AQA AS Biology

Revision Notes

1.5.4 The Structure of RNA

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)

Comparison between RNA nucleotide and DNA nucleotide, downloadable AS & A Level Biology revision notes

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)

mRNA as an example of RNA structure, downloadable AS & A Level Biology revision notes

Messenger RNA (mRNA) provides a good example of the structure of RNA

Exam Tip

You need to know the difference between DNA and RNA molecules (bases, number of strands, pentose sugar present, length).

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While studying Biochemistry at Oxford University, Amelia started her own tutoring service, helping to connect Science tutors with students in her local area. Amelia has experience teaching the sciences and Maths at all levels to UK and international students and, as well as being our Biology Lead, designs revision resources for Chemistry.
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