Overview
This lecture covers acids, bases, the pH scale, biological macromolecules, enzyme activity, and experimental methods for testing proteins, carbohydrates, and enzyme function.
Acids, Bases & pH
- Acids have a pH below 7 and release hydrogen ions (H+), bases have a pH above 7 and accept H+.
- The pH scale (0-14) measures the concentration of H+; 7 is neutral, below 7 is acidic, above 7 is basic.
- Strong acids ionize easily and have high H+ concentration; weak acids ionize less and have lower H+.
- pH is logarithmic; each step is a tenfold change in H+ concentration.
Biological Macromolecules
- Four major biological macromolecules: carbohydrates, lipids, proteins, nucleic acids.
- Macromolecule: large molecule made of smaller units called monomers (except lipids).
- Carbohydrates: provide energy (sugars, starch, cellulose).
- Proteins: structural and functional roles (enzymes, antibodies, hemoglobin).
- Lipids: energy storage, insulation, cell membranes (fats, oils, steroids).
- Nucleic acids: store and transmit genetic information (DNA, RNA).
Structure & Synthesis
- Polymers are chains of monomers linked by bonds.
- Dehydration synthesis forms polymers by removing water.
- Hydrolysis breaks polymers into monomers by adding water.
- Lipids are not true polymers, as they are not made of repeating monomers.
Carbohydrates & Proteins
- Carbohydrates: monosaccharides (glucose), disaccharides (sucrose), polysaccharides (starch, glycogen).
- Proteins: made of amino acids linked by peptide bonds; function depends on correct 3D shape.
Enzyme Activity & Denaturation
- Enzymes work best at specific temperatures (around 37°C) and neutral pH (about 7).
- Low temperatures slow enzyme activity; high temperatures or extreme pH denature enzymes, making them non-functional.
- Enzyme denaturation is not reversible.
Lab Tests & Indicators
- Biuret test: detects proteins by turning violet if peptide bonds are present.
- Iodine test: detects starch; positive result is blue-black, negative is brown/yellow.
- Benedict’s test: detects reducing sugars (glucose); positive result is orange-red, negative is blue.
- Controls are needed in tests: positive (known present) and negative (known absent).
Key Terms & Definitions
- Acid — Substance that donates H+ ions.
- Base — Substance that accepts H+ ions.
- pH Scale — Measures acidity/basicity (0-14 based on H+ concentration).
- Macromolecule — Large molecule made of monomers (except lipids).
- Monomer — Small, repeating unit in a polymer.
- Polymer — Molecule made of repeated monomers.
- Denaturation — Loss of a protein’s functional shape due to environmental stress.
Action Items / Next Steps
- Complete lab exercises: measuring pH, Biuret, iodine, and Benedict’s tests.
- Analyze the effect of pH and temperature on enzyme (amylase) activity.
- Record all colors and observations from each experiment for reference.