DNA

Question 1

DNA structure

Answer 1

• Two polynucleotide strands joined together to form double helix shape.
• The two strands are joined together by hydrogen bonds between bases.

Question 2

Antiparallel formation

Answer 2

• Each strand has a PHOSPHATE group (5’) at one end and a HYDROXYL group (3’) at other.
• The 2 parallel strands are arranged so that they run in opposite directions - they are said to be antiparallel.

Question 3

Complementary base pairing

Answer 3

• Adenine and Thymine are able to form 2 H-bonds so always join w/ each other.
• Cytosine and Guanine are able to form 3 H-bonds so join w/ each other.
• This is known as complementary base pairing.
• Small pyramidal joins with larger purine base.
• Complementary base pairing means there are equal amounts of ALL bases.

Question 4

Purifying DNA by precipitation

Answer 4

1) Break up cells by using blender or grinding it down - breaks down cell walls
2) Make a solution of detergent, salt and distilled water - detergent breaks down cell membrane, releasing cell contents into solution; salt breaks hydrogen bonds between DNA and water; salt binds to DNA and makes them clump together.
3) Add broken up cells to detergent solution in beaker.
4) Incubate beaker in water bath at 60 degrees for 15 mins - temp should stop enzyme in cells from working and breaking down DNA.
5) Put beaker in ice bath to cool.
6) Filter mixture and transfer filtered mixture to clean boiling tube.
7) Add protease enzymes - break down proteins associated w/ DNA in nuclei
8) Add layer of ethanol so it forms layer of DNA precipitate.
9) DNA will be white strands and can be picked up by spooling on glass rod.

Question 5

Explain how the structure of DNA is ideally suited to its role

Answer 5

• It is a polymer so it contains a lot of information.
• The base sequence of the DNA strand carries genetic information of an organism in the form of a code.
• Double stranded so the molecule is very stable.
• Double stranded so they can be accurately replicated.