BIOMOLECULES: PREVIOUS YEAR QUESTIONS

REVISION
1. What is meant by ‘reducing sugars’?
Answer: Reducing sugar contains aldehydic or ketonic group in the hemiacetal and
hemiketal forms and can reduceTollen’s reagent or Fehlmg’s solution.
2. Write the structure of the product obtained when glucose is oxidised with nitric acid.
Answer:

3. Write a reaction which shows that all the carbon atoms in glucose are linked in a
straight chain.
Answer:
On prolonged heating with HI, it forms n-hexane, shows that all the six carbon atoms
are linked in a straight chain :

4. What are the expected products of hydrolysis of lactose ?

Answer: On hydrolysis, lactose gives P-D-galactose and p-D-glucose.
5. Where does the water present in the egg go after boiling the egg?
Answer: Denaturation of proteins is a process that changes the physical and biological
properties of proteins without affecting the chemical composition of protein. In an egg,
denaturation of protein is the coagulation of albumin present in the white of an egg.
When an egg is boiled in water, the globular proteins present in it change to a rubber
like insoluble mass which absorbs all the water present in the egg by making hydrogen
bond with it.

6. Name a water soluble vitamin which is a powerful antioxidant. Give its one natural
source.
Answer: Water soluble vitamin : Vitamin C
Natural source : Amla

7. What is a glycosidic linkage?

Answer: The two monosaccharide units are joined together through an etheral or oxide
linkage formed by loss of a molecule of water. Such a linkage between two
monosaccharide units through oxygen atom is called glycosidic linkage.
8. What are the products of hydrolysis of sucrose?
Answer: Invert sugar: An equimolar mixture of glucose and fructose is obtained by
hydrolysis of sucrose in presence of an acid such as dil. HC1 or the enzyme invertase or
sucrase and is called invert sugar.

9. Write the name of linkage joining two amino acids.

Answer: Peptide linkage joins two amino acids.

10. Name the deficiency diseases resulting from lack of Vitamins A and E in the diet.
Answer: Deficiency of Vitamin A causes Xerophthalmia and deficiency of Vitamin E
causes Sterility

11. Name one oil soluble vitamin which is a powerful antioxidant and give its one
natural source.
Answer: Oil soluble Vitamine : Vitamin D
Natural source : Fish liver oil, butter, milk, eggs etc.

12. Name the only vitamin which can be synthesized in our body. Name the disease
caused due to the deficiency of this vitamin.
Answer:Vitamin which can be synthesized in our body : Vitamin A
Its deficiency causes Xerophthalmia.

13. Mention one important function of nucleic acids in our body.

Answer: Function of nucleic acid : Nucleic acids control the transmission of hereditary
characters from one generation to another.

14. Which of the two components of starch is water soluble?

Answer: Amylose is water soluble component of starch.

15. Which component of starch is a branched polymer of a-glucose and insoluble in

water?
Answer: Amylopectin.

16. What are the products of hydrolysis of maltose?

Answer:

17. What are enzymes?

Answer: Enzymes are protein molecules which act as catalyst in biochemical reaction.

18. Name the four bases present in DNA. Which one of these is not present in RNA?
Answer:
The four bases present in DNA are :
(i) Adenine (A)
(ii) Guanine (G)
(iii) Cytosine (C)
(iv) Thymine (T)
In RNA, Thymine (T) is absent. It has Uracil (U) in place of Thymine.

19. What are essential and non-essential amino acids in human food? Give one example
of each type.
Answer: Essential amino acids : Amino acids which the body cannot synthesize are
called essential amino acids.
Example : Valine, leucine etc. Therefore they must be supplied in diet.

Non-essential amino acids : Amino acids which the body can synthesize are called non-
essential amino acids. Therefore, they may or may not be present in diet.
Example : Glycine, alanine etc.

20. State clearly what are known as nucleosides and nucleotides.

Answer: Nucleoside : A nucleoside contains only two basic components of nucleic acids
i.e. a pentose sugar and a nitrogenous base. During their formation 1-position of the
pyrimidine or 9-position of the purine moitey is linked to C1 of the sugar (ribose or
deoxyribose) by a β-linkage.

Nucleotides : A nucleotide contains all the three basic components of nucleic acids, i.e. a
phosphoric acid group, a pentose sugar and a nitrogenous base. These are formed by
esterification of C5‘ – OH of the sugar of the nucleoside with phosphoric acid.

21. What is essentially the difference between a-form of glucose and p-form of glucose?
Explain.
Answer: In a-α-glucose, the OH group at C1 is towards right while in p-D-glucose, the
OH group at C1 is towards left.

22. Describe what you understand by primary structure and secondary structure of
proteins.
Answer: Primary structure of proteins : Proteins may have one or more polypeptide
chains. Each polypeptide in a protein has amino acids linked with each other in a
specific sequence which is known as primary structure of protein.

Secondary structure of proteins : The conformation which the polypeptide chains

assume as a result of hydrogen bonding is called the secondary structure of the protein.

Depending upon the size of the R groups, the two different secondary structures are
possible which are :

1. α-Helix structure : Intramolecular H-bonds present between the C = O of one

amino acid and N – H of fourth amino acid.
2. β-Pleated sheet structure : The two neighbouring polypeptide chains are held
together by intermolecular H-bonds.

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

DNA RNA
1. The sugar present in DNA is 2- 1. The sugar present in RNA is D-(-)
deoxy-(-) ribose. ribose.

2. DNA contains cytosine and thymine 2. RNA contains cytosine and uracil as
as pyrimidine bases. pyrimidine bases.

3. DNA has double standard α-helix 3. RNA has single stranded α-helix
structure. structure.
The base which are common to both DNA and RNA are :
 1. Adenine (A)
2. Guanine (G)
3. Cytosine (C)

24. Write such reactions and facts about glucose which cannot be explained by its open
chain structure.
Answer: Limitations of the open chain structure of glucose :

1. Glucose does not form NaHSO3 addition product. Despite having aldehyde-
ammonia group, it does not respond to 2,4-DNP test and does not respond to
Schiff’s reagent test.
2. Glucose penta acetate does not react with NH2OH due to absence of aldehydic
group.

25. Write down the structures and names of the products formed when D-glucose is
treated with
(i) Hydroxylamine
(ii) Acetic anhydride.
Answer:
(i) D-glucose reacts with hydroxylamine to form oxime.

(ii) D-glucose reacts with acetic anhydride to give penta-acetate.

26. Write down the structures and names of the products formed when D-glucose is
treated with
(i) Bromine water
(ii) Hydrogen Iodide (Prolonged heating).
Answer:
27. 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.
Answer:
Amino acids can be broadly classified into three classes i.e. acidic, alkaline and neutral
amino acids depending on the number of —NH2 group and — COOH group.

Acidic amino acids : Those a-amino acids such as aspartic acid, asparagine and glutamic
acid which contain two -COOH groups and one -NH2 group are called acidic amino
acids.

Alkaline or Basic amino acids : Those a-amino acids such as lysine, arginine and
histidine which
contain two -NH2 groups and one -COOH group, are called basic amino acids.

Neutral amino acids : Those a-amino acids such as glycine, alanine, valine etc. which
contain one -NH2 and one – COOH group, are called neutral amino acids.

Essential amino acids : Amino acids which the body cannot synthesize are called
essential amino acids.
Example : Valine, leucine etc. Therefore they must be supplied in diet.

Non-essential amino acids : Amino acids which the body can synthesize are called non-
essential amino acids. Therefore, they may or may not be present in diet.
Example : Glycine, alanine etc.

28. Differentiate between fibrous proteins and globular proteins. What is meant by the
denaturation of a protein?

Answer: :

Globular Proteins Fibrous Proteins

1. Globular proteins have almost 1. Polypeptide chains of fibrous proteins
spheroidal shape due to folding of the consist of thread like molecules which
polypeptide chain. tend to lie side by side to form fibres.
2. Globular proteins are soluble in water. 2. Fibrous proteins are insoluble in water.
3. Globular proteins are sensitive to small
changes of temperature and pH. Therefore 3. Fibrous proteins are stable to moderate
they undergo denaturation on heating or changes of temperature and pH.
on treatment with acids/bases
4. They do not have any biological activity
4. They possess biological activity that’s
but serve as chief structural material of
why they act as enzymes.
animal tissues.
Example: Maltase, invertase etc., Example: Keratin in skin, hair, nails and
hormones (insulin) antibodies, transport wool, collagen in tendons, fibroin in silk
agents (haemoglobin), etc. etc.

Denaturation of protein : Due to coagulation of globular protein under the influence of

change in temperature, change in pH etc., the native shape of the protein is destroyed
and biological activity is lost and the formed protein is called denaturated proteins and
the phenomenon is denaturation.

29. Define the following terms :

(i) Nucleotide
(ii) Anomers
(iii) Essential amino acids
Answer:
(i) Nucleotide : A nucleotide contains all the three basic components of nucleic acids, i.e.
a phosphoric acid group, a pentose sugar and a nitrogenous base. These are formed by
esterification of C5 -OH of the sugar of the nucleoside with phosphoric acid.
Structure of Nucleotide:

(ii) Anomers : A pair of stereoisomers which differ in configuration only around C1 are
called anomers. Two isomers are said to be anomers if the isomerisation in the
molecule is at first carbon.

(iii) Essential amino acids: Essential amino acids : Amino acids which the body cannot
synthesize are called essential amino acids. Example : Valine, leucine etc. Therefore
they must be supplied in diet.
Non-essential amino acids : Amino acids which the body can synthesize are called non-
essential amino acids. Therefore, they may or may not be present in diet.
Example ; Glycine, alanine etc.

30. (i) Write the structural difference between starch and cellulose.
(ii) What type of linkage is present in Nucleic acids?
(iii) Give one example each for fibrous protein and globular protein.
Answer:
(i) Starch contains the β-D-glucose as its monomer units while cellulose contains β-D-
glucose as its monomer units.
(ii) Phosphodiester linkages are present in Nucleic Adds
(iii) Globular protein : All enzymes and hormones like insulin.
Fibrous protein : Keratin in skin.