Chemistry of Carbohydrates 1 Biochemistry Slideshow – MBBS Lectures

Learning Outcomes

• Define carbohydrates

• Explain biochemical functions of
• carbohydrates

• Classify carbohydrates

Carbohydrates

• Carbohydrates are also called Saccharides (Greek Sakcharon meaning Sugar). Carbohydrates are the most abundant biomolecule on earth and one of the main macromolecules that living things are made up of
• They are organic compounds mainly composed of Carbon, Hydrogen and Oxygen. Many carbohydrates also contain Nitrogen and other elements

What are Carbohydrates?

• Hydrates of Carbons (or Carbon Hydrates)
• Carbon + H2O
• Cn(H2O)n

Note: Not all carbohydrates contain exactly 2:1 ratio of H:O as of water, and is true for only the basic units of carbohydrates.

Define Carbohydrates

• Carbohydrates are polyhydroxy aldehydes (H-C=O) or ketones (C=O), containing at least 3 carbon atoms.

Can you Visualize Either Aldehyde Or Ketone Group In ThisPolyhydroxy Alcohol?

But on hydrolysis it yields an Aldehyde and a Ketone

So the complete definition of carbohydrates will be:

CARBOHYDRATES ARE POLYHYDROXYLATED COMPOUNDS WITH ATLEAST THREE CARBON ATOMS, WITH POTENTIALLY ACTIVE CARBONYL GROUPS WHICH MAY BE EITHER AN ALDEHYDE OR KETONE GROUP; THEY ALSO CONTAIN THOSE COMPOUNDS, WHICH YIELD THEM ON HYDROLYSIS.

Functions Of Carbohydrates

• They are the chief source of energy.
  • Glycocalyx coat helps in cell recognition.
  • They can act as antigens.
  • Their degradation products act as promoters or catalysts.
  • Carbohydrates derivatives (such as cardiac glycosides, antibiotics) are used as drugs.
  • They can be used to synthesize fatty acids, cholesterol, amino acids, etc.
  • They form nucleic acids which store genetic information.
  • They form structural components in the body.
  • They form bulk of stool and prevent constipation.

Classification of CHO

• Based on Hydrolysis / Sacchar Units
• Based on functional group
• Based on Isomerism

Based on Hydrolysis and Number of Sacchar Units

1. Monosaccharaides (1 sacchar unit)
2. Disaccharides (2 sacchar units)
3. Oligosaccharides (3 to 10 sacchar units)
4. Polysaccharides (more than 10 sacchar units)

Monosaccharides

• Simple sugars, consisting of a single sacchar unit
  • These are the simplest form (or basic units) of carbohydrates which cannot be hydrolyzed.
  • Completely Soluble in water
  • Low molecular weight

Monosaccharides can be further classified or grouped on the basis of:

• Aldehyde or Ketone Group
• Aldoses (Aldomonosaccharides)
• Ketoses (Ketomonosaccharides)

• Carbon Chain Length
• Trioses (3 Carbons)
• Tetroses (4 Carbons)
• Pentoses (5 Carbons)
• Hexoses (6 Carbons)
• Heptoses (7 Carbons)

Examples of Monosaccharides:

Disaccharides

• Consist of 2 Sacchar Unit
• Usually soluble in water
• Higher molecular weight than monosaccharides
• Examples???

Sugarcane Sugar

Milk Sugar

Oligosaccharides

• Carbohydrate consisting of 3 to10 sacchar units
  • Less Soluble in water
  • Higher molecular weight
  • These have less importance in human body
• Examples:
  • Maltotriose, Raffinose, Stachyose, Dextrins.

Polysaccharides

• Complex carbohydrate consisting of more than 10 sacchar units
  • Not Soluble in water
  • Higher molecular weight

• Can be further classified on 2 basis:
  • The type of monomers (Homo & hetero polysaccharides)
  • Function (Structural, Storage & Water Binding Polysaccharides)

Based on functional group

Based on Isomerism

1. Enantiomers (Differ at penultimate carbon) L and D forms
2. Epimers (Differ at a Carbon other than anomeric carbon or the penultimate carbon)
3. Anomers (Differ at the anomeric carbon) α and β forms