Chapter 9 – Biomolecules Questions and Answers: NCERT Solutions for Class 11 Biology

1. What are macromolecules? Give examples.

Solution:
Macromolecules are the biomolecules that are formed by the polymerization of a huge number of micromolecules possessing higher molecular weight. Micromolecules are found in the colloidal state in the intercellular fluid due to their insoluble nature. Protein is a macromolecule.

2. Illustrate a glycosidic, peptide and a phospho-diester bond.

Solution:
Glycosidic bond – The bond between the individual monosaccharides is called a glycosidic linkage. This bond is formed between two carbon atoms of two adjacent monosaccharide units.

Peptide bond – It is a covalent bond. The amino acids in proteins are linked to one another through peptide bonds. It is formed between when the carboxyl group (-COOH) of one amino acid interacts with amino group (-NH2 ) of the adjacent amino acid when condensed.
Formation of Peptide bond – Example

Phospho-diester bond – that joins successive sugar molecules in a polynucleotide. It is a strong covalent bond formed between two adjacent sugar groups and phosphate. These are the bonds that form the sugar-phosphate backbone of the nucleic acids

3. What is meant by tertiary structure of proteins?

Solution:
It is a structure that forms when the secondary coiled polypeptides are folded to produce a hollow, wollen ball-like structure. It is folded such that the functional side groups appear on the surface while the inactive side groups are found inside.

4. Find and write down structures of 10 interesting small molecular weight biomolecules. Find if there is any industry which manufactures the compounds by isolation. Find out who are the buyers.

Solution:

Compound
Manufacturer
Buyer
Starch
Premier starch products private limited
Research institutes and laundries
Liquid Glucose
Imperial liquid glucose
Used in making flavored drink and in research
Enzymes like amylase, protease, and cellulase
Planet Biotech India
Used in research

5. Proteins have primary structure. If you are given a method to know which amino acid is at either of the two termini (ends) of a protein, can you connect this information to purity or homogeneity of a protein?

Solution:
Positional information of a protein is called the primary structure of the protein. The first amino acid in a protein is called N-terminal amino acid, and the last amino acid in a protein is called the C-terminal amino acid.
Yes, we can connect this information to check the purity or homogeneity of a protein. On the basis of carboxyl and amino groups, amino acids can be acidic, basic and neutral. Proteins can be acidic, basic and neutral.

6. Find out and make a list of proteins used as therapeutic agents. Find other applications of proteins (e.g., Cosmetics etc.)

Solution:
Following are the list of proteins used as therapeutic agents.
Insulin, Oxytocin, Immunoglobin, Antidiuretic Hormone( ADH), Thrombin, Fibrinogen, Renin and streptokinases.
Some other applications are:
Are used as artificial sweeteners. Thaumatin is a low-calorie sweetener.
Proteins are used as dietary supplements to maintain health
They are used in creams and shampoos

7. Explain the composition of triglyceride.

Solution:
When glycerol combines with three fatty acids on each of the OH groups through ester bonds, it is known as triglyceride.

All the three fatty acids of triglyceride in pure fat are similar while in mixed fat, they are dissimilar.

8. Can you describe what happens when milk is converted into curd or yoghurt, from your understanding of proteins

Solution:
During fermentation, milk protein such as casein is denatured which transforms globular proteins into fibrous proteins. This change is responsible for the production of curd or yoghurt.

9. Can you attempt building models of biomolecules using commercially available atomic models (Ball and Stick models).

Solution:
Yes, Biomolecules can be represented by ball and stick model. Here bonds which hold the molecule are
indicated by sticks while the atoms are represented by balls.
The figure below is a model of D-glucose where atoms of hydrogen are indicated by green balls, oxygen atoms are represented by pink balls and carbon atoms are represented by grey balls.

10. Attempt titrating an amino acid against a weak base and discover the number of dissociating
(ionizable) functional groups in the amino acid.

Solution:
The pH of the amino acid is recorded, and the weak base is slowly supplemented to the amino acids while continuously noting the pH. The number of changes recorded indicates the number of ionisable functional groups –COOH in the acidic range and –NH2in the alkaline range.

11. Draw the structure of the amino acid, alanine.

Solution:
The structure of Alanine is as follows:

12. What are gums made of? Is Fevicol different?

Solution:
Gums are heteropolysaccharides formed by different monosaccharide units associated by glycosidic bonds. On
the other hand, fevicol is different from gums as it is made up of synthetic polymers.

13. Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juice, saliva, sweat and urine for them.

Solution:
Qualitative test for proteins
Biuret test: Biuret test identifies the presence of proteins by turning the colour of the solution to light blue to purple.
Qualitative test for fats and oils
Grease test for oils: Certain oils give a translucent stain on blue paper. This test can be used to detect the presence of oils and fats.
Qualitative test for amino acids
Ninhydrin test:
Upon adding ninhydrin reagent to the solution, colour of the solution turns to pink, purple or blue based on the type of amino acid.
Test
Name of item
Procedure
Result
Conclusion
Biuret’s test
Fruit juice
Juice + biuret’s reagent
Change of color from light blue to purple
Presence of protein

Saliva
Saliva + biuret’s reagent
Change of color from light blue to purple
Presence of protein

Sweat
Sweat + biuret’s reagent
Colour does not change
Absence of protein

Urine
Drops of urine + biuret’s reagent
Change of color from light blue to purple
Presence of protein
Grease test
Fruit juice
Few drops of juice on brown paper
Translucent spot not observed
Absence of oils and fats

Saliva
Few drops of saliva on brown paper
Translucent spot not observed
Absence of oils and fats
Solubility test
Sweat
Water added with sweat
Oil presence
Fats or oils can be present

Urine
Water added to a few drops of urine
Slight oily presence
Fats may or may not be present
Ninhydrin test
Fruit juice
Juice+ninhydrin reagent (boil for few minutes)
Change of color from no color to purple, pink or blue
Presence of amino acids

Saliva
saliva+ninhydrin reagent (boil for few minutes)
Change of color from no color to purple, pink or blue
Presence of amino acids

Sweat
sweat+ninhydrin reagent (boil for few minutes)
No color change
Absence of amino acids

Urine
urine+ninhydrin reagent (boil for few minutes)
Depending upon type of amino acid, colourless solution changes to purple, pink or blue color
Presence of amino acids

14. Find out how much cellulose is made by all the plants in the biosphere and compare it with how much of paper is manufactured by man and hence what is the consumption of plant material by man annually. What a loss of vegetation!

Solution:
Biosphere produces about 100 billion tonnes of cellulose out of 170 billion tonnes of total organic matter. Production of paper consumes about 0.5 billion tonnes of wood. Trees are also utilized for other purposes including food, medicines, timber, spices etc. An approximate estimate of 1.5 billion tonnes of food is required. Wood requirement for various purposes includes 2 billion tonnes. Therefore, it is difficult to gauge the annual consumption of plant material by man. Thus, the use of cellulose led to a great loss to the vegetation.

15. Describe the important properties of enzymes.

Solution:
Almost all the enzymes are proteins. Important properties of enzymes are as follows:
They have a higher molecular weight and are complex macromolecules
They catalyse the biochemical reactions involved in the cell, assisting in breaking down larger molecules into simpler molecules or getting together two smaller molecules to form a larger one
Enzymes do not initiate but accelerate a reaction
They affect the rate of biochemical reaction and do not influence the direction of the reaction
They are action-specific
Higher turnover of enzymes causes an increase in the efficiency of a reaction. Most of the enzymes have high turnover number.
Enzymes are affected by temperature. As the temperature increases, enzymatic activity decreases. Maximum activity is observed at 30-40 degree Celsius.
Maximum activity is observed at 6-8 pH level
With an increase in substrate concentration, the enzymatic velocity also increases reaching maximum velocity