Nucleic acids are the instructions for building and maintaining living organisms. DNA is used by multi-cellular organisms, while RNA is used by viruses. Nucleic acids are made up of nucleotides, with DNA being double-stranded and RNA being single-stranded. Genes are small sections of instructions within nucleic acids, and the sequence of nucleotides is important for creating different products. Nucleic acids are necessary for replication and survival, and are present in all forms of life on earth.
Every living organism needs to carry instructions for building a new version of itself and for making products to keep it alive. These instructions are nucleic acids. All organisms with more than one cell use a nucleic acid called deoxyribonucleic acid (DNA), and less complicated ones, such as viruses, use ribonucleic acid (RNA). Each of these nucleic acids is a string of many individual molecules, and when the life form reads these molecules in sequence, it identifies which product to make.
Of the two nucleic acids, RNA is the least complicated. It exists as a single strand. DNA, on the other hand, pairs with another DNA strand, so it is present in cells as a double-stranded, spiral-shaped structure.
Each nucleic acid is a string, that is, composed of many building blocks, one after the other, called nucleotides. These nucleotides join together through chemical forces at each end of the block. Only four different nucleotides make up DNA. These are adenine (A), guanine (G), thymine (T) and cytosine (C.) RNA also has only four nucleotide blocks, but instead of thymine (T), it has uracil (U.)
A living being contains many nucleic acid instructions in its cells. Each cell can read the instruction string and make the relevant products. Because every organism needs to make many different products, the nucleic acid string contains many small sections of instructions. These sections are called genes and the cell generally reads each gene as the instructions for a particular product.
It’s the sequence of nucleotides that matters with nucleic acids, and complicated instructions require no more than four nucleotides. The human genome, for example, contains 3.2 billion nucleotides in each strand. Smaller organisms tend to have shorter nucleic acids, such as the bacterium Haemophilus influenzae at 1.8 million bases per strand.
An analogy is that the English language has 26 letters, but English speakers can put all these letters together, in different word combinations, and have complex conversations. A very simple example is when someone says “pots”. The same letters in reverse mean something completely different; “Stop.” So in another example, when the cell reads a gene with a sequence starting CCTTGGAA…, it will produce a different cell product than one starting AATTGGAA… even though the sequences are similar. The nucleic acid sequences in genes must be relatively accurate, otherwise the body may not be able to build the correct product.
Basically, nucleic acids function as the computer that organizes the cell. They also provide the instructions the cell needs to replicate. Without nucleic acid, a cell or organism cannot build another version of itself. Only those life forms that can replicate can survive into the next generation. This is why nucleic acids are present in every form of life on earth.
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