Protein sequence 

Your First Biopython Objects: Seq 

Let's make use of it.

Create a protein sequence (Figure 1).

What you’re doing: You’re storing a protein sequence in a Biopython Seq object.

Why not use a normal Python string?

• Strings don’t “know biology.”

• Biopython objects come with biology-aware behaviors and safer handling.

Copy/paste into a code cell

Code:

from Bio.Seq import Seq

protein_seq = Seq("MKTAYIAKQRQISFVKSHFSRQLEERLGLIEVQAN")

print(protein_seq)

Basic sanity check: check the length of your protein (Figure 2).

Copy/paste into a code cell

Code:

print("Protein length:", len(protein_seq))

Understanding Protein Sequences (the language of drug targets)

Proteins are written using one-letter amino acid codes:

A = Alanine, L = Leucine, K = Lysine, D = Aspartic acid, etc.

In CADD, amino acids matter because:

• Binding pockets often contain hydrophobic residues.

• Selectivity often depends on charged/polar residues.

• Mutations change amino acids and can cause drug resistance.