The Structure of RNA (Cambridge International AS Biology)

RNA Structure

Spec point — 6.1.5 · describe the structure of an RNA molecule, using the example of messenger RNA (mRNA)

• Like DNA:

  • The nucleic acid RNA (ribonucleic acid) is a polynucleotide

    • It is made up of many nucleotides linked together in a long chain

  • 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)

  • RNA nucleotides contain the pentose sugar ribose (instead of deoxyribose)

  • RNA molecules are only made up of one polynucleotide strand (they are single-stranded)

• Each RNA polynucleotide strand is made up of alternating ribose sugars and phosphate groups linked together

  • The nitrogenous bases of each nucleotide projecting out sideways from the single-stranded RNA molecule

There is much overlap of the nucleotides found in DNA and RNA; RNA nucleotides contain uracil (U) instead of thymine (T) and the sugar ribose instead of deoxyribose

An RNA nucleotide compared with a DNA nucleotide

• 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)

  • mRNA is the transcript copy of a gene that encodes a specific polypeptide

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

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