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Biotechnology : Principles and Processes

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Class 10 Class 12
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Besides better aeration and mixing properties, what other advantages do stirred tank bioreactors have over shake flasks ?

Stirred tank bioreactors provide advantage over shake flasks . besides aeration and mixing properties Stirred tank bioreactors are useful in a number of ways

(i) They provide optimum growth conditions (temperature, pH, substrate, salts, vitamins, oxygen) to achieve the desired product.

(ii) They are cost effective .

(iii) Due to baffles, oxygen transfer rate is very high

(iv) Capacity of stirred tank is more as compared to shake flasks.


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

Humans have 3 M of DNA per cell where M stands for molarity

Do eukaryotic cells have restriction endonucleases ? Justify your answer.

No, eukaryotic cells do not have restriction endonucleases. This is because the DNA of eukaryotes is highly methylated by a modification enzyme, called methylase. Methylation protects the DNA from the activity of restriction enzymes .These enzymes are present in prokaryotic cells where they help prevent the invasion of DNA by virus.

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

DNA molecules are bigger in size as compared to enzymes. Enzymes are proteins which are  synthesized from a small portion of DNA called genes therefore they are smaller than DNA molecules.

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.

 Action of restriction enzyme

 Action of restriction enzyme
â–² Fig. 7.3. EcoR

â–² Fig. 7.3. EcoRI cuts the DNA between bases G and A only when the sequence GAATTC is present in the DNA.