Question 1

Proteins can be modified by adding to protein residues.

Accepted Answer

A)  sugars and phosphate groups 
B)  hydroxyl and formyl groups 
C)  cystine 
D)  A and B 
E)  All of the above 
A)  sugars and phosphate groups 
B)  hydroxyl and formyl groups 
C)  cystine 
D)  A and B 
E)  All of the above

Question 2

The pKa of a certain weak acid is 4.0. Calculate the ratio of proton acceptor to proton donor at pH 7.0.

Accepted Answer

A)  1000:1 
B)  20:1 
C)  3:1 
D)  1:1 
E)  The ratio cannot be calculated without knowing the structure of the weak acid. 
A)  1000:1 
B)  20:1 
C)  3:1 
D)  1:1 
E)  The ratio cannot be calculated without knowing the structure of the weak acid.

Question 3

Which is used to hydrolyze the peptide bonds of a protein to yield free amino acids?

Accepted Answer

A)  PITC 
B)  SDS 
C)  CNBr 
D)  HCl 
A)  PITC 
B)  SDS 
C)  CNBr 
D)  HCl

Question 4

Which technique is used less for protein purification and more for the determination of molecular weights?

Accepted Answer

A)  affinity chromatography 
B)  SDS-PAGE 
C)  gel filtration 
D)  ion exchange chromatography 
A)  affinity chromatography 
B)  SDS-PAGE 
C)  gel filtration 
D)  ion exchange chromatography

Question 5

A protein that contains more isoleucine, phenylalanine and leucine than asparagine, lysine and arginine is most likely

Accepted Answer

A)  hydrophilic. 
B)  hydrophobic. 
C)  neutral. 
D)  low on the hydropathy index scale. 
A)  hydrophilic. 
B)  hydrophobic. 
C)  neutral. 
D)  low on the hydropathy index scale.

Question 6

Amino acids are named that because each one

Accepted Answer

A)  is a unique carboxylic acid. 
B)  has a standard configuration. 
C)  is a carboxyl derivative of an amide acid. 
D)  is an amino derivative of a carboxylic acid. 
A)  is a unique carboxylic acid. 
B)  has a standard configuration. 
C)  is a carboxyl derivative of an amide acid. 
D)  is an amino derivative of a carboxylic acid.

Question 7

Amino acids and amino acid derivatives can be used to modify proteins.

Accepted Answer

A) True 
 B)False

Question 8

The overall shape of a protein is greatly influenced by

Accepted Answer

A)  amino acid R group properties. 
B)  charged amino acids. 
C)  hydrophobic amino acids. 
D)  pH. 
E)  hydrophilic amino acids. 
A)  amino acid R group properties. 
B)  charged amino acids. 
C)  hydrophobic amino acids. 
D)  pH. 
E)  hydrophilic amino acids.

Question 9

What is the N-terminal for the pentapeptide Val-Ile-Glu-Arg-Tyr?

Accepted Answer

A)  the NH3+ group on the side chain of Arg 
B)  valine 
C)  tyrosine 
D)  tryptophan 
A)  the NH3+ group on the side chain of Arg 
B)  valine 
C)  tyrosine 
D)  tryptophan

Question 10

The pKaʹs of isoleucineʹs α-Carboxyl group and α-Amino group are 2.3 and 9.8, respectively. Calculate the isoelectric point.

Accepted Answer

A)  2.3 
B)  6.0 
C)  9.8 
D)  The isoelectric point cannot be calculated without the pKa value for the side chain. 
A)  2.3 
B)  6.0 
C)  9.8 
D)  The isoelectric point cannot be calculated without the pKa value for the side chain.

Question 11

Gel-filtration chromatography separates a mixture of proteins on the basis of .

Accepted Answer

A)  charge 
B)  size 
C)  affinity for ligands in the column matrix 
D)  density 
A)  charge 
B)  size 
C)  affinity for ligands in the column matrix 
D)  density

Question 12

Which structure below is appropriate for glycine at neutral pH?

Accepted Answer

A)  H2NCH2COOH 
B)  H2NCH2COO-  
C) ( +H3NCH2COO- ) 
D) ( +H3NCH2COOH) 
A)  H2NCH2COOH 
B)  H2NCH2COO-  
C) ( +H3NCH2COO- ) 
D) ( +H3NCH2COOH)

Question 13

The R group of an amino acid determines if it is

Accepted Answer

A)  hyrophilic or hydrophobic. 
B)  polar or nonpolar. 
C)  charged or uncharged. 
D)  an acid or a base. 
E)  All of the above 
A)  hyrophilic or hydrophobic. 
B)  polar or nonpolar. 
C)  charged or uncharged. 
D)  an acid or a base. 
E)  All of the above

Question 14

Amino acids which are not incorporated into polypeptides are converted into

Accepted Answer

A)  neurotransmitters. 
B)  methyl donors. 
C)  antibiotics. 
D)  blood flow controllers. 
E)  All of the above 
A)  neurotransmitters. 
B)  methyl donors. 
C)  antibiotics. 
D)  blood flow controllers. 
E)  All of the above

Question 15

The twenty standard amino acids are the only amino acids found in living organisms.

Accepted Answer

A) True 
 B)False

Question 16

Which substance is used to fractionate proteins based on differences in their solubility as a function of salt concentration?

Accepted Answer

A)  cellophane 
B)  sodium dodecyl sulfate 
C)  phenylisothiocyanate 
D)  ammonium sulfate 
A)  cellophane 
B)  sodium dodecyl sulfate 
C)  phenylisothiocyanate 
D)  ammonium sulfate

Question 17

Amino acids are neutral at the isoelectric pH.

Accepted Answer

A) True 
 B)False

Question 18

The liquid emerging from the bottom of a chromatography column is called the .

Accepted Answer

A)  eluate 
B)  supernatant 
C)  solute 
D)  lysate 
A)  eluate 
B)  supernatant 
C)  solute 
D)  lysate

Question 19

What is the net charge on the dipeptide Arg-Pro at pH 9.0? The table below gives the pKa?s of the ionizable groups on the free amino acids. $\begin{array}{|l|c|c|c|}
\hline \text { Free amino acid } & \begin{array}{c}
\text { pKa of } \
\alpha \text {-Carboxyl group }
\end{array} & \begin{array}{c}
\text { pKa of } \
\alpha \text {-amino group }
\end{array} & \begin{array}{c}
p \text { Ka of side } \
\text { chain }
\end{array} \
\hline \text { Arginine } & 1.8 & 9.0 & 12.5 \
\hline \text { Proline } & 2.0 & 10.6 & \cdots \
\hline
\end{array}$

Accepted Answer

A)  -1 
B)  -0.5 
C)  0 
D)  +0.5 
E)  +1 
A)  -1 
B)  -0.5 
C)  0 
D)  +0.5 
E)  +1

Question 20

What is the purpose of treating a protein with 2-mercaptoethanol?

Accepted Answer

A)  to hydrolyze the protein into its amino acids 
B)  to cleave the disulfide bonds 
C)  to derivatize any free sulfhydryl groups to prevent them from reforming disulfide bonds 
D)  to derivatize the N-terminal amino acid during the Edman degradation 
A)  to hydrolyze the protein into its amino acids 
B)  to cleave the disulfide bonds 
C)  to derivatize any free sulfhydryl groups to prevent them from reforming disulfide bonds 
D)  to derivatize the N-terminal amino acid during the Edman degradation

Exam 3: Amino Acids and the Primary Structures of Proteins

Proteins can be modified by adding to protein residues.

The pKa of a certain weak acid is 4.0. Calculate the ratio of proton acceptor to proton donor at pH 7.0.

Which is used to hydrolyze the peptide bonds of a protein to yield free amino acids?

Which technique is used less for protein purification and more for the determination of molecular weights?

A protein that contains more isoleucine, phenylalanine and leucine than asparagine, lysine and arginine is most likely

Amino acids are named that because each one

Amino acids and amino acid derivatives can be used to modify proteins.

The overall shape of a protein is greatly influenced by

What is the N-terminal for the pentapeptide Val-Ile-Glu-Arg-Tyr?

The pKaʹs of isoleucineʹs α-Carboxyl group and α-Amino group are 2.3 and 9.8, respectively. Calculate the isoelectric point.

Gel-filtration chromatography separates a mixture of proteins on the basis of .

Which structure below is appropriate for glycine at neutral pH?

The R group of an amino acid determines if it is

Amino acids which are not incorporated into polypeptides are converted into

The twenty standard amino acids are the only amino acids found in living organisms.

Which substance is used to fractionate proteins based on differences in their solubility as a function of salt concentration?

Amino acids are neutral at the isoelectric pH.

The liquid emerging from the bottom of a chromatography column is called the .

What is the net charge on the dipeptide Arg-Pro at pH 9.0? The table below gives the pKa?s of the ionizable groups on the free amino acids. Free amino acid pKa of \alpha -Carboxyl group pKa of \alpha -amino group p Ka of side chain Arginine 1.8 9.0 12.5 Proline 2.0 10.6 \@cdots

What is the purpose of treating a protein with 2-mercaptoethanol?

Introduction to Biochemistry

Water

Proteins: Three-Dimensional Structure and Function

Properties of Enzymes

Mechanisms of Enzymes

Coenzymes and Vitamins

Carbohydrates

Lipids and Membranes

Introduction to Metabolism

Glycolysis

Gluconeogenesis, the Pentose Phosphate Pathway, and Glycogen Metabolism

The Citric Acid Cycle

Electron Transport and Oxidative Phosphorylation

Photosynthesis

Lipid Metabolism

Amino Acid Metabolism

Nucleotide Metabolism

Nucleic Acids

Dna Replication, Repair, and Recombination

Transcription and Rna Processing

Protein Synthesis

Recombinant Dna Technology

Filters

The pK_aof a certain weak acid is 4.0. Calculate the ratio of proton acceptor to proton donor at pH 7.0.

The pK_aʹs of isoleucineʹs α-Carboxyl group and α-Amino group are 2.3 and 9.8, respectively. Calculate the isoelectric point.