The difference between nucleosides vs. nucleotides involves the presence or absence of a phosphate group. A nucleoside consists of a nucleobase and a sugar (ribose or deoxyribose) whereas a nucleotide contains a nucleobase, a sugar, and one or several phosphate groups. Hence, the main difference is nucleotides have phosphate groups and nucleosides do not.

You've probably heard of DNA (Deoxyribonucleic Acid) before, along with RNA (Ribonucleic Acid). However, you may be less familiar with the compounds found within them, nucleosides and nucleotides.

Nucleotides are molecules essential for creating life on Earth, but they should not be confused with the similarly named nucleoside molecules.  It's important to put this answer in context though, so let's take a closer look at the differences between nucleotides and nucleosides.  

Before looking at nucleotides and nucleosides, let's examine the bases that comprise DNA and RNA. DNA and RNA are made up of nitrogen bases also called nitrogenous bases.

The Five Nitrogenous Bases

There are five nitrogenous bases used to compose DNA and RNA: adenine, guanine, thymine, cytosine, and uracil. Each of the nitrogenous bases has a complementary base so the two will only ever pair together. Adenine pairs with thymine, while guanine pairs with cytosine.

The exception to this is uracil. DNA has adenine, guanine, thymine, and cytosine in it, but RNA lacks thymine, and it bonds with adenine instead. Adenine is a purine, along with guanine. The other bases are pyrimidines.

The Role of Nucleosides

Nucleosides have used in the medical field, where they can function as antiviral or anti-cancer devices. The Nucleosides go through the process of phosphorylation, bonding with phosphorous to create a nitrogenous base paired with sugar and phosphate, and a nucleotide

These nucleotides now have the famous phosphate backbone of DNA and function as the molecular building blocks for both RNA and DNA.

The Role of Nucleotides

Nucleotides can use some different methods Synthesis of nucleotides in living cells, in vivo synthesis, can be done from the building blocks of bases and sugars, or synthesized nucleotides. Enzymes break down old nucleotides, freeing their parts up for the synthesis of new nucleotides. The liver is the organ responsible for synthesizing nucleotides.

These molecules have a variety of functions, including functioning as messengers for hormones. The sugar-phosphate backbone of nucleotides is necessary for the nucleotides to link together and form the chains that comprise DNA and RNA. 

Differences Between DNA and RNA

Another difference between DNA and RNA is that DNA uses the sugar deoxyribose to form its nucleotides, while RNA uses the sugar ribose. Deoxyribose has one less oxygen atom than ribose does, hence the name deoxyribose.

The effect of DNA's double helix structure means that it can store genetic information over long periods of time, and even repair itself if part of the DNA chain is damaged.