Biochemical Tests Overview

Biochemical Tests

• Starch Test:
  • Add iodine solution.
  • Positive result: orange-brown iodine turns blue-black.
  • Identifies starch presence.
• Reducing Sugars Test:
  • Add Benedict's reagent and heat.
  • Positive result: blue solution turns green, yellow, orange, or brick red.
  • Color intensity indicates reducing sugar concentration (red = high concentration).
• Non-Reducing Sugars Test:
  • Perform Benedict's test first.
  • If negative, add acid and boil.
  • Cool and neutralize.
  • Heat and add Benedict's reagent again.
  • Positive result: solution turns orange or brick red.
  • Non-reducing sugars (e.g., sucrose) hydrolyze into reducing sugars (e.g., glucose, fructose) thus always giving a positive result.
• Proteins Test:
  • Add Biuret reagent (blue).
  • Positive result: solution turns purple.
• Lipids Test:
  • Dissolve sample in ethanol, shake.
  • Add distilled water.
  • Positive result: white emulsion (milky texture).

DNA (Deoxyribonucleic Acid)

• Function:
  • Determines amino acid sequence in proteins.
  • Holds the genetic code.
  • Transmits genetic information.
• Structure:
  • Two polynucleotide chains forming a double helix.
  • Monomer: nucleotide (phosphate group, deoxyribose sugar, nitrogenous base).
• Polynucleotide Formation:
  • Condensation reactions link nucleotides.
  • Phosphodiester bonds form.
  • Strong sugar-phosphate backbone results.
• Double Helix Formation:
  • Hydrogen bonds between complementary base pairs (cytosine-guanine, adenine-thymine).

RNA (Ribonucleic Acid)

• Structure:
  • Similar to DNA, but with differences:
    • Pentose sugar is ribose.
    • Uracil replaces thymine.
• Polymer:
  • Shorter than DNA.
  • Often single-stranded.
• Function:
  • mRNA: carries gene copies.
  • tRNA: involved in protein synthesis.
  • rRNA: combines with proteins to form ribosomes (critical for protein synthesis).

DNA Replication

• Semi-Conservative Replication:
  • One original strand combines with a newly synthesized strand.
• Steps:
  • DNA helicase unwinds by breaking hydrogen bonds.
  • Strands separate to act as templates.
  • Free nucleotides align with their complements.
  • DNA polymerase joins nucleotides.
  • Phosphodiester bonds form.
• Evidence:
  • Watson and Crick: discovered DNA's double helix structure.
  • Meselson and Stahl: experimentally proved semi-conservative replication.

ATP (Adenosine Triphosphate)

• Structure:
  • Nucleotide derivative.
  • Three phosphate groups.
  • Ribose sugar.
  • Adenine base.
• Function:
  • Immediate energy source for metabolism.
• Production:
  • ADP and inorganic phosphate combine (condensation reaction), catalyzed by ATP synthase.
• Energy Release:
  • Hydrolysis (breaking phosphate bonds) releases energy.
  • Catalyzed by ATP hydrolase.
• Phosphorylation:
  • Phosphate group transferred to other compounds, increasing reactivity.

Water

• Properties:
  • Metabolite: involved in reactions (condensation, hydrolysis, photosynthesis).
  • Excellent solvent: dissolves substances, aids transport.
  • High heat capacity: prevents temperature fluctuations, protects enzymes.
  • Large latent heat of vaporization: cooling effect (sweat, transpiration).
  • Strong cohesion (hydrogen bonds): allows continuous water columns in plants (xylem), provides surface tension.

Inorganic Ions

• Importance:
  • Found in solutions (cytoplasm, blood).
  • Variable concentrations.
• Key Ions and Functions:
  • Hydrogen ions (H+):
    • Affect pH (enzymes, hemoglobin), role in chemiosmosis (respiration, photosynthesis).
  • Iron ions (Fe2+):
    • Part of hemoglobin, oxygen transport.
  • Sodium ions (Na+):
    • Co-transport (glucose, amino acids), action potentials.
  • Phosphate ions (PO43-):
    • Found in DNA, RNA, ATP.
    • Involved in phosphodiester bonds and increasing reactivity (e.g., in ATP).

Explore the different biochemical tests used to identify essential macromolecules such as starch, reducing sugars, non-reducing sugars, and proteins. This quiz covers the methods and positive results for each test, providing a comprehensive understanding of biochemical analysis. Perfect for students of biochemistry or biology.