How are the structures of Carbohydrates related to their function?

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Amy Bowring

How are the structures of Carbohydrates related to their function?

Carbohydrates are named for their content of carbon, hydrogen, and oxygen. The ratio of hydrogen to oxygen is, with a few exceptions, is two hydrogen atoms for every one oxygen atom, as in water, giving the formula CH2O. Carbohydrates are the most abundant biomolecules and include sugars, starch, cellulose, glucose and glycogen. Carbohydrates are found in one of three forms, monosaccharides, disaccharides (both sugars) and polysaccharides.

Monosaccharides are the smallest and simplest of the carbohydrate and the word means literally ‘single sugar’. They have a general formula of (CH2O)n where n is a number between 3 and 9. They are classified according to the number of carbon atoms.

If the number of Carbon atoms is 3 then it is called a triose. If Carbon = 4, a tetrose, if Carbon = 5, a pentose and if Carbon = 6 then it is called a hexose.

Trioses: (e.g. glyceraldehydes), intermediates in respiration and photosynthesis.

Tetroses: rare.

Pentoses: (e.g. ribose, ribulose), used in the synthesis of nucleic acids (RNA and DNA), co-enzymes (NAD, NADP, FAD) and ATP.

Hexoses: (e.g. glucose, fructose), used as a source of energy in respiration and as building blocks for larger molecules.

All but one carbon atom have an alcohol (OH) group attached. The remaining carbon atom has an
aldehyde or ketone group attached.

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Hexoses are the most common and the best known and most abundant hexose is Glucose. Like all hexoses, Glucose has the formula C6H12O6. Glucose is a substrate for respiration therefore is essential for cardiac tissues.

α-Glucose                                β-Glucose                                 Fructose

The structural formula above of α-Glucose and β-Glucose and Fructose illustrate that although hexose sugars generally share the same basic ring structure; they differ from each other in the arrangement of various side groups. Substances such as these three, which have identical molecular formulas but different structural formulas, are known as structural isomers.

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