3.1.5 Nucleic Acids

Question 1

What is the structure of DNA?

Answer 1

• DNA is a polymer of nucleotides with 2 polypeptide chains.

• The two polypeptides run antiparallel to each other coiled into a double helix.

• Each nucleotide is made of a deoxyribose, a phosphate group and an organic nitrogenous base.

• The base may be adenine, thymine, guanine or cytosine.

• The adjacent nucleotides are joined to each other between the sugar and phosphate group in a condensation reaction which forms a phosphodiester bond.

• Complimentary base paring holds the 2 strands together with hydrogen bonds.

• Adenine → Thymine and Cytosine →
Guanine

Question 2

Compare the structure of DNA and RNA

Answer 2

• DNA contains deoxyribose whilst RNA
contains ribose.

• DNA can contain thymine, RNA cannot.

• RNA can contain uracil, DNA cannot.

• DNA is double stranded whilst RNA is single stranded.

• There is 1 type of DNA but 3 types of RNA (mRNA, rRNA and tRNA).

• DNA is much longer whilst RNA is much shorter

Question 3

What bond are nucleotides joined by?

Answer 3

Condensation reactions.

Question 4

What bond joins two nucleotides and where do they join?

Answer 4

It is called a phosphodiester bond and it is between the phosphate group of one nucleotide and the deoxyribose sugar of the other.