Question 1

Changing a single amino acid in a protein consisting of 325 amino acids would ________.

Accepted Answer

Changing a single amino acid in a protein can alter its primary structure, which can then affect the tertiary structure and biological activity depending on the location and significance of the amino acid change. Therefore, the answer is E since it covers all possible outcomes.

Question 2

At which level of protein structure are interactions between the side chains (R-groups) most important?

Accepted Answer

Interactions between the side chains (R-groups) are most important in determining the overall 3D shape and stability of a protein, which occurs at the tertiary level of protein structure. Primary structure refers to the linear sequence of amino acids, secondary structure refers to local folding patterns such as alpha helices and beta sheets, and quaternary structure refers to the interaction between multiple protein subunits. Therefore, the best choice is C, tertiary.

Question 3

Van der Waals interactions may result when ________.

Accepted Answer

Van der Waals interactions result when electrons are not symmetrically distributed in a molecule, leading to temporary charge imbalances that induce weak attractions between neighboring molecules. This phenomenon is also known as London dispersion forces. Hybrid orbitals, ionic bonds, polar covalent bonds, and hydrogen atom electron loss do not directly result in Van der Waals interactions.

Question 4

Proteins in biological systems ________.

Accepted Answer

Proteins are widely known as enzymes, which are biological catalysts that speed up chemical reactions by reducing the activation energy.

Question 5

What are prions?

Accepted Answer

Prions are misfolded versions of normal proteins that can cause disease. They are not mobile segments of DNA (A), tiny circular molecules of RNA that infect plants (B), viral DNA that attaches itself to the host genome and causes disease (C), or viruses that invade bacteria (E).

Question 6

-The structural level of a protein LEAST affected by a disruption in hydrogen bonding is the ________.

Accepted Answer

The primary structure of a protein is determined by its amino acid sequence, which is held together by peptide bonds rather than hydrogen bonds. Disruptions in hydrogen bonding mainly affect the secondary, tertiary, and quaternary structures, which involve the folding and interaction of the protein's backbone and side chains, not the primary sequence itself.

Question 7

An enzyme has a total of four active sites. When you denature the molecule and study its composition, you find that each active site occurs on a different polypeptide. Which of the following hypotheses does this observation support?

Accepted Answer

The observation that each active site occurs on a different polypeptide suggests that the enzyme has quaternary structure, meaning it is made up of multiple subunits. Each subunit contributes to the formation of an active site, allowing the enzyme to catalyze a specific reaction.

Question 8

Which of the following is the strongest evidence that protein structure and function are correlated?

Accepted Answer

The fact that denatured proteins, which have lost their native structure and shape, also lose their function is the strongest evidence for the correlation between protein structure and function. This suggests that the specific protein structure is required for the proper function of the protein. The other answer choices describe general features of proteins but do not provide direct evidence for the correlation between structure and function.

Question 9

The R-group, or side chain, of the amino acid serine is -CH2-OH. The R-group, or side chain, of the amino acid leucine is -CH2-CH-(CH3)2. Where would you expect to find these amino acids in a globular protein in aqueous solution?

Accepted Answer

Leucine has a hydrophobic R-group, which would be more likely located in the hydrophobic interior of a globular protein. Serine, on the other hand, has a hydrophilic R-group, which would be more likely located on the hydrophilic exterior of a globular protein. Therefore, leucine would be in the interior and serine would be on the exterior of the globular protein.

Question 10

Normal hemoglobin is a tetramer, consisting of two molecules of β hemoglobin and two molecules of α hemoglobin. In sickle-cell disease, as a result of a single amino acid change, the mutant hemoglobin tetramers associate with each other and assemble into large fibers. Based on this information alone, we can conclude that sickle-cell hemoglobin exhibits ________.

Accepted Answer

The single amino acid change in sickle-cell hemoglobin directly alters its primary structure, and the assembly of mutant hemoglobin tetramers into large fibers indicates an alteration in the quaternary structure. The effects on secondary and tertiary structures are not specified by the information given.

Question 11

-The structure depicted the accompanying figure shows the ________.

Accepted Answer

The answer of 
-The structure depicted the accompanying figure shows...

Question 12

Refer to the following paragraph and accompanying figure to answer the following question(s). 
-How many times does the protein in the figure cross the cell membrane?

Accepted Answer

The protein depicted is likely a G protein-coupled receptor (GPCR), which typically crosses the cell membrane seven times.

Question 13

Which level of protein structure do the α-helix and the β-pleated sheet represent?

Accepted Answer

The α-helix and the β-pleated sheet are examples of secondary protein structure, which refers to the way in which the amino acid chain folds or twists due to hydrogen bonding between amino acids. Primary structure refers to the linear sequence of amino acids, tertiary structure refers to the three-dimensional folding of the entire polypeptide chain, and quaternary structure refers to the arrangement of multiple polypeptide subunits in a protein complex. Therefore, the correct answer is B, which is the level of protein structure represented by the α-helix and the β-pleated sheet.

Question 14

If cells are grown in a medium containing radioactive 35S, which of these molecules will be labeled?

Accepted Answer

Proteins contain sulfur, which is present in 35S, so they will be labeled. Neither nucleic acids, phospholipids, nor amylose contain sulfur, so they will not be labeled.

Question 15

What type of covalent bond between amino acid side chains (R-groups) functions in maintaining a polypeptide's specific three-dimensional shape?

Accepted Answer

Disulfide bonds are covalent bonds formed by the oxidation of two sulfhydryl (-SH) groups. These bonds can form between certain amino acid side chains in a polypeptide and help to stabilize the protein's specific tertiary structure.

Question 16

The following questions are based on the 15 molecules illustrated in the accompanying figure. Each molecule may be used once, more than once, or not at all.  Which of the following molecules act as building blocks (monomers) of polypeptides?

Accepted Answer

Molecules 2, 7, and 8 are amino acids, which are the monomers that form polypeptides.

Question 17

In a normal cellular protein, where would you expect to find a hydrophobic amino acid like valine?

Accepted Answer

Hydrophobic amino acids like valine are nonpolar and repel water molecules. Therefore, they are typically found in the interior of the folded protein, away from any aqueous environment. Additionally, they can also be found in transmembrane portions of proteins, where they interact with the nonpolar fatty acid chains of the lipid bilayer. Choice A is correct but incomplete, while B and C are incorrect. Choice E is also incorrect because the distribution of hydrophobic amino acids in a protein is not random.

Question 18

Which of the groups shown above is a functional group that helps stabilize proteins by forming covalent cross-links within or between protein molecules?

Accepted Answer

The answer of  Which of the groups shown above...

Question 19

Misfolding of polypeptides is a serious problem in cells. Which of the following diseases are associated with an accumulation of misfolded polypeptides?

Accepted Answer

Both Alzheimer's and Parkinson's diseases are associated with the accumulation of misfolded polypeptides. Diabetes mellitus, while also involving misfolded proteins, is not typically associated with the accumulation of misfolded polypeptides in a way that results in the formation of characteristic aggregates as seen in Alzheimer's and Parkinson's.

Quiz 3: Protein Structure and Function