Test: Biotechnology: Principles & Processes - 1 - NEET MCQ

• Insertional inactivation is the inactivation of a gene upon insertion of another gene inside in its place or within its coding sequence.
• It help in identification of recombinant clones.

Topic in NCERT: Cloning sites

Line in NCERT: Selection of recombinants due to inactivation of antibiotics is a cumbersome procedure because it requires simultaneous plating on two plates having different antibiotics. Therefore, alternative selectable markers have been developed which differentiate recombinants from non-recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate. 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

• Having two antibiotic resistance genes in the same plasmid helps in identifying transformants.
• Transformants take up the plasmid and also integrate it into recombinant DNA.

Topic in NCERT: Cloning sites

Line in NCERT: 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 tetracycline containing medium. The transformants growing on ampicillin containing medium are then transferred on a medium containing tetracycline.

• In order to use the DNA for genetic engineering processes, it must be in pure form, free from other macromolecules.
• This is termed DNA isolation and is the pioneer step. Since the DNA is enclosed within the membranes, it is required to break open the cell to release DNA along with other macromolecules such as RNA, proteins, polysaccharides, lipids, etc. and from this mixture, DNA is purified.
• A release of DNA from a cell is achieved by treating the cells or tissues with enzymes such as lysozyme (bacteria), cellulose (plant cells), chitinase (fungus), etc.
• These enzymes degrade cell wall; plasma membrane degrading enzymes like lipase, etc., are also needed. Since yeast is a fungus and fungal cell wall is made of chitin (fungal cellulose), isolation of DNA necessarily requires the use of enzyme chitinase.

Line in NCERT: "chitinase (fungus)."

In agarose gel electrophoresis, the DNA fragments separate out (resolve) according to their size or length because of the sieving property of agarose gel. It means, the smaller the fragment size, the farther it will move.

Topic in NCERT: Separation and isolation of DNA fragments

Line in NCERT: "The DNA fragments separate (resolve) according to their size through sieving effect provided by the agarose gel."

Restriction enzymes are also called 'molecular scissors' as they cleave DNA at or near specific recognition sequences known as restriction sites. These enzymes make one incision on each of the two strands of DNA and are also called restriction endonucleases.

Line in NCERT: "Restriction enzymes belong to a larger class of enzymes called nucleases."

• Origin of replication is the specific DNA sequence on chromosome that which is responsible for initiating replication.
• Origin of replication is essential for replication of particular DNA segment.

Line in NCERT: "In a chromosome there is a specific DNA sequence called the origin of replication, which is responsible for initiating replication."

The groups of letters that form same words when read both forward and backward are called Palindrome. For example MALYALAM which read same from both side.

Topic in NCERT: Restriction Enzymes

Line in NCERT: "Do you know what palindromes are? These are groups of letters that form the same words when read both forward and backward, e.g., 'MALAYALAM'."

The Enzymes used to join foreign DNA to plasmid is ligases. The plasmid of bacteria replicate this DNA strands along with other which can be further transferred to target cells.

Topic in NCERT: Restriction Enzymes

Line in NCERT: "these can be joined together (end-to-end) using DNA ligases."

The separated DNA fragments can he visualised only after staining the DNA with a compound known as ethidium bromide followed by exposure to ultraviolet radiation (we cannot see pure DNA fragments in the visible light and without staining).

Line in NCERT: "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)."

EcoRI comes from Escherichia coli RY 13. In EcoRI, the letter ‘R’ is derived from the name of strain.

Topic in NCERT:  Restriction Enzymes

Line in NCERT: "In EcoRI, the letter 'R' is derived from the name of strain."

The separated DNA fragments can be visualized only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation. We can see bright orange coloured bands of DNA in aethidium bromide stained gel exposed to UV light.

Line in NCERT: "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 an ethidium bromide stained gel exposed to UV light."

• In gel electrophoresis, DNA molecules moves towards positively charged anode because DNA is negatively charged molecules.
• The molecules separate out due to difference in molecular weight.

Topic in NCERT: Separation and isolation of DNA fragments

Line in NCERT: "DNA is a negatively charged molecule, hence it moves towards the positive electrode (anode)"

• Rop genes in pBR322 codes for protein involved in replication of plasmid.
• Plasmid are able to take the foreign gene and to be transferred to target cells.

Topic in NCERT:Fig 9.4 caption

Line in NCERT: "rop codes for the proteins involved in the replication of the plasmid."

NCERT Line: 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.