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Significance of Carbon

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Carbon. Element number six. Right in the middle of the first row of the Periodic Table. So what?

Carbon is the most important element to life. Without this element, life as we know it would not exist. As you will see, carbon is the central element in compounds necessary for life-organic compounds. These compounds include carbohydrates, lipids, proteins and nucleic acids.

The Significance of Carbon

Why is carbon so important to organisms? The answer lies with carbon’s unique properties. Carbon has an exceptional ability to bind with a wide variety of other elements. Carbon makes four electrons available to form covalent chemical bonds, allowing carbon atoms to form multiple stable bonds with other small atoms, including hydrogen, oxygen, and nitrogen. Carbon atoms can also form stable bonds with other carbon atoms. In fact, a carbon atom may form single, double, or even triple bonds with other carbon atoms. This allows carbon atoms to form a tremendous variety of very large and complex molecules.

Organic Compounds

Carbon has the ability to form very long chains of interconnecting C-C bonds. This property allows carbon to form the backbone of organic compounds , carbon-containing compounds, which are the basis of all known organic life. Nearly 10 million carbon-containing organic compounds are known. Types of carbon compounds in organisms include carbohydrates, lipids, proteins, and nucleic acids. The elements found in each type are listed in the table below. Elements other than carbon and hydrogen usually occur within organic compounds in smaller groups of elements called functional groups . When organic compounds react with other compounds, generally just the functional groups are involved. Therefore, functional groups generally determine the nature and functions of organic compounds.

When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds including carbohydrates (sugars), lignans (important in plants), chitins (the main component of the cell walls of fungi, the exoskeletons of arthropods), alcohols, lipids and fats (triglycerides), and carotenoids (plant pigment). With nitrogen it forms alkaloids, and with the addition of sulfur in addition to the nitrogen, it forms amino acids which bind together to form proteins , antibiotics, and rubber products. With the addition of phosphorus to these other elements, carbon forms nucleotides which bond into nucleic acids (DNA and RNA), and adenosine triphosphate (ATP) , which is known as the energy currency of the cell. The properties of all these organic molecules is related to the composition of the elements that compose the molecule. Certain carbohydrates, proteins and nucleic acids are known as macromolecules, as they are very large polymers made of individual monomers.

The Miracle of Life: Carbohydrates, Proteins, Lipids & Nucleic Acids video can be viewed at http://www.youtube.com/watch?v=nMevuu0Hxuc (3:28).

A Comparison
Type of Compound Elements It Contains Examples Functions
Carbohydrates carbon, hydrogen, oxygen Glucose, Starch, Glycogen provides energy to cells, stores energy, forms body structures
Lipids carbon, hydrogen, oxygen Cholesterol, Triglycerides (fats), Phospholipids stores energy, forms cell membranes, carries messages
Proteins carbon, hydrogen, oxygen, nitrogen, sulfur Enzymes, Antibodies helps cells keep their shape/structure, makes up muscles, catalyzes chemical reactions, carries messages and materials
Nucleic Acids carbon, hydrogen, oxygen, nitrogen, phosphorus Deoxyribonucleic acid (DNA), Ribonucleic acid (RNA), Adenosine Triphosphate (ATP) contains instructions for proteins, passes instructions from parents to offspring, helps make proteins

The Table above lists the four types of organic compounds, the elements they contain, and examples and functions of each type of compound.

Condensation and Hydrolysis

Condensation reactions are the chemical processes by which large organic compounds are synthesized from their monomeric units. Hydrolysis reactions are the reverse process. During condensation reactions, water is produced from the two molecules being bonded together; an H from one monomer is joined to an -OH from another molecule, producing H 2 O.

Polymer Monomer Bond
carbohydrates monosaccharides glycosidic
lipids fatty acid ester*
proteins amino acids peptide
nucleic acids nucleotides phosphodiester**
  • The ester linkage is between a glycerol molecule and fatty acid chain.

See http://www.biotopics.co.uk/as/condensation_and_hydrolysis.html for additional information.

Vocabulary

  • adenosine triphosphate (ATP) : Energy-carrying molecule that cells use to power their metabolic processes; energy-currency of the cell.
  • amino acid : Small molecule that is a building block of proteins; the monomer of a polypeptide.
  • carbohydrate : Organic compound such as sugar or starch; major source of energy to living cells.
  • condensation reaction : A chemical reaction in which two molecules combine to form one single molecule, together with the loss of a small molecule, often water.
  • functional group : Part of organic compound that generally determines the nature and functions of the compound.
  • hydrolysis reaction : A chemical process in which a molecule of water is split, resulting in the separation of a large molecule into two smaller molecules.
  • lipid : Organic compound such as fat or oil.
  • macromolecule : A large molecule composed of individual monomer units.
  • nucleic acid : Organic compound such as DNA or RNA.
  • nucleotide : Monomer of nucleic acids, composed of a nitrogen-containing base, a five-carbon sugar, and a phosphate group.
  • organic compound : Compound found in living organisms; contains mainly carbon.
  • protein : Organic compound made of amino acids.

Summary

  • Carbon’s exceptional ability to form bonds with other elements and with itself allows it to form a huge number of large, complex molecules called organic molecules. These molecules make up organisms and carry out life processes.

Practice

Use this resource to answer the questions that follow.

  1. What is an organic compound?
  2. Describe the element carbon.
  3. What is the chemical composition of aspirin? Is it a natural or synthetic compound? Explain your answer.
  4. Describe organic reactions.

Also see the following for additional related information.

Review

  1. Why is carbon essential to all known life on Earth?
  2. What is an organic compound? Give an example.
  3. List the four main classes of organic compounds. What are examples of each?
  4. What is condensation of hydrolysis?
  5. What is a phosphodiester bond?

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