Question 1

The bonding of two amino acid molecules to form a larger molecule requires the ________.
A) release of a water molecule
B) release of a carbon dioxide molecule
C) addition of a carbon dioxide molecule
D) addition of a water molecule
E) addition of a water molecule and a carbon dioxide molecule

Accepted Answer

The bonding of two amino acids to form a dipeptide (a larger molecule) involves a dehydration synthesis reaction, where a water molecule is released. This occurs when the carboxyl group of one amino acid reacts with the amino group of another, forming a peptide bond and releasing water.

Question 2

Upon chemical analysis, a particular polypeptide was found to contain 100 amino acids. How many peptide bonds are present in this protein?
A) 101
B) 100
C) 99
D) 98
E) 97

Accepted Answer

There are 99 peptide bonds in a polypeptide with 100 amino acids. Each pair of adjacent amino acids is linked by a peptide bond, except for the first amino acid which does not have a bond on one end and the last amino acid which does not have a bond on the other end. Therefore, the number of bonds is equal to the number of amino acids minus one, which is 100-1=99.

Question 3

Refer to the accompanying figure to answer the following question(s). 
-Which bond is closest to the amino group of the molecule?
A) A
B) B
C) C
D) D
E) E

Accepted Answer

Bond A is closest to the amino group because it is directly attached to the nitrogen atom in the amino group.

Question 4

There are 20 different amino acids. What makes one amino acid different from another?
A) different side chains (R-groups) attached to a carboxyl carbon
B) different side chains (R-groups) attached to the amino groups
C) different side chains (R-groups) attached to an α carbon
D) different structural and optical isomers
E) different asymmetric carbons

Accepted Answer

The side chains (R-groups) attached to the α carbon of each amino acid are what distinguish one amino acid from another. The other answer choices do not accurately describe the differences between amino acids.

Question 5

Which two functional groups are always found in amino acids?
A) ketone and methyl groups
B) carbonyl and amino groups
C) carboxyl and amino groups
D) amino and sulfhydryl groups
E) hydroxyl and carboxyl groups

Accepted Answer

Amino acids always contain a carboxyl group (-COOH) and an amino group (-NH2).

Question 6

The chemical reaction illustrated in the accompanying figure ________.
A) is a hydrolysis reaction
B) results in a peptide bond
C) joins two fatty acids together
D) links two polymers to form a monomer
E) joins two phospholipids in a bilayer

Accepted Answer

The chemical reaction shown in the figure depicts a dehydration synthesis reaction, with the formation of a peptide bond between two amino acids.

Question 7

Which of the following involves an increase in entropy?
A) hydrolysis
B) reactions that join monomers
C) polymerization
D) chemical evolution

Accepted Answer

Hydrolysis involves the breaking of chemical bonds and the release of energy, leading to an increase in disorder or entropy.

Question 8

A peptide bond ________.
A) forms between the functional R-groups of different amino acids
B) forms between the central carbon and the amino R-group of a single amino acid
C) forms the primary structure of proteins
D) does not play a role in maintaining the tertiary structure of proteins

Accepted Answer

A peptide bond forms between the carboxyl group of one amino acid and the amino group of another amino acid, forming the primary structure of proteins. Choice A and B are incorrect because peptide bonds do not involve functional R-groups or the central carbon of an amino acid. Choice D is incorrect because peptide bonds do play a crucial role in maintaining the tertiary structure of proteins by linking amino acid residues together in a specific sequence.

Question 9

A hydrocarbon skeleton is covalently bonded to an amino group at one end and a carboxyl group at the other end. When placed in water this molecule would function ________.
A) only as an acid because of the carboxyl group
B) only as a base because of the amino group
C) as an acid and a base
D) as neither an acid nor a base
E) It is impossible to determine how it would function, based on the information provided.

Accepted Answer

The molecule is an amino acid, which contains both an amino group and a carboxyl group, allowing it to function as both an acid and a base.

Question 10

What component of amino acid structure varies among different amino acids?
A) the long carbon-hydrogen tails of the molecule
B) the presence of a central C atom
C) the components of the R-group
D) the glycerol molecule that forms the backbone of the amino acid

Accepted Answer

The R-group or side chain of amino acids varies among different amino acids. This is the part of the amino acid that differs between different types and determines their properties and functions. The other components of the amino acid structure are the same in all amino acids - a central carbon atom, an amino group, a carboxyl group, and a hydrogen atom.

Question 11

Why are polymerization reactions endergonic? Polymerization reactions ________.
A) reduce entropy
B) release heat, making the reactant monomers move faster
C) release energy
D) are at equilibrium

Accepted Answer

Polymerization reactions involve the formation of larger molecules from smaller molecules (monomers) which usually results in a decrease in entropy. Since the reaction is non-spontaneous and requires energy input to proceed, it is endergonic. Option B is incorrect because polymerization reactions do not typically release heat, and the movement of the reactants is not relevant to the endergonic nature of the reaction. Option C is incorrect because energy is required for the reaction to proceed. Option D is also incorrect because endergonic reactions are not at equilibrium.

Question 12

Refer to the accompanying figure to answer the following question(s). 
-At which bond would water need to be added to achieve hydrolysis of the peptide, back to its component amino acids?
A) A
B) B
C) C
D) D
E) E

Accepted Answer

Hydrolysis of a peptide bond involves breaking the bond between the carbonyl carbon and the nitrogen in the peptide linkage, which is typically represented by option C in diagrams of peptide chains.

Question 13

Suppose you discovered a new amino acid. Its R-group contains only hydrogen and carbon atoms. Predict the behavior of this amino acid.
A) It is hydrophobic.
B) It is hydrophilic.
C) Relative to the amino acids found in organisms, its interactions with water will be intermediate.
D) Relative to the amino acids found in organisms, its interactions with water will be very high.

Accepted Answer

The R-group containing only hydrogen and carbon atoms indicates that the amino acid is nonpolar. Nonpolar amino acids are usually hydrophobic, meaning they tend to avoid water and prefer to interact with other nonpolar molecules or surfaces.

Question 14

Amino acids are acids because they always possess which functional group?
A) amino
B) carbonyl
C) carboxyl
D) phosphate
E) hydroxyl

Accepted Answer

Amino acids always possess a carboxyl group, which is a functional group that can donate a proton and therefore act as an acid. The amino group in the name "amino acid" refers to the other functional group that amino acids contain.

Question 15

In solution, why do hydrolysis reactions occur more readily than condensation reactions?
A) Hydrolysis increases entropy and is exergonic.
B) Hydrolysis decreases entropy and is endergonic.
C) Hydrolysis decreases entropy and is exergonic.
D) Hydrolysis increases entropy and is endergonic.

Accepted Answer

Hydrolysis reactions involve the breaking of a compound into two or more components with the addition of water, which generally increases the disorder (entropy) in the system. These reactions are often exergonic, meaning they release energy, making them more favorable under standard conditions compared to condensation reactions, which build larger molecules from smaller ones and typically require an input of energy.

Question 16

Side chains of amino acids ________.
A) are all nonpolar
B) are nonpolar if they contain N or S
C) are all polar
D) may be polar or nonpolar

Accepted Answer

Side chains (also known as R groups) of amino acids can vary greatly in their chemical properties, which can be polar, nonpolar, acidic, or basic. The side chains containing N or S can be polar, acidic, or basic, while those that lack N or S are either nonpolar or weakly polar. Therefore, option D is correct, as amino acid side chains may be polar or nonpolar depending on their chemical composition. Option A and C are incorrect as they state that side chains are either all nonpolar or all polar, which is not true. Option B is incorrect as it only mentions N or S containing side chains, whereas other polar side chains exist.

Question 17

Refer to the accompanying figure to answer the following question(s). 
-Which bond is a peptide bond?
A) A
B) B
C) C
D) D
E) E

Accepted Answer

The peptide bond is a covalent bond that joins amino acids together in a protein chain. In the figure, bond C is the only bond between two amino acids, demonstrating a peptide bond.

Question 18

At about pH 7 in most cells, what happens to the carboxyl R-group on an amino acid?
A) It acts as a base and gains a proton, giving it a positive charge.
B) It acts as an acid and loses a proton, giving it a negative charge.
C) It is oxidized and tends to act as an electron acceptor in redox reactions.
D) It remains neutral, like water, and does not have a charge.

Accepted Answer

At approximately pH 7, the carboxyl R-group on an amino acid acts as an acid and loses a proton (H+), giving it a negative charge. This is because at this pH, there is an equal concentration of H+ and OH- ions in the solution, so the carboxyl group can donate a proton (H+) to the solution, making it negatively charged.

Question 19

At about pH 7 in most cells, what happens to the amino R-group on an amino acid?
A) It acts as a base and gains a proton, giving it a positive charge.
B) It acts as an acid and loses a proton, giving it a negative charge.
C) It is reduced and tends to act as an electron donor in redox reactions.
D) It remains neutral, like water, and does not have a charge.

Accepted Answer

At about pH 7, the amino R-group on an amino acid acts as a base and gains a proton, giving it a positive charge. This is because the amino group (-NH2) can accept a proton to become -NH3+, which is a common behavior in physiological pH conditions.

Question 20

Which one of the following is NOT a component of each monomer used to make proteins?
A) a phosphorus atom, P
B) an amino functional group, NH2
C) a side chain, R
D) a carboxyl group, COOH

Accepted Answer

The monomers used to make proteins are amino acids, which consist of an amino group (NH2), a carboxyl group (COOH), and a side chain (R). There is no phosphorus atom (P) in amino acids.

Quiz 3: Protein Structure and Function

The bonding of two amino acid molecules to form a larger molecule requires the ________.

Upon chemical analysis, a particular polypeptide was found to contain 100 amino acids. How many peptide bonds are present in this protein?

Refer to the accompanying figure to answer the following question(s) . -Which bond is closest to the amino group of the molecule?

There are 20 different amino acids. What makes one amino acid different from another?

Which two functional groups are always found in amino acids?

The chemical reaction illustrated in the accompanying figure ________.

Which of the following involves an increase in entropy?

A peptide bond ________.

A hydrocarbon skeleton is covalently bonded to an amino group at one end and a carboxyl group at the other end. When placed in water this molecule would function ________.

What component of amino acid structure varies among different amino acids?

Why are polymerization reactions endergonic? Polymerization reactions ________.

Refer to the accompanying figure to answer the following question(s) . -At which bond would water need to be added to achieve hydrolysis of the peptide, back to its component amino acids?

Suppose you discovered a new amino acid. Its R-group contains only hydrogen and carbon atoms. Predict the behavior of this amino acid.

Amino acids are acids because they always possess which functional group?

In solution, why do hydrolysis reactions occur more readily than condensation reactions?

Side chains of amino acids ________.

Refer to the accompanying figure to answer the following question(s) . -Which bond is a peptide bond?

At about pH 7 in most cells, what happens to the carboxyl R-group on an amino acid?

At about pH 7 in most cells, what happens to the amino R-group on an amino acid?

Which one of the following is NOT a component of each monomer used to make proteins?