Chapter: 10
Biomolecules-Revision Notes Grade 12
1. What is meant by ‘reducing sugars’?
Reducing sugar contains aldehydic or ketonic group in the hemiacetal
and hemiketal forms and can reduce Tollen’s reagent or Fehling’s solution.
2. Write the structure of the product obtained when glucose is oxidised with
nitric acid.
3. Write a reaction which shows that all the carbon atoms in glucose are
linked in a straight chain.
On prolonged heating with HI, it forms n-hexane, shows that all the six
carbon atoms are linked in a straight
chain :
4. Glucose on oxidation with bromine water yields gluconic acid. This reaction
confirms the presence of ………………….
aldehyde group in glucose
• The reaction is represented below:
5. What are the expected products of hydrolysis of lactose?
On hydrolysis, lactose gives alpha-D-galactose and Beta-D-glucose.
6. Where does the water present in the egg go after boiling the egg?
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.
7. Name a water-soluble vitamin which is a powerful antioxidant. Give its one
natural source
Water soluble vitamin: Vitamin C
Natural source: Amla
8. Differentiate between globular and fibrous proteins
Fibrous
• Fibre like structure
• Consist of polypeptide chains held by intermolecular
hydrogen bonding
• Fibrous proteins are stable to moderate changes of
temperature and pH.
• They do not have any biological activity but serve as chief
structural material of animal tissues.
• Generally insoluble in water.
• Eg: Keratin, Myosin
Globular
• Spherical Shape
• Poly peptide chains are coiled around by intramolecular
H-bonds
• Globular proteins are sensitive to small changes of
temperature and pH.(Undergo denaturation easily)
• They possess biological activity that’s why they act as
enzymes.
• Generally insoluble in water.
• Eg: Insulin, Albumin
9. What is a glycosidic linkage?
The two monosaccharide units are joined together through an oxide
or (ether) linkage formed by loss of a molecule of water. Such a linkage
between two monosaccharide units through oxygen atom is called glycosidic
linkage.
10. Explain Peptide linkage.
Peptide linkage: A peptide linkage is an amide linkage formed between – COOH
group of one α-amino acid and NH2 group of the other a-amino acid by loss of a
molecule of water.
11. Write the products of hydrolysis of lactose
Lactose on hydrolysis with dilute acids gives an equimolar mixture of D-
glucose and D-galactose.
12. What are the products of hydrolysis of maltose?
13. Which of the two components of starch is water soluble?
Amylose is water soluble component of starch. Amylopectin is water insoluble
component of starch.
14. State clearly what are known as nucleosides and nucleotides
Nucleoside: A nucleoside contains only two basic components of nucleic acids
i.e. a pentose sugar and a nitrogenous base
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
15. What is essentially the difference between α-glucose of glucose and beta-
form of glucose? Explain
Answer:
In a-α-glucose, the OH group at C1 is towards right while in beta-D-glucose,
the OH group at C1 is towards left.
16. Describe what you understand by primary structure and secondary
structure of proteins
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.
17. Write the main structural difference between DNA and RNA. Of the four
bases, name those which are common to both DNA and RNA.
DNA RNA
1. The sugar present in DNA is 2-deoxy-(-)
1. The sugar present in RNA is D-(-) ribose.
ribose.
2. DNA contains cytosine and thymine as 2. RNA contains cytosine and uracil as
pyrimidine bases. pyrimidine bases.
3. DNA has double standard α-helix structure. 3. RNA has single stranded α-helix structure.
18. Write down the structures and names of the products formed when D-
glucose is treated with
(i) Hydroxylamine
(ii) Acetic anhydride
(i) D-glucose reacts with hydroxylamine to form oxime.
(ii) D-glucose reacts with acetic anhydride to give penta-acetate.
19. 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.
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
