Q4. Describe briefly (a) bioreactors and (b) downstream processing. (NCERT Exercise 10 (b), (c), page 176.)
(a) Vessels in which raw materials are biologically converted into specific products, using microbial, plant, animal or human cells, in large volumes (100–1000 litres) under optimal conditions of temperature, pH, substrate, salts, vitamins and oxygen; the commonest are stirred-tank types (NCERT page 174). (b) The separation and purification of the product after the biosynthetic stage, followed by formulation with suitable preservatives, thorough clinical trials as for drugs and strict quality control testing (NCERT pages 174–175).
Q5. How can RNA be told apart from DNA? (NCERT Exercise 12 (b), page 176.)
In RNA every nucleotide has an extra –OH group at the 2′ position of the ribose, and RNA has uracil in place of thymine (NCERT Section 5.1, page 81). In DNA isolation, RNA is removed with the enzyme ribonuclease, which does not act on DNA (NCERT page 171).
Q6. What would be the molar concentration of human DNA in a human cell? (NCERT Exercise 4, page 175; an estimate.)
A diploid human nucleus before replication holds 46 DNA molecules (one per chromosome; mitochondrial DNA ignored) with 2 × 3.3 × 10 = 6.6 × 10 bp (NCERT Section 5.1, page 80, gives 3.3 × 10 bp for the haploid content). The DNA lies in the nucleus, so take its volume; assume, for this estimate only, a nucleus 6 µm across (NCERT Section 5.1, page 83, gives a typical nucleus only as approximately 10 m, an order of magnitude): volume = 4/3 × π × (3 × 10 m) ≈ 1.13 × 10 m = 1.13 × 10 L. Moles of DNA molecules = 46 ÷ (6.022 × 10, the Avogadro constant) ≈ 7.6 × 10 mol, so the concentration in the nucleus is about 7.6 × 10 ÷ 1.13 × 10 ≈ 6.8 × 10 M, under 1 nanomolar. Counted as base pairs, 6.6 × 10 ÷ (6.022 × 10) ≈ 1.1 × 10 mol in the same volume, about 0.1 M. Averaged over the whole, larger cell, both values are lower (our arithmetic; the sizes are assumptions).
Q7. Can you list recombinant proteins used in medical practice? (NCERT Exercise 1, page 175, asks for 10 and suggests an internet search.)
From NCERT’s own chapters: genetically engineered human insulin, for diabetes (NCERT Section 10.2.1, page 181); α-1-antitrypsin, made by transgenic animals, used to treat emphysema (NCERT Section 10.3, page 184); the hepatitis B vaccine, produced from yeast, for immunisation (NCERT Section 7.2.4, page 136); and streptokinase, modified by genetic engineering, a clot buster for patients who have had a myocardial infarction (NCERT Section 8.2, page 153). NCERT notes that about 30 recombinant therapeutics have been approved for human use worldwide (page 181); the rest of the ten is the internet search the Exercise asks for.
Q8. Why does a culture need large-scale production of a recombinant protein?
Small volume cultures cannot yield appreciable quantities of products, so bioreactors processing 100–1000 litres of culture were developed (NCERT page 174).