Biology Grade 9: Lipids

Biology Study Notes - Grade 9

• Lesson 1: Lipids
  • Lipids are fatty compounds performing various functions in the body
  • Lipids are polymers of fatty acids and glycerol
  • They're hydrophobic (water-fearing), insoluble in water
  • Four major lipid types exist: triglycerides, phospholipids, steroids, and waxes
  • Triglycerides: composed of fatty acids and glycerol, found in animal fats and plant oils
  • Phospholipids: have a glycerol backbone, two fatty acid tails, and a phosphate group; primary component of cell membranes
  • Steroids: have a four-fused-ring structure, including cholesterol, testosterone, and estrogen
  • Waxes: composed of fatty acids and alcohols, provide waterproofing functions
  • Saturated fatty acids have no double bonds, typically solid at room temperature; contribute to LDL cholesterol increase
  • Unsaturated fatty acids have one or more double bonds, typically liquid at room temperature; tend to decrease LDL cholesterol

Lesson 2: Proteins

• Proteins are polymers made of amino acids
  • Amino acids have a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a side chain (R group)
  • The side chain (R group) determines the specific properties of each amino acid
  • 20 types of amino acids
  • Amino acids link via dehydration reactions to form peptide bonds
  • Protein structure includes primary (sequence of amino acids), secondary (alpha-helices and beta-sheets), tertiary (3D shape), and quaternary (multiple polypeptide chains) structures
  • Protein shape and function are determined by their amino acid sequence

Lesson 3: Nucleic Acids

• Nucleic acids (DNA and RNA) are polymers of nucleotides
  • Nucleotides: composed of a five-carbon sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, thymine, or uracil)
  • DNA: double-stranded helix; stores genetic information
  • RNA: single-stranded; involved in protein synthesis
  • DNA's bases pair up: A with T, and G with C
  • RNA's bases pair up: A with U, and G with C

Lesson 4: The Two Major Categories of Cells

• Cells are the basic unit of life, either prokaryotic or eukaryotic
  • Prokaryotic cells: lack a nucleus and membrane-bound organelles (e.g., bacteria)
  • Eukaryotic cells: have a nucleus and membrane-bound organelles (e.g., plants, animals)

Lesson 5: Membrane Structure

• Cell membranes are selectively permeable, regulating the passage of substances into and out of a cell
  • The primary component is the phospholipid bilayer, with hydrophilic heads and hydrophobic tails, creating a barrier between the cell's interior and the external environment
  • Membrane proteins carry out various functions, such as transport and cell signaling
  • Cholesterol adds fluidity and stability to the membrane