Question

Identify the mis-matched pair from the following.
A. Agar – Polymer of glucose and sulphur containing carbohydrates
B. Chitin – Polymer of glucosamine
C. Peptidoglycan – Polysaccharides linked to peptides
D. Lipopolysaccharides – A complex of lipid and polysaccharide
E. Glycogen – Polymer of glucose

Answer 1

Hint: Agar, chitin, peptidoglycan, lipopolysaccharide, and glycogen are all polysaccharides. One of them is derivative of red algae and is composed of D-galactose and 3,6-anhydro-L-galactopyranose. It is gelatinous and is majorly used to grow cultures in the laboratory. It gives a jellylike constituency on cooling. It is insoluble in cold water.

Complete answer:
This is a mismatched pair as agar is not a polymer of glucose and sulphur containing carbohydrates.
Agar is a jellylike substance that is made of agarose and agaropectin. Agarose makes up 70 percent of the mixture and is a linear polymer containing repeating units of agarobiose. Agarobiose is a disaccharide that is made of D-galactose and 3,6-anhydro-L-galactopyranose. Agaropectin is present in a lesser quantity. It consists of smaller molecules and is made up of D-galactose and L-galactose occurring in an alternate manner.

So, by looking at the chemical composition, we know that agar does not contain sulphur. Agar is derived from red algae such as Gelidium and Gracilaria and due to its gelatinous properties, it is used extensively. It used as:
- A nutrient media to culture bacteria
- A solidifying agent in foods
- Cosmetics and medicines
- Thickening agent in ice-creams

Hence, the correct answer is option (A).

Additional information:
• Chitin is a long-chain polysaccharide made of N-acetylglucosamine. It can be found in the exoskeletons of arthropods and the cell wall of fungi.
• Peptidoglycan is a polymer made of sugars and amino acids. It forms links with N- acetylglucosamine and N-acetylmuramic acid.
• Lipopolysaccharide is a combination of a polysaccharide with a lipid. They are also known as endotoxins.
• Glycogen is a polysaccharide that is made up of units of glucose. It is a form of storage of energy.

Note: Agar is a heteropolysaccharide as it is made of two different types of polysaccharides. It is made up of agarose and agaropectin.
- Agarose is a polymer of galactose and is responsible for providing strength to the gel matrix.
- Agaropectin is a sulphonated compound that provides proper viscosity to the solutions of agar.