What Is a Carbohydrate or Saccharide?
Mono- Di- and Polysaccharides: Sugar's Sweet Organic Molecules
Oct 15, 2007
Inorganic and Organic Molecules
Even the experts don’t agree on how to define the difference between organic and inorganic substances, but a good, broad definition is as follows.
Inorganic molecules are essentially substances that don’t have carbon-hydrogen (C-H) bonds, whereas organic molecules are 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 carbohydrate is actually a descriptor of what these molecules are composed of. They are “carbon hydrates,” in a ratio of one carbon molecule to one water molecule (CH2O)n.
You may recognize carbohydrates as source of energy (starch, glycogen), but they fulfill a wide range of roles, including the structural materials of plants (cellulose in plant cell walls) and of some animals chitin of an insect’s exoskeleton.
Carbohydrates can also be components of other molecules such as DNA, RNA, glycolipids, glycoproteins, and adenosine triphosphate (ATP)
Saccharides
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
- examples are glucose and fructose
Disaccharides
- double sugars
- combination of two monosaccharides
- sucrose = glucose + fructose
- lactose = glucose + galactose
Polysaccharides
- polymers composed of several sugars
- can be same monomer (many of same monosaccharide) or mixture of monomers
- glycogen is the major stored carbohydrate in animals
- starch is storage polysaccharide of plants. It is a long chain of glucose molecules.
- chitin is a structural carb in some animals
- cellulose is the major structural carbohydrate in plants
Building and Breaking Down Sugars
Dehydration and hydrolysis are chemical reactions that make bigger (dehydration) and smaller (hydrolysis).
Dehydration Reactions
Dehydration is when one molecule contributes a hydrogen (H) and the other a hydroxyl group (OH), therefore the removal of a water molecule (H2O) results in the joining of two smaller molecules. With respect to carbohydrates, dehydration reactions make bigger carbohydrate molecules from smaller sugars.
Hydrolysis Reactions
Hydrolysis is the reverse of dehydration and is when the addition of a water molecule breaks (lyses) a larger molecule into two smaller molecules. With respect to carbohydrates hydrolysis, the bonds on the larger carbohydrate are broken through the addition of water. One of the smaller molecules receives a hydrogen (H) and the other received a hydroxyl group (OH)
Additional Organic Chemistry Resources
To learn more about organic molecules and cell biology, see Science Prof Online and the Organic Chemistry Help page or look to additional Suite101 articles including, What Is a Carbohydrate, Nucleotides and Nucleic Acids, What Is a Lipid, Amino Acids & Proteins and What are Organic Molecules.
Sources
Bauman, R. (2005) Microbiology.
Park Talaro, K. (2008) Foundations in Microbiology.
