Organic compounds always contain carbon along with other elements that are needed for living organisms to function. Carbon is the key element because it has four electrons in an outer electron shell that can hold eight electrons. As a result, it can form many types of bonds with other carbon atoms and elements such as hydrogen, oxygen and nitrogen. Hydrocarbons and proteins are good examples of organic molecules that can form long chains and complex structures. The organic compounds made up of these molecules are the basis for chemical reactions in the cells of plants and animals – reactions that provide the energy for finding food, for reproduction and for all the other processes necessary for life.
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An organic compound is a member of a class of chemicals containing carbon atoms linked to each other and to other atoms by covalent bonds and found in the cells of living organisms. Hydrogen, oxygen and nitrogen are typical elements that make up organic compounds in addition to carbon. Traces of other elements such as sulfur, phosphorous, iron and copper may also be present when needed for specific organic chemical reactions. The main groups of organic compounds are hydrocarbons, lipids, proteins and nucleic acids.
Characteristics of Organic Compounds
The four types of organic compounds are hydrocarbons, lipids, proteins and nucleic acids, and they perform different functions in a living cell. While many organic compounds are not polar molecules and therefore don't dissolve well in the water of a cell, they often dissolve in other organic compounds. For example, while carbohydrates such as sugar are slightly polar and dissolve in water, fats do not. But fats dissolve in other organic solvents such as ethers. When in solution, the four types of organic molecules interact and form new compounds as they come into contact within living tissue.
Organic compounds range from simple substances with molecules made up of a few atoms of only two elements to long, complex polymers whose molecules include many elements. Hydrocarbons for example, are made up of only carbon and hydrogen. They can form simple molecules or long chains of atoms and are used for cell structure and as basic building blocks for more complex molecules.
Lipids are fats and similar materials that are made up of carbon, hydrogen and oxygen. They help form cell walls and membranes and are a major component of food. Proteins are made up of carbon, hydrogen, oxygen and nitrogen, and they have two major functions in cells. They form part of the cell and organ structures, but they are also enzymes, hormones and other organic chemicals that take part in chemical reactions to produce the materials essential for life.
Nucleic acids are made up of carbon, hydrogen, oxygen, nitrogen and phosphorous. As RNA and DNA, they store the instructions for chemical processes involving other proteins. They are the helix-shaped molecules of the genetic code. The four types of organic molecules are all based on carbon and a few other elements, but they have different properties.
Hydrocarbons are the simplest organic compounds, and the simplest hydrocarbon is CH4 or methane. The carbon atom shares electrons with four hydrogen atoms to complete its outer electron shell.
Instead of bonding with only hydrogen atoms, a carbon atom can share one or two of its outer shell electrons with another carbon atom, forming long chains. For example, butane, C4H10, is made up of a chain of four carbon atoms surrounded by 10 hydrogen atoms.
A more complicated group of organic compounds are the lipids or fats. They include a hydrocarbon chain but also have a part where the chain bonds with oxygen. Organic compounds containing only carbon, hydrogen and oxygen are called carbohydrates.
Glycerol is an example of a simple lipid. Its chemical formula is C3H8O3, and it has a chain of three carbon atoms with an oxygen atom bonded to each one. Glycerol is a building block that forms the base of many more complex lipids.
Most proteins are very large molecules with complex structures that allow them to take on important roles in organic chemical reactions. In such reactions, parts of the proteins break apart, are rearranged or join with new chains. Even the simplest proteins have long chains and many subsections.
For example, 3-amino-2-butanol has the chemical formula C4H11NO, but it is really a sequence of hydrocarbon sections with a nitrogen and an oxygen atom attached. It is more clearly shown by the formula CH3CH(NH2)CH(OH)CH3, and the amino acid is used in chemical reactions to produce other proteins.
Nucleic acids form the basis of the genetic code of living cells and are long strings of repeating subunits. For nucleic acid deoxyribonucleic acid or DNA, for example, the molecules contain a phosphate group, a sugar and the repeating subunits cytosine, guanine, thymine and adenine. The part of a DNA molecule containing cytosine has a chemical formula C9H12O6N3P, and the sections containing different subunits form long polymer molecules located in the nucleus of cells.
Some organic compounds are the most complex molecules that exist, and they mirror the complexity of the chemical reactions that make life possible. Even with this complexity, the molecules are made up of relatively few elements, and all have carbon as a major component.