Proline and peptide backbone constraints
Understand proline's ring, its effect on backbone geometry and why calling it a universal helix breaker loses important context.
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Cysteine and disulfide bonds
Distinguish a cysteine thiol, a covalent disulfide link and the separate question of which residues are connected in a peptide.
Read the article →Histidine and metal coordination
Understand histidine's imidazole side chain, its possible role as a metal donor and the evidence needed to describe an actual coordination site.
Read the article →Methionine chemistry in peptide oxidation
Understand methionine's sulfur chemistry, sulfoxide stereochemistry and why an oxidation label needs a defined product and location.
Read the article →Asparagine and glutamine side-chain chemistry
Distinguish Asn and Gln side-chain amides from terminal amidation, and understand why deamidation needs a specified site, product and chemical setting.
Read the article →Aromatic amino acids and optical properties
Understand why residue composition and wavelength affect a peptide's UV signal, and why absorbance is not a direct measure of purity or identity.
Read the article →Peptide charge changes with pH
Understand protonation, average charge and why a peptide's charge description needs both its complete chemical identity and the surrounding pH.
Read the article →What is a peptide's isoelectric point?
Interpret pI as a net-charge balance, distinguish predicted and measured values, and avoid treating it as proof of solubility or a universal optimum.
Read the article →Hydrophobicity and hydrophilicity in peptide sequences
Read polar and non-polar tendencies in a peptide without confusing a residue scale with measured solubility, membrane entry or a complete surface map.
Read the article →Hydrogen bonding in peptide structure
Identify hydrogen-bond donors and acceptors, distinguish contacts within and between chains, and read dashed lines in structural figures with appropriate evidence.
Read the article →Electrostatic interactions between peptides
Understand how charge sign, distribution and solution conditions contribute to peptide interactions without assuming that opposite net charges guarantee binding.
Read the article →Salt bridges in peptide conformations
Recognise specific contacts between oppositely charged groups and distinguish a proposed salt bridge from evidence that it stabilises a peptide conformation.
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