Nucleotides - Coding Molecules

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Nucleic acids in living organisms

Nucleic acids come in two forms: DNA and RNA.

In living organisms these molecules hold the coded information to build that organism.

Almost all the DNA in a eukaryotic cell is found in the nucleus, where it acts as an information. RNA is found in 3 different forms. These three forms are needed to read and translate the information in order to produce the various proteins required to make the living functioning organism.

Nucleotides are monomers of nucleic acids

The monomer of all nucleic acids is called nucleotide.

Each single nucleotide is itself made by the joining of three subunits:

one phosphate

one sugar molecule

one organic nitrogenous base

The three subunits are joined by covalent bonds to form a single nucleotide molecule.

Nucleotides - common features

As nucleic acids code for the building of all living organisms, you might expect there to be a large number of different monomers available to produce such a code. In fact, just four different nucleotides make up the code carrying the instructions to make proteins in all living things.

The phosphate group in all nucleic acids is always the same.

The sugar molecule is a 5-carbon sugar, either deoxyribose or ribose.

There are 5 possible bases: adenine, thymine, cytosine, guanine and uracil.

Joining nucleotides together

A condensation reaction between the phosphate group of one nucleotide and the sugar of another nucleotide joins the two together. Repeating this bonding gives a long chain of nucleotides.

As nucleotides are bonded together to form chains, the 'backbone' of the molecule consists of a repeating sugar-phosphate chain. Organic bases project from the backbone. It is the sequence of these bases that forms coded information in nucleic acids.

From nucleotides to nucleic acids

Chains of nucleotides bonded together are called nucleic acids. When nucleotides are joined together to form long-chained polymers, only nucleotides carrying the same sugar molecule bind together. This means that nucleic acids can be described as ribonucleic acids when the sugar is ribose or deoxyribosenucleic acids when the sugar is deoxyribose.

Organic bases as either purines or pyrimidines

The five organic bases are grouped. Three are called pyrimidines (C+T+U) and two are called purines (A+G). Pyrimidines are smaller than purines.

Too much nucleic acid causes gout

Uric acid is produced when excess purines are broken down in the liver. It is excreted in the urine. Some people have too much uric acid in their blood. The uric acid is insoluble at lower temperatures, and forms crystals that are deposited at joints at the extremities such as the toes. The toe joint becomes very painful and swollen, a condition called gout.

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