What is the difference between an organic and an inorganic molecule? What substances are within the realm of organic chemistry? Read on and discover.

Inorganic and Organic Molecules

Inorganic molecules are substances that don’t have carbon-hydrogen (C-H) bonds; generally simple and are not normally found in living things. Things like mineral, metals and salts would be considered inorganic molecules

Organic molecules, substances that contain carbon-hydrogen bonds, are found in living things. The major classes of organic molecule include carbohydrates, proteins, lipids and nucleic acids.

Carbohydrates

The term carbohydrates is actually a descriptor of what these molecules are composed of; “carbon hydrates,” in a ratio of one carbon molecule to one water molecule (CH2O)n.

The word saccharide is a synonym for carbohydrate and is generally preceded with a prefix indicating the size of the molecule (mono-, di-, tri- poly-).

Monosaccharides

• single sugars (one molecule)
• simplest

Disaccharides

• double sugars
• combination of two monosaccharides

Polysaccharides

• polymers composed of several sugars
• can be same monomer (many of same monosaccharide) or mixture of monomers

Amino Acids

Proteins are polymers composed of monomers called amino acids.

Each amino acid contains contain a…

• base amino group ( -NH2)
• acidic carboxyl group ( -COOH)
• hydrogen atom

…all attached to same carbon atom (the α–carbon or alpha carbon). A fourth bond attaches α-carbon to a side group that varies among different amino acids. These side groups are important, as they affect the way a protein’s amino acids interact with one another, and how a protein interacts with other molecules.

Although there are hundreds of different amino acids, most organisms use only 21 to build proteins.

Peptide Bonds

These are the covalent bonds which link amino acids together into chains, like the beads on a necklace. A dipeptide is 2 amino acids linked together, a polypeptide, more than two.

Lipids

Lipids are molecules that are hydrophobic, not attracted to water because the non-polar covalent bonds linking carbon and hydrogen aren’t attracted to the polar bonds of water.

The four major groups of lipids include fats, phospholipids, waxes and steroids.

Fats

Fats and oils are made from two kinds of molecules:

• glycerol (a type of alcohol)
• three fatty acids (so known as triglycerides)

Phospholipids

The structure of these lipids include a hydrophobic, “water hating,” hydrocarbon tails and hydrophilic, water loving phosphate groups on the end. This means that phospholipids are soluble in both water and oil.

Our cell membranes are made mostly of phospholipids arranged in a double layer with the tails from both layers facing inward and the heads facing outward (lipid bilayer).

Waxes

Waes are esters of alcohol which are insoluble in water and difficult to break down. Wax forms protective and waterproof layers on some plants, bacteria, animal fur and integuments of insects.

Steroids

The central core of a cholesterol molecule, consisting of four fused rings, is shared by all steroids. Cholesterol is precursor to our sex hormones and Vitamin D. Our cell membranes contain a lot of cholesterol which helps to keep the membrane flexible and fluid even when our cells are exposed to cooler temperatures.

Nucleic Acids

Nucleic acids are polymers made up of nucleotide monomers.

Nucleotides

Each monomer of nucleic acid is a nucleotide and consists of 3 portions:

• a pentose sugar
• one or more phosphate groups
• one of five cyclic nitrogenous bases

Nucleic Acid Structure

Nucleotides linked by covalent bonds between phosphate of one nucleotide and sugar of next, forming a phosphate-sugar backbone. The nitrogenous bases extend from it like teeth of a comb.

Hydrogen bonds form between specific bases of two nucleic acid chains, forming a stable, double-stranded DNA molecule. Hydrogen bonding twists the phosphate-deoxyribose backbones into a helix, thus typical DNA is a double helix.

ATP: The energy transfer molecule

Adenosine 5'-triphosphate (ATP) is a multifunctional nucleotide, most important as the "molecular currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism.

Additional Organic Chemistry Resources

The website Science Prof Online and the page Organic Chemistry Help are excellent sources for more information on organic molecules.

Sources

Bauman, R. (2005) Microbiology.

Park Talaro, K. (2008) Foundations in Microbiology.