Nucleic acids

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DNA and RNA structureNucleic acids are information storage molecules that provide the directions for buildign proteins. There are two types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Nucleic acids are macromolecules mae of many similar smaller molecules joined in a long chain. These smaller molecuels are called nucleotides.NucleotidesNucleotides are made up of three smaller components. These are:a nitrogen containing base,a pentose sugar (5 carbon) and a phosphate groupnucleotide.jpg

In DNA there are 4 different nitrogen containing bases: adenine (A), thymine (T), guanine (G) and cytosine (C). RNA also contains 4 bases, but the base thymine is never found, in RNA this has been replaced with uracil (U).

The pentose sugar can be either ribose (in RNA) or deoxyribose (in DNA). These sugars are almost the same, except deoxyribose contains one less oxygen thatn ribose.

The phosphate group is the same in both molecules.


Polynucleotides are formed of long chains of alternating sugar and phosphate groups linked together with their bases projecting sideways.


  • RNA molecules are made of one single strand of polynucleotides.

  • DNA molecules are made of two polynucleotide strands lying side by side and runnign in opposite directions. The two strand are held together by hydrogne bonds between the bases. The pairing of bases is very precise: adenine alwasy joins with thymine and cytosine with guanine. This complementary base pairing is a very important feature of polynucleotides.


DNA is often referred to as a 'double helix'. This refers to the 3D shape that DNA molecules form. The hydrogen bonds linkin gthe bases, and therefore holdign the two strands together, can be broken relatively easily. This happens during DNA replication and also during protein synthesis.


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