A peptide bond is formed between __________.

Which of the following amino acids is considered basic?

Which of the following amino acids is basic?

Drain cleaners are a common household staple, used to open clogged drains in bathtubs and sinks. Human hair is a common culprit that clogs pipes, and hair is made predominately of protein. Drain cleaners are effective at breaking down proteins that have accumulated in plumbing. Drain cleaners can be either acidic or basic, and are also effective at breaking down fats that have accumulated with proteins.

A typical reaction—reaction 1—which would be expected for a drain cleaner on contact with human hair, would be as follows in an aqueous solution:

Another reaction that may occur, reaction 2, would take place as follows in an aqueous solution:

In reaction 1, an organic acid forms as a product of the reaction of the original protein and drain cleaner. What quality of the resulting anion contributes most to the acidity of the product?

Which two functional groups are included in every amino acid, and take part in amino acids binding together?

All amino acids have at least two pKa values, one corresponding to the carboxylic acid, and one corresponding to the amine functionality. Some amino acids with polar side chains also have a pKa associated with the sidechain functionality.

Phenylalanine has pKa values of 2.58 (carboxylic acid) and 9.24 (NH2).

Arginine has pKa values of 2.01 (carboxylic acid), 9.04 (NH2), and 12.48 (side chain).

Valine has pKa values of 2.29 (carboxylic acid) and 9.72 (NH2).

For this problem, consider a molecule made of up of three amino acids, as described below.

HO-phenylalanine-arginine-valine-NH2

What would the overall charge of this molecule be at a pH of 7?

Which of the following amino acids contain(s) a hydrophilic functional group in its side chain?

I. Serine

II. Valine

III. Phenylalanine

IV. Tyrosine

V. Threonine

A polar amino acid in a highly basic solution is titrated with a strong acid. When will exactly half of the amino acid molecules be negatively charged?

A researcher stains a transmembrane protein. The membrane-spanning region of the protein is stained red, whereas the other regions are stained blue. Which of the following will you most likely find in the red region?

I. Glycine, which has a side chain of

II. Cysteine, which has a side chain of

III. Alanine, which has a side chain of

What is the reasoning behind the planar geometry of peptide bonds in proteins?