Manipulating DNA

Question 1

What is a palindromic sequence of nucleotides?

Answer 1

They are sequences that consist of anti parallel base pairs (they read the same in opposite directions

Question 2

What are ‘sticky ends’?

Answer 2

• sometimes the cut with restriction enzymes leaves sticky ends which is a small overhang of unpaired bases (single stranded DNA) at each end of the fragment
• sticky ends can be used to bind (anneal) the DNA fragment to another piece of DNA that has sticky ends with complementary sequences

Question 3

Explain the process of gel electrophoresis

Answer 3

• a DNA sequence is cut using restriction enzymes so it is now in DNA fragments
• a fluorescent tag is added to all the DNA fragments so they can be viewed under UV light
• the DNA is placed into a well in a slab of gel and covered in a buffer solution that conducts electricity
• an electrical current is passed through the gel
• DNA fragments are negatively charged so they move towards the positive electrode at the far end of the gel (anode)
• small DNA fragments move faster and travel further through the gel so the DNA fragments separate according to size
• the DNA fragments are viewed as bands under UV light

Question 4

What is a DNA probe?

Answer 4

• it is a single stranded short length of DNA that have a specific base sequence that is complementary to the target sequence (the sequence your looking for)
• this means that the DNA probe will bind to the target sequence if its present in a sample of DNA
• a DNA probe also has a label attached to it so that it can be detected, this could be
- a radioactive label (detected using X-Ray film)
- a fluorescent label (detected using UV light)

Question 5

What can DNA probes be used for?

Answer 5

• to locate a specific desired gene that is wanted for genetic engineering
• to identify the same gene on a variety of different genome from separate species when conducting genome comparison studies
• to identify the presence or absence of an allele for a particular genetic disease

Question 6

What are restriction enzymes?

Answer 6

• restriction enzymes are enzymes that recognise specific palindromic sequences (recognition sequences) and cut the DNA at these places
• different restriction enzymes cut at different specific recognition sequences because the shape of the recognition sequence is complementary to the enzymes active site