General Biology I ORGANIC CHEMISTRY AND CELLS Lecture 4

• Organic molecules contain Carbon and Hydrogen
• Organic molecules are abundant in living organism

Macromolecules
• Carbohydrates, Lipids, Protein, and Nucleic Acids

Carbon has 4 electrons in its outer shell

• It can make up to four bonds

• Usually single or double bonds

• can form nonpolar or polar bonds

Molecules with polar bonds are water soluble

Molecules with nonpolar bonds (like hydrocarbons) are not very water soluble

Structural isomers – contain the same atoms but in different bonding relationships
Stereoisomers - identical bonding relationships, but the spatial positioning of the atoms differs in the two isomers

• Cis-trans isomers -positioning around double bond

• Enantiomers -mirror image molecules

• Enzymes- recognize one enantiomer usually do not recognize the other

Polymer formation by dehydration (condensation) reactions

• The process repeats to form long polymers
• A polymer can consist of thousands of monomers
• Dehydration is catalyzed by enzymes

Dehydration → Form a Polymer

Breakdown of a polymer by hydrolysis reactions

• A molecule of water is added back each time a monomer is released
• The process repeats to break down long polymer
• Hydrolysis is catalyzed by enzymes

Hydrolysis → break apart a monomer

Four Major Classes of Organic Molecules Found in Living Cells

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids
  

Carbohydrates

Atoms → Carbon, Hydrogen and Oxygen in a 1:2:1 ratio

Monomer → Monosaccharide

Name of Bond → glycosidic

Examples → Glucose, galactose (-ose)
Starches and cellulose

Functions → primary energy source
structural (cellulose)

Glucose Isomers

Disaccharide → “Two” “Sugar”
Glycosidic bond
Examples: sucrose, maltose, lactose

Polysaccharide → “Many” ” sugars”
Energy storage – starch, glycogen
Structural – cellulose, chitin, glycosaminoglycans, peptidoglycan

Alpha Bonds

• OC Bond

• Helix

Beta Bonds

• B bond

• pleated

Lipids → Fats

• Also known as triglycerides

• Formed by bonding glycerol to 3 fatty acids

• Joined by dehydration; resulting bond is an ester bond

Fatty acids

• Saturated – all carbons have the maximal amount of hydrogens
  ◦ Tend to be solid at room temperature

• Unsaturated – contain one or more double bonds
  ◦ Tend to be liquid at room temperature (known as oils)
  ◦ Cis forms naturally; trans formed artificially
  ◦ Trans fats are linked to disease
  Monounsaturated → one double bond
  Polyunsaturated → many double bonds
  

Fats
Fats are important for energy storage

• 1 gram of fat stores more energy than 1 gram of glycogen or starch

Fats can also be structural, providing cushioning and insulation

Phospholipids → make up the cell membrane
Formed from glycerol, two fatty acids and a phosphate group
Phospholipids are amphipathic molecules
Phosphate head – polar/hydrophilic
Fatty acid tail – nonpolar/hydrophobic

Steroids

• Four interconnected rings of carbon atoms

• Usually insoluble in water

• Example: Cholesterol

Waxes

• Many plants and animals produce lipids called waxes that are secreted onto their surface

• Very nonpolar; barrier to water loss

  
  

Lipids

Atoms → Carbon, Hydrogen, Oxygen
Monomer → Fatty Acid
Name of Covalent bond → Ester
Examples → Triglyceride, phospholipid, steroids, waxes
Function → secondary energy source, structural (insulation)