Chapter 2
Organic Chemistry
Organic compounds always contain Carbons and Hydrogens.
Most chemical compounds in living organisms contain backbones of covalently bonded carbons.
Carbons are usually covalently bonded in that they: - form large complex molecules essential to living systems.
- are extremely versatile because of 4 electrons in the outermost ring – can bond with up to four other atoms to achieve the “Octet Rule”.
Carbons can form – chains, branches, and rings.
Carbon backbones carry a variety of functional groups – small clusters of atoms that determine many properties of an organic molecule as well as distinguish one molecule from another.
5 Functional Groups
1. Carboxyl Group -COOHe.g. amino acids, sugars, proteins
2. Hydroxyl Group -OHe.g. sugar, alcohol
3. Methyl Group -CH3e.g. fats, oils, steroids, amino acids
4. Amino Group -NH2e.g. amino acids, protein
5. Phosphate Group -H2PO4e.g. nucleic acid, ATP
Monomers and Polymers
Carbons form large complex molecules called Macromolecules: Carbohydrates - CH2O
Lipids – CHO
Proteins – CHON & S
Nucleic Acids- CHONP
Polymers – large complex molecules made up of smaller subunits,
Monomers – smaller subunits of the polymer or macromolecule (terms are interchangeable)
e.g. proteins are polymers and amino acids are monomers
Polymerization – the joining of monomers to form polymers occurs by way of Dehydration Synthesis or Condensation.
Monomer + Monomer → Dimer + H2O
e.g. glucose + fructose → sucrose + H2O
The opposite of Dehydration Synthesis is Hydrolysis in which H2O is used to split a molecule.
Dimer + H2O → Monomer + Monomer
e.g. Sucrose + H2O → glucose + fructose
Note: Dehydration occurs – in cytoplasm during protein synthesis, and enzyme production.
Hydrolysis - occurs in liver when blood sugar levels drop. Liver cells breakdown the polymer of glycogen into monomers of glucose to be released into the blood.
Isomers – compounds that have the same molecular formula but different structure and properties.
- same amount of atoms, but arranged differently
e.g. ethanol and dimethyl ether have C2H6O as their molecular formula, but the position of the atoms and therefore the behavior is different.
I. Carbohydrates
Composition: CHO (1:2:1) ratio or CH2O (2:1) ratio of 2 hydrogens to O
- a carbohydrate means hydrate of carbon because of 2:1 ratio of H to O (which are the same as H2O).
- carbohydrates tend to be hydrophilic (water loving) for this reason.
- can exist as chain or ring
- includes sugars, starches, and cellulose
Types of Carbohydrates:
Monosaccharides – simple sugars of 3 – 7 carbon atoms that exist as one sugar unit.
- in living systems: 5 carbon molecule – pentose e.g. ribose
6 carbon molecule – hexose e.g. glucose
- monosaccharides are usually sweet in taste.
Disaccharides – two sugar units linked by a glycosidic bond.
- bond forms between carbon 1 of a molecule and carbon 4 of the next molecule.
- caused by dehydration synthesis or condensation.
Examples of Disaccharides:
glucose + glucose = maltose (malt sugar from barley)
glucose + fructose = sucrose (table sugar)
glucose + galactose = lactose (milk sugar)
Polysaccharides – (polymers) most abundant of carbohydrates. includes, starches, glycogen, and cellulose.
- macromolecule consisting of repeating units of simple sugars, usually glucose ≈1000 units
- can be branched.
Types of Polysaccharides:
Starch – storage form of carbohydrates in plants.
- consists of branched and unbranched glucose units ≈ 3000 units.
- stored in plants and released when energy is needed for cellular work (hydrolyzed by plant).
Glycogen – storage form of carbohydrates in animals
- highly branched glucose unit
- stored in the liver and muscle cells
Cellulose – most abundant carbohydrate in plants.
- unbranched polysaccharide compound of ≈10,000 units.
- forms cell wall of plants
- not digestible by most animals, but serves as roughage (good for the colon).
Uses: important biological molecules e.g. glucosamine: present in shellfish and used for joint repair.
glycoprotein: found on cell membranes as markers.