NCERT Solutions for Chapter 11 Biotechnology:Principles And Processes

1. Can you list 10 recombinant proteins which are used in medical practice? Find out where they are used as therapeutics (use the internet).

Ans:

• Human insulin – Diabetes
• Human growth hormone – Dwarfism cure
• Blood clotting factor Y1H/IX – Haemophilia
• TPA (tissue plasminogen activator) – Heart attack/strokes
• PDGF (platelet derived growth factor) – Stimulates wound healing
• Interferon – Treatment of viral infection
• Interleukin – Enhances immune reaction
• Hepatitis B vaccine – Prevention of infectious disease
• Herpes Vaccine – Prevention of infectious disease
• DNase I – Treatment of cystic fibrosis

2. Make a chart (with diagrammatic representation) showing a restriction enzyme, the substrate DNA on which it acts, the site at which it cuts DNA and the product it produces.

Ans: Name of the Restriction enzyme – Bam HI.

The substrate DNA on which it acts – NCERT Solutions For Class 12 Biology Biotechnology Principles And Processes Q2

3. From what you have learnt, can you tell whether enzymes are bigger or DNA is bigger in molecular size? How did you know?

Ans: Both DNA (deoxyribonucleic acid) and enzymes are macromolecules. DNA is a polymer of deoxyribonucleotides and enzymes are proteins, hence these are polymers of amino acids. But DNA is bigger in molecular size as compared to proteins because the synthesis of proteins is regulated by a small segment of DNA, called genes, and also a large number of proteins can be synthesised by a DNA molecule.

4. What would be the molar concentration of human DNA in a human cell? Consult your teacher.

Ans: The molar concentration of DNA in a human cell is 2 mg/ml of cell extract.

5. Do eukaryotic cells have restriction endonucleases? Justify your answer.

Ans: No, eukaryotic cells do not have restriction endonucleases because DNA molecules of eukaryotes are heavily methylated. All the restriction endonucleases have been isolated from various strains of bacteria.

6. Besides better aeration and mixing properties, what other advantages do stirred tank bioreactors have over shake flasks?

Ans:

• Shake flasks are used for growing and mixing the desired materials on a small scale in the laboratory. A large-scale production of desired biotechnological products is done by using ‘bioreactors’. Besides better aeration and mixing properties, the bioreactors have the following advantages:
  • Small volumes of cultures are periodically withdrawn from the reactor for sampling.
  • It has a foam control system, pH control system, and temperature control system.
  • Facilitates even mixing and oxygen availability throughout the bioreactor.

7. Collect 5 examples of palindromic DNA sequences by consulting your teacher. Better try to create a palindromic sequence by following base-pair rules.

Ans: Palindrome nucleotide sequences in the DNA molecule are groups of bases that form the same sequence when read both forward and backward. Five examples of palindromic DNA sequences are as follows:

• 5′-—————GGATCC——————3’
  3′—————CCTAGG—————–5′
• 5’—————AAGCTT——————3′
  3′——————TTCGAA —————-5′
• 5′—————–ACGCGT—————–3′
  3′——————TGCGGA————– 5′
• 5′———- ACTAGT————3′
  3′——————TGATCA————5′
• 5′—————AGGCCT—————3′
  3′——————TCCGGA————–5′

8. Can you recall meiosis and indicate at what stage a recombinant DNA is made?

Ans: Recombinant DNA is formed due to crossing over between non-sister chromatids of homologous chromosomes. It occurs during the pachytene stage of prophase of meiosis I.

9. Can you think and answer how a reporter enzyme can be used to monitor transformation of host cells by foreign DNA in addition to a selectable marker?

Ans: A reporter enzyme can be used to differentiate transformed cells by tracking down the activity of its corresponding genes (receptor gene). For example, β-galactosidase (Lac Z) activity is not found in transformed cells, so they appear white in color. The others, which appear blue in color, indicate that cells do not carry foreign DNA.

10. Describe briefly the following:

(a) **Origin of replication**: This is a sequence from where replication starts, and any piece of DNA linked to this sequence can be made to replicate within the host cells. This sequence is also responsible for controlling the copy number of the linked DNA. So, if one wants to recover many copies of the target DNA, it should be cloned in a vector whose origin supports a high copy number.

(b) **Bioreactors**: Bioreactors are vessels in which raw materials are biologically converted into specific products by microbes, plant and animal cells, and/or their enzymes. The bioreactor provides optimum growth conditions and facilitates achieving the desired products. The most commonly used bioreactor is of the stirring type. A stirred tank bioreactor is usually a cylindrical vessel or a vessel with a curved base to facilitate mixing of the contents. In the sparged stirred tank bioreactor, sterile air bubbles are sparged. The stirrer facilitates the mixing and oxygen availability throughout the bioreactor. A bioreactor has an agitator system, an oxygen delivery system, a foam control system, a temperature control system, a pH control system, and sampling ports.

(c) **Downstream Processing**: The product obtained is subjected to a series of processes, collectively called downstream processing, before it is made into a finished product ready for marketing. The two main processes are separation and purification. The product is then formulated with suitable preservatives. Such formulations have to undergo clinical trials in the case of drugs.

11. Explain briefly:

(a) **PCR**: Polymerase chain reaction (PCR) is an in vitro method for enzymatically replicating DNA without using a living organism, such as E. coli or yeast. It involves three steps:

• Denaturation of the desired double-stranded DNA to single-stranded DNA (ssDNA).
• Annealing of primers to ssDNA.
• Extension of primers by Taq DNA polymerase, isolated from Thermus aquaticus.

Uses: Amplification of desired genes/gene cloning.
Advantages: More output, greater efficiency, less error-prone, less human interference, and cyclic automation.

(b) **Restriction enzymes and DNA**: Restriction enzymes are a group of enzymes used to cleave or cut DNA strands, each having a characteristic base sequence at which it cleaves. They restrict foreign DNA from entering the normal cell by digesting it at various recognition sites. These enzymes produce sticky ends, and the recognition sites are palindromic. Restriction enzymes are believed to be a mechanism evolved by bacteria to resist viral attack and to help in the removal of viral sequences.

(c) **Chitinase**: Chitinase is an enzyme that breaks down glycosidic bonds in the chitin cell wall of fungal cells to facilitate their transformation.