Biotechnology: Principles and Processes - MCQ Test
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Showing questions 21 - 40 of 40
21. In agarose gel electrophoresis, how do DNA fragments separate?
The DNA fragments separate (resolve) according to their size through sieving effect provided by the agarose gel. Hence, the smaller the fragment size, the farther it moves.
22. How are separated DNA fragments visualised in agarose gel electrophoresis?
The separated DNA fragments can be visualised only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation (you cannot see pure DNA fragments in the visible light and without staining). You can see bright orange coloured bands of DNA in a ethidium bromide stained gel exposed to UV light.
23. What is 'elution' in the context of DNA fragment separation?
The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece. This step is known as elution.
24. Which of the following features are required to facilitate cloning into a vector?
The following are the features that are required to facilitate cloning into a vector. (i) Origin of replication (ori)... (ii) Selectable marker... (iii) Cloning sites.
25. What is the function of a 'selectable marker' in a cloning vector?
In addition to ‘ori’, the vector requires a selectable marker, which helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants.
26. In the context of selectable markers, if a foreign DNA is ligated into the BamH I site of the tetracycline resistance gene in vector pBR322, what will be the result?
The ligation of alien DNA is carried out at a restriction site present in one of the two antibiotic resistance genes. For example, you can ligate a foreign DNA at the BamH I site of tetracycline resistance gene in the vector pBR322. The recombinant plasmids will lose tetracycline resistance due to insertion of foreign DNA but can still be selected out from non-recombinant ones by plating the transformants on ampicillin containing medium.
27. What is 'insertional inactivation' in the context of selectable markers?
In this, a recombinant DNA is inserted within the coding sequence of an enzyme, β-galactosidase. This results into inactivation of the gene for synthesis of this enzyme, which is referred to as insertional inactivation.
28. How are recombinant colonies identified using the β-galactosidase system with a chromogenic substrate?
The presence of a chromogenic substrate gives blue coloured colonies if the plasmid in the bacteria does not have an insert. Presence of insert results into insertional inactivation of the β-galactosidase gene and the colonies do not produce any colour, these are identified as recombinant colonies.
29. Which of the following is a naturally occurring plant pathogen that has been modified into a cloning vector for plants?
For example, Agrobacterium tumifaciens, a pathogen of several dicot plants is able to deliver a piece of DNA known as ‘T-DNA’ to transform normal plant cells into a tumor and direct these tumor cells to produce the chemicals required by the pathogen... The tumor inducing (Ti) plasmid of Agrobacterium tumifaciens has now been modified into a cloning vector which is no more pathogenic to the plants but is still able to use the mechanisms to deliver genes of our interest into a variety of plants.
30. To force bacteria to take up plasmid DNA, they must first be made 'competent'. This is typically achieved by treating them with:
This is done by treating them with a specific concentration of a divalent cation, such as calcium, which increases the efficiency with which DNA enters the bacterium through pores in its cell wall. Recombinant DNA can then be forced into such cells by incubating the cells with recombinant DNA on ice, followed by placing them briefly at 420C (heat shock), and then putting them back on ice.
31. Which of the following methods are used to introduce alien DNA into host cells?
In a method known as micro-injection, recombinant DNA is directly injected into the nucleus of an animal cell. In another method, suitable for plants, cells are bombarded with high velocity micro-particles of gold or tungsten coated with DNA in a method known as biolistics or gene gun. And the last method uses ‘disarmed pathogen’ vectors, which when allowed to infect the cell, transfer the recombinant DNA into the host.
32. Which enzyme is used to break open bacterial cells during the isolation of genetic material (DNA)?
This can be achieved by treating the bacterial cells/plant or animal tissue with enzymes such as lysozyme (bacteria), cellulase (plant cells), chitinase (fungus).
33. After treating cells with appropriate enzymes to release DNA, how are RNA and proteins removed during DNA isolation?
The RNA can be removed by treatment with ribonuclease whereas proteins can be removed by treatment with protease.
34. What is the final step to precipitate purified DNA out of the suspension during isolation?
Purified DNA ultimately precipitates out after the addition of chilled ethanol. This can be seen as collection of fine threads in the suspension.
35. What does PCR stand for, and what is its primary purpose in biotechnology?
PCR stands for Polymerase Chain Reaction. In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro.
36. Which enzyme is crucial for PCR and is known for its thermostability, isolated from a bacterium called Thermus aquaticus?
Such repeated amplification is achieved by the use of a thermostable DNA polymerase (isolated from a bacterium, Thermus aquaticus), which remain active during the high temperature induced denaturation of double stranded DNA.
37. The ultimate aim in almost all recombinant technologies, after cloning the gene of interest, is to produce a desirable:
In almost all recombinant technologies, the ultimate aim is to produce a desirable protein. Hence, there is a need for the recombinant DNA to be expressed.
38. What are bioreactors, and what is their typical volume capacity?
To produce in large quantities, the development of bioreactors, where large volumes (100-1000 litres) of culture can be processed, was required. Thus, bioreactors can be thought of as vessels in which raw materials are biologically converted into specific products, individual enzymes, etc., using microbial plant, animal or human cells.
39. Which of the following are components of a typical stirred-tank bioreactor?
If you look at the figure closely you will see that the bioreactor has an agitator system, an oxygen delivery system and a foam control system, a temperature control system, pH control system and sampling ports so that small volumes of the culture can be withdrawn periodically.
40. What processes are collectively referred to as 'downstream processing'?
After completion of the biosynthetic stage, the product has to be subjected through a series of processes before it is ready for marketing as a finished product. The processes include separation and purification, which are collectively referred to as downstream processing. The product has to be formulated with suitable preservatives. Such formulation has to undergo thorough clinical trials as in case of drugs. Strict quality control testing for each product is also required.