Write the products obtained after hydrolysis of lactose.

The hydrolysis reaction of lactose generates the galactose and glucose moieties. Specifically the galactose is β-D galactose and the glucose is β-D glucose. This is represented as follows: The bond which joins the two different sugar molecules is called a glycosidic bond. The position of the hydroxyl group at the anomeric carbon (marked as *) labels the sugar molecules as α and β. If the hydroxyl group is above then it is β but if the hydroxyl group is below then it is α. Hence the product obtained by hydrolysis of lactose is β-D galactose and β-D glucose.

Give the plausible explanation for the following: Starch and cellulose both contain glucose unit as monomer, yet they are structurally different.

Starch consists of two components - amylose, and amylopectin. Amylose is a long linear chain of α - D - + - g l u c o s e units joined by C 1 - C 4 glycosidic linkage ( α - link). Amylopectin is a branched-chain polymer of α -D-glucose units, in which the chain is formed by C 1 - C 4 glycosidic linkage and the branching occurs through C 1 - C 6 glycosidic linkage. On the other hand, cellulose is a straight-chain polysaccharide of β -D-glucose units joined by C 1 - C 4 glycosidic linkage ( β -link).

Give the plausible explanation for the following: The two strands in DNA are not identical but are complementary.

The two strands of DNA's helical helix are held together by hydrogen bonds formed between certain pairs of nucleotides. Adenine makes a hydrogen link with thymine, whereas cytosine produces a hydrogen bond with guanine. As a result, the two strands are mutually beneficial. DNA is made up of two strands of nucleic acid chains that are coiled around each other in a double helix shape. Hydrogen bonding connects the bases of one strand of DNA to the bases of the other strand. Because the bases can only base pair in a complimentary fashion, this hydrogen bonding is exceedingly particular. Adenine has only two hydrogen bonds with thymine, but guanine has three hydrogen bonds with cytosine. As a result, the two strands of DNA are complementary in the sense that the sequence of bases in one strand determines the sequence of bases in the other. As a result, the DNA stands cannot be identical, but they are complimentary.

Write chemical reactions to show that open structure of D-glucose contains the following : Five alcohol groups

Glucose on reaction with acetic anhydride forms glucose pentacetate on acetylation. This reaction confirms that five - OH (alcohol) groups are present in glucose and that too on different carbon atoms, otherwise the resulting pentacetate would be highly unstable.

Write chemical reactions to show that open structure of D-glucose contains the following : Straight chain

To show that open structure of D-glucose contains straight chain, heat it with HI . Reaction of D-Glucose with HI to form n-hexane indicates that the six carbons are linked in a straight chain. This is because HI is a strong hydrogenating agent. On reacting with glucose in excess it replaces all the - OH and carboxyl groups with hydrogen, covering it into n-hexane.

Write chemical reactions to show that open structure of D-glucose contains the following : Aldehyde as carbonyl group

Glucose reacts with hydrogen cyanide to form cyanohydrin and with hydroxylamine to form an oxime. The reactions clearly indicate the presence of an aldehyde as a carbonyl group in glucose.

Differentiate between the following : Fibrous proteins and Globular proteins

Fibrous proteins Globular proteins When the polypeptide chains run parallel and are held together by hydrogen and disulphide bonds, then fibre– like structure is formed. These are called fibrous proteins. They are generally insoluble in water. These are formed when the chains of polypeptides coil around to give a spherical shape. These are usually soluble in water.

Differentiate between the following : Amylose and Amylopectin

Amylose Amylopectin Amylose is a polysaccharide made of several D-glucose units. They are linked by 1,4-glycosidic bonds. Amylopectin is a polymer of several D-glucose molecules. 80% of amylopectin is present in starch. Amylopectin molecules are linked by α-1,4-glycosidic bonds and α-1,6-glycosidic bonds.

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What is the basic structural difference between glucose and fructose?

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