Question 1

Three different proteins, A, B, and C, from a plant were studied.In each case, a glycine residue was changed to an alanine.Changes in the biological activities of the mutated proteins were then measured, and the results are shown in the table below.  Which statement about structure-function relationships in proteins is supported by the data?

Accepted Answer

The data shows that changing a single glycine residue to an alanine residue results in significant changes in the biological activities of the mutated proteins. This suggests that even a small change in the primary structure can have a significant effect on the tertiary structure and consequently the function of the protein. Thus, option B is the most appropriate choice, stating that a protein's function changes only when changes in primary structure alter its tertiary structure. The other options are not fully supported by the given data.

Question 2

Refer to the diagram below, showing a condensation reaction.  This reaction does not occur during the formation of a(n)

Accepted Answer

The diagram shows the formation of a disulfide bond, which does not involve a condensation reaction. Peptide bonds, glycosidic linkages, ester linkages, and the formation of a disaccharide from two monosaccharides all involve condensation reactions.

Question 3

A protein contains a section partially embedded in a cell membrane and another section that extends out into the external environment.Which statement could be true about this protein?

Accepted Answer

The fact that the protein has a section partially embedded in a cell membrane and another section that extends out into the external environment suggests that the protein is likely a membrane protein. Membrane proteins typically have a long stretch of hydrophobic amino acids that embeds in the lipid bilayer of the membrane and a stretch of hydrophilic amino acids that protrudes on either side of the membrane. Therefore, choice B, which describes a protein composed of a long stretch of hydrophobic amino acids followed by a stretch of hydrophilic amino acids, is the most likely explanation for this protein's structure.

Question 4

A student claims that all triglycerides have the exact same properties, since they are all composed of the same units: a glycerol molecule and three fatty acids.Which statement provides the best response to this claim?

Accepted Answer

Triglycerides vary in their hydrocarbon chains, which can differ in length and have different numbers of double bonds. This variability results in different physical properties and biological functions among different types of triglycerides. Therefore, the claim that all triglycerides have the same properties is incorrect. Choice A is incorrect because the pattern of ester linkages can vary among different types of triglycerides. Choice B only explains the nonpolar nature of triglycerides, which is not relevant to the claim. Choice C only discusses the randomness of hydrocarbon chain motion, which does not refute the claim. Choice E is also irrelevant as it does not address the properties of triglycerides.

Question 5

Each amino acid has a unique _______ group.

Accepted Answer

The R-group, also known as the side chain, varies between different amino acids and is what gives each amino acid its unique properties. The amino group (NH2), carboxyl group (COOH), and hydroxyl group (OH) are common functional groups found on amino acids, but they are not unique to each amino acid. The phosphate group (PO4) is not typically found in amino acids.

Question 6

Molecules containing a large number of hydroxyl groups are

Accepted Answer

Molecules containing a large number of hydroxyl groups are typically polysaccharides or polyols, which are soluble in water due to the presence of polar hydroxyl groups that can form hydrogen bonds with water molecules.

Question 7

All amino acids have an optical isomer except

Accepted Answer

Glycine is the only amino acid without an optical isomer because it has two hydrogen atoms attached to its central carbon atom, making it achiral.

Question 8

Which description applies to polysaccharides, polypeptides, and polynucleotides?

Accepted Answer

Polysaccharides, polypeptides, and polynucleotides are all polymers, which means they consist of repeating subunits. They can be broken down into their monomers by hydrolysis reactions.

Question 9

Aldehydes and ketones are very similar in that they both contain

Accepted Answer

Aldehydes and ketones both contain a carbonyl group, but aldehydes have a terminal carbonyl group while ketones have a central carbonyl group. The carbonyl group is also known as a keto group, which is found in both aldehydes and ketones. Therefore, choice C is the correct answer. Choices A, B, D, and E are incorrect because they do not accurately describe the functional group found in aldehydes and ketones.

Question 10

Refer to the figure below.  The molecules in the figure are

Accepted Answer

The answer of Refer to the figure below.  The...

Question 11

Two biologically important polymers of glucose contain the same number of monomers and have the same mass, yet one is soluble in water and the other is not.This can be explained by the fact that the two polymers

Accepted Answer

The solubility difference between two glucose polymers, despite having the same number of monomers and mass, can be attributed to the type of glycosidic linkages they have. These linkages determine the polymer's structure and how it interacts with water. For example, cellulose and starch are both made of glucose units, but cellulose (which has β-1,4-glycosidic linkages) is insoluble in water, whereas starch (with α-1,4-glycosidic linkages) is soluble. This difference in linkage type affects the overall structure and hydrogen bonding capability with water, leading to differences in solubility.

Question 12

In condensation reactions, the atoms that make up a water molecule are derived from

Accepted Answer

In condensation reactions, two molecules combine and a small molecule, such as water, is released. The atoms that form this small molecule derive from both reactants, making choice C the correct answer.

Question 13

All of the following are macromolecules except

Accepted Answer

Salt is not a macromolecule; it is an ionic compound made up of positively charged ions (cations) and negatively charged ions (anions). The other options listed are all macromolecules: RNA and DNA are nucleic acids, glycogen is a polysaccharide, and proteins are made up of long chains of amino acids.

Question 14

Two identical samples of a purified protein were subjected to different treatment steps.The biological activity of the protein after each step was measured, as summarized in the table below.  Which statement about structure-function relationships in proteins is consistent with the data?

Accepted Answer

The data suggests that the biological activity of the protein was reduced after the sample was treated with urea, indicating that the protein's three-dimensional structure was disrupted. Amino acids buried in the protein's interior are typically responsible for stabilizing its three-dimensional structure, while amino acids on the surface of the protein tend to be involved in interactions with other molecules. The fact that the protein's biological activity was reduced after treatment with urea suggests that the amino acids critical for stabilizing its structure were indeed on the protein's interior.

Question 15

A functional group that releases energy when removed by hydrolysis is the _______ group.

Accepted Answer

When a phosphate group is removed by hydrolysis, energy is released. This is because the breaking of the phosphate bond releases a large amount of energy due to the unstable nature of the phosphate group when it is not attached to a molecule. This energy is often used by cells for various processes, such as muscle contractions and synthesis of molecules like ATP. The other functional groups listed do not release energy when removed by hydrolysis.

Question 16

The amino acid sequence of a protein isolated from human blood cells is the same as the amino acid sequence of a protein isolated from chimpanzees.Which statement related to this observation is accurate?

Accepted Answer

The fact that the amino acid sequence of the protein is the same in both humans and chimpanzees suggests that the proteins have the same function in both organisms. This is because the amino acid sequence determines the three-dimensional structure of the protein, and the structure determines the function. Therefore, if the sequence is the same, the structure is likely to be the same, and the function is likely to be the same.

Question 17

Polymerization reactions in which polysaccharides are synthesized from monosaccharides

Accepted Answer

Polymerization reactions result in the formation of water molecules as monomers are joined together to form polymers. Choice A is incorrect because phosphodiester bonds are formed between nucleotides in nucleic acids, not monosaccharides. Choice B is incorrect because there is no involvement of phosphates in the synthesis of polysaccharides from monosaccharides. Choice C is incorrect because hydrolysis is the opposite of polymerization, and breaks down large molecules into smaller ones. Choice D is incorrect because van der Waals forces are weak, non-covalent bonds that are not strong enough to hold monomers together in a polymer.

Question 18

Which is not a correct monomers → polymer construction?

Accepted Answer

Celluloses are a type of polysaccharide, not a monomer. Triglycerides are constructed from fatty acids and glycerol.

Question 19

Refer to the table below.  Which statement about amino acids 1 and 2 is valid, given all of the data provided in the table?

Accepted Answer

The answer of Refer to the table below.  Which...

Question 20

Refer to the figure below.  Which of the following is broken during hydrolysis reactions that release the molecule's monomers as products?

Accepted Answer

The answer of Refer to the figure below.  Which...

Quiz 3: Proteins, Carbohydrates, and Lipids

Refer to the diagram below, showing a condensation reaction. This reaction does not occur during the formation of a(n)