Question

(a) (i) Why should a cell be made competent to take up an alien DNA? How can a bacterial cell be made competent using calcium ions? Explain.
(ii) (1) State the importance of gel electrophoresis in biotechnology.
(2) Explain the principle on which this technique works.
(3) Mention why ethidium bromide is used in this technique.
OR
(b) (i) How was Bt cotton, the genetically modified crop, has greatly helped the cotton farmers to increase their crop yield?
(ii) Describe the mechanism that leads to the death of bollworms feeding on Bt cotton plants.

Hint:

(a) (i) Competent cells are crucial in biotechnology to introduce plasmids or foreign DNA for genetic manipulation.
(ii) Gel electrophoresis is a fundamental technique for DNA analysis, with ethidium bromide aiding in DNA visualization.
(b) (i) Bt cotton is an example of genetic engineering used in agriculture to combat pests without using excessive chemical pesticides.

Answer 1

(a) (i) - Why should a cell be made competent? A cell needs to be made competent to allow the uptake of foreign DNA into its cytoplasm during genetic transformation.
- Competence using calcium ions:
-- Bacterial cells are treated with a solution of calcium chloride (CaCl2).
-- Calcium ions create pores in the bacterial cell wall, allowing DNA to enter.
-- A heat-shock step (at 42°C) further facilitates DNA uptake by the bacterial cells.
(ii) (1) Gel electrophoresis is used to separate DNA fragments based on their size, allowing analysis, purification, or further genetic manipulations.
(2) - DNA fragments are negatively charged due to their phosphate backbone.
- When an electric current is applied, DNA fragments move towards the positive electrode.
- Smaller fragments move faster, while larger fragments move slower through the gel matrix.
(3) Ethidium bromide is an intercalating dye that binds to DNA, fluorescing under UV light, which helps visualize DNA bands.
OR
(b) (i) Bt cotton was genetically modified by introducing a gene from the bacterium Bacillus thuringiensis (Bt). The Bt gene produces a protein toxic to bollworms but safe for other organisms. When expressed in cotton plants, this protein provides resistance to bollworms.
(ii) 1. Bollworms ingest the Bt toxin while feeding on cotton plants.
2. In the insect’s alkaline gut, the toxin is activated and binds to specific receptors in the gut lining.
3. This binding creates pores in the gut wall, leading to leakage of gut contents and eventual death of the insect.