Biology Class 11 NCERT Solutions: Chapter 9 Biomolecules Part 3 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q: 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?


Yes, if we are given a method to know the sequence of proteins, we can connect this information to the purity of a protein. It is known that an accurate sequence of a certain amino acid is very important for the functioning of a protein. If there is any change in the sequence, it would alter its structure, thereby altering the function. If we are provided with a method to know the sequence of an unknown protein, then using this information, we can determine its structure and compare it with any of the known correct protein sequence. Any change in the sequence can be linked to the purity or homogeneity of a protein.

For example, any one change in the sequence of haemoglobin can alter the normal haemoglobin structure to an abnormal structure that can cause sickle cell Anaemia.

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


Proteins used as therapeutic agents are as follows:

1. Thrombin and fibrinogen - They help in blood clotting.

2. Antigen (antibody) - It helps in blood transfusion.

3. Insulin - It helps in maintaining blood glucose level in the body.

4. Renin - It helps in osmoregulation.

Proteins are also commonly used in the manufacture of cosmetics, toxins, and as biological buffers.

Q. 7 Explain the composition of triglyceride.


Triglyceride is a glyceride, which is formed from a single molecule of glycerol, esterified with three fatty acids. It is mainly present in vegetable oils and animal fat.

Q_7_Structure of Triglyceride

The general chemical formula of triglyceride is , where , and are fatty acids these three fatty acids can be same or different.

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


Proteins are macromolecules formed by the polymerization of amino acids. Structurally, proteins are divided into four levels.

(A) Primary structure - It is the linear sequence of amino acids in a polypeptide chain.

(B) Secondary structure - The polypeptide chain is coiled to form a three-dimensional structure.

(C) Tertiary structure - The helical polypeptide chain is further coiled and folded to form a complex structure.

(D) Quaternary structure - More than one polypeptide chains assemble to form the quaternary structure.

Milk has many globular proteins. When milk is converted into curd or yoghurt, these complex proteins get denatured, thus converting globular proteins into fibrous proteins. Therefore, by the process of denaturation, the secondary and tertiary structures of proteins are destroyed.

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


Ball and stick models are molecular models that can be used to describe the structure of biomolecules.

In ball and stick model, the atoms are represented as balls whereas the bonds that hold the atoms are represented by the sticks. Double and triple bonds are represented by springs that form curved connections between the balls. The size and colour of various atoms are different and are depicted by the relative size of the balls.

It is the most fundamental and common model of representing biomolecular structures.

Ball and Stick Model

In the above ball and stick model of D-glucose, the oxygen atoms are represented by red balls, hydrogen atoms by blue balls, while carbon atoms are represented by grey balls.

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


Titrating a neutral or basic amino acid against a weak base will dissociate only one functional group, whereas titration between acidic amino acid and a weak acid will dissociate two or more functional groups.

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


Structure of alanine

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