IGCSE Biology Paper-4: Specimen Questions with Answers 139 - 140 of 279

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Passage

Cotton, Gossypium hirsutum, is grown for the fibers that form within the fruits after fertilization, as shown in Fig.

Fibers from the fruits of cotton plants are used in the textile industry.

The Fibres
  • Cotton plants have been genetically engineered to produce a protein that is toxic to the caterpillars of several insect pests. This gives the cotton plants resistance to the pests.
  • The cry gene for pest resistance was isolated from the bacterium Bacillus thuringiensis and inserted into the cells of cotton plants as shown in Fig.
Bacterial DNA

Question 139 (2 of 5 Based on Passage)

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Short Answer▾

An enzyme cuts the cry gene from the DNA of B. thuringiensis.

Explain how the DNA is inserted into the plasmid.

Explanation

In a typical DNA cloning procedure, the gene or other DNA fragment of interest is first inserted into a circular piece of DNA called a plasmid. The insertion is done using enzymes that “cut and paste” DNA i.e.. DNA ligase, and it produces a molecule of recombinant DNA, or DNA assembled out of fragments from multiple sources.

Molecule of Recombinant

Question 140 (3 of 5 Based on Passage)

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Short Answer▾

An enzyme cuts the cry gene from the DNA of B. thuringiensis.

State the name of the regions labelled A on Fig.

Explanation

Restriction enzymes cut the strand of DNA a little away from the center of the palindrome sites but between the same two bases of the opposite strands. This leaves single stranded unpaired bases at cut ends. These ends with unpaired bases are called sticky ends or cohesive ends. The latter are named so because they form hydrogen bonds with their complementary cut counter parts. The sticky ends facilitate the action of the enzyme DNA ligase.

Endonuclease and Sticky Ends

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