The Structure and Function of Large Biological Molecules

  • Molecules of Life: Essential for life, including carbohydrates, proteins, nucleic acids, and lipids, each with specific functions and roles in living organisms.

  • Macromolecules: Large molecules made up of smaller subunits called monomers. Examples include proteins (amino acids), nucleic acids (nucleotides), and polysaccharides (sugars).

  • Polymer-Monomer Relationship: Monomers link to form polymers, demonstrating both unity (common building blocks) and diversity (varied combinations leading to unique structures and functions in organisms).

  • Dehydration Synthesis vs. Hydrolysis:

    • Dehydration Synthesis: The process of joining two molecules by removing a water molecule, forming a bond.

    • Hydrolysis: The process of breaking a bond by adding water, resulting in the separation of monomers.

  • Polynucleotides, Nucleic Acids, and Nucleotides: Nucleic acids (DNA and RNA) are polymers made of nucleotide monomers, which consist of a nitrogenous base, a sugar, and a phosphate group.

  • Structure of a Nucleotide: Composed of a nitrogenous base (purines: adenine, guanine; pyrimidines: cytosine, thymine in DNA or uracil in RNA), a pentose sugar (deoxyribose in DNA, ribose in RNA), and a phosphate group.

  • Joining Nucleotides: Nucleotides are linked by phosphodiester bonds during dehydration reactions, creating a sugar-phosphate backbone in nucleic acids.

  • DNA Base Interactions: Bases pair through hydrogen bonds (A-T and C-G pairing), contributing to the stability of the DNA double helix structure via hydrogen bonding.

  • Structure of DNA: A double helix shape formed by two polynucleotide strands with a sugar-phosphate backbone and complementary base pairing, exhibiting directionality (5' to 3' ends).

  • DNA vs. RNA Structure: DNA is double-stranded with deoxyribose sugar; RNA is single-stranded with ribose sugar, differing in nitrogenous bases (thymine in DNA compared to uracil in RNA).

  • Functions of Proteins:

    • Storage

    • Transport

    • Coordination

    • Response to stimuli

    • Movement

    • Support

  • Amino Acid and Polypeptide Relationship: Amino acids are the monomers that form polypeptides through dehydration synthesis, resulting in peptide bonds.

  • Composition of Polypeptides: Consist of a backbone, an amino end (N-terminus), a carboxyl end (C-terminus), and side chains (R groups) which determine properties.

  • Parts of an Amino Acid: Each contains an alpha carbon, amino group, carboxyl group, and R group (side chain).

  • Categorizing Amino Acids: Based on R group chemical properties (e.g., polar, nonpolar, acidic, or basic).

  • Four Levels of Protein Structure:

    1. Primary Structure: Sequence of amino acids.

    2. Secondary Structure: Hydrogen-bonded formations (α-helix, β-pleated sheets).

    3. Tertiary Structure: Overall three-dimensional shape, influenced by side chain interactions.

    4. Quaternary Structure: Arrangement of multiple polypeptide subunits. (ex. Hemoglobin because it is made of four separate polypeptide subunits)

  • Effects of DNA Mutations: Can lead to changes in protein structure and function, impacting cellular processes.

  • Protein Denaturation: The unfolding of proteins due to environmental changes (temperature, pH), leading to loss of function.

  • Flow of Information: DNA -> RNA -> Protein; genes encode for proteins, linking genome to phenotype.

  • Function of Carbohydrates: Serve as energy sources and structural components for cells.

  • Monosaccharides: Simple sugars (e.g., glucose) that serve as monomers for carbohydrates.

  • Disaccharides: Formed from two monosaccharides (e.g., sucrose formed from glucose and fructose).

  • Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose, chitin) with varied functions.

  • Starch and Glycogen: Storage polysaccharides in plants and animals, respectively, used for energy.

  • Cellulose and Chitin: Structural polysaccharides in plant cell walls and fungal cell walls, respectively.

  • General Structure of Lipids: Hydrophobic molecules, primarily consisting of fatty acids and glycerol.

  • Fat Structure: Composed of glycerol and fatty acids, formed through dehydration synthesis.

  • Major Function of Fats: Energy storage and insulation.

  • Saturated vs. Unsaturated Fats: Saturated fats contain no double bonds (solid at RT)

  • Unsaturated fats contain one or more double bonds, affecting fluidity. (liquid at RT)

  • Trans Fats: Unsaturated fats that have been chemically altered; often linked to health risks.

  • Phospholipid Structure and Function: Composed of two fatty acids, phosphate group, and glycerol; form cell membranes.

  • Steroid Structure and Function: Characterized by four fused carbon rings; serve diverse biological roles including hormones.