NCERT Solutions Class 12 Biology Chapter 9: Biotechnology Principles and Processes

Compared to DNA molecules, enzymes are smaller in size. We can say this as DNA comprises genetic material essential for the normal development and functioning of living entities. A DNA molecule consists of instructions required for the synthesis of DNA molecules and proteins. Whereas enzymes are the proteins that are synthesised from genes – a small fragment of DNA. These are crucial in the production of the polypeptide chain.

 

The molar concentration of human DNA in a human cell can be given as

6.023 x 1023 x Total number of chromosomes

6.023 x 1023 x 46

2.77 x 1023 moles

Therefore, 2.77 x 1023 moles is the molar concentration of DNA in each of the diploid cells in humans.

 

No, eukaryotic cells do not have restriction endonucleases, as the DNA of eukaryotes is highly methylated by methylase – a modification enzyme. This methylation safeguards the DNA from the action of restriction enzymes. In prokaryotic cells, these enzymes are present, which aid in preventing the invasion of DNA by viruses.

 

A process involving a reduction in the quantity of genetic material is termed Meiosis, which is a type of cell division. It occurs in two phases, namely meiosis I and meiosis II.

In the pachytene event of prophase I, chromosomes cross over, wherein the exchange of segments between non-sister chromatids of homologous chromosomes occurs. This leads to the formation of recombinant DNA in the process of meiosis.

 

The recombinant proteins used in medical practice are obtained from recombinant DNA technology. In this technology, particular genes are transferred from one organism to another with the help of vectors and restriction enzymes as molecular tools.

Listed below are 10 recombinant proteins.

 

Steps in the formation of recombinant DNA by the action of restriction endonuclease enzyme – EcoRI.

It can be diagrammatically represented as follows:

 

Stirred tank bioreactors are developed for the large-scale production of biotechnology products, whereas the shake flask method is applied for the small-scale production of biotechnological products carried out in a laboratory.

The stirred tank bioreactor has a few advantages over shake flasks. They are as follows:

(i) For the testing and sampling process, small amounts of culture can be drawn out from the reactor.

(ii) Presence of a control system to regulate the pH and temperature.

(iii) To regulate the foam, the stirred tank bioreactors have a foam breaker.

 

(a) PCR

In molecular biology, PCR, or polymerase chain reaction, is a technique to amplify a gene or a fragment of DNA in order to get multiple copies. It is widely used in the gene manipulation process. The phenomenon involves the in vitro synthesis of sequences with the help of a template strand, a primer and a thermostable DNA polymerase enzyme produced by a bacterium known as Thermus aquaticus. The enzyme uses the building blocks deoxynucleotides (dNTPs) in order to extend the primer.

The following are the three steps in PCR:

(i) Initially, the double-stranded DNA molecules are heated to a high temperature to separate the two strands into a single-stranded DNA molecule. This process is referred to as denaturation.

(ii) This DNA molecule is then used as a template strand to synthesise a new strand by the DNA polymerase enzyme. The process is termed annealing, which leads to the replication of the original DNA molecule, and the process is carried out for multiple cycles to obtain multiple copies of the rDNA fragment.

(iii) Primer is extended by Taq DNA polymerase isolated from Thermits aquatics.

(b) Restriction enzymes and DNA

In molecular biology, restriction enzymes are molecular scissors used to cut DNA sequences from a particular site. It has a critical role to play in the gene manipulation process. These enzymes identify a particular six-base pair sequence, referred to as the recognition sequence, and snip the sequence at specific sites. For instance, the recognition site for the ECORI enzyme is given below.

Restriction enzymes are grouped into two types:

(i) Endonuclease – iI is a type of restriction enzyme that cuts within the DNA at specific sites. It serves as a significant tool in genetic engineering. Typically, it is used to make a snip in the sequence to get DNA fragments possessing sticky ends. These ends are later fused by the enzyme DNA ligase.

(ii) Exonuclease – This type of restriction enzyme removes the nucleotides either from the 3’ or 5’ ends of the DNA molecule.

(c) Chitinase

It is a class of enzymes that are used for the degradation of chitin, which forms the main component of the cell wall of fungi. Hence, to isolate the DNA enveloped within the cell membrane of the fungus, the Chitinase enzyme is used to break the cell to release its genetic material.

 

A sequence of DNA that reads the same, whether read from 5’ -> 3’ or from 3’ -> 5’direction, is a palindromic sequence. These are the sites for the action of restriction enzymes. Almost all of the restriction enzymes are palindromic sequences.

Listed below are 5 examples of palindromic sequences, and they are

 

To monitor the transformation of host cells by foreign DNA, a reporter gene can be used. They serve as a selectable marker to find out if the host cell has used up the foreign DNA else the foreign gene is expressed in the cell. The reporter gene and the foreign gene are placed by scientists in the same DNA construct. This collective DNA construct is introduced into the cell, where the reporter gene is used as a selectable marker to discover the successful uptake of foreign genes or the genes of interest. In a jellyfish, the lac Z gene is an example of a reporter gene that encodes for a green fluorescent protein.

 

(a) Origin of replication

It can be defined as a DNA sequence in a genome where replication is initiated. The process of replication initiation can either be uni-directional or bi-directional. Any piece of DNA, when linked to this sequence, can be made to replicate within the host cells. The sequence is also responsible for controlling the copy of the number of the linked DNA. Hence, to recover many copies of target DNA, it should be cloned in a vector whose origin supports a high copy number.

(b) Bioreactor

They are large vessels that are used for the large-scale production of biotechnological products from raw resources. In order to obtain the required product, these bioreactors offer optimal conditions by supplying optimum pH, temperature, vitamin, oxygen, etc. They have an oxygen delivery system, a foam control system, and a temperature and pH control system. Also, they consist of a sampling port to withdraw a small quantity of culture for the purpose of sampling.

(c) Downstream processing

It is a method of separating and purifying foreign gene products once the biosynthetic stage is completed. Then, the product is exposed to different procedures to separate and purify the product. Once the process is completed, the product is formulated and made to undergo several clinical trials for quality checks and other related assessments.

 

The differences are as follows:

(a) Plasmid DNA and Chromosomal DNA

(b) RNA and DNA

(c) Exonuclease and Endonuclease