Protein Structure and Function Quiz

Protein Structure and Function

• Proteins are organic nitrogenous compounds composed of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). Nitrogen makes up 16% of a protein's mass. Other elements like sulfur, phosphorus, and iron can also be found in certain specialized proteins. Examples include casein (milk protein) containing phosphorus and hemoglobin (an oxygen-transporting blood protein) requiring iron.

Amino Acids: The Building Blocks

• Proteins are long chains of amino acids.
• Amino acids are the monomers that form protein polymers.

Amino Acid Structure

• Central carbon atom (alpha-carbon)
• Amino group (-NH₂)
• Carboxyl group (-COOH)
• Hydrogen atom (-H)
• Variable R-group (side chain): This group varies among different amino acids, determining their unique chemical properties.

Peptide Bonds

• Amino acids link together through peptide bonds.
• A peptide bond is formed between the carboxyl group of one amino acid and the amino group of another, releasing a water molecule (condensation reaction).

Polypeptides and Proteins

• Chains of amino acids connected by peptide bonds are called polypeptides.
• Proteins are polypeptides with more than 50 amino acids.

Levels of Protein Structure

• Primary: The linear sequence of amino acids.
• Secondary: Local folding patterns (alpha-helix, beta-sheet) stabilized by hydrogen bonds.
• Tertiary: The overall three-dimensional shape of a protein stabilized by various interactions (hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic interactions).
• Quaternary: The arrangement of multiple polypeptide chains in a protein (e.g. hemoglobin).

Types of Bonds

• Covalent: Strong chemical bonds like peptide bonds that hold the amino acid sequence together. Not affected by denaturation.
• Non-covalent: Weak physical bonds like hydrogen bonds, ionic bonds that maintain the 3D structure and can be disrupted by changes in environment (denaturation).

Protein Classification

• Simple proteins: Hydrolyze to yield only amino acids (Ex: Albumin, Myosin, Collagen, Keratin, Elastin, Glutelins)
• Conjugated proteins: Composed of a protein part and a non-protein part (Ex: Glycoproteins [hormones, blood groups], Phosphoproteins [milk protein, egg yolk], Metalloproteins [insulin, ferritin/iron], Lipoproteins [LDL, HDL], Nucleoproteins [chromatin], Chromoproteins [chlorophyll])
• Derived proteins: Denatured or modified forms of simple or conjugated proteins (Ex: resulting from changes in pH, heat or certain chemicals).

Protein Denaturation

• Denaturation is the loss of a protein's three-dimensional structure.
• Denaturation causes loss of function.
• Causes include high temperature, high pressure radiation (X-rays, UV rays), strong acids/bases, organic solvents, and changes in pH.