The Structure of RNA
- Like DNA, the nucleic acid RNA (ribonucleic acid) is a polynucleotide – it is made up of many nucleotides linked together in a chain
- Like DNA, RNA nucleotides contain the nitrogenous bases adenine (A), guanine (G) and cytosine (C)
- Unlike DNA, RNA nucleotides never contain the nitrogenous base thymine (T) – in place of this they contain the nitrogenous base uracil (U)
- Unlike DNA, RNA nucleotides contain the pentose sugar ribose (instead of deoxyribose)
An RNA nucleotide compared with a DNA nucleotide
- Unlike DNA, RNA molecules are only made up of one polynucleotide strand (they are single-stranded)
- RNA polynucleotide chains are relatively short compared to DNA
- Each RNA polynucleotide strand is made up of alternating ribose sugars and phosphate groups linked together, with the nitrogenous bases of each nucleotide projecting out sideways from the single-stranded RNA molecule
- The sugar-phosphate bonds (between different nucleotides in the same strand) are covalent bonds known as phosphodiester bonds
- These bonds form what is known as the sugar-phosphate backbone of the RNA polynucleotide strand
- The phosphodiester bonds link the 5-carbon of one ribose sugar molecule to the phosphate group from the same nucleotide, which is itself linked by another phosphodiester bond to the 3-carbon of the ribose sugar molecule of the next nucleotide in the strand
- An example of an RNA molecule is messenger RNA (mRNA), which is the transcript copy of a gene that encodes a specific polypeptide. Two other examples are transfer RNA (tRNA) and ribosomal RNA (rRNA)
Messenger RNA (mRNA) provides a good example of the structure of RNA
Examiner Tip
You need to know the difference between DNA and RNA molecules (bases, number of strands, pentose sugar present, length).
