PYQs of BIOMOLECULES

Define the Following:

Q1. Fibrous protein Fibrous proteins are long, strand-like proteins
that provide structure and support to cells and
tissues. They are also known as scleroproteins.

Invert Sugar An equimolar mixture of glucose and fructose

produced on hydrolysis of sucrose is called
invert sugar. It is called so because sucrose is
dextro rotator whereas its hydrolysis product is
laevo rotatory.
Native protein Protein found in a biological system with a
unique three-dimensional structure and
biological activity is called a native protein

Polysaccharides Carbohydrates that yield a large number of

monosaccharide units hydrolysis are called
Polysaccharides.
For e.g. Starch, cellulose, etc.
Glycosidic linkage Two monosaccharides on condensation
produces a disaccharide. In the disaccharide
molecule, the two cyclic structures each related
to the reactant monosaccharide molecule are
bonded by glycosidic linkage.
Oligosaccharides Oligosaccharides are produced when two or
more monosaccharides combine by O-
glycosidic bonds. Some Examples are sucrose,
maltose and lactose.
Denaturation of protein Denaturation of proteins is an irreversible
change in which proteins get precipitated when
they are heated with alcohol, there is change in
pH. Protein is uncoiled and its shape is
destroyed. Characteristic biological activity is
lost.
Examples include the following:
(i) Boiling of egg coagulates egg white.
(ii) Milk is converted to curd.
Vitamins Vitamins are a group of organic compounds that
are extremely necessary and essential for
normal growth and functioning of the human
body. They are required in very
small quantities but cannot be synthesized by
the body itself, and can only be sourced from
outside.
Nucleotide A nucleotide consists of three units, which are
covalently linked. They are:

1. Nitrogenous bases – Purine and

Pyrimidine
2. Pentose Sugar – Ribose and
Deoxyribose
3. Phosphate – monophosphate,
diphosphate, triphosphate

Anomers Anomers → Anomers are stereoisomers of

cyclic sugars that differ in configuration only at
the hemiacetal or hemiketal carbon.
Ex- α -D-Glucose and β -D-Glucose are
anomers.

Essential amino acids Essential amino acids → The amino acids,

which cannot be synthesised in the body and
must be obtained through diet, are known as
essential amino acids.
Ex- Histidine, leucine, etc.

Tertiary structure of protein The tertiary structure of a protein is the three-

dimensional shape of a protein. It's the result of
interactions between the amino acid side chains
and the backbone of a polypeptide chain.
OR
The helical polypeptide chain undergoes coiling
and folding to form a complex three dimensional
shape referred to as tertiary structure of
proteins. These coils and folds are arranged to
hide the non-polar amino acid chains and to
expose the polar side chains. The tertiary
structure is held together by the weak bonds
formed between various parts of the polypeptide
chain.
Disaccharides A disaccharide (also called a double sugar )
is the sugar formed when two monosaccharides
(simple sugars) are joined by glycosidic linkage

Peptide Linkage It is an amide linkage formed between – COOH

group of one α-amino acid and NH2 group of the
other α-amino acid by loss of a molecule of
water. – CO – NH – bond is called Peptide
linkage.
 Primary structure A biocatalyst is a natural substance that
accelerates biochemical reactions. It can be an
enzyme or a hormone.
Polypeptides Polypeptides are polymers of amino acids
bonded by peptide containing less than 100
amino acids. For example, oxytocin,
vasopressin, etc.

Q2. Differentiate between the following:

a. Amylose and Amylopectin

b. Globular protein and Fibrous protein

 c. Essential amino acids and Non-essential amino acids
Essential amino acids are the amino acids which have to be taken in through diet as they
“CAN NOT” be produced by the body e.g., valine , leucine.
Non-essential amino acids are those which are produced by our body, e.g., glucine , alanine.
d. Nucleotide and Nucleoside
Nucleotides:
• Composition is a nitrogenous base, a sugar, and one or more phosphate groups.
• Are the building blocks of DNA and RNA.
• Play important roles in processes like DNA replication, RNA transcription and
translation.
• Can be modified to carry energy or information in the form of phosphate groups.
Nucleosides:
• Consist of a nitrogenous base and sugar, but no phosphate groups.
• Are precursors to nucleotides.
• Play roles in DNA repair, RNA processing, and other cell processes.
• Can be modified to carry energy or information in the form of sugar modifications.
e. Native and denatured protein
 Protein found in a biological system with unique three-dimensional structure and
biological activity is called native protein.
 When a protein in its native form is subjected to change such as change in pH, its
secondary and tertiary structures are destroyed and its loses biological activity. The
protein thus formed is called denatured protein.
f. DNA and RNA

g. Glucose na Starch
 h. Write one difference between α-helix and β-pleated structures of proteins.
In α-helix structure of proteins, the peptide chains are coiled to form right handed helix
involving hydrogen bonding. In β-pleated structure of proteins, the peptide chains lie side by
side joined together by inter-molecular hydrogen bonding.
Q3. Give the plausible explanation for the following :
a. Glucose doesn’t give 2,4-DNP test.
b. The two strands in DNA are not identical but are complementary.
c. Starch and cellulose both contain glucose unit as monomer, yet they are
structurally different
a. Since the aldehydic group is involved in the ring formation, it is not free to react with 2,4-
DNP. Therefore, glucose does not give a positive result in the 2,4-DNP test, indicating
that while it has an aldehydic group in its linear form, it is not accessible in its cyclic form.
b. The DNA has a double helix structure. The two strands of DNA are held by the hydrogen
bonds between the bases on two strands. Thymine(T) pairs with adenine(A) through two
hydrogen bonds and cytosinepairs with guanine (G) through three hydrogen bonds.
Thus, two strands are complementary to each other.
c. Starch and cellulose both contain glucose unit as monomer, yet they are structurally
different because Starch is a polymer of - glucose while cellulose is a polymer of -
glucose.
Q4. (a) What are amino acids?
(b) Why are amino acids amphoteric?
a. Amino Acids are the organic compounds which combine to form proteins. They are,
therefore, referred to as the building components of proteins. These biomolecules are
known to be involved in several biological and chemical functions in the human body.
b. An amphoteric substance is one which can act as an acid as well as a base.Amino acids
show amphoteric behaviour. Amino acids are bi-functional molecules. They contain
carboxylic (−COOH) group that acts as an acid and an amino (−NH2) group that acts as
a base.
Q5. What are the expected products of hydrolysis of :
a. Lactose
b. Maltose
c. Sucrose
d. Starch
e. Cellulose
a. β-D galactose and β-D glucose
b. α−D−glucose + α−D−glucose
c. α−D−glucose + β −D−fructose
d. α−D−glucose
e. β -D-glucose
Q6. What is meant by ‘reducing sugars’? (All India 2010)
Ans: Reducing sugar contains aldehydic or ketonic group in the hemiacetal and hemiketal
forms and can reduce
Tollen’s reagent or Fehling’s solution.
Q7. Write a reaction which shows that all the atoms in glucose are linked in a straight
chain.
Ans : On prolonged heating with HI, glucose gives n-hexane. This suggests that all the six
carbon atoms are linked in straight chain.

Q8. Account for the following:

a. There are 5 –OH groups in glucose.
b. Glucose is a reducing sugar
(a) Glucose when reacts with acetic anhydride forms pentaacetate derivative which
indicates the presnece of 5 −OH groups in glucose.

(b) Glucose is a reducing sugar because it has a free aldehyde group that can be
oxidized and can reduce tollen’s reagent, fehling’s reagent and benedict’s reagent.
Q9. (a) How can you explain the absence of an aldehyde group in the pentaacetate of
D-glucose? (cyclic structure of glucose)
OR
Write such reactions and facts about glucose which cannot be explained by open
chain structure.
 Glucose reacts with hydroxylamine to form an oxime whereas the pentacetate of
glucose does not react with hydroxyl amine indicating the absence of free -CHO
group.
 Despite having the aldehyde group, glucose does not give Schiff’s test and it does not
form the hydrogensulphite addition product with NaHSO3.
 Glucose is found to exist in two different crystalline forms which are named as α and
β. The a-form of glucose (m.p. 419 K) is obtained by crystallisation from concentrated
solution of glucose at 303 K while the b-form (m.p. 423 K) is obtained by
crystallisation from hot and saturated aqueous solution at 371 K.

Q10. What is meant by the pyranose structure of glucose

membered cyclic structure of glucose is called pyranose structure (α−orβ−), in analogy with
heterocyclic compound pyran.
Q11. What happens when glucose is treated with the following compounds

Q12. What is essentially the difference between the α form and β form of glucose.

α−form of glucose and β-form of glucose differ only in the configuration of the hydroxyl group
at C1 in cyclic structure of glucose/hemiacetal form of glucose.

Q13. What is the anomeric carbon in (a) Glucose (b) Fructose

Ans : Glucose – C 1
Fructose – C 2
Q14. What is the structural feature characterising reducing sugars?
The characteristics structural features of reducing sugars is the presence of either aldehydic
group; (-CHO) such as glucose, mannose, galactose, etc. or α-ketol group (-CO-CH2OH) as
present in fructose.
Q15. What are reducing and non reducing sugars?
(i) Reducing sugars: Those carbohydrates which contain free aldehyde or ketonic group and
reduces Fehling’s solution and Tollen’s reagent are called reducing sugars. All
monosaccharides whether aldose or ketone are reducing sugars.
(ii) Non - reducing sugars: Carbohydrates which do not reduce Tollen’s reagent and
Fehling’s solution are called non - reducing sugars. Example Sucrose. They do not have free
aldehyde group.
Q16. What is glycogen? How it is different from starch?

The carbohydrate which is stored in animal body is called glycogen . It is also known as
animal starch. Starch is a polysaccharide which is stored in plants where as glycogen in
stored in animals (liver, muscles and brain).
→Glycogen mainly resembles amylopectin of starch in structure but glycogen is more
branched than amylopectin .
Q17. What type of linkage is present in (a) Carbohydrates (b)Proteins (c) Nucleic
Acid
Ans: a. Glycosidic linkage b. Peptide bond c. Phosphodiester linkage

Q18. What is zwitter ionic form of amino acid?

OR
Name the species formed when the aqueous solution of amino acid is dissolved in
water?
Ans: At a specific PH the amino acid carries both the +ve and -ve charges in equal number
and exists as dipolar ion. It is also called as zwitterionic form. At his point, the net charge on
it is zero.

Q19. What are enzymes?

OR
What are biocatalysts? Give an example.
Ans: The enzymes are biological catalysts produced by the living cells which catalyse
biochemical reactions in living organisms. Chemically enzymes are naturally occurring
simple or conjugate proteins. For example, maltase, amylase, invertase, etc.
Q20. What are the three types of RNA molecules which perform different functions ?

The three main types of RNA molecules are:

1. Messenger RNA (mRNA) - It encodes the amino acid sequence of polypeptides.
2. Transfer RNA (tRNA) - It transfers amino acids to the ribosomes during protein synthesis.
3. Ribosomal RNA (rRNA) - It forms the structural and functional components of ribosomes.
Q21. What are vitamins? Deficiency of which vitamins cause convulsions and
pernicious anaemia?
Ans : Organic compound required in the diet in small amounts to perform specific biological
functions for normal maintenance of optimum growth and heath of the organism are called
vitamins.
(i) Vitamin B 12 (ii) Vitamin B 6
Q22. 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.
Ans: This is due to presence of carboxylic acid as well as amino groups.
* Amino acids which contain two group and one —NH2 group are called acidic amino acid,
e.g., aspartic acid.
* Amino acids which contain two —NH2 group and one group are called basic amino acids,
e.g., lysine.
* Amino acids which contain one and one —NH2 group are called neutral amino acids, e.g.,
glycine.
Q23. What are essential and non-essential amino acids? Name one of each type.
Ans: * Amino acids that cannot be synthesized by the body and must be supplied in the diet
are called essential amino acids, e.g., lysine, valine, leucine, etc.
* The amino acids which are synthesized by our body are called non-essential amino acids,
e.g., alanine, glycine, etc.
Q24. How are vitamins classified? Name the vitamin responsible for coagulation of
blood?
Ans: Vitamins are classified based on their solubility.
Fat Soluble Vitamins are - Vitamin A, D, E, and K. Water soluble vitamins are Vitamin B
complex vitamins and vitamin C.
Vitamin K is responsible for the coagulation of blood.
Q25. Name the bases present in RNA? Which one of these is not present in DNA ?
Ans : Bases present in RNA are adenine, guanine, cytosine and uracil.
Uracil is not present in DNA. Instead of uracil, thymine is present in DNA.
Q26. Write the main structural difference between DNA and RNA. Of the two bases,
thymine and uracil, which one is present in DNA ?
Ans: DNA is a long polymer with a deoxyribose and phosphate backbone and four different
bases : Adenine, Guanine, Cytosine and Thymine.
RNA is a polymer with a ribose and phosphate backbone and four different bases, Adenine,
Guanine , Cytosine and Uracil. DNA has double helical structural and RNA has single helical
structural.
Thymine is persent is DNA.
Q27. The two strands in DNA are not identical but are complementary. Explain.
Ans: Each strand consist of 4 bases which are Adenine, Guanine, Thymine and Cytosine.
These complementary bases are the following:
Adenine (A) ⇔Thymine (T)
Cytosine (C) ⇔Guanine (G)
‘⇔’ This symbol represents that both the left and right hand side bases are
complementary to each other.
The two strands are internally connected by hydrogen bonding between complementary
bases. The two strands of DNA are not identical because their sequence of bases has to be
complementary to each other. Ex- If one sequence is ATCG the other has to be TAGC.
Q28. Name the unit formed by the attachment of a base to 1' Position of sugar in a
nucleoside.
Ans: Nucleoside

Q29. What is DNA fingerprinting? Mention its application.

Ans: The technique which is used to identify and analyze the variation on the basis of
variation and polymorphism in DNA sequence is called as DNA fingerprinting.
Application of DNA fingerprinting are as follows:
a) Used to identify crime suspect
b) Paternity testing
c) Used to find out evolutionary history of an organism.
Q30. What is DNA fingerprinting? Mention its application.
Ans: A sequence of bases on DNA is unique for a person and is the genetic material
transferred to the individual from the parent which helps in the determination of paternity.
Q31. Three amino acids are given below:
Alanine CH3CH(COOH)(NH2) Aspartic acid HOOC-CH2CH(COOH)(NH2) and Lysine
H2N- (CH2)4-CH(COOH)(NH2)
i. Make two tripeptides using these amino acids and mark the peptide linkage in
both cases.
ii. Represent Alanine in the zwitter ionic form.