Proteins

Complete acid hydrolysis (e.g., 6M HCl at 110°C for 24 hours) cleaves all peptide bonds in a protein, releasing the constituent free amino acids. Partial hydrolysis yields smaller peptides (di-, tri-, and oligopeptides).

Primary structure is the linear, genetically determined sequence of amino acids in a polypeptide chain, held together by covalent peptide bonds. This sequence dictates all higher levels of protein structure.

Peptide bond formation is a dehydration synthesis. The carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH₂) of another, releasing a water molecule (H₂O) and forming a covalent amide linkage (-CO-NH-).

Basic amino acids have side chains that accept protons. Lysine contains an ε-amino group that is positively charged at physiological pH.

Secondary structures are stabilized by hydrogen bonding between peptide backbone atoms rather than side chains.

In an α-helix, the carbonyl oxygen of residue i hydrogen bonds with the amide hydrogen of residue i+4, producing the stable helical conformation.

The hydrophobic effect causes non-polar side chains to cluster in the interior, minimizing contact with water and stabilizing the folded structure.

Quaternary structure exists only in proteins composed of more than one polypeptide chain, such as hemoglobin.

Collagen contains the repeating sequence Gly-X-Y. Glycine occurs every third residue, allowing tight packing of the triple helix.

The polar head interacts with water inside and outside the cell.

The peptide bond exhibits resonance between the carbonyl oxygen and the amide nitrogen. This resonance gives the C-N bond approximately 40% double-bond character, restricting rotation and making the six atoms of the peptide group lie in a single plane.

Neutral fats are uncharged due to the absence of phosphate groups.

Esterification is a condensation reaction because water is removed.

Glycerol is a three-carbon alcohol forming the backbone of triglycerides.

Double bonds prevent close packing, lowering the melting point.

Triglycerides lack phosphate groups and function mainly in energy storage.

Esterification releases one water molecule per ester bond formed.

Fatty acid chains repel water and face inward within the membrane.

All three fatty acids attached to glycerol are the same in simple triglycerides.