Chemical Basis of Life - Organic Compounds

Carbon Atom

• Atomic number: 6
• Electron configuration: 2, 4
• Carbon atom has 4 valence electrons
• Can form 4 covalent bonds with C, H, O, and N atoms
• Forms molecules with straight chains, branched chains, and ring/cyclic structures

Organic Compounds

• Chemical compounds that consist of carbon
• Examples: hydrocarbons (molecules consisting only of carbon and hydrogen)
• Carbon and hydrogen atoms have similar electronegativity, making simple hydrocarbons nonpolar
• Functional groups can attach to hydrocarbons, making them polar

Biological Macromolecules

• Simple molecules combine to form large molecules (macromolecules)
• Often polymers
• Monomer: repeating unit that serves as the building block for polymer synthesis
• Polymer: giant molecule consisting of many similar repeating subunits linked by covalent bonds
• Examples: carbohydrates, proteins, nucleic acids

Synthesis and Breakdown of Polymers

• Monomers connect through dehydration reactions, releasing water molecules
• Each monomer contributes part of the water molecule released during the reaction
• Every time a bond forms between monomers, a water molecule is removed
• Hydrolysis: reverse reaction, adding water to break bonds and disassemble macromolecules

Carbohydrates

• Macromolecules containing C, H, and O
• Molar ratio of H:O is 2:1
• Empirical formula: Cx(H2O)y
• Classified into 3 categories: monosaccharides, disaccharides, and polysaccharides

Monosaccharides

• Simplest carbohydrates
• Contain carbonyl group (C=O) and multiple hydroxyl groups (-OH)
• Formula: (CH2O)n
• All monosaccharides are reducing sugars
• Classified by:
  1. Number of carbon atoms (trioses, tetroses, pentoses, hexoses, heptoses)
  2. Placement of carbonyl group (aldose or ketose sugar)
  3. Chiral handedness (L-sugars or D-sugars)

Hexoses

• Monosaccharides with 6 carbon atoms
• Examples: glucose, galactose, fructose
• Glucose is a major nutrient for cells
• Ring structure forms in aqueous solutions

Functions of Monosaccharides

• Primary source of energy for living organisms
• Substrate for biosynthesis
• Involved in cell-cell recognition and signaling

Disaccharides

• Composed of two sugar molecules
• Examples: sucrose, lactose
• Can be hydrolyzed into subunits
• All are reducing sugars (except sucrose)

Polysaccharides

• Composed of many sugar molecules
• Examples: starch, glycogen, cellulose
• Classified into:
  1. Starch: mixture of amylose and amylopectin
  2. Glycogen: similar to starch, but more branched
  3. Cellulose: complex carbohydrate, provides structural support in plant cell walls
• Functions:
  • Energy storage
  • Structural support
  • Cellular communication

Derivatives of Carbohydrates

• Chitin: complex carbohydrate in exoskeletons of arthropods
• Hemicellulose: mixture of sugar monomers, serves as a structural component in plant cell walls
• Pectin: complex polysaccharide found in plant cell walls, particularly in fruits

Identification Tests for Carbohydrates

• Molisch's test
• Benedict's test
• Fehling's test
• Seliwanoff's test
• Barfoed's test
• Iodine test for starch