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.

What is the basic structural difference between glucose and fructose?

Glucose is an aldehyde and whereas fructose is a ketone and has following structure according to Fischer projections. Another difference is the number of chiral carbons in glucose is 4 whereas in fructose is 3 . Also the number of 2 ° alcohol is 4 for glucose and 3 for fructose.

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.

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.

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter 14 - Biomolecules>CBSE-2019>Q 14

MEDIUM

12th CBSE

IMPORTANT

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

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