Biomolecules

• This study guide provides a detailed review of the structural characteristics, classifications, and biological roles of essential biomolecules, including carbohydrates, proteins, enzymes, vitamins, nucleic acids, and hormones.

Carbohydrates

• Definition and Origin:
  • Chemically defined as optically active polyhydroxy aldehydes or ketones, or compounds that produce them upon hydrolysis.
  • Name derived historically from the general formula Cₓ(H₂O)y, viewing them as "hydrates of carbon."
• Reducing vs. Non-reducing Sugars:
  • Reducing sugars: Carbohydrates capable of reducing Fehling's solution and Tollens' reagent (e.g., all monosaccharides).
  • Non-reducing sugars: Have aldehydic or ketonic groups bonded, preventing them from acting as reducing agents (e.g., sucrose).
• Glucose Molecular Structure Evidence (HI Reaction):
  • Prolonged heating of glucose with hydrogen iodide (HI) forms n-hexane.
  • This indicates all six carbon atoms in glucose are linked in a straight chain.
• Glycosidic Linkage:
  • An oxide linkage formed by the loss of a water molecule when two monosaccharide units join through an oxygen atom.
  • It is the fundamental bond connecting individual sugar units to create disaccharides and polysaccharides.

Proteins and Amino Acids

• Zwitter Ions in Amino Acids:
  • Formed when the carboxyl group loses a proton and the amino group accepts one in an aqueous solution.
  • A dipolar ion that is internally neutralized, containing both positive and negative charges, exhibiting amphoteric behavior.
• Protein Denaturation:
  • Occurs when a protein is subjected to physical or chemical changes (e.g., shifts in temperature or pH).
  • Globules unfold and helices uncoil.
  • Secondary and tertiary structures are destroyed, while the primary structure (amino acid sequence) remains intact.

Vitamins

• Vitamin Solubility and Storage:
  • Fat-soluble vitamins (A, D, E, K): Stored in the liver and adipose tissues; do not require daily replacement.
  • Water-soluble vitamins (B group, C): Readily excreted in urine; cannot be stored by the body (except B₁₂); require regular dietary intake.

Nucleic Acids

• Nucleic Acid Hydrolysis:
  • Complete hydrolysis of DNA or RNA yields three distinct components: a pentose sugar, phosphoric acid, and nitrogen-containing heterocyclic bases.
  • Sugar in DNA is β-D-2-deoxyribose.
  • Sugar in RNA is β-D-ribose.
• DNA Fingerprinting:
  • The identification of a unique sequence of bases on an individual's DNA, identical for every cell.
  • Considered more reliable than traditional finger indentations because DNA sequences cannot be altered by surgery or treatment.

Hormonal Regulation

• Insulin and Glucagon:
  • Act as intercellular messengers to regulate blood glucose levels.
  • Insulin: Lowers high blood glucose.
  • Glucagon: Increases blood glucose.
  • Together, they maintain blood glucose within a narrow, healthy limit.

Suggested Essay Questions (Topics for Further Study)

1. The Hierarchy of Protein Architecture: Discuss the four levels of protein structure (primary, secondary, tertiary, and quaternary), stabilizing bonds, and impact of primary sequence changes on biological activity.
2. Structural Diversity in Polysaccharides: Compare and contrast the structures and biological functions of starch, cellulose, and glycogen, explaining how glycosidic linkages (C1-C4 vs. C1-C6) and branching distinguish them.
3. The Chemical Evidence for Glucose Structure: Detail chemical reactions (acetylation, oxidation) proving the presence of carbonyl group, aldehydic nature, five hydroxyl groups, and the reasons for proposing cyclic hemiacetal forms.
4. The Role of Vitamins and Deficiency Diseases: Analyze vitamin classification by solubility, provide examples of four vitamins, their dietary sources, and associated physiological consequences or deficiency diseases.
5. Nucleic Acids as the Basis of Life: Explain the double-strand helix structure of DNA (Watson and Crick), focusing on complementary base pairing and the primary functions of nucleic acids (transmission of hereditary traits and protein synthesis).

Glossary of Key Terms