BIO NMDCAT

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.

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.

Triglycerides serve as the principal storage form of energy in adipose tissue.

Each triglyceride contains three ester linkages joining glycerol to fatty acids.

One hydroxyl group of glycerol is linked to a phosphate group, while the other two are linked to fatty acids.

Amphipathic molecules contain both hydrophilic and hydrophobic regions, allowing bilayer formation.

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.

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.

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 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.