Proteins and Amino Acids Overview

Proteins and Amino Acids

• Proteins are composed of 20 different amino acids joined in various combinations and sequences.
• This allows for a vast array of protein types with diverse functions, including enzymes, hormones, antibodies, transporters, and structural components like muscle fibers, feathers, and spider webs.
• Enzymes are highly specialized catalysts for almost all cellular reactions, making them crucial for understanding life's chemistry.
• Amino acids are the building blocks of proteins, like letters forming words.
• Amino acids have characteristic side chains with unique chemical properties, which determines their role in protein function.
• Amino acids bond together through peptide bonds, forming a linear sequence called the primary structure.

Amino Acid Classification

• Amino acids are categorized by their side chain (R-group) properties.
• Nonpolar, aliphatic: Glycine, Alanine, Proline, Valine, Leucine, Isoleucine, Methionine
• Polar, uncharged: Serine, Threonine, Cysteine, Asparagine, Glutamine
• Positively charged: Lysine, Arginine, Histidine
• Negatively charged: Aspartate, Glutamate
• Aromatic: Phenylalanine, Tyrosine, Tryptophan

Amino Acid Properties

• Amino acids are amphoteric, meaning they can act as both acids and bases.
• They can donate or accept protons (H+).
• The ability to donate a proton correlates to the acidity and affects the pH(pK).
• The titration curve of an amino acid reveals critical information.

Titration Curve and pI

• The titration curve plots pH against the amount of added base, providing important information about the pKa values of the amino acid's ionizing groups.
• pKa values indicate the pH at which half of the amino acid molecules are deprotonated.
• The isoelectric point (pI) is the pH where the amino acid carries a net zero charge, existing primarily as a zwitterion.
• For amino acids without ionizable R-groups, the pI is the arithmetic mean of the pKa values of the acidic and basic groups.
• Amino acids with charged R-groups have a more complex titration curve with three distinct stages.