BIOL 150: lecture 4 (40-81)

Carbohydrates: Disaccharides

• Disaccharides consist of two monosaccharides joined by a glycosidic bond, a type of covalent bond linking sugar molecules.
• Sucrose, or table sugar, is formed from one glucose molecule and one fructose molecule through glycosidic linkage.
• Maltose, known as beer sugar, is comprised of two glucose molecules.
• Lactose, the milk sugar, consists of one galactose molecule and one glucose molecule.
• Glycosidic linkages can be classified as α (between two alpha sugars) and β (between two beta sugars).

Polysaccharides

• Polysaccharides are complex carbohydrates consisting of chains of monosaccharides linked by glycosidic bonds.
• Ideal for energy storage, polysaccharides are large, insoluble in water, and can fold into compact shapes for easy conversion to sugars when needed.
• Glycogen is a branched polysaccharide found in animal cells, primarily stored in the liver and muscles, serving as the main carbohydrate reservoir for glucose.
• Cellulose, the most abundant organic compound on Earth, allows for permeability of water and solutes, crucial for cellular function.

Lipids

• Lipids characterize several classes, including triglycerides, phospholipids, and steroids.
• Saturated fats are triglycerides with fatty acids containing the maximum number of hydrogens, making them solid at room temperature and closely packed.
• Unsaturated fats contain double bonds in fatty acids, resulting in kinks that prevent tight packing, leading to liquid forms like oils.
• Phospholipids form the foundation of cell membranes, creating a bilayer with hydrophobic lipid ends facing inward and hydrophilic phosphate ends outward.

Steroids

• Steroids have a unique structure, comprising a fused ring system of three cyclohexanes and one cyclopentane.
• Steroids, including cholesterol and sex hormones, have numerous carbon-hydrogen bonds, rendering them non-polar.
• Cholesterol, a key component in cell membranes, can lead to health issues such as atherosclerosis when deposited in the blood vessel walls.

Hormones

• Testosterone, the primary male hormone, is synthesized from cholesterol and drives the development of male reproductive organs and secondary sexual characteristics.
• Estrogen and progesterone, primary female hormones, regulate functions in the uterus and ovaries, impacting the menstrual cycle.

Proteins

• Proteins are polymers made of amino acids and are crucial for structural components in tissues.
• Amino acids consist of an alpha carbon, an amine group, a carboxyl group, a hydrogen atom, and a variable side chain (R group).
• Out of hundreds of amino acids, only 20 are typically used to construct proteins, linked through peptide bonds into polypeptides.
• Protein structure is classified into four levels:
  • Primary structure (amino acid sequence),
  • Secondary structure (hydrogen bond formations),
  • Tertiary structure (3D arrangement, stabilized by disulfide bonds),
  • Quaternary structure (arrangement of multiple polypeptide chains).
• Denaturation disrupts secondary and tertiary structures, uncoiling proteins without breaking the primary peptide bonds.

Enzymes

• Enzymes are proteins that act as catalysts, facilitating reactions and increasing their rates significantly.
• Each enzyme is highly specific, acting on particular substrates to produce specific products.
• Enzymes can catalyze reactions in both forward and reverse directions, showcasing their versatility in metabolic processes.