Question

Student to attempt either option (A) or (B):
(A) Give an account of the generalised structure of an antibody molecule produced by B-lymphocytes in response to the pathogen. 
OR 
(B) Other than public awareness and counselling, enlist four measures taken up by NACO, WHO and other NGOs to prevent the spread of HIV infection in the society.

Hint:

Antibodies are specific to antigens and made of two heavy and two light chains. HIV prevention includes awareness, safe sex, safe blood, and ART programs.

Answer 1

(A) Step 1: An antibody is a Y-shaped glycoprotein made by B-lymphocytes in response to an antigen.
Step 2: Structure of an antibody molecule:

• Composed of four polypeptide chains — two identical light (L) chains and two identical heavy (H) chains.
• Chains are held together by disulfide bonds.
• Each chain has a variable region and a constant region.
• The variable region forms the antigen-binding site — specific to each antigen.
• The constant region determines the antibody class (IgA, IgG, etc.).

Step 3: The specificity of the antibody is due to the antigen-binding sites present on the variable regions of the light and heavy chains. 
OR 
(B) Step 1: Public awareness and counselling are essential to prevent HIV spread. In addition to these, the following measures are taken:

• Ensuring safe blood transfusion by proper screening.
• Use of disposable syringes and needles.
• Promoting safe sex practices (e.g., use of condoms).
• Providing antiretroviral therapy (ART) to infected individuals.

Step 2: Organizations like NACO and WHO also promote voluntary testing and confidentiality to reduce stigma and improve early diagnosis.