Cysteine is an unusual amino acid. Although each of the normal biological amino acids have the L configuration (with the exception of glycine, which is achiral), meaning they can be drawn with the Fischer projection as shown:

the fact that cysteine contains a sulfur group makes the side chain a higher priority than the carboxylic acid. Therefore, the absolute configuration of cysteine will be R, and not S like the other amino acids.

The isoelectric point is the average of the two pK_a values around which the molecule has an overall neutral charge. In the case of glutamate, the amino acid is in its neutral (zwitterion) form in between the lower two pK_a values. Taking the average of the two values gives the pI.

The isoelectric point is the average of the two pK_a values around which the molecule has an overall neutral charge. In the case of lysine, the amino acid is in its neutral (zwitterion) form in between the higher two pK_a values. Taking the average of the two values gives the pI.

Treatment of a peptide with Edman's reagent () will remove the N-terminal amino acid. The PTH derivative will look as follows:

In the molecule in the question, a sec-butyl replaces the R group. This is the amino acid isoleucine.

First step: Deprotonation of alpha hydrogen and formation of the malonic ester enolate.

Second step: bimolecular nucleophilic substitution, resulting in addition of the isopropyl group to the alpha carbon.

Third step: hydrolysis of amide and ester bonds, followed by decarboxylation

The synthesis forms valine, because the alkyl halide that is attacked is an isopropyl group (Valine's side chain is an isopropyl group). A more detailed mechanism is shown below.

Pyrimidine is one classification of a nucleotide base that is formed of only one six-membered heterocyclic ring. Cytosine and thymine (of DNA) and uracil (of RNA) are all pyrimidines while adenine and guanine are classified as purines. One way to help you remember this is that pyrimidines, like pyramids, are "sharp." Sharp things "CUT" Cytosine, Uracil, Thymine.

The correct answer is hydrogen bonding. The hydrogens on the amine groups of each base can hydrogen bond with the nitrogens and oxygens in the adjacent base. Three hydrogen bonds are formed between cytosine and guanine, and these three bonds are what make up the "rungs" of the ladder, that is the DNA double helix.

Originally, bromine is in the axial position and the other two substituents are equatorial. During a chair flip, all substituents become inverted in their positions. Therefore, the bromine will be found in the equatorial position and both the chlorine and alcohol will be found in the axial position.

By definition, an organic compound is a compound that contains carbon. Organic chemistry is the study of carbon-containing molecules.

By definition, isomers are compounds that share the same molecular formula but have differing molecular structures. 1-butanol and 2-butanol share the same formula, but the hydroxyl group can be located on either the first or second carbon on the molecule, yielding two different structures that share the same molecular formula. The other answers have different molecular formulas and are thus not isomers.