State how Agrobacterium tumifaciens has been made a useful cloning vector to transfer DNA to plant cells.


Agrobacterium is a pathogen that affects several dicots and delivers a piece of DNA known as ‘T-DNA’ to transform normal cells to tumor cells. This potential of Agrobacterium has been used to transfer desired gene into the plant. The desired gene is inserted in the T-DNA region and the bacterium is allowed to infect the plant. In this way, the desired changes are made in the plant.

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What triggers activation of protoxin to active Bt toxin of Bacillus thuringiensis in boll worm?

  • Moist surface of midgut

  • Alkaline pH of gut

  • Acidic pH of stomach

  • Body temperature


B.

Alkaline pH of gut

Bacillus thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein. These protein exist as inactive protoxins but once an insect ingest the inactive toxin, it is converted into an active form of toxin due to alkaline pH of the gut which solubilize the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and eventually cause death of insect.


Which of the following is true for Golden rice?

  • It is pest resistant, with a gene from Bacillus thuringiensis

  • It is drought tolerant, developed using Agrobacterium vector

  • It has yellow grains, because of a gene introduced from a primitive variety of rice

  • It is Vitamin A enriched, with a gene from daffodil


D.

It is Vitamin A enriched, with a gene from daffodil

Golden rice is vitamin A enriched rice, with a gene from daffodil and is rich in carotene.


How are 'sticky ends' formed on a DNA strand? Why are they so called?


Sticky ends are produced by restriction enzymes. These enzymes cut the strand of DNA a little away from the centre of the palindrome sites but between the same two bases on the opposite strands. This leaves single-stranded portions at the ends. These overhanging stretches are called 'sticky ends'. 

These are called sticky ends because they form hydrogen bonds with their complementary cut counterparts. This stickiness of the ends facilitates the action of the enzyme DNA ligase.
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Mention the type of host cells suitable for the gene guns to introduce an alien DNA.


Plant cells are considered suitable for the gene guns to introduce an alien DNA.

 

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