DNA probes

Question 1

What is a DNA probe?

Answer 1

a short single strand of DNA labelled with either a radioactive or fluorescent marker, with bases complementary with required gene

Question 2

What reaction is used to make DNA probes?

Answer 2

PCR

Question 3

Describe the DNA sequence that is needed to make a DNA probe

Answer 3

short, with complementary base sequence to the desired allele

Question 4

Why is it important to wash away unattached DNA probes?

Answer 4

so unbound DNA probes are washed away, therefore there is not a false positive result

Question 5

How would you determine the base sequence for the mutant allele (the allele that causes the disease)?

Answer 5

DNA sequencing/DNA library

Question 6

What is DNA hybridisation?

Answer 6

when a section of DNA or RNA binds with a single stranded section of DNA with complementary bases.

Question 7

Describe how radioactive probes could be used to show that a gene is present within a fragment of DNA?

Answer 7

• expose bases (form single strands)
• probe will bind to gene/sequence of alleles
• use autoradiography to show bound probes

Question 8

How might a complementary strand of mRNA affect the production of a protein by a gene?

Answer 8

• complementary bases would form hydrogen bonds
• ribosome could not bind, preventing translation

Question 9

How is DNA broken down into smaller fragments?

Answer 9

using restriction endonucleases, which cuts DNA at a specific point in the base sequence

Question 10

Why might identifying the strain of bacteria causing a disease help improve treatment?

Answer 10

• can determine if resistant to antibiotic, so treatment will be effective

Question 11

How could cDNA stop the production of a protein?

Answer 11

• will bind to mRNA
• forming double stranded mRNA
• this will prevent the ribosome from joining
• preventing translation

Question 12

Why are probes needed?

Answer 12

because DNA is invisible on a membrane

Question 13

Why are exons used, not introns?

Answer 13

• introns are not translated
• mutations in exons effect a/a sequence and therefore the 3° structure of a protein
• important to know whether or not an exam is effective rather than an intron

Question 14

How can DNA be used to scan for harmful mutations?

Answer 14

• amplify using PCR
• cut using RE
• separate using gel electrophoresis
• add DNA probes
• show under UV or X-ray films