MCQs

At the isoelectric point (pI), the amino group is protonated (-NH₃⁺) and the carboxyl group is deprotonated (-COO⁻). The molecule carries equal positive and negative charges, making it electrically neutral overall, termed a zwitterion.

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.

Acylglycerols are esters formed by the reaction of glycerol with one or more fatty acids.

Triglycerides provide concentrated energy storage in adipose tissue.

A phospholipid has two fatty acids and one phosphate-containing group attached to glycerol.

Ester linkages form between glycerol hydroxyl groups and fatty acid carboxyl groups.

Pancreatic lipase acts mainly in the small intestine after emulsification by bile salts.

Lipids contain more hydrogen atoms and fewer oxygen atoms, producing more ATP upon oxidation.

Phospholipids form the structural framework of cellular membranes.

Condensation reactions release water during ester bond formation.

Double bonds are the defining feature of unsaturated fatty acids.

Phospholipids exhibit lateral movement, contributing to membrane fluidity.

Each hydroxyl group of glycerol forms one ester bond with a fatty acid.

Glycerol contains three hydroxyl (-OH) groups.

Hydrophobic tails avoid water and remain inside the membrane.

Neutral fats (triglycerides) have three fatty acids and no phosphate group.