More practice questions

4. Q4. Diagrammatically represent the experimental steps in cloning and expressing a human gene (say the gene for growth hormone) into a bacterium like E. coli. (NCERT Exercise 9, page 187.)

   Show answerHide answer

   The steps, each leading to the next, follow recombinant DNA technology (NCERT Section 9.3):

   1. Isolate the human growth hormone gene. Use a copy without introns (a cDNA, as NCERT’s ADA therapy did, page 182), because removing introns by splicing is a process of eukaryotes (reasoned from NCERT Section 5.5).
   2. Cut the gene and a plasmid vector such as pBR322 with the same restriction enzyme, so that their sticky ends match.
   3. Join them with DNA ligase: recombinant DNA.
   4. Make E. coli cells competent with calcium, and put the recombinant DNA in by a heat shock (ice, 42 °C, ice).
   5. Pick out the transformants on an antibiotic plate, and the recombinants by insertional inactivation.
   6. Grow the recombinant bacteria in a bioreactor, where the gene is expressed and the hormone is made.
   7. Downstream processing: separate and purify the hormone, formulate it, and test it.

5. Q5. Does our blood have proteases and nucleases? (NCERT Exercise 12, page 187.)

   Show answerHide answer

   Yes. Blood clotting depends on the enzyme thrombin, which converts the plasma protein fibrinogen into fibrin (NCERT Class 11 Biology, Chapter 15). Beyond the NCERT text: thrombin is a protease, an enzyme that cuts proteins (Wikipedia, “Thrombin”, facts in our words), and blood also carries nucleases, for example the DNA-cutting enzyme DNase I (Wikipedia, “Deoxyribonuclease I”, facts in our words).

6. Q6. Consult the internet and find out how to make an orally active protein pharmaceutical. What is the major problem to be encountered? (NCERT Exercise 13, page 187.)

   Show answerHide answer

   The major problem is digestion: a protein taken by mouth is broken down by the protein-digesting enzymes of the gut before it can act, which is why insulin is not given orally (reasoned from NCERT page 181). An orally active protein medicine therefore has to be shielded from the gut’s protein-digesting enzymes until it is absorbed, and must still cross the gut wall into the blood intact (reasoned from this chapter).

7. Q7. What was the main challenge in making human insulin by rDNA techniques, and how was it met?

   Show answerHide answer

   Getting insulin assembled into its mature form. Eli Lilly (1983) made the A and B chains separately in E. coli from two DNA sequences put into plasmids, then extracted the chains and joined them by disulphide bonds into human insulin (NCERT page 182).

8. Q8. How can ELISA show that a person is infected?

   Show answerHide answer

   ELISA works by antigen-antibody interaction: it detects either the pathogen’s antigens (proteins, glycoproteins and so on) or the antibodies the body has made against the pathogen (NCERT page 183).