Proteins and amino acids

Question 1

Which of the amino acids below have a small polar side chain containing a hydroxyl group?
Select one or more:
a. Glycine
b. Serine
c. Threonine
d. Lysine
e. Leucine

Answer 1

Serine and Threonine

Question 2

Which of the following amino acids have a positively charged side chain at neutral pH?

Select one or more:

a. Arginine
b. Lysine
c. Glycine
d. Aspartate
e. Glutamate

Answer 2

Arginine and Lysine

Question 3

Which of the following amino acids have a negatively charged side chain at neutral pH?

Select one or more:

a. Arginine
b. Alanine
c. Asparagine
d. Aspartate
e. Glutamate

Answer 3

Aspartate and Glutamate

Question 4

Which of the following amino acids have sulfur-containing side chains?

Select one or more:

a. Histidine
b. Cysteine
c. Metionine
d. Proline
e. Valine

Answer 4

Cystein and Metionine

Question 5

Which amino acid has a guanidine group in its side chain?

Select one:

a. Histidine
b. Lysine
c. Tyrosine
d. Arginine
e. Tryptophan

Answer 5

Arginine

Question 6

Which of the following amino acids have four carbon atoms?

Select one or more:

a. Aspartate
b. Threonine
c. Asparagine
d. Proline

Answer 6

Aspartate, Threonine and Asparagine

Question 7

Which of the following amino acids have five carbon atoms?

Select one or more:

a. Glutamate
b. 2: Glutamine
c. 3. Histidine
d. 4. Proline
e. 5.Glycine

Answer 7

Glutamate, glutamine and proline

Question 8

Which of the following amino acids have six carbon atoms?

Select one or more:

a. Leucine
b. Isoleucine
c. Histidine
d. Proline
e. Glycine

Answer 8

Leucine, isoleucine and histidine

Question 9

Which of the following amino acid side chains are nonpolar?

Select one or more:

a. Valine
b. Leucine
c. Asparagine
d. Lysine

Answer 9

Valine and leucine

Question 10

Which of the following amino acid side chains are polar?

Select one or more:

a. Glutamine
b. Leucine
c. Asparagine
d. Threonine

Answer 10

Glutamine, asparagine and threoline

Question 11

Pair the amino acids with their character! 1. Proline 2. Arginine 3. Glutamate a. neutral b. acidic c. basic

Select one:

a. 1-a, 2-c, 3-b
b. 1-a, 2-b, 3-c
c. 1-b, 2-c, 3-a
d. 1-b, 2-a, 3-c
e. 1-c, 2-a, 3-b

Answer 11

1-a, 2-c, 3-b

Question 12

Pair the amino acids with their character!1. Glutamine 2. Lysine 3. Aspartate / a. neutral b. acidic c. basic

Select one:

a. 1-a, 2-b, 3-c
b. 1-a, 2-c, 3-b
c. 1-b, 2-c, 3-a
d. 1-b, 2-a, 3-c
e. 1-c, 2-a, 3-b

Answer 12

1-a, 2-c, 3-b

Question 13

Select the correct statements!

Select one or more:

a. Acidic amino acids have a net negative charge at neutral pH.
b. The isoelectric point of acidic amino acids is at acidic pH.
c. The isoelectric point of the acidic amino acids can be calculated as the average of their three pKa values.
d. Asparagine is a acidic amino acid.

Answer 13

a. Acidic amino acids have a net negative charge at neutral pH.
b. The isoelectric point of acidic amino acids is at acidic pH.

Question 14

Select the correct statements!

Select one or more:

a. Neutral amino acids have no net charge at neutral pH.
b. neutral amino acids have a positive and a negative charge at neutral pH.
c. The isoelectric point of the neutral amino acids can be calculated as the average of their pKa values.
d. Glutamine is a neutral amino acid.

Answer 14

a. Neutral amino acids have no net charge at neutral pH.
b. neutral amino acids have a positive and a negative charge at neutral pH.
c. The isoelectric point of the neutral amino acids can be calculated as the average of their pKa values.
d. Glutamine is a neutral amino acid.

Question 15

Select the correct statements!

Select one:

a. Leucine has two asymmetrical centers.
b. Only D-amino acids can be found in proteins.
c. Natural amino acids are dextrorotatory.
d. Glycine has no chiral center.
e. Proline is not active optically.

Answer 15

d. Glycine has no chiral center

Question 16

What is the dominant form of Arginine at pH 6.0? (pKa values of Arginine are 2.2, 9.0 and 12.5).

Select one:

a. Two positive and one negative charges
b. One positive and two negative charges
c. One negative and one positive charges
d. One negative charge
e. One positive charge

Answer 16

a. Two positive and one negative charges

Question 17

What is the dominant form of Glutamate at pH 7.0? (pKa values of Glutamate are 2.2, 5.6 and 9.2).B:Two positive and one negative charges

Select one:

a. One negative charge
b. One negative and one positive charges
c. One positive and two negative charges
d. One positive charge

Answer 17

d. one positive charge

Question 18

What is the dominant form of Histidine at pH 8.0? (pKa values of Histidine are 1.8, 6.0 and 9.2).B:Two positive and one negative charges

Select one:

a. One positive and one negative charges
b. Two negative and one positive charges
c. One negative charge
d. One positive charge

Answer 18

a. One positive and one negative charges

Question 19

What is the dominant form of Glycin at low pH (pH=1)?

Select one:

a. NH2–CH2–COO-
b. NH3+–CH2–COOH
c. NH3+–CH2–COO-
d. NH2–CH2–COOH
e. NH2–CH3+–COO-

Answer 19

b. NH3+–CH2–COOH

Question 20

Select the correct statements!

Select one or more:

a. Glutamate has a negative charge on its side chain at the isoelectric pH.
b. Glutamate has a negative charge on its side chain at neutral pH.
c. Arginine has a positive charge on its side chain at the isoelectric pH.
d. Arginine has a positive charge on its side chain at neutral pH.

Answer 20

b. Glutamate has a negative charge on its side chain at neutral pH.
c. Arginine has a positive charge on its side chain at the isoelectric pH.
d. Arginine has a positive charge on its side chain at neutral pH.

Question 21

Lysine at its isoelectric point has….

Select one:

a. a deprotonated a-carboxyl group, a deprotonated–a-amino group and a protonated e-amino group.
b. a deprotonated a-carboxyl group, a protonated a-amino group and a deprotonated e-amino group.
c. a protonated a-carboxyl group, a protonated a-amino group and a deprotonated e-amino group.
d. a protonated a-carboxyl group, a deprotonated a-amino group and a protonated–e-amino group.
e. a deprotonated a-carboxyl group, a deprotonated a-amino group and a deprotonated e-amino group.

Answer 21

a. a deprotonated a-carboxyl group, a deprotonated–a-amino group and a protonated e-amino group.

Question 22

Which of the following statements are true for the isoelectric form of amino acids?

Select one or more:

a. All the naturally occuring amino acids have one positive and one negative charges.
b. The a-amino group of all the naturally occuring amino acids has a positive charge.
c. The a-carboxyl group of all the naturally occuring amino acids has a negative charge.

Answer 22

a. All the naturally occuring amino acids have one positive and one negative charges.
b. The a-amino group of all the naturally occuring amino acids has a positive charge.
c. The a-carboxyl group of all the naturally occuring amino acids has a negative charge.

Question 23

At neutral pH a tetrapeptide of glycylalanylarginylglutamate has…

Select one:

a. two positive and three negtive charges
b. two positive and one negative charges
c. one positive and one negative charges
d. one positive and two negative charges
e. two positive and two negative charges

Answer 23

e. two positive and two negative charges

Question 24

The arginyllysylaspartate tripeptide has

Select one or more:

a. its isoelectric point at basic pH.
b. three positive and two negative charges at neutral pH.
c. two positive and two negative charges at its isoelectric point.

Answer 24

a. its isoelectric point at basic pH.
b. three positive and two negative charges at neutral pH.
c. two positive and two negative charges at its isoelectric point

Question 25

The chirality of an amino acid results from the fact that its a–carbon:

Select one:

a. is bonded to four different chemical groups.
b. is a carboxylic acid.
c. is symmetric.
d. is in the L absolute configuration in naturally occurring proteins.
e. has no net charge.

Answer 25

a. is bonded to four different chemical groups.

Question 26

Of the 20 standard amino acids, only ___________ is not optically active. The reason is that its side chain ___________.

Select one:

a. alanine; is a simple methyl group
b. glycine; is a hydrogen atom.
c. glycine; is unbranched.
d. lysine; contains only nitrogen.
e. proline; forms a covalent bond with the amino group.

Answer 26

b. glycine; is a hydrogen atom.

Question 27

Which of the following statements about formation of cystine is correct?

Select one:

a. There is a peptide linkage between two cysteines.
b. Two –CH2–SH groups are oxidized to form a –CH2–S–S–CH2– disulfide bridge between two cysteines
c. Two cystines are released when a –CH2–S–S–CH2– disulfide bridge is reduced to –CH2–SH.
d. Cystine is an example of a nonstandard amino acid, derived by linking two different standard amino acids.
e. Cystine is formed by the oxidation of the carboxylic acid group on cysteine.

Answer 27

b. Two –CH2–SH groups are oxidized to form a –CH2–S–S–CH2– disulfide bridge between two cysteines

Question 28

In a highly basic solution, pH = 13, the dominant form of glycine is:

Select one:

a. NH2–CH2–COO-.
b. NH2–CH2–COOH.
c. NH3+–CH2–COOH.
d. NH3+–CH2–COO-.
e. NH2–CH3+–COO-.

Answer 28

a. NH2–CH2–COO-.

Question 29

For amino acids with neutral side chain, at any pH below the pI of the amino acid, the population of amino acids in solution will:

Select one:

a. have a net positive charge.
b. have no charged groups.
c. have no net charge.
d. have positive and negative charges in equal concentration.
e. have a net negative charge.

Answer 29

a. have a net positive charge.

Question 30

An octapeptide composed of four repeating glycylalanyl units has:

Select one:

a. a single free amino group on an alanyl residue.
b. two free amino and two free carboxyl groups.
c. a single free amino group on a glycyl residue and a single free carboxyl group on an alanyl residue
d. two free carboxyl groups, both on glycyl residues.
e. a single free amino group on an alanyl residue and a single free carboxyl group on a glycyl residue.

Answer 30

c. a single free amino group on a glycyl residue and a single free carboxyl group on an alanyl residue

Question 31

At the isoelectric pH of a tetrapeptide:

Select one:

a. there are four ionic charges
b. the amino and carboxyl termini are not charged.
c. two internal amino acids of the tetrapeptide cannot have ionizable R groups.
d. the total net charge is zero.
e. only the amino and carboxyl termini contribute charge.

Answer 31

d. the total net charge is zero.

Question 32

Which of the following describes the overall three-dimensional folding of a polypeptide?

Select one:

a. primary structure
b. secondary structure
c. tertiary structure
d. quaternary structure
e. none of the above

Answer 32

c. tertiary structure

Question 33

By adding SDS (sodium dodecyl sulfate) during the electrophoresis of proteins, it is possible to:

Select one:

a. preserve a protein’s native structure and biological activity
b. separate proteins exclusively on the basis of molecular weight.
c. determine a protein’s isoelectric point.
d. determine the amino acid composition of the protein.
e. determine an enzyme’s specific activity.

Answer 33

b. separate proteins exclusively on the basis of molecular weight.

Question 34

Specific enzyme activity:

Select one:

a. is the enzyme activity (expressed as units'') of a specific protein. b. is the enzyme activity (enzyme asunits’’) in a milligram of protein.
c. is the enzyme activity (expressed as ``units’’) in a mol of protein.
d. refers to proteins other than enzymes.
e. refers only to purified proteins.

Answer 34

b. is the enzyme activity (enzyme as ``units’’) in a milligram of protein.

Question 35

The backbone of two amino acid residues in a protein can be described as:

Select one:

a. Ca–C–N–Ca–C–N
b. Ca–N–Ca–C–Ca–N–Ca–C
c. Ca–N–C–C–N–Ca–
d. C–N–Ca–Ca–C–N
e. Ca–Ca–C–N–Ca–Ca–C

Answer 35

a. Ca–C–N–Ca–C–N

Question 36

Which of the following bond-pairs within a peptide backbone show free rotation around both bonds?

Select one:

a. C¬O and N–C
b. N–Ca and N–C
c. Ca–C and N–Ca
d. C¬O and N–C?
e. N–C and Ca–C

Answer 36

Ca–C and N–Ca

Question 37

In the a helix the hydrogen bonds:

Select one:

a. occur only between some of the amino acids of the helix.
b. occur mainly between electronegative atoms of the R groups.
c. are perpendicular to the axis of the helix.
d. occur mainly between electronegative atoms of the backbone.
e. occur only near the amino and carboxyl termini of the helix.

Answer 37

d. occur mainly between electronegative atoms of the backbone.

Question 38

In an helix, the R groups on the amino acid residues:

Select one:

a. stack within the interior of the helix.
b. generate the hydrogen bonds that form the helix.
c. are located outside of the helix spiral.
d. cause only right-handed helices to form.
e. alternate between the outside and the inside of the helix.

Answer 38

c. are located outside of the helix spiral.

Question 39

A D-amino acid would interrupt an a helix made of L-amino acids. Another naturally occurring constraint on the formation of an a helix is the presence of:

Select one:

a. a negatively charged Arginine residue.
b. a positively charged Lysine residue.
c. two Glycine residues side by side.
d. a nonpolar residue near the carboxyl terminus.
e. a Proline residue.

Answer 39

e. a Proline residue.

Question 40

Thr and/or Leu residues tend to disrupt an a helix when they occur next to each other in a protein because:

Select one:

a. of the possible covalent interactions between the Thr and/or Leu side chains.
b. both amino acids are highly hydrophobic.
c. the R group of neither amino acid can form a hydrogen bond.
d. of electrostatic repulsion between the Thr and/or Leu side chains.
e. of steric hindrance between the bulky Thr and/or Leu side chains.

Answer 40

e. of steric hindrance between the bulky Thr and/or Leu side chains.

Question 41

Amino acid residues commonly found at the end of b turn are:

Select one:

a. Pro and Gly.
b. Ala and Gly.
c. two Cys.
d. hydrophobic.
e. those with ionized R groups.

Answer 41

b. Ala and Gly.

Question 42

A sequence of amino acids in a certain protein is found to be -Ser-Gly-Pro-Gly-. The sequence is most probably part of a:

Select one:

a. b turn.
b. parallel b sheet.
c. a helix.
d. a–sheet.
e. antiparallel b sheet.

Answer 42

a. b turn.

Question 43

The three-dimensional conformation of a protein may be strongly influenced by amino acid residues that are very far apart in sequence. This relationship is in contrast to secondary structure, where the amino acid residues are:

Select one:

a. restricted to only about seven of the twenty standard amino acids found in proteins
b. always side by side.
c. generally on different polypeptide strands.
d. generally near the polypeptide chain’s amino terminus or carboxyl terminus.
e. generally near each other in sequence.

Answer 43

e. generally near each other in sequence.

Question 44

Which of the following statements is false?

Select one:

a. a-keratin is a protein in which the polypeptides are mainly in the a-helix conformation
b. Silk fibroin is a protein in which the polypeptide is almost entirely in the b conformation.
c. Collagen is a protein in which the polypeptides are mainly in the a-helix conformation
d. Gly residues are particularly abundant in collagen.
e. Mutations in collagen have been shown to be responsible for some human diseases

Answer 44

c. Collagen is a protein in which the polypeptides are mainly in the a-helix conformation

Question 45

To alter the shape of the a-keratin chains–as in hair waving– the a-keratin chains have undergone one chemical step resulting the conversion of disulfid bridges to Cysteins. What subsequent steps are required?

Select one:

a. chemical reduction and then chemical oxidation
b. chemical oxidation and then shape remodeling
c. shape remodeling and then chemical reduction
d. shape remodeling and then chemical oxidation
e. chemical reduction and then shape remodeling

Answer 45

d. shape remodeling and then chemical oxidation

Question 46

Kendrew’s studies of myoglobin structure demonstrated that:

Select one:

a. “corners” between a-helical regions invariably contained a glycine residue, which, because of its unique properties, cannot fit into the helix
b. the a–helix predicted by Pauling and Corey was not found in myoglobin; b-pleated sheet structure was found.
c. the structure was very compact, with virtually no internal space available for water molecules.
d. highly polar or charged amino acid residues tended to be located at the interior of the protein.
e. the structure of myoglobin proved to be completely different from that of hemoglobin, as expected from their very different biological roles.

Answer 46

c. the structure was very compact, with virtually no internal space available for water molecules.

Question 47

Which of the following statements about oligomeric proteins is false?

Select one:

a. Some subunits may have nonprotein prosthetic groups.
b. All subunits must be identical.
c. Contain more than one N-terminals
d. Some oligomeric proteins can further associate into large fibers.
e. Many have regulatory roles.

Answer 47

b. All subunits must be identical.

Question 48

Which of the following statements about proteins is false?

Select one:

a. Nonpolar amino acid side chains are mostly located on the surface of the water soluble proteins.
b. Most of the globular proteins are compact.
c. Proteins are sometimes conjugated with carbohydrates or fats.
d. Many proteins have more then one polypeptides .
e. proteins consist of amino acids linked by peptide bonds.

Answer 48

a. Nonpolar amino acid side chains are mostly located on the surface of the water soluble proteins.

Question 49

Which of the following statements about proteins is true?

Select one:

a. Proteins that contain a-helical regions never contain b–sheets
b. Proteins are generally very loosely structured.
c. In water-soluble proteins, hydrophobic (nonpolar) amino acid residues are generally buried and not exposed to water.
d. Detergents (such as sodium dodecyl sulfate, SDS) will not affect the structure of a protein that contains disulfide (–S–S–) bonds.
e. Hydrogen bonds are not important in the structure of proteins.

Answer 49

In water-soluble proteins, hydrophobic (nonpolar) amino acid residues are generally buried and not exposed to water.

Question 50

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

Select one:

a. two different ligands can bind to the same binding site.
b. the binding of the ligand to the protein is covalent.
c. multiple molecules of the same ligand can bind to the same binding site.
d. the binding of a molecule to a binding site affects the binding of an additional molecule to the same site.
e. the binding of a molecule to its binding site affects the binding properties of another site on the same protein.

Answer 50

e. the binding of a molecule to its binding site affects the binding properties of another site on the same protein.

Question 51

Select the correct statements!

Select one or more:

a. Basic amino acids have a net positive charge at neutral pH.
b. The isoelectric point of basic amino acids is at basic pH.
c. The isoelectric point of the basic amino acids can be calculated as the average of their three pKa values.
d. Arginine is a basic amino acid.

Answer 51

a. Basic amino acids have a net positive charge at neutral pH.
b. The isoelectric point of basic amino acids is at basic pH.
d. Arginine is a basic amino acid.