Introduction

Ribonucleic acid acts as both an information carrier between
genetic material (DNA) and the protein products these genes
encode, and as part of the cellular machinery for protein synthesis.
Ribonucleic acid is complex molecule which in its simplest form
consist of a single unbranched chain of subunits, known as
nucleotides. These chains are made by repeating the same basic
nucleotides over and over. Each nucleotide in the chain contains
the following three parts :-

• 1. A phosphate backbone, connected to
• 2. A Ribose sugar, which in turn connects to
• 3. A Purine or Pyrimidine Base

Whilst the phosphate backbone and ribose sugar remain constant
for every nucleotide, the nucleotides vary in which base is
attached to the sugar. Their are four bases which occur in the RNA
of organisms of Earth, these being the purines, adenine (A) and
Guanine (G), and the pyrimidines cytosine (C) and uracil (U).

Anatomy

RNA is in many respects very similar to DNA structurally. The
molecules differ most strikingly in that the sugar in the nucleotides
contains an extra hydroxide group (Ribose as opposed to
Deoxyribose) and that DNA uses the pyrimidine thymine (T) rather
than uracil. DNA also tends to form double stranded helices
whereas RNA tend to remain single stranded. However, the single
strands of RNA can double back on themselves in what are
referred to as hairpin loops to form regions of double helical RNA.
These regions are formed with the phosphate and ribose units on
the outside with the bases on the inside. The bases interact to
form hydrogen bonds¹ such as to pair C opposite G and A opposite
U (as opposed to T in DNA) and is also able to form weaker bonds
between G and U. RNA differs further from DNA in that this base
pairing is frequently imperfect, some of the apposing bases may
not be complementary (eg C opposite A, or G opposite G) and one
or more bases may be looped out of the helical region to aid the
pairing of others further along the chain. The proportion of such
helical regions within RNA chains varies over a wide range with a
value of around 50% being typical.

Replication

Protein Production