Full Answer Section

Lipids

• Structure: Primarily composed of carbon and hydrogen atoms, with a much lower proportion of oxygen than carbohydrates. They are hydrophobic (water-insoluble). Key types include:
  • Fats (triglycerides): Consist of a glycerol molecule attached to three fatty acid chains.
  • Phospholipids: Similar to fats but with one fatty acid replaced by a phosphate group, giving them a hydrophilic (water-loving) head and hydrophobic tails.
  • Steroids: Characterized by a four-ring carbon structure (e.g., cholesterol, hormones like testosterone and estrogen).
• Function:
  • Long-term energy storage: Fats store more energy per gram than carbohydrates.
  • Cell membrane component: Phospholipids form the basic structure of all cell membranes, creating a selective barrier.
  • Hormones: Steroid hormones act as chemical messengers.
  • Insulation and protection: Fats provide thermal insulation and cushion organs.

3. Proteins

• Structure: Complex macromolecules made up of amino acids linked together by peptide bonds to form long chains called polypeptides. Each protein has a unique three-dimensional shape (conformation) that is crucial for its function. This shape arises from four levels of structure:
  • Primary: Linear sequence of amino acids.
  • Secondary: Local folding patterns (alpha-helices and beta-sheets) stabilized by hydrogen bonds.
  • Tertiary: Overall 3D shape of a single polypeptide chain, due to interactions between R-groups.
  • Quaternary: Arrangement of multiple polypeptide chains (subunits) in a complex protein.
• Function: Proteins are incredibly diverse and perform a vast array of functions:
  • Enzymes: Catalyze biochemical reactions.
  • Structural: Provide support (e.g., collagen in connective tissue, keratin in hair and nails).
  • Transport: Carry substances (e.g., hemoglobin transports oxygen).
  • Defense: Antibodies protect against pathogens.
  • Hormones: Some hormones are proteins (e.g., insulin).
  • Movement: Actin and myosin are involved in muscle contraction.

4. Nucleic Acids

• Structure: Polymers made up of repeating units called nucleotides. Each nucleotide consists of three components: a five-carbon sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base (Adenine, Guanine, Cytosine, Thymine in DNA; Adenine, Guanine, Cytosine, Uracil in RNA).
  • DNA (Deoxyribonucleic Acid): Typically a double helix structure.
  • RNA (Ribonucleic Acid): Usually a single-stranded structure.
• Function:
  • Genetic information storage: DNA stores the genetic blueprint for all cellular activities and traits.
  • Genetic information expression: RNA is involved in expressing the genetic information from DNA to create proteins (e.g., mRNA, tRNA, rRNA).
  • Energy currency: ATP (Adenosine Triphosphate), a modified nucleotide, is the primary energy currency of the cell.