BIOCHEM LEC

• All living things are made up of four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids
• Macromolecules


  Large molecules composed of thousands of covalently connected atoms
• Molecular structure and function are inseparable
• Polymer


  A long molecule consisting of many similar building blocks
• Monomer


  Small building-block molecules
• Classes of life's organic molecules that are polymers

  • Carbohydrates
  • Proteins
  • Nucleic acids
• Synthesis and breakdown of polymers

  1. Dehydration reaction: two monomers bond, losing a water molecule

  2. Hydrolysis: polymer is disassembled to monomers, adding a water molecule
• Each cell has thousands of different macromolecules
• Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species
• An immense variety of polymers can be built from a small set of monomers
• Carbohydrates


  Include sugars and the polymers of sugars
• Monosaccharides


  The simplest carbohydrates, or single sugars
• Polysaccharides


  Carbohydrate macromolecules, polymers composed of many sugar building blocks
• Monosaccharides


  Have molecular formulas that are usually multiples of CH2O
• Glucose


  The most common monosaccharide
• Classification of monosaccharides


  • By location of carbonyl group (aldose or ketose)
  • By number of carbons in carbon skeleton
• Though often drawn as linear skeletons, in aqueous solutions many sugars form rings
• Monosaccharides


  Serve as a major fuel for cells and as raw material for building molecules
• Disaccharide


  Formed when a dehydration reaction joins two monosaccharides
• Glycosidic linkage


  The covalent bond formed between two monosaccharides
• Polysaccharides


  Have storage and structural roles
• Starch


  A storage polysaccharide of plants, consisting entirely of glucose monomers
• Amylose


  The simplest form of starch
• Glycogen


  A storage polysaccharide in animals, stored mainly in liver and muscle cells
• Cellulose


  A major component of the tough wall of plant cells, a polymer of glucose with different glycosidic linkages than starch
• Alpha (α) and beta (β) glucose


  Two ring forms of glucose that determine the structure and properties of polysaccharides
• Polymers with α glucose are helical, while polymers with β glucose are straight</b>
• Parallel cellulose molecules held together by hydrogen bonds between strands are grouped into microfibrils, which form strong building materials for plants
• Enzymes that digest starch by hydrolyzing α linkages can't hydrolyze β linkages in cellulose
• Cellulose in human food passes through the digestive tract as insoluble fiber
• Some microbes use enzymes to digest cellulose, and many herbivores have symbiotic relationships with these microbes
• Chitin


  Another structural polysaccharide, found in the exoskeleton of arthropods and cell walls of fungi
• Lipids are the one class of large biological molecules that do not form polymers
• Lipids


  Have little or no affinity for water, being hydrophobic due to consisting mostly of hydrocarbons
• Most biologically important lipids

  • Fats
  • Phospholipids
  • Steroids
• Fats


  Constructed from glycerol and fatty acids
• Glycerol


  A three-carbon alcohol with a hydroxyl group attached to each carbon
• Fatty acid


  Consists of a carboxyl group attached to a long carbon skeleton
• Triacylglycerol (triglyceride)


  A fat molecule with three fatty acids joined to glycerol by ester linkages
• Fats separate from water because water molecules form hydrogen bonds with each other and exclude the fats