Nucleic Acids — Definition

Definition

Imagine the blueprint for building and operating a complex machine like a human body. That blueprint, containing all the instructions, is essentially what nucleic acids are for living organisms. They are incredibly important biomolecules, right up there with proteins, carbohydrates, and lipids.

At their core, nucleic acids are long chains made up of repeating smaller units called 'nucleotides'. Think of nucleotides as the individual bricks that build a very long wall, where the wall is the nucleic acid.

Each of these 'nucleotide bricks' has three main parts:

1
A sugar molecule — This is a five-carbon sugar. In DNA, it's called deoxyribose, and in RNA, it's called ribose. The difference is just one oxygen atom.
2
A phosphate group — This is a molecule containing phosphorus and oxygen. It's what gives nucleic acids their acidic properties and helps link the nucleotides together.
3
A nitrogenous base — These are ring-shaped molecules containing nitrogen. There are five main types: Adenine (A), Guanine (G), Cytosine (C), Thymine (T), and Uracil (U). DNA uses A, G, C, and T, while RNA uses A, G, C, and U (Uracil replaces Thymine).

When these nucleotides link up, they form a 'polynucleotide chain'. The phosphate group of one nucleotide connects to the sugar of the next, creating a strong 'sugar-phosphate backbone'. The nitrogenous bases stick out from this backbone, like rungs on a ladder.

There are two primary types of nucleic acids:

Deoxyribonucleic Acid (DNA) — This is the famous double helix. It's like two polynucleotide chains twisted around each other. The bases from one chain pair up with bases from the other chain (A always pairs with T, and G always pairs with C) using weak hydrogen bonds, holding the two strands together. DNA is the primary genetic material in almost all living things, storing all the instructions for making an organism. It's found mainly in the nucleus of cells.
Ribonucleic Acid (RNA) — Unlike DNA, RNA is usually a single polynucleotide chain. It's involved in taking the instructions from DNA and using them to make proteins. There are different types of RNA, like messenger RNA (mRNA) which carries the genetic message, ribosomal RNA (rRNA) which forms part of the protein-making machinery (ribosomes), and transfer RNA (tRNA) which brings the correct amino acids to the ribosome. RNA is found both in the nucleus and the cytoplasm.

In simple terms, nucleic acids are the carriers of genetic information, dictating everything from your eye color to how your cells function. They are the fundamental molecules of heredity and life.