• Like DNA, the nucleic acid RNA (ribonucleic acid) is a?polynucleotide?– it is made up of?many nucleotides?linked together in a?long 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)
• 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

• mRNA is a single-stranded molecule
• It is made up of a sugar-phosphate backbone and exposed unpaired bases
• Uracil bases are present instead of thymine bases (which are found in DNA)

Structure of an mRNA molecule

tRNA

• tRNA is a single-stranded molecule
• It has a sugar-phosphate backbone
• It has a folded shape
  • There are hydrogen bonds between some of the complementary bases

   

• Amino acids bind to a specific region of the molecule
• The specific anticodon found on the tRNA molecule is complementary to a specific codon on an mRNA molecule

Structure of a tRNA molecule