Organic Compounds (Biochemistry)
There are more compounds composed of carbon than any other element. Since carbon is always found in organic (living) compounds, the chemistry of carbon is referred to as “organic” chemistry or “bio”chemistry. Carbon is the key element in plastics, synthetic fibers, foods, medicines, and all petroleum products. Petroleum products are composed of hydrogen and carbon and are called “hydrocarbons”. The oil used to make petroleum products came from once living things that died long ago. So, petroleum is considered “organic” chemistry because the oil which made the petroleum products came from once living things. The only carbon compounds that do not exist in living things are carbon monoxide and carbon dioxide. These two are the only carbon compounds which are not considered organic.
Carbon forms so many compounds because it has four “valence” electrons. Carbon has an atomic number of six. Therefore, it has two electrons in its first energy shell and four in its outer energy shell. Since carbon wants eight electrons in its outer energy shell it has the potential to form four covalent bonds with other carbon atoms or with different atoms. The valence electron configuration of carbon allows it to bond chemically with almost all other elements.
Carbons often bond with hydrogen to form hydrocarbons. Hydrocarbons are compounds which contain only hydrogen and carbon. The simplest hydrocarbon is methane. Methane is CH4. Other hydrocarbons are: ethane—C2H6, propane—C3H6, and butane—C4H10. The number of carbons tells you haw many carbons are in the backbone of the compound. The hydrocarbons with a short backbone consisting of 1-5 carbons are gases. Those having 6-20 carbon backbones are liquid. Those having more than 20 carbons tend to be solids such as waxes.
Many different compounds can be made from hydrocarbons by replacing one of the hydrogen with a different functional group. A functional group is an atom or a group of atoms that replaces one or more hydrogen in a hydrocarbon. An example of a functional group is the hydroxyl ion (OH ). When the hydroxyl ion replaces one of the hydrogen in a hydrocarbon, it forms an alcohol. There are four classes of organic compounds that are very important to living things; they are (1) carbohydrates, (2) lipids, (3) proteins, and (4) nucleic acids.
A very important part of biochemistry deals with how food from organic compounds becomes fuel for the cells of our body. The fuel part of food consists of carbohydrates (sugars and starches), lipids(fats), and proteins. Nucleic acids will be discussed later.
The organic compounds which are the most important to living things for fuel are carbohydrates. Carbohydrates are composed of carbon, hydrogen, and oxygen. They include sugars, starches, and cellulose. The carbohydrates are used by living things for energy. The main carbohydrate used by animals to produce usable energy is glucose—C6H12O6. Table sugar is called sucrose and is produced from sugar cane. Its molecular formula is C12H22O11. Starch is a long chain of sugar molecules used by plants to store energy. Starch is converted to glucose when needed. Animals store energy as glycogen (animal starch) and fat.
Two other important organic compounds are lipids (fats) and protein. Carbohydrates do not contain an organic acid. Fats and protein do contain an organic acid. If the carbon backbone of a fat is composed of carbons bonded to each other with single bonds, each carbon can be “saturated” with hydrogen. This is called a “saturated” fat. If there are some double bonds between the carbons forming the backbone of the fat, the carbons cannot be saturated with hydrogen and it is an ”unsaturated” fat. If there are a lot of these double bonds, it is called “polyunsaturated”. Polyunsaturated fats are better foods than saturated fats.
Proteins are polymers of amino acids. A polymer is a long chain of repeating units. An amino acid is an organic acid with an amine group. The amine group is NH2. Therefore, any compound with an organic acid and an amine group is an amino acid. There are about 20 amino acids. When many amino acids are joined together they form a protein. Proteins are very important to the structure and functioning of living things.
Nucleic acids are not important as a source of fuel or building materials; they serve a more important purpose. The main functions of nucleic acids are information storage (DNA), protein synthesis (RNA) and energy transfer (ATP). Nucleic acids are composed of subunits known as nucleotides. There are only a few types of nucleotides. Nucleotides consists of a sugar, a nitrogen containing base, and a phosphate group.
Most of these organic molecules are what we call “macromolecules”= large molecules. This is because they are polymers. Polymers are large structures made by putting together smaller structures. The making and breaking down of these macromolecules is accomplished by two processes: hydrolysis and dehydration synthesis. When two things are joined together, water is removed. Dehydration synthesis means to make by removing water. To break a large molecule into smaller pieces, water must be added. Hydrolysis means to split by adding water.