Proteins

Their bilayer regulates movement of substances across membranes.

Phospholipids contain additional phosphate-containing head groups compared to triglycerides.

Lipids contain more C-H bonds, producing more ATP during oxidation.

The phospholipid bilayer provides stability while remaining fluid.

A monoglyceride consists of glycerol esterified with a single fatty acid.

Bile salts break large fat droplets into smaller droplets, increasing surface area for lipase.

All 20 standard amino acids (except proline, which is an imino acid) are α-amino acids. They contain a central α-carbon to which an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom, and a variable R-group are attached.

Saturated fatty acids lack carbon-carbon double bonds.

Essential amino acids lack the necessary biosynthetic pathways in the organism. For humans, there are nine essential amino acids (e.g., lysine, valine, phenylalanine). Non-essential amino acids can be synthesized from common metabolic intermediates.

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.

Heat disrupts weak interactions but usually leaves the covalent peptide backbone intact.

Chaperones bind exposed hydrophobic regions of unfolded proteins, preventing aggregation and promoting correct folding.

Histidine's pKa is close to physiological pH, making it ideal for acid-base catalysis.

β-sheets are classified according to the orientation of adjacent strands.

The heme prosthetic group contains Fe²⁺, which reversibly binds oxygen.

Protein function depends on proper folding into the native three-dimensional structure.

The oxidizing environment of the endoplasmic reticulum promotes the formation of disulfide bonds in secreted and membrane proteins.