Here we discuss the basic components or molecules that the cell is comprised of. This is more a Chemistry 101 lesson than anything else.

There are four classes of organic molecules in a cell, we’ll discuss one in each post.

Carbohydrates; As the name indicates, they consist of a Carbon atom (Carbo-) attached to a Hydrogen and an Oxygen atom in the ratio of 2:1, similar to water H2O (-hydrate from hydra in latin meaning water). They have a general chemical formula of (CH2O)n where n is usually any number ranging from 2 onwards.

The most popular carbohydrates have n= 3 (triose) or 5 (pentose) or 6 (hexose). Since most carbohydrates are sweet and sugary, sugar nomenclature end with “ose.”

They can be classified as single unit sugars which are called monosaccharides (mono means one, saccharide means sugar), or disaccharide (“di” means two therefore two unit sugars joined together), or oligosaccharides (3 to 50 unit sugars joined together) or polysaccharides (“poly” means many and it is above 50 units of sugar joined together). The bond that holds the saccharides together to form carbohydrates is called glycosidic bondand is formed by the loss of a water molecule when two carbohydrates come together and are subsequently joined by the oxygen atom of one of the two saccharides molecules.

Glycosidic bond being formed by the proximity of two monosaccharides.


Carbohydrates are usually used  as a food source since sugars are used to convert into energy (a process explained in detail in Chapter 5) . Example: Glucose (C6H12O6) is a monosaccharide or single unit sugar and is a common source of energy for the body. However, glucose is generally stored as an aggregated giant molecule starch in plants or glycogen in animals. They are polysaccharides or polymers (macromolecules). Actually “poly” means many, and “mer” means molecules therefore it means many molecules.

Three important disaccharides are maltose, lactose, and sucrose which are used as fodder to either make the storage macromolecules or to break-down into monosaccharides for converting the sugar into energy.


In addition to it’s role as energy storage, carbohydrates are also used in plant cell wall in the form of the polysaccharide cellulose to give the cell structure, and is an important signal receptor on the plasma membrane of cells where the signal will induce the cell to perform specific functions (more in chapter 7). This is done when oligosaccharides linked to proteins on the plasma membrane work as signal receptors or markers for cell recognition and interaction.

Next post, we’ll talk about fats!