Biomolecules — CBSE Class 12 board PYQs

The specific sequence in which amino acids are arranged in a protein is called its:

What is the basic structural difference between glucose and fructose?

Write the products obtained after hydrolysis of lactose.

What is meant by 'reducing sugars'?

Name the deficiency diseases resulting from lack of vitamins A and E in the diet.

Describe the following: functions of carbohydrates in plants.

Under what condition does each protein take the shape that is energetically most stable?

Why is cellulose in our diet not nourishing?

In what sense are the two strands of DNA not identical but complementary to each other?

What are heterocyclic bases? Give an example of a nitrogenous heterocyclic base.

State a use for the enzyme streptokinase in medicine.

Name two of the different types of RNA molecules found in the cells of organisms.

Name one important function of nucleic acids in our body.

State any one characteristic of enzymatic catalysts.

Define the term denaturation in relation to proteins.

Classify the following sugars into monosaccharides and disaccharides: galactose, glucose, lactose and maltose.

Case study — Vitamins: certain organic compounds required in small amounts in our diet whose deficiency causes specific diseases. Most vitamins cannot be synthesised in our body, but plants can synthesise almost all of them; gut bacteria produce some. The term 'vitamin' was coine …

Case study — Vitamins (same passage as above).
OR (c) Why can't vitamin C be stored in our body? Name the disease caused by the deficiency of this vitamin.

Give the reaction of glucose with acetic anhydride. Which group's presence is confirmed by this reaction?

Give reasons for any three of the following observations:
a) The pentaacetate of glucose does not react with hydroxylamine.
b) Amino acids behave like salts.
c) Water-soluble vitamins must be taken regularly in the diet.
d) The two strands in DNA are complementary to each other.

Give a plausible explanation for each of the following:
(a) Glucose doesn't give the 2,4-DNP test.
(b) The two strands in DNA are not identical but are complementary.
(c) Starch and cellulose both contain glucose units as monomer, yet they are structurally different.

Differentiate between the following:
(i) amylose and amylopectin
(ii) peptide linkage and glycosidic linkage
(iii) fibrous proteins and globular proteins

Write chemical reactions to show that the open structure of D-glucose contains:
(i) a straight chain
(ii) five alcohol groups
(iii) an aldehyde as the carbonyl group

Define the following with an example of each:
(a) polysaccharides
(b) denatured protein
(c) essential amino acids

(a) Write the product formed when D-glucose reacts with concentrated HNO₃.
(b) Amino acids show amphoteric behaviour. Why?
(c) Write one difference between the α-helix and β-pleated structures of proteins.

After watching a TV programme about carcinogens (potassium bromate and potassium iodate) in bread and bakery products, Rupali, a Class XII student, campaigned for her school canteen to replace bakery products with protein- and vitamin-rich food like fruits, salads and sprouts; th …

i) Write the names of the two monosaccharides obtained on hydrolysis of lactose.
ii) Why can vitamin C not be stored in our body?
iii) What is the difference between a nucleoside and a nucleotide?

i) Which one of the following is a disaccharide: starch, maltose, fructose, glucose?
ii) What is the difference between a fibrous protein and a globular protein?
iii) Name the vitamin whose deficiency causes bone deformities in children.

Explain what is meant by:
i) peptide linkage
ii) pyranose structure of glucose

Write the main structural differences between DNA and RNA. Of the four bases, name those which are common to both DNA and RNA.

What is essentially the difference between the α-form and β-form of glucose? Explain.

Describe what you understand by the primary structure and secondary structure of proteins.

What are essential and non-essential amino acids in human food? Give one example of each type.

Name the products of hydrolysis of sucrose. Why is sucrose not a reducing sugar?

Explain the following terms:
i) invert sugar
ii) polypeptides

Amino acids may be acidic, alkaline or neutral. How does this happen? What are essential and non-essential amino acids? Name one of each type.

Name two fat-soluble vitamins, their sources, and the diseases caused by their deficiency in diet.

Name the four bases present in DNA. Which one of these is not present in RNA?

Name two water-soluble vitamins, their sources, and the diseases caused by their deficiency in diet.

Explain what is meant by:
i) a peptide linkage
ii) a glycosidic linkage

List any four vitamins. Mention the chief sources and functions of two of them.

Describe the following:
i) glycosidic linkage
ii) peptide linkage

List the reactions of glucose which cannot be explained by its open-chain structure.

Define the following terms in relation to proteins:
i) peptide linkage
ii) denaturation

Answer the following questions briefly:
i) What are reducing sugars?
ii) What is meant by denaturation of a protein?
iii) How is oxygen replenished in our atmosphere?

Explain the following terms:
i) mutarotation
ii) avitaminosis

Explain the term mutarotation, giving an example.

i) Which forces are responsible for the stability of the α-helix?
ii) What is a denatured protein?

State two main differences between globular proteins and fibrous proteins.

a) What are denaturation and renaturation of proteins?
b) Give a reason: amylase present in the saliva becomes inactive in the stomach.

Name the main disease caused by lack of the vitamin, and its source, for each of: A, B₆ and E.

Write the chemical equations for the reactions of glucose with:
i) acetic anhydride
ii) NH₂OH
Also draw the Fischer projections of D-glucose and L-glucose.

Name the diseases caused by the deficiency of vitamins A, E, B₁₂ and H.

a) Describe the following, giving one example: nucleotides.
b) List four functions of carbohydrates in living organisms.

Name the chemical components which constitute nucleotides. Write any two functions of nucleotides in a cell.

Write four characteristic features of enzymes. Name a disease which is caused by the deficiency of a particular enzyme.

What role do enzymes have in the functioning of our bodies?

State the difference between the following pairs:
i) α-helix and β-pleated structure
ii) primary and secondary structures of a protein

Answer the following queries about proteins:
i) How are proteins related to amino acids?
ii) How are oligopeptides different from polypeptides?
iii) When is a protein said to be denatured?

Define the following and give one example of each:
a) isoelectric point
b) mutarotation
c) enzymes

i) Write one reaction of D-glucose which cannot be explained by its open-chain structure.
ii) What type of linkage is present in nucleic acids?
iii) Give one example each of a water-soluble vitamin and a fat-soluble vitamin.