3.1.5 Nucleic acids are important information-carrying molecules

Question 1

What is a nucleotide made up of?

Answer 1

• a pentose sugar (ribose/deoxyribose)
• a nitrogen-containing organic base (A, T/U, C, G)
• a phosphate group

Question 2

What are the four possible bases on each nucleotide?

Answer 2

• Adenine (A)
• Thymine (T) or Uracil (U)
• Cytosine (C)
• Guanine (G)

Question 3

What are the differences between DNA and RNA in terms of function?

Answer 3

DNA
- stores genetic information for inherited characteristics
RNA
- transfers genetic information from the DNA to the ribosomes to make polypeptides

Question 4

How is the DNA suited to carry out its function?

Answer 4

• It is a very stable molecule and can pass from generation to generation without change.
• It is a very large molecule and can carry a large amount of genetic information.
• The two strands are able to separate easily as they are held together by weak hydrogen bonds.
• As the base pairs are held within the deoxyribose-phosphate backbone, the genetic is protected from outside forces

Question 5

Describe how nucleotides are joined together in DNA.

[3 marks]

Answer 5

• Nucleotides are joined between the phosphate group of one nucleotide and the (deoxyribose) sugar of the next…
• …by phosphodiester bonds…
• …in a condensation reaction.

Question 6

Describe how two single polynucleotides strands are joined to make a double helix.
[3 marks]

Answer 6

• Two polynucleotide strands join through hydrogen bonding between the base pairs.
• Base pairing is complementary.
• The two antiparallel polynucleotide strands twist to form a DNA double helix.