (Ka = 1.74 × 10−5, pKa = 4.76)
  d. succinate (Ka = 2.34 × 10−6, pKa = 5.63)
  e. tris-hydroxymethyl aminomethane (Ka = 8.32 × 10−9, pKa = 8.07)

 

ANSWER:   e

 

31. When preparing an acetate buffer at pH 4.5 with 0.01 M solutions of acetic acid (pKa = 4.8) and sodium acetate, the volume of acetic acid needed would be ____ the volume of sodium acetate solution.

  a. equal to
  b. less than half of
  c. more than half of
  d. about six times
  e. about twice

 

ANSWER:   e

 

32. Hypoventilation is characterized by inability to excrete CO2 rapidly enough and can be caused by all EXCEPT:

  a. anesthetics.
  b. depressant drugs.
  c. narcotics.
  d. lung diseases.
  e. encephalitis.

 

ANSWER:   e

 

33. Aspirin contains a carboxylic acid with a pKa of 3.5. Which of the following is true?

  a. Aspirin will be mostly protonated in the stomach
  b. Aspirin will be mostly protonated in the bloodstream
  c. Aspirin will be easily absorbed in the stomach due to its negative charge
  d. Aspirin will be easily transported in the bloodstream due to its negative charge
  e. both a and d are correct

 

ANSWER:   e

 

34. If a weak acid is 25% deprotonated at pH 4, what would the pKa be?

  a. 3.40
  b. 3.52
  c. 4.48
  d. 4.60
  e. cannot determine from given information

 

ANSWER:   c

 

35. Which of the following would be the conjugate acid of hydrogen phosphate, HPO4-2?

  a. H2PO4
  b. H3PO4
  c. H2PO4-2
  d. H2PO4
  e. none of the above

 

ANSWER:   a

 

36. Formic acid is the active agent in an ant bite.  What is the ratio of base/acid for formic acid (pKa = 3.9) in the blood stream at pH 7.4?

  a. 3.16 × 10-4
  b. 3.16 × 103
  c. 0.54
  d. 1.90
  e. cannot be determined based upon the provided information

 

ANSWER:   b

 

37. Which of the following statements is INCORRECT about the nature of the hydrogen bond

  a. The donor is a hydrogen atom bonded to an atom that is less electronegative than hydrogen.
  b. The more linear the bond, the stronger the interaction.
  c. The acceptor is a fairly electronegative atom containing a nonbonding pair of electrons.
  d. It is a type of noncovalent bond.
  e. All of the above statements are true about the nature of the hydrogen bond.

 

ANSWER:   a

 

38. A weak acid is 33% dissociated at pH 5.0. What is the pKa for this acid?

  a. 4.5
  b. 4.7
  c. 5.3
  d. 5.5
  e. cannot be determined from the information provided

 

ANSWER:   c

 

39. ​Discuss the dielectric constant of water. Write the equation used to calculate the dielectric constant.

ANSWER:   The attractions between the water molecules interacting with, or hydrating, ions in solution are much stronger than the attractions between oppositely charged ions. Water’s ability to surround ions in dipole interactions and diminish their attraction for each other is a measure of its dielectric constant, D. Indeed, ionization in solution depends on the dielectric constant of the solvent; otherwise, the strongly attracted positive and negative ions would unite to form neutral molecules. The strength of the dielectric constant is related to the force, F, experienced between two ions of opposite charge separated by a distance, r, as given in the relationship

F = e1e2/Dr2

where e1 and e2 are the charges on the two ions.​

TOPICS:   2.1 What Are the Properties of Water?

 

40. Calculate the equilibrium constant, Keq, for 1 L of pure water.​

ANSWER:   The dissociation of water into hydrogen ions and hydroxyl ions occurs to the extent that 10−7 mol of H+ and 10−7 mol of OH are present at equilibrium in 1 L of water at 25°C.

The equilibrium constant for this process is​

where brackets denote concentrations in moles per liter. Because the concentration of H2O in 1 L of pure water is equal to the number of grams in a liter divided by the gram molecular weight of H2O, or 1000/18, the molar concentration of H2O in pure water is 55.5 M (molar). The decrease in H2O concentration as a result of ion formation ([H+], [OH] = 10−7M) is negligible in comparison; thus, its influence on the overall concentration of H2O can be ignored. Therefore,

TOPICS:   2.1 What Are the Properties of Water?

 

41. Explain weak electrolytes with an example.​

ANSWER:   Substances with only a slight tendency to dissociate to form ions in solution are called weak electrolytes. Acetic acid, CH3COOH, is a good example:

The acid dissociation constant is represented as KaKis also termed an ionization constant because it states the extent to which a substance forms ions in water. The relatively low value of Kfor acetic acid reveals that the un-ionized form, CH3COOH, predominates over H+ and CH3COO− in aqueous solutions of acetic acid. Viewed another way, CH3COO, the acetate ion, has a high affinity for H+.

TOPICS:   2.2 What Is pH?

 

42. Discuss the Phosphate Buffer System in living systems.​

ANSWER:   The intracellular pH of most cells is maintained in the range between 6.9 and 7.4. Phosphate is an abundant anion in cells, both in inorganic form and as an important functional group on organic molecules that serve as metabolites or macromolecular precursors. Phosphate has a characteristic pK2 of 7.2. At physiological pH, phosphate can donate or accept hydrogen ions to buffer any changes in pH. For example, if the total cellular concentration of phosphate is 15 mM (millimolar) and the pH is 7.3, the distribution of the major phosphate species is given by

 

Thus, if [HPO42 –] + [H2PO4] = 15mM, then

[HPO42 –] = 8.33 mM and [H2PO4] = 6.67 mM

TOPICS:   2.3 What Are Buffers, and What Do They Do?

 

43. Explain the role that water plays in living systems.​

ANSWER:   Water is a “poor” solvent for nonpolar substances. Thus, through hydrophobic interactions, lipids coalesce, membranes form, boundaries are created delimiting compartments, and the cellular nature of life is established. Because of its very high dielectric constant, water is a medium for ionization. Ions enrich the living environment in that they enhance the variety of chemical species and introduce an important class of chemical reactions. They provide electrical properties to solutions and therefore to organisms. The thermal properties of water allow effective temperature regulation in living organisms. The heat generated within an organism as a result of metabolism can be efficiently eliminated through evaporation or conduction of water.

TOPICS:   2.4 What Properties of Water Give It a Unique Role in the Environment?

 

1. The intrinsic properties of the 20 amino acids include all EXCEPT:

  a. α-Carbon is symmetric.
  b. The capacity to polymerize.
  c. Novel acid-base properties.
  d. Varied structure and chemical functionality in side chains.
  e. Chirality.

 

ANSWER:   a

 

2. The amino and carboxyl groups of amino acids react in a head-to-tail fashion, eliminating water, and forming a covalent ____ linkage typically referred to as a(n) ____ bond.

  a. ester, aromatic
  b. anhydride, phosphoanhydride
  c. amide, peptide
  d. dehydration, hydrogen
  e. none of the above

 

ANSWER:   c

 

3. All of the statements about the classification of these amino acids are correct EXCEPT:

  a. Aspartic acid and asparagine are acidic amino acids.
  b. Alanine and valine are neutral, nonpolar amino acids.
  c. Serine and glutamine are polar, uncharged amino acids.
  d. Lysine and arginine are basic amino acids.
  e. Tyrosine and phenylalanine are aromatic amino acids.

 

ANSWER:   a

 

4. The difference between serine and homoserine is the same as between cysteine and homocysteine. This change from the common amino acid is:

  a. one additional methylene (−CH2−) group.
  b. one additional carboxyl group.
  c. two additional amine groups.
  d. presence of a ring system.
  e. one additional amine group.

 

ANSWER:   a

 

5. Which of the following amino acids has more than one chiral carbon?

  a. serine
  b. lysine
  c. threonine
  d. cysteine
  e. aspartic acid

 

ANSWER:   c

 

6. Which of the listed amino acids is classified as a basic amino acid?

  a. leucine
  b. phenylalanine
  c. aspartate
  d. asparagine
  e. lysine

 

ANSWER:   e

 

7. All of the amino acids EXCEPT ____ have both free α-amino and free α-carboxyl groups.

  a. aspartic acid
  b. proline
  c. asparagine
  d. lysine
  e. valine

 

ANSWER:   b

 

8. The amino acid with a side-chain pKa near neutrality and which therefore plays an important role as proton donor and acceptor in many enzyme catalyzed reactions is:

  a. histidine.
  b. cysteine.
  c. proline.
  d. serine.
  e. methionine.

 

ANSWER:   a

 

9. The pKa of the α−carboxyl group of an amino acid is ____ by the presence on the amine group.

  a. greatly increased (>2 pH units)
  b. greatly decreased (> 2 pH units)
  c. unchanged
  d. slightly increased (1-2 pH units)
  e. slightly decreased (1-2 pH units)

 

ANSWER:   b

 

10. At which of the following pH values would histidine (pKa values of 1.8, 6.0 and 9.2) be found with a net negative charge?

  a. 1.0
  b. 4.0
  c. 8.0
  d. 11.0
  e. none of the above

 

ANSWER:   d

 

11. What is the pH of a serine solution in which the α−amine group (pKa 9.2) is 33% deprotonated?

  a. 8.7
  b. 8.9
  c. 9.0
  d. 9.5
  e. 9.8

 

ANSWER:   b

 

12. Glutamic acid has pKa values of 2.2, 4.3, and 9.7. Calculate the isoelectric point for glutamic acid.

  a. 3.25
  b. 4.3
  c. 5.4
  d. 7.0
  e. 8.6

 

ANSWER:   a

 

13. If the pI of a peptide is 4.6, ____ might be present while ____ would probably be absent.

  a. Glu / Lys
  b. His / Ser
  c. Arg / His
  d. Asp / Gly
  e. Cys / Tyr

 

ANSWER:   a

 

14. The pKa of the cysteine side chain ____ group is 8.32, so it is about 11% deprotonated at pH ____.

  a. acid, 3.2
  b. amino, 8.5
  c. hydroxyl, 10.2
  d. sulfhydryl, 7.4
  e. none of the above

 

ANSWER:   d

 

15. Which of the peptides would absorb light at 280 nm?

  a. Ala-Lys-His
  b. Ser-Gly-Asn
  c. Ala-Ala-Trp
  d. Val-Pro-Leu
  e. Ser-Val-Ile

 

ANSWER:   c

 

16. Which of the following amino acids absorbs light most strongly between 250 and 300 nm?

  a. His
  b. Phe
  c. Trp
  d. Tyr
  e. None of the above absorb light in this range

 

ANSWER:   c

 

17. All are true for stereoisomers EXCEPT:

  a. A diastereomer is a nonsuperimposable non-mirror image.
  b. An enantiomer is a nonsuperimposable mirror image.
  c. Diastereomers have different melting points.
  d. Diastereomers rotate plane polarized light in equal but opposite directions.
  e. None, all are true.

 

ANSWER:   d

 

18. All are true statements about L-isoleucine EXCEPT:

  a. Its enantiomer is named D-isoleucine.
  b. L-alloleucine would be its diastereomer.
  c. It contains a total of two asymmetric or chiral carbons.
  d. It can also be named as (2S,3S)-isoleucine using the (R,S) system.
  e. Its diastereomer would be named D-leucine.

 

ANSWER:   e

 

19. Which of the following is classified as a neutral polar amino acid?

  a. Asp
  b. Leu
  c. His
  d. Ser
  e. Trp

 

ANSWER:   d

 

20. For the peptide Ala-His-Glu-Val-Asp-Cys-Lys-Leu, what is the net charge at pH 3?

  a. -1
  b. 0
  c. +1
  d. +2
  e. +3

 

ANSWER:   d

 

21. Where Cα is the α-carbon, N represents the amide nitrogen and Co is the carbonyl carbon of amino acids in a peptide, the peptide backbone of a protein consists of the repeated sequence:

  a. −Cα−N−Co
  b. −N−Co−Cα
  c. −N−Cα−Co
  d. −Co−Cα−N−
  e. none of the above

 

ANSWER:   c

 

22. The peptide bond has partial ____ character.

  a. hydrogen bond
  b. double bond
  c. triple bond
  d. van der Waals bond
  e. all of the above

 

ANSWER:   b

 

23. Which of the following IS NOT a result of resonance in peptide bonds?

  a. approximately 40% double bond (coplanar) character.
  b. restricted rotation in the peptide backbone at the N−Cα bond and Cα−Co bond.
  c. the coplanar six atoms of the peptide bond group of atoms.
  d. a Cα−carbon that is out of the coplanar group of atoms.
  e. Co−N bond distance that is shorter than normal, but longer than C=N bonds.

 

ANSWER:   d

 

24. Which of the following atoms IS NOT contained within the amide plane of the peptide backbone?

  a. Cα-carbon.
  b. amide nitrogen.
  c. side chain carbons.
  d. carbonyl carbon.
  e. none, all are included.

 

ANSWER:   c

 

25. Discuss the amino acids that occur only rarely in proteins.​

ANSWER:   There are several amino acids that occur only rarely in proteins and are produced by modifications of one of the 20 amino acids already incorporated into a protein. Pyrrolysine and selenocysteine are incorporated naturally into proteins through specific modifications that occur during the reactions of protein synthesis. Both selenocysteine and pyrrolysine bring novel structural and chemical features to the proteins that contain them. Hydroxylysine and hydroxyproline are found mainly in the collagen and gelatin proteins. Pyroglutamic acid is found in a light-driven proton-pumping protein called bacteriorhodopsin. γ-carboxyglutamic acid is found in calcium-binding proteins.​
TOPICS:   4.1 What Are the Structures and Properties of Amino Acids?

 

26. Discuss the side-chain groups of amino acids that undergo ionizations.​

ANSWER:   ​Histidine contains an ionizable imidazolium proton, and arginine carries a guanidinium function. The β-carboxyl group of aspartic acid and the γ-carboxyl side chain of glutamic acid exhibit pKa values intermediate to the α-COOH on one hand and typical aliphatic carboxyl groups on the other hand. In a similar fashion, the -amino group of lysine exhibits a pKa that is higher than that of the α-amino group but similar to that for a typical aliphatic amino group. These intermediate side-chain pKa values reflect the slightly diminished effect of the a-carbon dissociable groups that lie several carbons removed from the side-chain functional groups. The para-OH group of tyrosine and the —SH group of cysteine also show a significant degree of dissociation.
TOPICS:   4.2 What Are the Acid-Base Properties of Amino Acids?

 

27. Explain the chirality of amino acid molecules.​

ANSWER:   A molecule that has four different groups attached to the α-carbon atom is said to be asymmetric or chiral. All amino acids except glycine are chiral. The two possible configurations for the α-carbon constitute nonsuperimposable mirror-image isomers, or enantiomers. Enantiomeric molecules display optical activity—the ability to rotate the plane of polarization of plane-polarized light. Clockwise rotation of incident light is referred to as dextrorotatory behavior, and counterclockwise rotation is called levorotatory behavior. The magnitude and direction of the optical rotation depend on the nature of the amino acid side chain. Some protein-derived amino acids at a given pH are dextrorotatory and others are levorotatory, even though all of them are of the L-configuration.​
TOPICS:   4.4 What Are the Optical and Stereochemical Properties of Amino Acids?

 

28. Discuss the principles on which methods of amino acid separation are based.​

ANSWER:   All the methods used for the separation and analysis of amino acids take advantage of the relative differences in the physical and chemical characteristics of amino acids, particularly ionization behavior and solubility characteristics. Separations of amino acids are usually based on partition properties (the tendency to associate with one solvent or phase over another) and separations based on electrical charge. In all of the partition methods, the molecules of interest are allowed (or forced) to flow through a medium consisting of two phases—solid-liquid, liquid-liquid, or gas-liquid. The molecules distribute themselves between the two phases depending on their particular properties and their consequent preference for associating with one or the other phase. Methods important for amino acid separations include ion exchange chromatography, gas chromatography (GC), and high-performance liquid chromatography (HPLC).​
TOPICS:   4.6 How Are Amino Acid Mixtures Separated and Analyzed?

 

29. Explain the classification of peptides based on the number of amino acids they contain.​

ANSWER:   Peptide is the name assigned to short polymers of amino acids. Peptides are classified according to the number of amino acid units in the chain. Each unit is called an amino acid residue, the word residue denoting what is left after the release of H2O when an amino acid forms a peptide link upon joining the peptide chain. Dipeptides have two amino acid residues, tripeptides have three, tetrapeptides four, and so on. After about 12 residues, this terminology becomes cumbersome, so peptide chains of more than 12 and less than about 20 amino acid residues are usually referred to as oligopeptides, and when the chain exceeds several dozen amino acids in length, the term polypeptide is used. The distinctions in this terminology are not precise.​
TOPICS:   4.7 What Is the Fundamental Structural Pattern in Proteins?

 

 

Reviews

There are no reviews yet.

Be the first to review “Test Bank For Biochemistry 6th Edition Reginald Garrett”

Your email address will not be published. Required fields are marked *