DNA and RNA are nucleic acids.

They are chains made of a building blocks called nucleotides. So, in essence, nucleic acids are polynucleotides.

Most people have seen diagrams of DNA. Whereas DNA is double-stranded, RNA is typically single-stranded but there is one form of RNA that is double-stranded.

The Structure of DNA GIF


Each nucleotide is made of three parts:

Find the phosphate, (pentose) sugar, and nitrogenous base on the right side of the figure below.

228 Nucleotides-01


As you can see from the figure, the pentose (5-carbon) sugar is ribose in RNA and deoxyribose in DNA.

There are two classes of nitrogenous (nitrogen-containing) bases: purines and pyrimidines.

A mnemonic device that you can use to remember which nitrogenous bases are purines and which ones are pyrimidines is this:

For the purines: PUR As Gold

The two purines are Adenine and Guanine.

For pyrimidines: PY CUT

The pyrimidines are Cytosine, Uracil, and Thymine.

RNA contains the nitrogenous bases of:

DNA contains these four nitrogenous bases:

As you can tell from the figure below, DNA consists of two strands. The nitrogeneous bases of one strand base pair the nitrogenous bases of the other strand.

Guanine base pairs with Cytosine
Thymine base pairs with Adenine

DNA chemical structure


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