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.
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 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.
Their bilayer regulates movement of substances across membranes.
Phospholipids contain additional phosphate-containing head groups compared to triglycerides.
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