Carbohydrates: Study Notes

For the complete syllabus, check out our PMDC MDCAT Syllabus 2025 article.

Carbohydrate:

• Group of organic compounds containing carbon, oxygen and hydrogen in which hydrogen and oxygen are mostly found in the same ratio as in H2O i.e. 2:1 and thus called hydrated carbons.
• Carbohydrates can be defined as polyhydric alcohols which contains potentially active aldehyde or ketone functional group.

CLASSIFICATION:

MONOSACCHARAIDES (Simple sugars)

• GLUCOSE: Found in ripe fruit, sweet corns and honey. On the other hand it is also found in starch, sweet corn. In sugar cane it is associated with fructose.
• FRUCTOSE: Most abundant hexose found in nature generally called "fruit sugar"
• GALACTOSE: Is found largely in combined state in lactose (milk disaccharide)

OLIGOSACCHARIDES:

• The carbohydrate molecule which yield 2-10 monosaccharide molecules.

SUCROSE

• It is found in most plants. It is stored in large amount in sugar cane & beetroot.
• Glucose + Fructose —> Sucrose + H2O

LACTOSE

• It is found solely in milk
• Glucose + Galactose —> Lactose + H2O

MALTOSE:

• It can be extracted from malt, which is prepared from sprouting barley. 
• Glucose + Glucose —> Maltose + H2O

POLYSACCHARIDES:

They are formed by high molecular weight carbohydrates which on hydrolysis yield mainly monosaccharide or products related to hundreds or thousands of monosaccharide.

STARCH:

• It is the most important reserve food material of higher plants, found in cereals, legumes, potatoes and other vegetables.
• Starch is a polymer of a glucose but is absent from animals where the equivalent is glycogen.
• Starch has two components, amylase (straight chain, joined by 1, 4 bonds) and amylopectin (Branched, formed by 1, 6 glycosidic bonds).

CELLULOSE:

• Cellulose is a β glucose polymer produced by plants.
• The glucose units are joined in straight chain & no branching in the cellulose molecule is indicated.
• It is the main constituent of plant cell wall & moat abundant carbohydrate in nature.
• It is a structural as well as an important food sources for some animals, bacteria and fungi.

GLYCOGEN:

• It is also a reserve polysaccharide found mainly in bacteria, fungi, liver and muscle tissues of animal.
• It is also commonly known as animal starch.
• It is insoluble in water & stored in granular form.
• It is very similar in structure to amylopectin but shows more branching.

​

Explore our MDCAT webapp for tests, video lectures, and complete prep resources.