Biological Macromolecules 3 - Proteins & Nucleic Acids

Proteins

• Overview

  • Proteins are polymers made up of monomers called amino acids.

  • Commonly associated with food sources, but their functions extend beyond energy and nutrition.

  • Serve structural, catalytic, movement, defensive, and signaling roles in biological systems.

• Amino Acids

  • Consist of a central carbon atom bonded to:

    • An amino group (NH₂) [side]

    • A carboxy group (COOH) [other side]

    • A hydrogen atom

    • A variable side chain (R group)

  • There are 20 different types of amino acids.

  • Peptide bonds connect amino acids to form polypeptides.

• Protein Structure

  • Form Determines Function

    • The three-dimensional structure of a protein is crucial for its functionality.

    • Misfolded proteins can lead to diseases, e.g., prion diseases like mad cow disease.

  • Levels of Protein Structure:

    • Primary Structure: Sequence of amino acids linked by peptide bonds.

    • Secondary Structure: Forms due to hydrogen bonding among amino acids, creating shapes like:

      • Alpha helices (spiral shapes)

      • Beta-pleated sheets (accordion-like folds)

      • Random coils (unstructured regions)

    • Tertiary Structure: Overall three-dimensional shape formed by various side chain interactions, including:

      • Hydrogen bonds

      • Ionic bonds

      • Disulfide bridges

      • Van der Waals forces

    • Quaternary Structure: Assembly of multiple polypeptides into larger structures, e.g., collagen and hemoglobin.

  • Examples:

    • Collagen: structural protein composed of three helical polypeptides.

    • Hemoglobin: carries oxygen and carbon dioxide, made up of multiple polypeptide strands and iron.

• Polypeptide vs. Protein

  • Polypeptide: Sequence of amino acids;

  • Protein: Functional three-dimensional structure composed of one or more polypeptides.

Nucleic Acids

• Overview

  • Includes DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

  • DNA encodes genetic information that is inherited; RNA aids in protein synthesis by acting as a messenger between DNA and ribosomes.

• Nucleotides

  • Monomers of nucleic acids, each comprising three parts:

    • Five-carbon sugar (deoxyribose in DNA, ribose in RNA)

    • Phosphate group

    • Nitrogenous base (varies):

      • In DNA: adenine, thymine, cytosine, guanine

      • In RNA: adenine, uracil, cytosine, guanine

  • Types of Nitrogenous Bases:

    • Pyrimidines: Cytosine, thymine (DNA), uracil (RNA) [smaller bases]

    • Purines: Adenine, guanine [larger double-ring bases]

• Structure of Nucleic Acids

  • Nucleotides are linked via phosphodiester bonds to form a sugar-phosphate backbone.

  • Nucleotide bases extend from the backbone, not bonded to neighboring nucleotides.

• Differences Between RNA and DNA

  • DNA: Double-stranded, contains deoxyribose and thymine.

  • RNA: Single-stranded, contains ribose and uracil instead of thymine.

Recap Questions

• Components of a Nucleotide:

  • Five-carbon sugar, phosphate group, nitrogenous base.

• Difference Between Pyrimidines and Purines:

  • Pyrimidines: single-ring; Purines: double-ring.

• Major Differences Between DNA and RNA:

  • DNA: Deoxyribose, double-stranded.

  • RNA: Ribose, single-stranded.

Conclusion

• Overview completed on biological macromolecules: carbohydrates, proteins, lipids, and nucleic acids.

• Understanding of their structures, functions, and roles in living organisms is essential for greater biological comprehension.