Amino acids can be identified by their full names, a three-letter code, and a one-letter symbol. The one-letter symbol of glutamic acid is E. The one-letter symbol of proline is P. The one-letter symbol of isoleucine is I. The one-letter symbol of alanine is A.

A prosthetic group fits the definition listed in the question. These groups help specific proteins carry out their functions. Prosthetic groups can be inorganic (e.g. a metal ion) or organic (e.g. a vitamin, lipid, or sugar). Heme is an example of a prosthetic group (for the hemoglobin protein), but would be the wrong answer because the question asks for the general name of the defined structure. An alpha helix is a common secondary structure of proteins and has nothing to do with the function of prosthetic groups. Chaperonins are proteins that provide optimal conditions for folding of other proteins, ensuring that proteins fold correctly. These also have nothing to do with prosthetic groups.

All twenty amino acids contain the same backbone, which includes an alpha amino and alpha carboxyl group (). All amino acids also contain a variable R-group (also known as a "side chain"), and it is this group that distinguishes one amino acid from another. Therefore, the correct answer is that not all amino acids contain nitrogen in their side chains. While all 20 amino acids contain nitrogen within their backbone, only seven have nitrogen within the side chain.

Within the side chain of tyrosine, there is a phenol group. However, a phenol group contains neither sulfur nor nitrogen. Methionine and cysteine are the only two amino acids that contain sulfur, which is worth memorizing. Seven amino acids contain nitrogen, including arginine and asparagine.

Typically, nonpolar amino acids have side chains containing only carbons and hydrogens. The side chain on glycine contains only a hydrogen, and is nonpolar. The side chains on leucine and isoleucine contain nothing but carbons and hydrogens, so they are also nonpolar. Finally, the side chain on tryptophan does contain a nitrogen. However, tryptophan is large enough and contains enough carbons to balance out the increased electronegativity of the nitrogen within the side chain. Therefore, tryptophan, along with the rest of the answer choices, is nonpolar.

The word hydrophobic means "water fearing". Knowing this, you can eliminate the answer choice "near water". Typically, the exterior of a protein is surrounded by water, so we can also eliminate that answer choice. It is true that hydrophobic amino acids will cluster away from water. The interior of a protein typically is away from water, so the correct answer is "Both the interior of a protein and away from water."

Because of the unique structure of proline (its side chain is actually attached to its amino backbone group), it forms kinks within a chain of amino acids. These kinks are due to a lack of hydrogen bonding in comparison to other amino acids. Therefore, this is an example of the secondary structure of a protein being disrupted. Secondary structure is the term used to describe folding of the polypeptide chain due to hydrogen bonding between the backbone amino and carboxyl groups. Primary structure refers to the amino acid order itself. Tertiary relates to R-group interactions between residues that are farther apart in the chain. Finally, quaternary structure occurs at the most "macro" level, and refers to interactions between subunits of a protein.

"Asp" refers to aspartic acid; "Trp" refers to tryptophan; "Phe" refers to phenylalanine; and "Arg" refers to arginine. 

A peptide bond is made from joining the amino group of one amino acid to the carboxyl group of another. A tetrapeptide is a peptide consisting of four amino acids, which are connected via peptide bonds. There are several ways in which these four amino acids could be joined. Any of the four could be located at the first position; any of the remaining three could be located at the second position; either of the remaining two at the third position, etc. Thus, there are  possible tetrapeptides.

Asp-Trp-Phe-Arg

Asp-Trp-Arg-Phe

Asp-Arg-Phe-Trp

Asp-Arg-Trp-Phe

Asp-Phe-Trp-Arg

Asp-Phe-Arg-Trp

Phe-Asp-Trp-Arg

Phe-Asp-Arg-Trp

Phe-Trp-Asp-Arg

Phe-Trp-Arg-Asp

Phe-Arg-Trp-Asp

Phe-Arg-Asp-Trp

Trp-Asp-Phe-Arg

Trp-Asp-Arg-Phe

Trp-Phe-Arg-Asp

Trp-Phe-Asp-Arg

Trp-Arg-Phe-Asp

Trp-Arg-Asp-Phe

Arg-Asp-Phe-Trp

Arg-Asp-Trp-Phe

Arg-Phe-Trp-Asp

Arg-Phe-Asp-Trp

Arg-Trp-Phe-Asp

Arg-Trp-Asp-Phe

Different proteins have different optimal temperature and pH ranges, values at which they function best. Outside of these ranges, they can become denatured. Thus, treatments of heat, low pH, or high pH can cause proteins to denature. 

Detergents denature proteins in a different way. Detergents are amphipathic, meaning that they have both hydrophobic and hydrophilic regions. Because all membrane proteins are also amphipathic (they must be in order to remain anchored in the lipid bilayer), the detergent can be attracted to these regions and force the membrane proteins apart.

Non-proteinogenic amino acids are those which are not found in the genetic code of any organism. These are also called "unnatural" amino acids, as compared to "natural" amino acids which are found in the genetic code. Isoleucine, proline, and asparagine are three of approximately one hundred and forty "natural" amino acids. Ornithine is a non-proteinogenic amino acid that has a role in the urea cycle.