Practice Questions

The α-carbon of 19 of the 20 standard amino acids is attached to four different groups, making it a chiral center. With very rare exceptions, ribosomes exclusively incorporate amino acids with the L-configuration into proteins. Glycine has two hydrogens and is thus achiral.

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.

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.

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.

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

The phospholipid bilayer provides stability while remaining fluid.

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

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

Their bilayer regulates movement of substances across membranes.

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