DNA and RNA
Nucleic acids come in two main forms. The names are long, but they break down simply.
DNA
Full name: Deoxyribonucleic acid
Building unit: Deoxyribonucleotide
Main job: storing genetic information
Where it is: mainly inside the nucleus
RNA
Full name: Ribonucleic acid
Building unit: Ribonucleotide
Main job: playing an important role in protein synthesis
Where it is: in the nucleus and the cytoplasm
Looking at the names of nucleic acids
The only difference between the names is the prefix "deoxy", meaning "less oxygen". The pentose sugar part of DNA has one oxygen atom fewer than the sugar part of RNA. Tiny as that is, it makes DNA more stable — and that is what allows DNA to store information over a long time.
The shape of a DNA molecule
A DNA molecule is a double helix — two chains twisted around each other like the strands of a rope. Picture a ladder that has been twisted. Base pairs are what hold the two chains together.
The four bases
The complete set of instructions for building an entire organism is written in that four-letter alphabet.