Biotechnology Past Papers

Concept:

Viral tissue tropism determines host cell specificity based on surface receptor interactions.

Solution:

Viruses engineered for human gene therapy targeting human blood cells (such as hematopoietic stem cells or lymphocytes) belong to the category of modified mammalian/animal viruses (e.g., retroviruses, lentiviruses, adenoviruses).

Why other options are incorrect:

• Algal virus: Algal viruses specifically infect photosynthetic eukaryotic algae and cannot infect human target tissues.



• Fungal virus: Mycoviruses infect fungal organisms exclusively and do not possess tropism for human blood cells.



• Bacterial virus: Bacteriophages specifically infect bacterial cells and cannot naturally infect human somatic cells.

Concept:

Clonal expansion and specificity of monoclonal antibody synthesis.

Solution:

Monoclonal antibodies are identical immunoglobulins produced by a single clone of B-lymphocytes or hybridoma cells. Because they originate from genetically identical parent cells, they possess identical antigen-binding specificity and structure.

Why other options are incorrect:

• Therapeutic proteins: Broad medical classification including recombinant hormones, clotting factors, and enzymes, not limited to single immune cell clones.



• Immunoglobulins: Broad umbrella term for all antibody molecules, including polyclonal mixtures secreted by diverse plasma cell lineages.



• Recombinant proteins: Any protein expressed from recombinant DNA technology in host expression systems.

Concept:

Cellular totipotency in plant tissue culture experiments.

Solution:

In 1958, F.C. Steward demonstrated cellular totipotency by culturing isolated phloem explants from wild carrot roots (Daucus carota) in coconut milk medium, successfully regenerating fully functional mature carrot plants.

Why other options are incorrect:

• Radish: Not used in Steward's landmark 1958 plant cellular totipotency tissue culture studies.



• Corn: Monocotyledonous plant model not utilized in Steward's original phloem explant experiments.



• Maize: Maize was not the experimental plant model used to demonstrate complete cell totipotency in 1958.

Concept:

Electrophoretic mobility of charged biological macromolecules.

Solution:

Gel electrophoresis separates biomolecules (DNA, RNA, proteins) based on size and charge as an applied external electric field forces negatively charged molecules (such as polyanionic DNA) to migrate toward the positive anode.

Why other options are incorrect:

• By diffusion: Passive random molecular movement down concentration gradients does not achieve directional separation.



• Active transport: ATP-dependent cellular transport mechanisms are absent in inanimate agarose/polyacrylamide gel matrices.



• Under the influence of agar: The porous gel matrix acts as a molecular sieve; it does not supply the driving force for migration.

Concept:

Milestones of the Human Genome Project (HGP).

Solution:

Human chromosome 22 was the first human chromosome to be fully sequenced, with its final sequence published in December 1999.

Why other options are incorrect:

• 1990: The year the Human Genome Project was officially launched internationally.



• 2003: The year the complete draft of the entire human genome was officially announced.



• 2005: Subsequent milestone year for other individual chromosome completions (e.g., Chromosome X).