DNA probes and gel electrophoresis

Question 1

The scientists used a radioactively labelled DNA probe to show that the
cells of tobacco plant leaves contained the SUT1 gene.
Describe how they would do this.

Answer 1

• use restriction endonuclease to isolate gene
• treat dNa sample, heating it so becomes single stranded
• add DNA probes which are complementary to DNA sequence of gene which bind to gene
  -put X ray film

Question 2

Suggest how the production of ‘antisense’ SUT1 mRNA in type A plants
would reduce the expression of the SUT1 gene.

Answer 2

• antisense mRNA has complimentary base sequence to SUT1 base sequences
• so antisense binds to SUT1 mRNA
• prevents ribosome from binding
• so mRNA cannot be translated

Question 3

what is a DNA probe

Answer 3

• short single strand of DNA
  -complimentary to sequence of DNA

Question 4

Describe how the DNA is broken down into smaller fragments.

Answer 4

-restriction endonuclease cuts DNA at specific recognitions sites.

( VNTRS are only used for gel electrophoresis which s not asked in the question)

Question 5

The DNA on the nylon membrane is treated to form single strands. Explain
why.

Answer 5

so DNA probes can anneal

Question 6

Explain how the use of DNA probes produced the results in the diagram.

Answer 6

short single stranded DNA complementary to DNA sequences
binds to DNA base sequences and glows