Part 3 - Proteins

Macromolecules - Proteins

Overview of Proteins

• Proteins are essential macromolecules that perform a variety of functions within biological cells.

• They are composed of amino acids, which serve as the monomers for protein polymerization.

Nutrition Facts (Example Serving)

• Serving Size: 216g

• Calories: 590 (from Fat: 306)

• Total Fat: 34g (52% DV)

• Saturated Fat: 11g (55% DV)

• Cholesterol: 85mg (28% DV)

• Sodium: 1070mg (45% DV)

• Total Carbohydrate: 47g (16% DV)

• Dietary Fiber: 3g (12% DV)

• Sugars: 8g

• Protein: 24g

• Vitamins: A (6%), C (6%), Calcium (30%), Iron (25%)

• Percent daily values are on a 2,000 calorie diet.

Structure of Proteins

• Amino Acids: Building blocks of proteins; 20 types with varying chemical properties.

• Peptide Bond Formation: Amino acids link via peptide bonds to form polypeptides.

Hierarchical Structure of Proteins

• Primary Structure: Linear sequence of amino acids.

• Secondary Structure: Folding into alpha helices and beta sheets due to hydrogen bonding.

• Tertiary Structure: 3D shape resulting from interactions between R-groups.

• Quaternary Structure: Complex formed by multiple polypeptides interacting.

• Denaturation: Extreme heat or pH can disrupt hydrogen bonds and denature proteins.

Functions of Proteins

• Enzymes: Catalysts that speed up chemical reactions.

• Antibodies: Protect against pathogens by recognizing and binding to them.

• Motor & Contractile Proteins: Motor proteins move cell components; contractile proteins enable muscle contraction.

• Signaling Molecules: Hormones that facilitate cell communication.

• Structural Support: Provide shape and support to cells.

• Transport Proteins: Regulate the movement of substances into and out of cells.

Properties of Amino Acids

• Amino acids consist of:

  • Carboxyl group (-COOH)

  • Amino group (-NH2)

  • Variable side chains (R-groups): Determines biochemical properties.

• Hydrophobic vs Hydrophilic R-groups:

  1. Nonpolar R-groups: Hydrophobic, aggregate in aqueous solutions.

  2. Polar R-groups: Hydrophilic, form hydrogen bonds, soluble in water.

Protein Structure and Stability

Secondary Structure

• Formation due to hydrogen bonding between carbonyl groups.

• Includes:

  • α-helices

  • β-pleated sheets

  • Increased hydrogen bonds contribute to stability.

Tertiary and Quaternary Structure

• Tertiary Structure:

  • Result of multi-type interactions (hydrogen, hydrophobic, ionic, and disulfide bonds).

  • Determines overall 3D structure of a single polypeptide.

• Quaternary Structure:

  • Formed by the assembly of multiple polypeptide chains.

Summary of Protein Structure

Folding and Function

• Proteins generally fold spontaneously into stable states upon synthesis.

• Disruption of folding (due to heat or pH) leads to denaturation, impacting function.

• Molecular chaperones assist in proper protein folding.

Importance of Primary Structure

• The primary structure of a protein dictates its higher-level structures and function.

• Even a single amino acid substitution can significantly affect protein functionality.