Chapter 6 Practice Questions

These are practice questions that may help you ensure that you understand the objectives. This is not a practice examination to be used for assesment of your progress in the course. The practice examination for chapters 4 - 7 will be taken later after you finish chapter 7.
1 All amino acids used in protein synthesis contain four substituents, which are attached to the alpha carbon atom, an amino group, a carboxylic acid group, a hydrogen atom and a side chain group. Which of the following statements is true?
  1. Both the amino group and the carboxyl group carry a charge at physiological pH
  2. At physiological pH the amino group is negatively charged
  3. Both the amino group and the carboxyl group are uncharged at physiological pH
  4. At physiological pH the carboxyl group is positively charged
  5. The pKa for the a-carboxyl group is about 9-10 and the pKa for the a-amino group is about 2
2 For 19 out of 20 amino acids, the alpha carbon has four different substituents, thus the a-carbon is asymmetric, and amino acids may exist in either the L or D configuration. All of the following statements are true regarding the L and D configuration of amino acids, EXCEPT
  1. L and D forms occur equally in living organisms
  2. L and D forms cannot be superimposed by rotating the molecule
  3. L forms are the predominant form found naturally in humans
  4. D amino acids occur rarely in humans
3 1. Which of the following statements about amino acids is INCORRECT?
  1. Except for glycine, they have an asymmetric a-carbon atom
  2. They are zwitterionic
  3. They have no more than two pKa’s
  4. Occur in animals almost exclusively in the optically active L-form
4 The peptide bond:
  1. Results from condensation of any R-group or side chain of different amino acids with each other
  2. Results from the condensation reaction between the alpha-carboxyl group of one amino acid with the alpha-amino group of a second amino acid
  3. Results from the condensation reaction between the alpha-carboxyl group of one amino acid with the alpha-carboxyl group of a second amino acid
  4. Results from the condensation reaction between the alpha-carboxyl group of one amino acid and ammonia
  5. Results from the condensation reaction between the alpha-carboxyl group of one amino acid and ammonium ion
5 Which of the following answers correctly matches the abbreviations with the amino acids
  1. GLU – glutamate, GLN – glutamine, TRP – tryptophan, TYR – tyrosine
  2. GLU – glutamate, GLN – glutamine, TRP – tyrosine, TYR – tryptophan
  3. GLU – glutamine, GLN – glutamate, TRP – tryptophan, TYR – tyrosine
  4. GLU – glycine, GLN – glutamine, TRP – tryptophan, TYR – tyrosine
  5. GLU – glutamate, GLN – glycine, TRP – tryptophan, TYR – tyrosine
6 Which of the following is the three-letter abbreviation for asparagine?
  1. Asp
  2. Aspn
  3. Asgn
  4. Asn
  5. Arg
7 The functions of the individual amino acids and their roles in protein structure are related mainly to the chemical properties of their side chains. Amino acids are divided into groups based on the relative polarity of their side chains, which indicates their tendency to react. Which of the following statements is true?
  1. The most hydrophobic amino acids have side chains with either a negative or positive charge at physiological pH
  2. The most hydrophobic amino acids have side chains that are polar but uncharged at physiological pH
  3. The most hydrophilic amino acids have no oxygen or nitrogen in their side chains
  4. The most hydrophilic amino acids have side chains that are polar but uncharged at physiological pH
  5. The most hydrophobic amino acids have side chains that are unpolar and uncharged at physiological pH
8 Amino acid R-groups:
  1. That are hydrophilic are usually found on the interior of proteins
  2. Of glutamine and asparagine are uncharged polar amino acids
  3. Of Leucine, isoleucine, tyrosine and phenylalanine are hydrophilic
  4. Of serine, glutamine and histidine are hydrophobic
  5. Aspartate, glutamate, and lysine are hydrophobic
9 Which of the following statements is true regarding sulfhydryl compounds and disulfide bonds?
  1. Covalent disulfide bonds may be formed between 2 molecules of cysteine or between 2 cysteine residues in a protein
  2. One disulfide compound is called a cystine
  3. One hydrogen atom is lost from each cysteine when cystine is formed
  4. Reduction of cystine produces cysteine
  5. All of the above are correct
10 Which of the following is INCORRECT about disulfide bonds?
  1. A covalent linkage formed from the sulfhydryl group (-SH) of each of two cysteine residues will produce a cystine residue
  2. Contributes to the stability of the three dimensional shape of the protein molecule
  3. R-group of cysteine contains a sulfhydryl group (-SH)
  4. Two cysteines become reduced to form a dimer, cystine
  5. Contains a covalent linkage between two sulfur atoms
11 Electrostatic interactions can happen between the R-groups of:
  1. Glycine and Aspartate
  2. Leucine and Isoleucine
  3. Lysine and Aspartate
  4. Arginine and lysine
  5. Lysine and lysine
12 A salt bond is an electrostatic interaction which occurs between:
  1. A non-polar aliphatic amino acid and a positively charged amino acid
  2. A polar uncharged amino acid and a non-polar aliphatic amino acid
  3. A negatively charged amino acid and a positively charged amino acid
  4. An aromatic amino acid and an aliphatic amino acid
  5. A polar uncharged amino acid and an aromatic amino acid
13 Which of the following pairs of amino acids could form a salt bond at pH = 7.4?
  1. Glutamate and Arginine
  2. Glycine and Aspartate
  3. Valine and lysine
  4. Leucine and histidine
  5. Histidine and Histidine
14 A “salt” bond would form between each of the following amino acid pairs EXCEPT?
  1. Aspartate and Glutamate
  2. Aspartate and Histidine
  3. Glutamate and Arginine
  4. Lysine and Glutamate
  5. Lysine and Aspartate
15 Which of the following amino acids has a side group with a pKa = 12.5?
  1. Glutamic acid
  2. Lysine
  3. Arginine
  4. Histidine
  5. Aspartic acid
16 The pKa of the R-group of Glutamic Acid is?
  1. 6.0
  2. 4.1
  3. 10.5
  4. 2.0
  5. 12.5
17 The charge on Histidine at a pH greater than 10 would be:
  1. -1
  2. 0
  3. +1
  4. +2
  5. +3
18 At physiological pH (7.4), the R- groups of which of the following amino acids would carry a negative charge?
  1. Aspartic acid and Arginine
  2. Glutamic acid and Histidine
  3. Histidine and Arginine
  4. Lysine and Arginine
  5. Aspartic acid and Glutamic acid
19 The pI for an amino acid is the:
  1. pH at which an amino acid is electrically neutral
  2. pKa value of the functional groups attached to the alpha-carbon
  3. Net pKa value for the ionizable side chains
  4. The same for all but one of the twenty amino acids
  5. Is proportional to the number of oxygen atoms in the amino acid
20 For each of the twenty amino acids found in proteins, which of the following statements regarding their isoelectric point (pI) is correct?
  1. The isoelectric point is pH at which the net charge on the molecules in solution is 0
  2. The isoelectric point is pH at which the charge of the alpha-amino groups equals the charge on the alpha-carboxyl groups
  3. The isoelectric point is pH at which the α-carboxyl and α-amino groups are uncharged
  4. B and C are correct
  5. A and B are correct
21 Which of the following amino acids has an isoelectric point of 7.6?
  1. Lysine
  2. Histidine
  3. Arginine
  4. Glutamic acid
  5. Aspartic acid
22 In sickle cell disease, the substitution of valine for glutamate is considered a non-conservative amino acid replacement because:
  1. Hydrophobic branched amino acid substituted for a negatively charged amino acid
  2. Nonpolar side chain substituted for a basic side chain
  3. One hydrophobic side chain is substituted for another hydrophobic side chain
  4. One hydrophilic side chain is substituted for another
  5. A basic R-group is substituted for a hydrophobic R-group
23 The substitution of Valine for Glutamate in sickle cell hemoglobin
  1. Is considered a conservative replacement because both amino acids carry a negative charge at physiological pH
  2. Is considered a conservative replacement because at physiological pH both amino acids carry a positive charge
  3. Is considered a non-conservative replacement because at physiological pH Glutamate is a hydrophobic amino acid, while Valine is a negatively charged amino acid.
  4. Is considered a non-conservative replacement because at physiological pH Valine is a hydrophobic amino acid, while Glutamate is a negatively charged amino acid.
  5. Is considered a non-conservative replacement because at physiological pH Glutamate is a hydrophobic amino acid, while Valine is an aromatic amino acid
24 Which of the following statements about amino acid sequence is correct?
  1. All amino sequences are read from the C- to the N- terminal end of the peptide
  2. Valylglycylleucine has the amino acid leucine in the N-terminal of the tripeptide
  3. The C-terminal is written to the right and the N-terminal to the left
  4. The C-terminal is written to the left and the N-terminal to the right
  5. Valylglycylleucine has the amino acid valine in the C-terminal of the tripeptide
25 Sickle cell disease results from a point (missense) mutation of the b-globin of:
  1. Glutamine for valine
  2. Valine for glutamate
  3. Hydrophobic amino acid for another hydrophobic amino acid
  4. Hydrophilic amino acid for another hydrophilic amino acid
  5. Hydrophilic amino acid for a hydrophobic amino acid
26 Variants of an allele that occur with a significant frequency in the population are referred to as polymorphisms. Which of the following statements regarding the sickle cell variant is true?
  1. The sickle cell allele is the result of a point mutation.
  2. Persistence of the sickle cell allele is most likely attributable to the selective pressure for the heterozygous mutant phenotype
  3. Persistence of the sickle cell allele is most likely attributable to the selective pressure for the homozygous mutant phenotype
  4. A & B are correct
  5. A & C are correct
27 The sickle cell allele makes up more than 5% of the total alleles for the beta-globin gene in the African Americans. If an allele makes up more than 1 % of the total alleles, it is considered a polymorphism. This means that
  1. The Sickle Cell gene (allele) represents a polymorphism
  2. 5% of African Americans have Sickle Cell disease
  3. Less than 1 in 400 African Americans have Sickle Cell trait.
28 Which of the following is less soluble and precipitates in urine to form renal stones (calculi)?
  1. Cystine
  2. Valine
  3. Glycine
  4. Glutamate
29 Cal Kulis suffers from a rare disorder called Cystinuria, which is caused by A mutation in a transport protein
  1. that normally reabsorbs cystine, arginine, and lysine from the kidney lumen back into the renal tubular cells
  2. that results in uric acid kidney stones
  3. tor keeping cystine from passing from the blood into the kidney tubules
  4. that adds water to the bladder so that compounds of low solubility do not precipitate
  5. that causes an ecess of cystine to be synthesized in the liver
30 Which insulin therapy has amino acids proline at position 28 and lysine at position 29 of the beta-chain reversed?
  1. Bovine
  2. Humulin
  3. Lispro (Humalog)
  4. All of the above
31 All of the following statements regarding Humulin are true, EXCEPT?
  1. Humulin is a synthetic form of human insulin
  2. Humulin is identical in structure to native bovine insulin
  3. The cost of Humulin is now low enough that most patients are being switched from bovine insulin to Humulin
  4. One advantage of Humulin over bovine insulin is that Humulin does not stimulate the formation of antibodies where bovine insulin can
  5. Humulin is produced by recombinant DNA techniques that insert human DNA sequences for the insulin A and B chains into the E. coli or yeast genome
32 1. The enzyme creatine kinase is an example of a protein that exists as tissue-specific isozymes. Which of the following forms of creatine kinase are found primarily in cardiac muscle?
  1. The BB form alone
  2. The MM form alone
  3. Both the MM and MB forms
Answers

1. Answer: A. Chapter 6, Objective 1: What is the approximate pKa for all alpha-amino groups and for all alpha-carboxyl groups? Are they charged at pH=7?


2. Answer: A. Chapter 6, Objective 2: Which stereoisomer is most prevalent for any amino acid, the D- or the L- form?

3. Answer: C. Chapter 6, Objective 2: Which stereoisomer is most prevalent for any amino acid, the D- or the L- form?

4. Answer: B. Chapter 6, Objective 3: Be able to recognize a peptide or amide bond and be able to tell the difference.

5. Answer: A. Chapter 6, Objective 4: Be able to recognize the three-letter abbreviations for the 20 amino acids!

6. Answer: D. Chapter 6, Objective 4: Be able to recognize the three-letter abbreviations for the 20 amino acids!

7. Answer: E. Chapter 6, Objective 5: Be able to name the structures of all 20 amino acids. Be able to say which contain R-groups that are nonpolar, polar, or charged! Be able to predict which R groups should be soluble in water and which should not.

8. Answer: B. Chapter 6, Objective 5: Be able to name the structures of all 20 amino acids. Be able to say which contain R-groups that are nonpolar, polar, or charged! Be able to predict which R groups should be soluble in water and which should not.

9. Answer: E. Chapter 6, Objective 6: Be able to recognize cysteine, cystine, a sulfhydryl group, and a disulfide bond. Which are more oxidized and which are more reduced?

10. Answer: D. Chapter 6, Objective 6: Be able to recognize cysteine, cystine, a sulfhydryl group, and a disulfide bond. Which are more oxidized and which are more reduced?

11. Answer: C. Chapter 6, Objective 7: Be able to recognize a salt bond (electrostatic interaction).

12. Answer: C. Chapter 6, Objective 7: Be able to recognize a salt bond (electrostatic interaction).

13. Answer: A. Chapter 6, Objective 8: Given any two amino acids, predict whether their R-groups could form a salt bond at pH = 7.4.

14. Answer: A. Chapter 6, Objective 8: Given any two amino acids, predict whether their R-groups could form a salt bond at pH = 7.4.

15. Answer: C. Chapter 6, Objective 9: What are the pKa=s for the R-groups of aspartic acid, Glutamic acid, histidine, lysine, and Arginine?

16. Answer: B. Chapter 6, Objective 9: What are the pKa(s) for the R-groups of aspartic acid, Glutamic acid, histidine, lysine, and Arginine?

17. Answer: A. Chapter 6, Objective 10: Given the pH, predict whether the R-groups of the amino acids aspartic acid, glutamic acid, histidine, lysine, and arginine would be neutral or would carry a net negative or net positive charge.

18. Answer: E. Chapter 6, Objective 10: Given the pH, predict whether the R-groups of the amino acids aspartic acid, Glutamic acid, histidine, lysine, and Arginine would be neutral or would carry a net negative or net positive charge.

19. Answer: A. Chapter 6, Objective 12: Define the pI (the isoelectric point) for an amino acid.

20. Answer: A. Chapter 6, Objective 12: Define the pI (the isoelectric point) for an amino acid.

21. Answer: B. Chapter 6, Objective 13: Given any amino acid except cysteine and tyrosine, be able to predict the isoelectric point!

22. Answer: A. Chapter 6, Objective 14: Is the substitution of Valine for a Glutamate in sickle cell hemoglobin a conservative replacement? What about the substitution of an Aspartate for a glutamate?

23. Answer: D. Chapter 6, Objective 14: Is the substitution of Valine for a Glutamate in sickle cell hemoglobin a conservative replacement? What about the substitution of an Aspartate for a glutamate?

24. Answer: C. Chapter 6, Objective 15: Given the written sequence for a protein, be able to identify the amino-terminus, the carboxyl-terminus, and the R-groups for each residue.

25. Answer: B. Chapter 6, Objective 16: Concerning Michael Sichel: To the extent covered in this chapter, explain his disease in terms of amino acids. In the African American population, is the Sickle Cell allele a polymorphism?

26. Answer: D. Chapter 6, Objective 16: Concerning Michael Sichel: To the extent covered in this chapter, explain his disease in terms of amino acids. In the African American population, is the Sickle Cell allele a polymorphism?

27. Answer: A. Chapter 6, Objective 16: Concerning Michael Sichel: To the extent covered in this chapter, explain his disease in terms of amino acids. In the African American population, is the Sickle Cell allele a polymorphism?

28. Answer: A. Chapter 6, Objective 17: Concerning Cal Kullis: To the extent covered in this chapter, explain his disease in terms of amino acids.

29 Answer: A. Chapter 6, Objective 17: Concerning Cal Kullis: To the extent covered in this chapter, explain his disease in terms of amino acids.

30. Answer: C. Chapter 6, Objective 18: Concerning Di Abetes and in terms of amino acids, explain the difference between pork insulin, lispro, and synthetic human insulin. What are the possible advantages of each?

31. Answer: B. Chapter 6, Objective 18: Concerning Di Abetes and in terms of amino acids, explain the difference between pork insulin, lispro, and synthetic human insulin. What are the possible advantages of each?

32. Answer: C. Chapter 6, Objective 19: Concerning Ann Jeina, describe the isozymes of creatine kinase found in her body, their release following injury, and their use in diagnosing a myocardial infarction. Why do they react differently as antigens and why do they move differently in an electric field?

gyonuschot@une.edu