Question 1

What is the pI,and how is it determined for amino acids that have nonionizable R groups?

Accepted Answer

The pI is the isoelectric point.It occur

Question 2

For amino acids with neutral R groups,at any pH below the pI of the amino acid,the population of amino acids in solution will have:

Accepted Answer

A) a net negative charge. 
B) a net positive charge. 
C) no charged groups. 
D) no net charge. 
E) positive and negative charges in equal concentration. 
A) a net negative charge. 
B) a net positive charge. 
C) no charged groups. 
D) no net charge. 
E) positive and negative charges in equal concentration.

Question 3

Distinguish between homologs,paralogs,and orthologs as classes of related proteins.

Accepted Answer

Homologs are any members of a

Question 4

What factors would make it difficult to interpret the results of a gel electrophoresis of proteins in the absence of sodium dodecyl sulfate (SDS)?

Accepted Answer

Without SDS,protein migration through a

Question 5

Which of the following refers to particularly stable arrangements of amino acid residues in a protein that give rise to recurring patterns?

Accepted Answer

A) Primary structure 
B) Secondary structure 
C) Tertiary structure 
D) Quaternary structure 
E) None of the above 
A) Primary structure 
B) Secondary structure 
C) Tertiary structure 
D) Quaternary structure 
E) None of the above

Question 6

Why do amino acids,when dissolved in water,become zwitterions?

Accepted Answer

Near pH = 7,the carboxylic aci

Question 7

The amino acid histidine has three ionizable groups,with pKa values of 1.8,6.0,and 9.2.
(a)Which pKa corresponds to the histidine side chain? 
(b)In a solution at pH 5.4,what percentage of the histidine side chains will carry a positive charge?

Accepted Answer

(a)6.0; 
(b)80%.(See

Question 8

At the isoelectric pH of a tetrapeptide:

Accepted Answer

A) only the amino and carboxyl termini contribute charge. 
B) the amino and carboxyl termini are not charged. 
C) the total net charge is zero. 
D) there are four ionic charges. 
E) two internal amino acids of the tetrapeptide cannot have ionizable R groups. 
A) only the amino and carboxyl termini contribute charge. 
B) the amino and carboxyl termini are not charged. 
C) the total net charge is zero. 
D) there are four ionic charges. 
E) two internal amino acids of the tetrapeptide cannot have ionizable R groups.

Question 9

Why do smaller molecules elute after large molecules when a mixture of proteins is passed through a size-exclusion (gel filtration)column?

Accepted Answer

The column matrix is composed of cross-l

Question 10

Which of the following is correct with respect to the amino acid composition of proteins?

Accepted Answer

A) Larger proteins have a more uniform distribution of amino acids than smaller proteins. 
B) Proteins contain at least one each of the 20 different standard amino acids. 
C) Proteins with different functions usually differ significantly in their amino acid composition. 
D) Proteins with the same molecular weight have the same amino acid composition. 
E) The average molecular weight of an amino acid in a protein increases with the size of the protein. 
A) Larger proteins have a more uniform distribution of amino acids than smaller proteins. 
B) Proteins contain at least one each of the 20 different standard amino acids. 
C) Proteins with different functions usually differ significantly in their amino acid composition. 
D) Proteins with the same molecular weight have the same amino acid composition. 
E) The average molecular weight of an amino acid in a protein increases with the size of the protein.

Question 11

The average molecular weight of the 20 standard amino acids is 138,but biochemists use 110 when estimating the number of amino acids in a protein of known molecular weight.Why?

Accepted Answer

A) The number 110 is based on the fact that the average molecular weight of a protein is 110,000 with an average of 1000 amino acids. 
B) The number 110 reflects the higher proportion of small amino acids in proteins,as well as the loss of water when the peptide bond forms. 
C) The number 110 reflects the number of amino acids found in the typical small protein,and only small proteins have their molecular weight estimated this way. 
D) The number 110 takes into account the relatively small size of nonstandard amino acids. 
E) The number 138 represents the molecular weight of conjugated amino acids. 
A) The number 110 is based on the fact that the average molecular weight of a protein is 110,000 with an average of 1000 amino acids. 
B) The number 110 reflects the higher proportion of small amino acids in proteins,as well as the loss of water when the peptide bond forms. 
C) The number 110 reflects the number of amino acids found in the typical small protein,and only small proteins have their molecular weight estimated this way. 
D) The number 110 takes into account the relatively small size of nonstandard amino acids. 
E) The number 138 represents the molecular weight of conjugated amino acids.

Question 12

Which two amino acids differ from each other by only one atom?

Accepted Answer

A) Ser and Thr 
B) Leu and Ile 
C) Ala and Ser 
D) Asp and Asn 
E) Ser and Cys 
A) Ser and Thr 
B) Leu and Ile 
C) Ala and Ser 
D) Asp and Asn 
E) Ser and Cys

Question 13

A polypeptide is hydrolyzed,and it is determined that there are 3 Lys residues and 2 Arg residues (as well as other residues).How many peptide fragments can be expected when the native polypeptide is incubated with the proteolytic enzyme trypsin?

Accepted Answer

Six fragments would be expecte

Question 14

The chirality of an amino acid results from the fact that its $\alpha$ carbon:

Accepted Answer

A) has no net charge. 
B) is a carboxylic acid. 
C) is bonded to four different chemical groups. 
D) is in the l absolute configuration in naturally occurring proteins. 
E) is symmetric. 
A) has no net charge. 
B) is a carboxylic acid. 
C) is bonded to four different chemical groups. 
D) is in the l absolute configuration in naturally occurring proteins. 
E) is symmetric.

Question 15

All of the amino acids that are found in proteins,except for proline,contain a(n):

Accepted Answer

A) amino group. 
B) carbonyl group. 
C) carboxyl group. 
D) ester group. 
E) thiol group. 
A) amino group. 
B) carbonyl group. 
C) carboxyl group. 
D) ester group. 
E) thiol group.

Question 16

In a mixture of the five proteins listed below,which should elute second in size-exclusion (gel- filtration)chromatography?

Accepted Answer

A) cytochrome c Mr = 13,000 
B) immunoglobulin G Mr = 145,000 
C) ribonuclease A Mr = 13,700 
D) RNA polymerase Mr = 450,000 
E) serum albumin Mr = 68,500 
A) cytochrome c Mr = 13,000 
B) immunoglobulin G Mr = 145,000 
C) ribonuclease A Mr = 13,700 
D) RNA polymerase Mr = 450,000 
E) serum albumin Mr = 68,500

Question 17

How does the shape of a titration curve confirm the fact that the pH region of greatest buffering power for an amino acid solution is around its pK's?

Accepted Answer

In a certain range around the pK_a</

Question 18

Conjugated proteins contain chemical substituents in addition to amino acids.List three classes of conjugated proteins and identify the type of prosthetic group associated with each one.

Accepted Answer

Any of the following are acceptable answ

Question 19

Even when a gene is available and its sequence of nucleotides is known,chemical studies of the protein are still required to determine:

Accepted Answer

A) molecular weight of the protein. 
B) the amino-terminal amino acid. 
C) the location of disulfide bonds. 
D) the number of amino acids in the protein. 
E) whether the protein has the amino acid methionine in its sequence. 
A) molecular weight of the protein. 
B) the amino-terminal amino acid. 
C) the location of disulfide bonds. 
D) the number of amino acids in the protein. 
E) whether the protein has the amino acid methionine in its sequence.

Question 20

The term "proteome" has been used to describe:

Accepted Answer

A) regions (domains)within proteins. 
B) regularities in protein structures. 
C) the complement of proteins expressed by an organism's genome. 
D) the structure of a protein-synthesizing ribosome. 
E) the tertiary structure of a protein. 
A) regions (domains)within proteins. 
B) regularities in protein structures. 
C) the complement of proteins expressed by an organism's genome. 
D) the structure of a protein-synthesizing ribosome. 
E) the tertiary structure of a protein.

Exam 3: Amino Acids, peptides, and Proteins

What is the pI,and how is it determined for amino acids that have nonionizable R groups?

For amino acids with neutral R groups,at any pH below the pI of the amino acid,the population of amino acids in solution will have:

Distinguish between homologs,paralogs,and orthologs as classes of related proteins.

What factors would make it difficult to interpret the results of a gel electrophoresis of proteins in the absence of sodium dodecyl sulfate (SDS)?

Which of the following refers to particularly stable arrangements of amino acid residues in a protein that give rise to recurring patterns?

Why do amino acids,when dissolved in water,become zwitterions?

The amino acid histidine has three ionizable groups,with pKa values of 1.8,6.0,and 9.2. (a)Which pKa corresponds to the histidine side chain? (b)In a solution at pH 5.4,what percentage of the histidine side chains will carry a positive charge?

At the isoelectric pH of a tetrapeptide:

Why do smaller molecules elute after large molecules when a mixture of proteins is passed through a size-exclusion (gel filtration)column?

Which of the following is correct with respect to the amino acid composition of proteins?

The average molecular weight of the 20 standard amino acids is 138,but biochemists use 110 when estimating the number of amino acids in a protein of known molecular weight.Why?

Which two amino acids differ from each other by only one atom?

A polypeptide is hydrolyzed,and it is determined that there are 3 Lys residues and 2 Arg residues (as well as other residues).How many peptide fragments can be expected when the native polypeptide is incubated with the proteolytic enzyme trypsin?

The chirality of an amino acid results from the fact that its α\alphaα carbon:

All of the amino acids that are found in proteins,except for proline,contain a(n):

In a mixture of the five proteins listed below,which should elute second in size-exclusion (gel- filtration)chromatography?

How does the shape of a titration curve confirm the fact that the pH region of greatest buffering power for an amino acid solution is around its pK's?

Conjugated proteins contain chemical substituents in addition to amino acids.List three classes of conjugated proteins and identify the type of prosthetic group associated with each one.

Even when a gene is available and its sequence of nucleotides is known,chemical studies of the protein are still required to determine:

The term "proteome" has been used to describe:

The Foundations of Biochemistry

Water

The Three-Dimensional Structure of Proteins

Protein Function

Enzymes

Carbohydrates and Glycobiology

Nucleotides and Nucleic Acids

Recombinant Dna Technology

Lipids

Biological Membranes and Transport

Biosignaling

Principles of Bioenergetics

Glycolysis, gluconeogenesis, and the Pentose Phosphate Pathway

Principles of Metabolic Regulation

The Citric Acid Cycle

Fatty Acid Catabolism

Amino Acid Oxidation and the Production of Urea

Oxidative Phosphorylation and Photophosphorylation

Carbohydrate Biosynthesis in Plants and Bacteria

Lipid Biosynthesis

Biosynthesis of Amino Acids, nucleotides, and Related Molecules

Integration and Hormonal Regulation of Mammalian Metabolism

Genes and Chromosomes

Dna Metabolism

Rna Metabolism

Protein Metabolism

Regulation of Gene Expression

Filters

The amino acid histidine has three ionizable groups,with pK_a values of 1.8,6.0,and 9.2. (a)Which pK_a corresponds to the histidine side chain? (b)In a solution at pH 5.4,what percentage of the histidine side chains will carry a positive charge?

The chirality of an amino acid results from the fact that its $\alpha$ carbon: