Biotechnology Principles and Processes Test - 12

Restriction endonucleases acts as a knife for the DNA. A restriction enzyme (or restriction endonuclease) is an enzyme that cuts DNA at or near specific recognition nucleotide sequences known as restriction sites. Restriction enzymes are commonly classified into three types, which differ in their structure and whether they cut their DNA substrate at their recognition site, or if the recognition and cleavage sites are separate from one another. To cut DNA, all restriction enzymes make two incisions, once through each sugar-phosphate backbone (i.e. each strand) of the DNA double helix.

Biolistic gun or gene gun method initially developed to transfer the gene in plant cell directly. It is a method involving the transfer of genes to the plants without the use of any vectors (plasmid etc.). Thus, the correct answer is option A.

Restriction endonucleases recognize specific sequences in the DNA and cut the DNA into fragments. The specific sites are 4-6 bp long and are called as restriction sites. Each restriction endonuclease has a specific restriction site which allows the enzyme to be suitable to be used in the genetic engineering techniques. 

Palindromic sequences are the one which is read same forward and backward. The base sequence of one strand being read the same as its complementary strand when both are read in the 5' to 3' direction. Thus, the correct answer is option D.

Correct Option: D

1. Trichoderma harzianum is a bio fungicide and is used for suppression of various disease-causing fungal pathogens. Penicillium expansum, blue mold, causes postharvest decay of stored apples and produces the carcinogenic mycotoxin patulin.
2. Meloidogyne incognita, southern root-knot nematode" or the "cotton root-knot nematode", is a nematode with multiple hosts.
3. Agrobacterium tumefaciens is a soil-plant pathogenic bacterium that carries Ti plasmid. It can transfer a particular segment of the tumor-inducing (Ti) plasmid into the nucleus of infected cells.
4.  The transferred T-DNA is then integrated into the host genome and transcribed with it. 
5. This ability of Agrobacterium tumefaciens to transfer the T-DNA in host genome is explored in genetic engineering to transfer the desired DNA segment, carrying the gene of the interest, into genome of selected organisms. Option D is the correct answer. 

Manipulation of DNA reuires small DNA segments of an organism that constitute specific genes. There is a upper limit to the size of DNA segments that can be cloned in any of the available vectors. This poses a need of digestion of large DNA into fragments that can be inserted into the vector DNA. Restriction endonucleases recognize specific 4- to 8-bp sequences, called restriction sites and then cleave both DNA strands at this site. Restriction sites commonly are short palindromic sequences which are read same on each DNA strand in the 5'-->3' direction. This creates DNA fragments carrying desired genes with sticky ends that are then easily inserted in vector DNA by DNA ligase enzyme. Transcriptase enzyme catalyze the transcription of RNA molecules and, hence, are of no use in DNA manipulation. Primase enzymes forms small DNA/RNA segments that serve as primer for polymerase enzyme which can not sythesize the DNA/RNA de novo. 

Polymerase chain reaction (PCR) is the process in which the amplification of the gene of interest is carried out with two sets of primers and a thermostable DNA polymerase enzyme Taq polymerase. The process involves the following steps: 

• In 1997, the first transgenic cow, Rosie, produced human alpha-lactalbumin enriched milk at 2.4 grams per litre.
• This transgenic milk is a more nutritionally balanced product than natural bovine milk and could be given to babies or the elderly with special nutritional or digestive needs. 
• Restriction enzymes are DNA-cutting enzymes found in bacteria (and harvested from them for use). Because they cut within the molecule, they are often called restriction endonucleases.
• They are not used for isolation of DNA.
• Downstream processing refers to the recovery and purification of biosynthetic products, particularly pharmaceuticals, from natural sources such as animal or plant tissue or fermentation broth, including the recycling of salvageable components and the proper treatment and disposal of waste.
• Downstream processing is usually considered a specialized field in biochemical engineering. 
• Pathogens like the bacteriophage vectors are disarmed and allowed to infect the bacterial cells. They transfer the rDNA into the host.
  Hence, the correct option is D.
  

Electrophoresis is a technique used in the laboratories in order to separate macromolecules (DNA, RNA) based on size. The technique applies a negative charge so proteins move towards a positive charge. This is used for both DNA and RNA analysis.
So, the DNA fragments generated by restriction endonucleases in a chemical reaction can be separated by this process of gel electrophoresis.

So the correct answer is 'Electrophoresis'