"Protein"

Proteins are fundamental macromolecules that perform a vast array of functions within organisms. 

Types of Proteins

• Structural Proteins: Provide support (e.g., collagen, keratin, actin).
• Enzymatic Proteins: Catalyze biochemical reactions (e.g., amylase, DNA polymerase).
• Transport Proteins: Carry molecules across membranes (e.g., hemoglobin, albumin).
• Hormonal Proteins: Regulate physiological processes (e.g., insulin, glucagon).
• Receptor Proteins: Facilitate cell signaling (e.g., G-protein-coupled receptors).
• Defensive Proteins: Protect against pathogens (e.g., antibodies, complement proteins).

Storage Proteins: Store nutrients (e.g., ferritin for iron storage).

Biochemistry of Proteins

Structure:

• Primary Structure: Linear sequence of amino acids linked by peptide bonds.
• Secondary Structure: Local folding patterns such as α-helices and β-sheets stabilized by hydrogen bonds.
• Tertiary Structure: Overall 3D shape due to interactions like disulfide bridges, hydrophobic interactions, and hydrogen bonds.
• Quaternary Structure: Complexes formed by multiple polypeptide chains (e.g., hemoglobin has four subunits).

Folding Mechanism:

• Protein folding is driven by hydrophobic interactions, ionic bonds, and hydrogen bonds.
• Chaperone proteins assist in proper folding.
• Misfolding can lead to diseases like Alzheimer’s (amyloid plaques) and prion diseases (e.g., Creutzfeldt-Jakob disease).

Enzymatic Activity:

• Enzymes are proteins that accelerate reactions by lowering activation energy.
• Active sites bind to substrates, forming enzyme-substrate complexes.
• Enzymes follow models like the “lock and key” or “induced fit” mechanism.