DNA

Question 1

Describe the structure of DNA.

Answer 1

• It is a polymer
• Has two strands which are coiled to form a double helix
• Strands linked by complementary base pairs joined together by weak hydrogen bonds
• Made up of nucleotides

Question 2

Describe the structure of a DNA nucleotide.

Answer 2

• Sugar-phosphate backbone
• One of four different bases is attached to the sugar

Question 3

Describe how DNA is stored in the nucleus of eukaryotic cells.

Answer 3

It is stored as chromosomes, which are long, coiled-up molecules of DNA

Question 4

What is meant by the term ‘double helix’?

Answer 4

A double stranded spiral

Question 5

DNA is a polymer.

Explain what this means.

Answer 5

It is made up of lots of repeating units, these being nucleotides

Question 6

(Exam-style question)

Answer 6

Question 7

What is a genome?

Answer 7

All of an organism’s DNA

Question 8

Explain what is meant by the term ‘gene’.

Answer 8

A section of DNA that codes for a particular protein

Question 9

Describe how you can extract DNA from fruit.

Answer 9

• Mash your fruit and put it in a beaker containing a solution of detergent and salt
• Filter mixture to get froth and insoluble bits of cell out
• Add ice-cold ethanol to filtered mixture
• DNA will start to come out of solution as it’s not soluble in cold ethanol
• It will appear as a stringy white precipitate that can be fished out with a glass rod

Question 10

Why is it useful to use detergent when extracting DNA from fruit cells?

Answer 10

Detergent breaks down cell membrane to release DNA

Question 11

Why is it useful to use salt when extracting DNA from fruit cells?

Answer 11

Salt helps the DNA to stick together