Submitted by: Ellen Burns–Vice President
In dearly every cell of every living organism, there exists a complete set of instructions for creating that organism and regulating its cellular structures and activities over its lifetime. That set of instructions is called a genome.
A genome is organized into distinct, microscopic units called chromosomes. Chromosomes are coiled threads of deoxyribonucleic acid–DNA–that is composed of two long chains of nucleotides bound together in pairs to form a double helix. (A nucleotide is one of the building blocks of nucleic acids, such as DNA. A nucleotide is made up of three parts: a base, a sugar, and a phosphate. The bases lie flat like steps of a staircase. The sugar and phosphate form the backbone of the nucleic acid. DNA is composed of four different kinds of nucleotide.)
Three and a half billion of these nucleotide pairs make up the human genome.
Specific sequences of nucleotide bases within a DNA strand–called genes–are the cells’ instructions for producing proteins. Scientists estimate that 80,000 to 100,000 of these basic units of heredity exist within the human genome. Proteins perform a wide variety of physiological tasks. They facilitate processes such as digestion, breathing, immune responses, the production of heat and energy, and the movement of fluids in and out of cells.