Even when the sequence of nucleotides for a gene is available and genomic analyses can be performed, direct chemical techniques on the physical protein are still required to determine:

• A. The molecular weight of a simple protein.
• B. The N-terminal amino acid residue.
• C. The total number of amino acid residues in the protein.
• D. The location of disulfide bonds.

Answer: (D)

Verified step by step guidance

1. Understand that genomic analyses provide information about the nucleotide sequence of a gene, which can be translated into the amino acid sequence of a protein. However, this does not provide information about post-translational modifications or the three-dimensional structure of the protein.
2. Recognize that disulfide bonds are covalent bonds formed between the sulfur atoms of cysteine residues in a protein. These bonds are important for the stability and function of the protein's tertiary and quaternary structures.
3. Learn that direct chemical techniques, such as mass spectrometry or X-ray crystallography, are required to determine the location of disulfide bonds within a protein. These techniques can provide detailed information about the protein's structure and any modifications that have occurred after translation.
4. Consider that while the sequence of amino acids can be predicted from the gene sequence, the formation of disulfide bonds is a post-translational modification that cannot be inferred from the gene sequence alone. It requires experimental validation.
5. Explore how techniques like mass spectrometry can be used to analyze the protein's structure by breaking the protein into smaller fragments and identifying the presence and location of disulfide bonds through the mass differences and fragmentation patterns.