Peptide bonds connect amino acids into a polypeptide. Read its sequence from the N-terminus to the C-terminus. DNA determines the sequence; changing one residue can change the resulting protein’s behavior. Insulin has two mature chains connected by disulfide bonds.
In sickle-cell disease, a mutation replaces glutamate with valine at position 6 of the hemoglobin beta chain. The new hydrophobic patch promotes aggregation of deoxygenated hemoglobin, distorting red blood cells and obstructing blood flow.
An alpha helix coils around its axis. Backbone carbonyl and amino groups four residues apart form hydrogen bonds; each turn contains about 3.6 residues. R groups point outward.
A beta sheet aligns extended strands. Hydrogen bonds connect their backbones; strands can run parallel or antiparallel. R groups alternate above and below the sheet.
Heat or extreme pH can cause denaturation: loss of the native fold and often function. Peptide bonds usually remain intact, preserving primary structure. Some proteins refold when conditions recover; others aggregate. Chaperones help proteins fold and limit aggregation.
An attraction between a hydrogen bonded to an electronegative atom and another electronegative atom. Backbone hydrogen bonds stabilize protein secondary structure.
Hydrophobic
Interacting poorly with water. Nonpolar side chains often gather in a soluble protein’s interior.
Hydrophobic effect
The tendency of nonpolar surfaces to cluster in water, reducing their exposure to water and helping stabilize folded proteins.
Insulin
A peptide hormone from pancreatic beta cells that lowers blood glucose by promoting uptake and storage and reducing glucose production.
A covalent amide linkage between the carboxyl carbon of one amino acid and the amino nitrogen of the next.
pH
A measure of acidity, defined as the negative base-10 logarithm of hydrogen ion activity. Lower pH means greater acidity; pH influences amino acid charge.
