There are approximately 30 trillion human cells in the body. They can be grouped into over 200 types of cell. Each human began as a single fertilized egg cell but developed into a highly complex being. Deoxyribonucleic acid (DNA) is the blueprint for the human body that enables a single cell to develop into a much more complex organism.
DNA lives in the nucleus of every cell forming long structures called chromosomes . Humans have 23 pairs of chromosomes. DNA is a two-stranded molecule that twists into a helical structure. Each strand of DNA is composed of unique sequences of four key building blocks that are referred to as nucleobases . These nucleobases pair with a complementary base on the other strand of the molecule. Adenine (A) always pairs with thymine (T) and guanine (G) always pairs with cytosine (C). It is the unique sequence of these building blocks that define how to make a human. There are sections of the DNA sequence called genes that provide instructions for the cell on how to build different proteins from amino acids . Proteins are essential components of the body’s structure and perform many vital functions .
If you took the DNA from all the cells in your body and lined it up, end to end, it would form a strand 6000 million miles long (but very, very thin)! — Universtiy of Leicester