The Structure and Function of Large Biological Macromolecules

The Molecules of Life

Living organisms are composed of large molecules called macromolecules, which are essential for structure and function. These macromolecules are built from smaller units and play diverse roles in biology.

• Macromolecules: Large molecules formed by joining smaller organic molecules (monomers).

• Four Major Classes:

  • Carbohydrates – Monosaccharides (e.g., glucose, fructose)

  • Proteins – Amino acids (e.g., glycine, serine)

  • Lipids – Glycerol and fatty acids (e.g., triglycerides, phospholipids)

  • Nucleic Acids – Nucleotides (e.g., DNA and RNA nucleotides: A, T, U, G, C)

Monomers and Polymers

Macromolecules are often polymers, long chains of repeating subunits (monomers) joined by covalent bonds.

• Monomers: Small building-block molecules (e.g., amino acids, monosaccharides).

• Polymers: Large molecules made by joining many monomers.

Dehydration Synthesis and Hydrolysis

• Dehydration Synthesis (Condensation Reaction): Joins two monomers by removing a water molecule (one monomer loses a hydroxyl group, the other loses a hydrogen).

• Hydrolysis: Breaks down polymers by adding water, splitting covalent bonds between monomers.

Carbohydrates Serve as Fuel and Building Material

Types of Carbohydrates

• Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose). General formula:

• Disaccharides: Two monosaccharides joined by a glycosidic linkage (e.g., sucrose, lactose, maltose).

• Polysaccharides: Large polymers of sugars (e.g., starch, cellulose, glycogen, chitin).

Disaccharide Examples

Starch vs. Cellulose

• Starch: Storage polysaccharide in plants, composed of glucose monomers joined by α (alpha) linkages. Easily digested by humans and animals.

• Cellulose: Structural polysaccharide in plant cell walls, composed of glucose monomers joined by β (beta) linkages. Not digestible by humans; provides fiber.

Role of Symbiosis in Cellulose Digestion

• Some animals rely on symbiotic microbes to digest cellulose, as they lack the necessary enzymes.

Lipids: A Diverse Group of Hydrophobic Molecules

Lipids are hydrophobic molecules important for energy storage, membrane structure, and signaling.

Types of Lipids

Saturated vs. Unsaturated Fats

• Saturated Fats: No double bonds, solid at room temperature (e.g., butter).

• Unsaturated Fats: One or more double bonds, liquid at room temperature (e.g., olive oil).

Energy Storage in Plants and Animals

• Plants: Store energy as starch in roots and seeds.

• Animals: Store energy as fat in adipose cells.

Proteins: Structure and Function

Proteins are polymers of amino acids with diverse functions, including catalysis, structure, transport, and signaling.

Protein Structure

• Polypeptide: Polymer of amino acids linked by peptide bonds.

• Peptide Bond: Covalent bond between amino acids, formed by dehydration synthesis.

Levels of Protein Structure

• Primary: Sequence of amino acids.

• Secondary: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.

• Tertiary: 3D shape stabilized by interactions among R groups (hydrophobic interactions, ionic bonds, disulfide bridges).

• Quaternary: Association of multiple polypeptide chains.

Denaturation

• Proteins can lose their structure and function due to changes in pH, temperature, or solvent.

Chaperonins

• Proteins that assist in the proper folding of other proteins.

Amino Acid Structure

• Central carbon, amino group, carboxyl group, hydrogen atom, and R group (side chain).

• General formula:

Nucleic Acids: Store and Transmit Hereditary Information

Nucleic acids (DNA and RNA) are polymers of nucleotides that store genetic information.

Nucleotide Structure

• Phosphate group

• Pentose sugar: Ribose (RNA) or deoxyribose (DNA)

• Nitrogenous base: Purines (A, G), Pyrimidines (C, T, U)

DNA Structure

• Double helix with antiparallel strands.

• Base pairing: A-T (or A-U in RNA), G-C.

Chapter 6: A Tour of the Cell

Microscopy and Cell Study

• Light Microscope: Uses visible light to view cells; limited resolution.

• Electron Microscope: Uses electron beams for higher resolution; includes transmission (TEM) and scanning (SEM) types.

• Cell Fractionation: Technique to separate cell components by size and density.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic: No nucleus, DNA in nucleoid, no membrane-bound organelles (e.g., bacteria, archaea).

• Eukaryotic: Nucleus, membrane-bound organelles (e.g., plants, animals, fungi, protists).

Compartmentalization in Eukaryotic Cells

• Organelles allow for specialized functions and increased efficiency.

The Nucleus and Ribosomes

• Nucleus: Contains DNA, surrounded by nuclear envelope (double membrane).

• Nucleolus: Site of ribosomal RNA synthesis.

• Ribosomes: Sites of protein synthesis; can be free in cytoplasm or bound to rough ER.

Endomembrane System

• Components: Nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vacuoles, plasma membrane.

• Rough ER: Studded with ribosomes, synthesizes proteins.

• Smooth ER: Synthesizes lipids, detoxifies chemicals.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes for breakdown of macromolecules.

• Vacuoles: Storage and maintenance of cell turgor in plants.

Free vs. Bound Ribosomes

• Free Ribosomes: Float in cytosol, synthesize proteins for use within the cell.

• Bound Ribosomes: Attached to ER or nuclear envelope, synthesize proteins for export or membranes.

Summary Table: Endomembrane System Components

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard General Biology curriculum.