Chemistry
Chemistry of Proteins
Quick fact
The human body can produce tens of thousands of different proteins, yet they are all made from only 20 standard amino acids linked together in different sequences.
Why this is interesting
You carry trillions of microscopic machines inside you, each assembled from just 20 simple building blocks. How can a chain of amino acids fold itself into a shape that runs your body?
Read the full explanation
Understanding Chemistry of Proteins
Imagine a string of beads, where each bead is one of 20 types—some with sticky, water-repelling surfaces, others with charged or flexible parts. That string is the protein's primary structure: the exact order of amino acids joined by peptide bonds. But the string doesn't stay straight. Chemical attractions and repulsions between the beads cause the chain to twist into regular patterns like coils (alpha helices) or pleated sheets (beta sheets)—this is secondary structure. Then, interactions between side chains (e.g., hydrophobic forces, hydrogen bonds, ionic bonds) fold the whole chain into a compact, unique 3D shape—the tertiary structure. Sometimes multiple folded chains assemble together into a final quaternary structure. The final shape determines the protein's role: a crevice might bind a specific molecule, a flexible region might act like a hinge.
A deeper explanation
The chemistry of proteins revolves around the peptide bond—a covalent link formed between the carboxyl group of one amino acid and the amino group of another, releasing water. This bond is rigid and planar, restricting rotation and contributing to the backbone's geometry. The side chains (R groups) vary in size, charge, polarity, and hydrophobicity, driving non-covalent interactions that dictate folding. Hydrophobic side chains cluster to avoid water, forming a core; hydrogen bonds stabilize helices and sheets; ionic bonds (salt bridges) link oppositely charged groups; and disulfide bridges (covalent bonds between cysteine residues) lock parts of the chain together. The precise sequence of amino acids (encoded by DNA) therefore encodes the folding pathway. Misfolding can lead to diseases like Alzheimer's or prion disorders. Understanding this chemical basis explains why heat or pH changes can denature a protein—disrupting the non-covalent interactions and unfolding the structure, often irreversibly, causing loss of function.