Biology: Chemical Elements and Enzymes

Chemical Elements

  • Molecules in Living Organisms
    • Three main categories: carbohydrates, proteins, and lipids.
    • Organic Molecules: Composed of carbon, thus all entries in this category are carbon-containing compounds.

Breakdown of Major Categories:

  • Molecule Types
    • Carbohydrate:
    • Composed of sugars.
    • Essential for energy supply and cellular functions.
    • Protein:
    • Made from amino acids.
    • Important for structure, function, and regulation of body's tissues and organs.
    • Lipid:
    • Comprised of fatty acids and triglycerides.
    • Vital for energy storage, cellular structure, and signaling.

Practical: Food Tests

  • Preparing a Sample
    • For solid foods:
    1. Break up the food using a pestle and mortar.
    2. Transfer the crushed food to a test tube and add distilled water.
    3. Mix thoroughly with a glass rod.
    4. Filter using a funnel and filter paper to collect the solution.
    • Proceed with the food tests as outlined.

Tests for Nutrients:

  • Test for Glucose (Reducing Sugar)

    • Steps:
    1. Add Benedict's solution to the sample in a test tube.
    2. Heat for 5 minutes in a boiling water bath.
    3. Observe color change post-heating.
    • Positive Test: Color changes from blue to orange/brick red.

  • Test for Starch Using Iodine

    • Steps:
    1. Add drops of iodine solution to the food sample.
    • Positive Test: Color changes from orange-brown to blue-black.

  • Test for Protein

    • Steps:
    1. Add drops of Biuret solution to the food sample.
    • Positive Test: Color changes from blue to violet/purple.

  • Test for Lipids

    • Steps:
    1. Mix the food sample with 4 cm³ of ethanol; shake well.
    2. Allow the solution to sit until it dissolves.
    3. Strain the solvent into another test tube.
    4. Add an equal volume (4 cm³) of cold distilled water to the ethanol solution.
    • Positive Test: Appearance of a cloudy emulsion.

Enzymes as Biological Catalysts

  • Definition of Enzymes
    • Enzymes are proteins that function as biological catalysts, accelerating chemical reactions without being altered or consumed in the process.
    • Produced in living cells, essential for maintaining life through metabolic reactions.

Importance of Enzymes:

  • Allows digestion of food to occur rapidly: without enzymes, digestion would take approximately 2-3 weeks; with enzymes, it takes about 4 hours.
  • Products from one enzyme reaction usually serve as substrates for subsequent reactions.

Mechanism of Enzyme Action:

  1. Specificity: Enzymes are specific to their substrates due to complementary shapes at the active site.
  2. Formation of Enzyme-Substrate Complex: When the substrate binds, this interaction forms the enzyme-substrate complex.
  3. Release of Products: After the reaction, products are released from the active site, and the enzyme remains unchanged, ready to catalyze more reactions.
  • Stepwise Enzyme Action:
    1. Substrates and enzymes randomly collide in solution.
    2. A collision results in the formation of an enzyme-substrate complex, prompting the reaction.
    3. Products are yielded from the substrate and released, allowing the enzyme to remain unaltered.

Lock and Key Model of Enzyme Function:

  • Specificity Explained:
    • Enzymes fit specific substrates like a key fits a lock; only the correct substrate will bind to the enzyme's active site.

Factors Affecting Enzyme Action: Temperature

  • Structural Aspects of Enzymes: Enzymes are proteins with unique shapes determined by their amino acid sequences, held together by various bonds.

  • Optimal Temperature for Enzyme Activity:

    • Generally, enzymes function best at an optimum temperature, which is approximately 37°C in humans.
    • Above this temperature:
    • Enzyme bonds may break, leading to a loss of shape, termed denaturation.
    • Denaturation is irreversible; the enzyme cannot regain its structure or its functional activity.

  • Effects on Reaction Rates:

    • Increasing temperature up to optimum enhances activity due to increased kinetic energy causing more frequent collisions with substrate molecules.
    • At lower temperatures, enzyme activity slows due to insufficient kinetic energy, leading to fewer successful substrate collisions.
    • At temperatures exceeding the optimum, while collisions may increase, the denaturation renders the active site incompatible with the substrate, resulting in a decrease in successful reactions.

  • Graphical Representation: The relationship between temperature and enzyme activity is graphically represented, displaying the distinct phases of enzyme denaturation and optimal activity.