Question 1

If protein A has a pI of 3.1, protein B has a pI of 6.8, and protein C has a pI of 8.9, which protein would elute FIRST from a cation exchange column at pH 7?

Accepted Answer

At a pH of 7, the cation exchange column will be negatively charged and will bind positively charged proteins. Protein A has the lowest pI, meaning it has more positively charged residues at pH 7 than the other two proteins. Therefore, protein A will bind to the column more strongly and will elute last. Protein C has the highest pI, meaning it has fewer positively charged residues at pH 7 than the other two proteins, and will therefore elute first. Protein B will elute between proteins A and C. Thus, A will elute last and C will elute first.

Question 2

How are sequential reactions controlled in the Edman degradation procedure?

Accepted Answer

A high pH step is followed by a low pH step in the Edman degradation procedure to control the sequential reactions. This process allows for the selective cleavage and identification of amino acids from the N-terminus of a peptide chain.

Question 3

The structure below is a molecule used in the sweeteners Equal® and NutraSweet®. When heated, the peptide bond will hydrolyze into methanol and which two amino acids?

Accepted Answer

The peptide bond in this molecule connects aspartic acid and phenylalanine. When heated, it will hydrolyze into methanol and these two amino acids.

Question 4

Iodoacetamides, maleimides, benzyl halides, and bromomethyl ketones can all be used to modify the _____ group on _____ residues.

Accepted Answer

Iodoacetamides, maleimides, benzyl halides, and bromomethyl ketones are all reagents that specifically target sulfhydryl (-SH) groups on cysteine (Cys) residues. Therefore, the correct answer is D, sulfhydryl and Cys.

Question 5

Which item is NOT a biochemical use/function of peptides of small molecular weight?

Accepted Answer

All the answer choices are correct as peptides can serve as artificial sweeteners, hormones, poisons, and antibiotics.

Question 6

Which of the lanes in the gel below would represent an "uninduced" sample?

Accepted Answer

The answer of Which of the lanes in the gel...

Question 7

Describe the structures of the amino acids phenylalanine and aspartate in the ionization state you would expect at pH 7.0. Why is aspartate very soluble in water, whereas phenylalanine is much less soluble?

Accepted Answer

The answer of Describe the structures of the amino acids...

Question 8

According to the table, size-exclusion (gel-filtration) chromatography could NOT be used to separate which protein mixture? Protein
MW
PI
A
12,500
3)2
B
13,200
5)7
C
13,500
10)5
D
25,200
6)3
E
36,900
5)8
F
78,400
6)1

Accepted Answer

Size-exclusion (gel-filtration) chromatography separates molecules based on size, not isoelectric point (PI). Proteins A, B, and C have very similar molecular weights, making them difficult to separate using this method.

Question 9

The gel below illustrates the purification of the RecA protein from E. coli. This gel was loaded from the top. Which statement BEST describes how proteins "run" in an SDS gel?

Accepted Answer

In SDS-PAGE, proteins are separated primarily by molecular weight. The SDS detergent denatures the proteins, and the negatively charged SDS molecules bind to the exposed hydrophobic regions, giving a uniform negative charge to the protein. Since the gel matrix acts like a physical sieve, the smaller proteins can move more easily through the matrix and will travel further down the gel, while the larger proteins will move more slowly and remain higher up in the gel. Therefore, the smallest MW proteins are on the bottom, and the largest are on the top.

Question 10

A protein with a high percentage of lysine and arginine residues would be BEST purified and concentrated with which type of column?

Accepted Answer

Proteins with a high percentage of lysine and arginine residues are positively charged at physiological pH, making them suitable for purification using cation exchange chromatography, which binds positively charged molecules.

Question 11

What does the molecule SDS do to proteins?

Accepted Answer

SDS (Sodium Dodecyl Sulfate) is a detergent that denatures proteins by disrupting non-covalent bonds in the protein, leading to the unfolding of the protein. Additionally, SDS imparts a negative charge to the protein, which is proportional to the length of the protein, thus allowing for the separation of proteins based on size during SDS-PAGE.

Question 12

Only one of the common amino acids has no free $\alpha$-amino group. Name this amino acid.

Accepted Answer

The answer of Only one of the common amino acids...

Question 13

A protein with a high percentage of aspartate and glutamate residues would be BEST purified and concentrated with which type of column?

Accepted Answer

Aspartate and glutamate residues are negatively charged at physiological pH, therefore, an anion exchange column would be best as it will specifically bind and separate the protein based on its negatively charged residues.

Question 14

Selective precipitation of a protein from a crude extract is MOST effective by which molecule?

Accepted Answer

Ammonium sulfate is commonly used to selectively precipitate proteins from a crude extract based on their solubility at different salt concentrations. By gradually increasing the concentration of ammonium sulfate in a solution, proteins will eventually precipitate out of solution at their isoelectric point or at a specific salt concentration that is unique to each protein. Urea is commonly used for denaturing proteins but does not selectively precipitate them. Sodium dodecyl sulfate and EDTA are commonly used for protein solubilization and metal ion chelation, respectively, but do not selectively precipitate proteins from a crude extract.

Question 15

The "signature sequence" shown below represents a portion of a protein from four different organisms.  a. At which position(s) are amino acid residues invariant?
b. At which position(s) are amino acids limited to positively charged residues?
c. At which position(s) are amino acids limited to negatively charged residues?
d. At which position(s) are amino acids limited to nonpolar residues?

Accepted Answer

The answer of The "signature sequence" shown below represents a...

Question 16

The "signature sequence" shown below represents a portion of a protein from four different organisms. The proteins can be classified as:

Accepted Answer

The proteins can be classified as both homologs and orthologs. They are homologs because they share a similar signature sequence, indicating a common ancestry. They are also orthologs because they are found in different organisms but have a similar function, indicating that they evolved through speciation events.

Question 17

According to the table, ion-exchange chromatography would be the LEAST effective method to separate which protein mixture? Protein
MW
PI
A
12,500
3)2
B
13,200
5)7
C
13,500
10)5
D
25,200
6)3
E
36,900
5)8
F
78,400
6)1

Accepted Answer

Ion-exchange chromatography separates proteins based on their isoelectric points (pI). Proteins B, E, and F have similar pI values (5.7, 5.8, and 6.1, respectively), making it difficult to separate them using this method.

Question 18

R. Bruce Merrifield provided an innovation to synthesize peptides. Which statement does NOT describe part of his technology?

Accepted Answer

The statement "The peptide product must be purified between each step of the cycle" is not true. In fact, one advantage of Merrifield's technology is that purification is not necessary until after the entire peptide is synthesized.

Question 19

What are the structural characteristics common to all amino acids found in naturally occurring proteins?

Accepted Answer

The answer of What are the structural characteristics common to...

Question 20

Briefly describe the five major groupings of amino acids.
79.
A
B
C
D
E
Tyr-Lys-Met
Gly-Pro-Arg
Asp-Trp-Tyr
Asp-His-Glu
Leu-Val-Phe
Which one of the above tripeptides:
____ (a) is most negatively charged at pH 7?
____ (b) will yield DNP-tyrosine when reacted with l-fluoro-2,4-dinitrobenzene and hydrolyzed in acid?
____ (c) contains the largest number of nonpolar R groups?
____ (d) contains sulfur?
____ (e) will have the greatest light absorbance at 280 nm?

Accepted Answer

The answer of Briefly describe the five major groupings of...

Quiz 3: Amino Acids, Peptides, and Proteins

If protein A has a pI of 3.1, protein B has a pI of 6.8, and protein C has a pI of 8.9, which protein would elute FIRST from a cation exchange column at pH 7?

How are sequential reactions controlled in the Edman degradation procedure?

The structure below is a molecule used in the sweeteners Equal® and NutraSweet®. When heated, the peptide bond will hydrolyze into methanol and which two amino acids?

Iodoacetamides, maleimides, benzyl halides, and bromomethyl ketones can all be used to modify the _ group on _ residues.

Which item is NOT a biochemical use/function of peptides of small molecular weight?

Which of the lanes in the gel below would represent an "uninduced" sample?

Describe the structures of the amino acids phenylalanine and aspartate in the ionization state you would expect at pH 7.0. Why is aspartate very soluble in water, whereas phenylalanine is much less soluble?

According to the table, size-exclusion (gel-filtration) chromatography could NOT be used to separate which protein mixture? Protein MW PI A 12,500 3) 2 B 13,200 5) 7 C 13,500 10) 5 D 25,200 6) 3 E 36,900 5) 8 F 78,400 6) 1

The gel below illustrates the purification of the RecA protein from E. coli. This gel was loaded from the top. Which statement BEST describes how proteins "run" in an SDS gel?

A protein with a high percentage of lysine and arginine residues would be BEST purified and concentrated with which type of column?

What does the molecule SDS do to proteins?

Only one of the common amino acids has no free $\alpha$ -amino group. Name this amino acid.

A protein with a high percentage of aspartate and glutamate residues would be BEST purified and concentrated with which type of column?

Selective precipitation of a protein from a crude extract is MOST effective by which molecule?

The "signature sequence" shown below represents a portion of a protein from four different organisms. The proteins can be classified as:

According to the table, ion-exchange chromatography would be the LEAST effective method to separate which protein mixture? Protein MW PI A 12,500 3) 2 B 13,200 5) 7 C 13,500 10) 5 D 25,200 6) 3 E 36,900 5) 8 F 78,400 6) 1

R. Bruce Merrifield provided an innovation to synthesize peptides. Which statement does NOT describe part of his technology?

What are the structural characteristics common to all amino acids found in naturally occurring proteins?

Quiz 3: Amino Acids, Peptides, and Proteins

If protein A has a pI of 3.1, protein B has a pI of 6.8, and protein C has a pI of 8.9, which protein would elute FIRST from a cation exchange column at pH 7?

How are sequential reactions controlled in the Edman degradation procedure?

The structure below is a molecule used in the sweeteners Equal® and NutraSweet®. When heated, the peptide bond will hydrolyze into methanol and which two amino acids?

Iodoacetamides, maleimides, benzyl halides, and bromomethyl ketones can all be used to modify the _____ group on _____ residues.

Which item is NOT a biochemical use/function of peptides of small molecular weight?

Which of the lanes in the gel below would represent an "uninduced" sample?

Describe the structures of the amino acids phenylalanine and aspartate in the ionization state you would expect at pH 7.0. Why is aspartate very soluble in water, whereas phenylalanine is much less soluble?

According to the table, size-exclusion (gel-filtration) chromatography could NOT be used to separate which protein mixture? Protein MW PI A 12,500 3) 2 B 13,200 5) 7 C 13,500 10) 5 D 25,200 6) 3 E 36,900 5) 8 F 78,400 6) 1

The gel below illustrates the purification of the RecA protein from E. coli. This gel was loaded from the top. Which statement BEST describes how proteins "run" in an SDS gel?

A protein with a high percentage of lysine and arginine residues would be BEST purified and concentrated with which type of column?

What does the molecule SDS do to proteins?

Only one of the common amino acids has no free α\alphaα -amino group. Name this amino acid.

A protein with a high percentage of aspartate and glutamate residues would be BEST purified and concentrated with which type of column?

Selective precipitation of a protein from a crude extract is MOST effective by which molecule?

The "signature sequence" shown below represents a portion of a protein from four different organisms. The proteins can be classified as:

According to the table, ion-exchange chromatography would be the LEAST effective method to separate which protein mixture? Protein MW PI A 12,500 3) 2 B 13,200 5) 7 C 13,500 10) 5 D 25,200 6) 3 E 36,900 5) 8 F 78,400 6) 1

R. Bruce Merrifield provided an innovation to synthesize peptides. Which statement does NOT describe part of his technology?

What are the structural characteristics common to all amino acids found in naturally occurring proteins?

Iodoacetamides, maleimides, benzyl halides, and bromomethyl ketones can all be used to modify the _ group on _ residues.

Only one of the common amino acids has no free $\alpha$ -amino group. Name this amino acid.