7.4.pdf

Amino Acids and Peptide Bonds: An amino acid has a central carbon (α carbon) attached to: ○ A hydrogen atom (H) ○ A carboxyl group (–COOH) ○ An amino group (–NH2) ○ A side chain (R group) that varies between amino acids When amino acids bond,...

Amino Acids and Peptide Bonds: An amino acid has a central carbon (α carbon) attached to: ○ A hydrogen atom (H) ○ A carboxyl group (–COOH) ○ An amino group (–NH2) ○ A side chain (R group) that varies between amino acids When amino acids bond, they lose water, forming a residue (monomer). The primary structure of proteins (peptide chain) is made of amino acid residues. Different bonds and interactions between amino acids (hydrogen, ionic, disulfide, polar/nonpolar) help form complex protein structures. Amino acids contain carbon, hydrogen, oxygen, nitrogen, and sulfur in various chemical forms. A peptide bond forms when the carboxyl group of one amino acid reacts with the amino group of another, releasing water (dehydration synthesis). Peptides are chains of fewer than 50 amino acids: ○ Dipeptides = 2 amino acids ○ Tripeptides = 3 amino acids ○ Oligopeptides = up to 20 amino acids ○ Polypeptides = up to 50 amino acids Proteins are made of long chains of amino acids or multiple polypeptides, allowing for a huge variety of proteins due to different chain lengths and R groups. Protein shape and function: A protein’s size and amino acid sequence determine its shape, which is essential for its function. Example: Rhizobia bacteria form nodules on legume roots, and the plant produces leghemoglobin, a protein that carries nitrogen or oxygen. Leghemoglobin binds oxygen at a specific part of the protein (the active site), and even a slight change in the shape can stop it from working properly. Levels of protein structure: 1. Primary structure: The sequence of amino acids in a polypeptide chain. 2. Secondary structure: Local folding into α-helices or β-pleated sheets due to hydrogen bonding between parts of the backbone. 3. Tertiary structure: The overall 3D shape of a polypeptide, formed by various interactions (e.g., disulfide bridges, hydrogen bonds, ionic bonds). 4. Quaternary structure: The structure formed when multiple polypeptide subunits come together, like in hemoglobin with its four subunits. Protein folding: Proteins fold into their 3D shape to become functional (called the native structure). If unfolded, they become denatured and lose function. Conjugated proteins: Some proteins have non-protein parts attached.  Glycoproteins have carbohydrates attached. Lipoproteins have lipids attached.