Springdales school, Dhaula kuan

Class XII
Biomolecules

1. Define carbohydrates. How are carbohydrates classified on the basis of their behaviour on hydrolysis?

Ans. Optically active polyhydroxy aldehydes or polyhydroxy ketones or substances which give these on hydrolysis
are termed as Carbohydrates. Carbohydrates are classified on the basis of hydrolysis as:

2. What are reducing and non-reducing sugars? Give example of each.

Ans.

Characteristic Reducing Sugars Non-Reducing Sugars

Capable of reducing other substances by Lacks the ability to donate electrons in

Definition
donating electrons. redox reactions.

Carbonyl group is involved in a

Functional Group Contains a free aldehyde or ketone group.
glycosidic linkage.

Examples Glucose, fructose, maltose, lactose, etc. Sucrose (table sugar), trehalose, etc.

Fehling's Solution
Reduces copper ion in Fehling's Reaction. Does not react in Fehling's Reaction.
Reaction

Benedict's Solution Does not react with Benedict's

Reduces copper ions in Benedict's solution
Reaction solution.

Chemical Structure Contains a free aldehyde or ketone group. Lacks a free aldehyde or ketone group.

Does not have a glycosidic linkage between the Has a glycosidic linkage between the
Glycosidic Linkage
monosaccharide units. monosaccharide units.

3. How is Glucose prepared? Write the reactions when D-Glucose reacts with following: (a)Hydrocyanic acid,
HCN (b) acetic anhydride (c) Tollen’s reagent (d)HI (e)ConcHNO3 (f)Phenyl Hydrazine (g) Hydroxylamine
(h)Bromine water
4. Write the reaction which show that
a) all the carbon atoms in glucose are linked in a straight chain.

b) the presence of an aldehydic group in a glucose molecule?

c) the presence of five —OH groups in glucose molecule?

5. Under what conditions glucose is converted to gluconic and saccharic acid?

6. Explain Pyranose structure of glucose.

Glucose’s pyranose ring is formed when a hydroxyl group at the 5th carbon position (C-5) of
a glucose molecule is reacted with an aldehyde group attached to the 1st carbon position (C-1) of the
same glucose molecule. Hence, intramolecular hemiacetal molecules are formed.

7. What is the basic structural difference Glucose and Fructose?

 8. Classify the following into monosaccharides and disaccharides.Ribose,2 deoxyribose, maltose, galactose,
fructose and lactose.
Ans. Ribose, 2-deoxyribose, galactose, and fructose are monosaccharides. Maltose and Lactose are
disaccharides.
9. What are the hydrolysis products of (a) Sucrose. (b) Lactose (c)Maltose.

Ans. The products of hydrolysis for the given disaccharides are: 1. Sucrose: glucose + fructose 2. Maltose: glucose
+ glucose 3. Lactose: glucose + galactose

10. Name the sugar present in milk. How many monosaccharide units are present in it? What are such
oligosaccharides called?

Ans. Sugar present in the milk is Lactose. It is a disaccharide formed by glucose and galactose.

11. Glucose or sucrose are soluble in water but cyclohexane or benzene are insoluble in water. Explain.

12. What do you understand by the term glycosidic linkage?

Ans. Glycosidic linkage refers to the linkage formed between two monosaccharide units through an oxygen atom
by the loss of a water molecule.

13. Which sugar is called invert sugar?

OR
Sucrose is dextrorotatory but the mixture obtained after hydrolysis is laevorotatory. Explain.

Ans.

14. What is glycogen? How is it different from starch?

Ans.
15. Define the term Anomers.

Ans. Anomers are cyclic monosaccharides or glycosides that are epimers, differing from each other in
the configuration of C-1 if they are aldoses or in the configuration at C-2 if they are ketoses.
16. An optically active compound having molecular formula C6H12O6 is found in two isomeric forms (A) and
(B) in nature. When (A) and (B) are dissolved in water they show the following equilibrium.

(A) ↔ Equilibrium mixture ↔ (B)

1110 52.20 19.20

(i) What are such isomers called?

Ans. Anomers

(ii) Can they be called enantiomers? Justify your answer

Ans. To determine whether two molecules are enantiomers, we need to check if they are non-superimposable
mirror images of each other. In this case, since the two molecules are not mirror images of each other, they
cannot be enantiomers.

(iii) Draw the cyclic structure of isomer (A)

Ans.

17. Name the two components of starch. How do they differ from each other.

Ans. he two components of starch are: 1. Amylose 2. Amylopectin

Feature Amylose Amylopectin

Branched chain of α-D-glucose units linked by α-

Chemical Linear chain of α-D-glucose units
1,4-glycosidic bonds with occasional α-1,6-
Structure linked by α-1,4-glycosidic bonds.
glycosidic branches.

Lower molecular weight compared

Molecular to amylopectin. Consists of Higher molecular weight compared to amylose.
Weight approximately 200 to 1,000 glucose Can consist of several thousand glucose units.
units.

Highly branched structure with numerous side

Branching Unbranched
chains, forming a tree-like structure.

Number of
Typically 20-30 glucose units per Can have thousands of glucose units in the main
Glucose
chain. chain with additional branches.
Units

More soluble in water due to its

Solubility Less soluble in water due to its branched
linear structure. Forms a colloidal
in Water structure. Does not form a clear solution.
solution.
 18. Amino acids may be acidic ,alkaline or neutral.How does this happen.

Ans. This is due to presence of carboxylic acid as well as amino groups.

* Amino acids which contain two -COOH group and one —NH2 group are called acidic amino acid, e.g.,
aspartic acid. * Amino acids which contain two —NH2 group and one -COOH group are called basic amino
acids, e.g., lysine.
Amino acids which contain one -COOH and one —NH2 group are called neutral amino acids, e.g., glycine.
* 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.

18. Write a note on zwitter ion and isoelectric point.

Ans. The isoelectric point is a point where the net charge on a molecule is neutral (i.e. it is neither positive nor
negative). Zwitterions have an isoelectric point that helps to calculate the pH value of the ion. It is represented as
pI, pH (I), or IEP. The solubility of a molecule is also affected by its isoelectric point.

19. What do you understand by the term Peptide linkage?

Ans. A peptide linkage is a chemical bond formed between two molecules when the carboxyl group of one
molecule reacts with the amino group of the other molecule, releasing a molecule of water ( H 2O ).

20. Distinguish between the following:

(a)Essential &Nonessential amino acids

Essential Amino Acids: Non- essential amino acids

Amino acids which can't be created in our body but Amino acids which can be created in our body itself
can only be received from proper food or diet are are Non- essential amino acids. Examples-alanine,
called Essential Amino Acids. arginine, asparagine, aspartic acid.
Examples- Histidine, Isoleucine, Lysine Examples- Histidine, Isoleucine, Lysine.
(b) Fibrous &Globular Proteins

(c)α-helix and β-pleated sheet proteins

 21. What type of bonding helps in stabilizing the α-helix structure of proteins.

Ans. The α-helix structure of proteins is stabilized by intramolecular H-bonding between C = O of one amino acid
residue and the N – H of the fourth amino acid residue in the chain.

22. How do you explain the amphoteric behaviour of amino acids?

Ans. Amino acids have both acidic (carboxyl) group and basic (amino) group in the same molecule. In the aqueous
solution the carboxyl group losses proton while α-amino group accepts that proton. This results to fomation of
zwitter ion.
This zwitter ionic form of α amino acid shows amphoteric behaviour, i.e. act both as acid and base.

23. What is Denaturation of proteins?

Ans. When a protein in its native form, is subjected to physical change like change in temperature or chemical
change like change in pH, the hydrogen bonds are disturbed. Due to this, globules unfold and helix get uncoiled
and protein loses its biological activity. This is called denaturation of protein.

24. What is the biological effect of Denaturation on the structure of proteins?

Ans. During denaturation secondary and tertiary structures are destroyed but primary structure remains intact.

25. Where does the water present in the egg go after boiling the egg.

Ans. When an egg is boiled, the globular proteins (albumin of egg white) coagulate (denature) to a rubber like
insoluble mass. This insoluble mass absorbs all water present in egg as it makes hydrogen bonds with it.

26. The melting point and solubility in water of amino acids are generally higher than that of the
corresponding haloacids.Explain.

ans. Amino acids exist as zwitter ions. Because of this dipolar salt-like character, they have strong dipole-dipole
attractions . Hence, their melting points are higher than halo-acids

27. Define vitamins. How are vitamins classified?

Ans. Vitamins are organic molecules that are essential to an organism in small quantities for proper metabolic
function.

28. Name the main sources and deficiency diseases caused due to lack of vitamin A, C, E, B1, B2, B6 , B12 E &K.

Ans.

29. Why cannot Vitamin C be stored in our body?

ans. Vitamin C is soluble in water and can easily be excreted out through urine. Thus, it can’t be stored in the
body.

30. Define Nucleic acids. How are they classified? Mention their two important functions.

Ans. Nucleic acids are the biopolymers made up of sugar, phosphate and nitrogenous bases. Nucleic acid term is
referred for DNA and RNA together.
The function of DNA is the transmission of genetic information and the medium of long-term storage. RNA's
function is to transmit the genetic code required for creating protein from the nucleus to the ribosome.

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are two major types of nucleic acids.

31. Write the important differences between DNA and RNA.

Ans.
 Parameter DNA RNA

Full form deoxyribonucleic acid ribonucleic acid

Structure DNA is a double-stranded helix RNA is a single-stranded helix

composed of a long chain of composed of a short chain of
nucleotides. nucleotides.

Function transmits genetic information to In order to produce proteins,

generate new cells and organisms. it sends the genetic code from
long-term conservation of genetic the nucleus to the ribosomes.
data.

Nitrogenous GC(Guanine pairs with Cytosine) A- GC(Guanine pairs with

bases T(Adenine pairs with Thymine). Cytosine) A-U(Adenine pairs
with Uracil)

Composition Phosphate backbone, deoxyribose The phosphate backbone and

sugar. ribose sugar.
the bases adenine, guanine, the bases adenine, guanine,
cytosine, and thymine. cytosine, and uracil.

Propagation DNA is self-replicating. Synthesized from DNA.

32. What is the difference between a nucleoside and a nucleotide?

Ans.

Nucleotide Nucleoside

The chemical composition of

A nucleoside has a chemical composition
nucleotide consists of a phosphate
that consists of a sugar and a base without
group, a sugar and a nitrogenous
the phosphate group.
base.

Some of the major examples of Some of the key examples of nucleosides

nucleotides are adenosine, are the same as nucleotides only with the
guanosine etc. addition of phosphate groups.
 33. What is phosphodiester linkage.

Ans. A phosphodiester linkage is a covalent bond that forms between the phosphate group of one nucleotide and the
hydroxyl group on the sugar of another nucleotide, creating a sugar-phosphate backbone in nucleic acids like DNA
and RNA.

34. The two strands in DNA are not identical but are complementary. Explain.

Ans. In the helical structure of DNA, the two strands are held together by hydrogen bonds between specific pairs of
bases. Cytosine forms a hydrogen bond with guanine, while adenine forms a hydrogen bond with thymine. As a
result, the two strands are complementary to each other.

35. What are different types of RNA molecules which perform different functions.?

Ans. There are three roles of RNA in protein synthesis. Messenger RNA (mRNA) is translated into protein by the
joint action of transfer RNA (tRNA) and the ribosome, which is composed of numerous proteins and two major
ribosomal RNA (rRNA) molecules.