Thursday, January 21, 2010

Biomolecules are complex organic molecules. These molecules form the basic structural constituent of a living cell. The organic compounds such as amino acids, nucleotides and monosaccharides serve as building blocks of complex biomolecules. The important biomolecules are proteins, carbohydrates and fats, enzymes, vitamins, hormones and nucleic acids. Some of the biomolecules are polymers. For e.g., starch, proteins, nucleic acids are condensation polymers of simple sugars, amino acids and nucleotides respectively.

The Cell
The cell is the fundamental structural and functional unit of living organisms. Cells need energy for active transport, to move molecules between the environment and the cells across cells or within cells. Cells obtain energy by oxidation of molecules like glucose. This oxidation takes place in a complex and controlled way by means of enzymes which are biocatalysts.
Photosynthesis and Energy
Energy for life processes basically comes from the sun. During photosynthesis, green plants absorb energy from the sun to make glucose and oxygen from carbon dioxide and water.

Carbohydrates - Introduction
Carbohydrates are the organic molecules that are composed of elements carbon, hydrogen and oxygen. These carbohydrates are referred to as saccharides. Carbohydrates are defined as polyhydroxy-aldehydes or polyhydroxy ketones or compounds, which produce them on hydrolysis. They supply energy and serve as structural constituents.

Carbohydrates are classified into three groups based on the number of sugar units and upon their behaviour towards hydrolysis. They are
* Monosaccharides
* Oligosaccharides and
* Polysaccharides.

These are the simple carbohydrates that cannot be hydrolysed to simpler compounds. They are sweet to taste, crystalline and soluble in water. They are commonly known as sugars. They are further classified based on the functional group and number of carbon atoms. They are aldoses and ketoses.

Monosaccharide - Glucose
Glucose occurs in nature in free as well as combined form. It is present in sweet fruits and honey. Ripe grapes contain ~ 20% of glucose.
Anomeric Carbon
A pair of stereoisomers that differ in configurations around C-1 are called anomers and the C-1 carbon is called anomeric carbon. The a and b - cyclic forms of D-glucose are known as anomers. In this case, a-anomers of glucose contains the -OH group towards right at C-1 position and b-anomer of glucose contains the -OH group towards left at C-1 position. So, D-glucose exists in two stereo isomeric forms with different specific rotations and melting points.

Sucrose is made up of a-D-Glucose and b-D-fructose held together by a glycosidic bond, between C1 of a-glucose and C2 of b-fructose. The reducing groups of glucose and fructose are involved in glycosidic bond, so it is a non-reducing sugar.


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