Final answer:
By analyzing the DNA sequence of a gene, the amino acid sequence of a polypeptide can be deduced, and hydropathy analysis can be used to predict whether it is a transmembrane protein. Hydrophobic alpha-helical domains and the presence of N-terminal signal sequences and stop-transfer sequences help identify membrane-spanning regions.
Step-by-step explanation:
It is indeed possible to predict whether a polypeptide encoded by a gene is likely to be a transmembrane protein by analyzing the DNA sequence of the gene. Using the central dogma of molecular biology, the DNA sequence can be transcribed and translated to determine the amino acid sequence of the polypeptide. Then a hydropathy analysis can be used to assess the hydrophobicity of these amino acids. Hydrophobic alpha-helical domains, which are typically non-polar, are characteristic of proteins that span the membrane. By looking at the pattern of hydrophobic and hydrophilic residues within the polypeptide sequence, one can predict the presence of membrane-spanning regions. For instance, the red blood cell protein glycophorin A has hydrophobic alpha-helical domains that anchor it in the membrane, indicating its role as a transmembrane protein.
Moreover, transmembrane proteins often have N-terminal signal sequences and one or more stop-transfer sequences, which trap the protein within the membrane's fatty acid interior. If multiple stop-transfer sequences are present, this can lead to a protein that spans the membrane multiple times, thus confirming its transmembrane nature. These features can be predicted from the sequence of a gene thanks to advances in molecular biology and bioinformatics tools such as hydropathy plots.