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|Chapter 11:||Biotechnology: Principles and Processes|
NCERT Solutions for class 12 Biology Chapter 11
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Principles of Biotechnology
- Genetic Engineering: The techniques used to alter the chemistry of genetic material (DNA/RNA) and introduction of it into organisms to change its phenotype.
- Chemical Engineering: Use of contamination free chemical engineering process of growth of desired microbe or cell in large quantity to obtain biotechnological product like enzyme, antibiotic, vaccine etc.
- Cloning Vectors: A small, self-replicating DNA molecule into which foreign DNA is inserted. It replicates inside the host cell. The vectors that may be used in genetic engineering are plasmids, bacteriophages, animal, plant, virus, YACs and BACs and some yeasts.
- Plasmid: Extra chromosomal, self-replicating circular DNA molecule found in certain bacteria and in some yeasts. It has a few genes. Plasmids are used as cloning vectors in genetic engineering. Plasmids were discovered by William Hays and Joshua Leduberg in 1952. The most widely used vector in cloning is pBR322.
- Ti Plasmid: It is an extrachromosomal, double stranded and self-replicating DNA molecule found in Agra bacteriumtumifaciens. If causes tumour in plants.
But now Ti Plasmid has been modified into a cloning vector by which desired genes can be delivered into many plants.
- Features of cloning vector: Origin of replication (Ori) selectable marker and cloning sites are the features that are required to facilitate cloning into a vector.
- Origin of Replication (Ori): This is a sequence from where replication starts and any piece of DNA when 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.
- Cloning Sites: A location on a cloning vector into where a foreign gene can be introduced is called recognition site. The vector must have very few (preferably single) recognition sites. The presence of more than one recognition sites within the vector will produce several fragments which will make the process of gene cloning more complicated. Therefore, the foreign DNA is ligated at a restriction site present in one of the two antibiotic resistance gene.
- Selectable Marker: It is a gene which helps in identifying and eliminating non-trans formants from trans formants (having recombinant DNA) by selectively permitting the growth of trans formants. The process through which as piece of DNA is introduced in a host bacterium is called transformation. The genes encoding resistance to antibiotics are considered useful selectable marker for E coli.
- Small Size of Vector: This facilitates the introduction of DNA into the host easily.
From what you have learnt, can you tell whether enzymes are bigger or DNA is bigger in molecular size? How did you know?
What would be the molar concentration of human DNA in a human cell?
⇒ Total number of chromosomes × 6.023 × 10^23
⇒ 46 × 6.023 × 10^23
⇒ 2.77 × 10^23 moles
Hence, the molar concentration of DNA in each diploid cell in humans is 2.77 × 10^23 moles.
Do eukaryotic cells have restriction endonucleases? Justify your answer.
Besides better aeration and mixing properties, what other advantages do stirred tank bioreactors have over shake flasks?
Stirred tank bioreactors have several advantages over shake flasks. Some of them are
Small volumes of culture can be taken out from the reactor for sampling or testing.
It has a foam breaker for regulating the foam.
It has a control system that regulates the temperature and pH.
Can you recall meiosis and indicate at what stage a recombinant DNA is made?
During the pachytene stage of prophase I, crossing over of chromosomes takes place where the exchange of segments between non-sister chromatids of homologous chromosomes takes place. This results in the formation of recombinant DNA.
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?
The researchers place the reporter gene and the foreign gene in the same DNA construct. Then, this combined DNA construct is inserted in the cell. Here, the reporter gene is used as a selectable marker to find out the successful uptake of genes of interest (foreign genes). An example of reporter genes includes lac Z gene, which encodes a green fluorescent protein in a jelly fish. The others, which appear blue in colour, indicate that cells do not carry foreign DNA.