DNA consists of two complementary strands that twist into a double helix. The sequence of bases — adenine, thymine, cytosine, and guanine — carries biological information.
Adenine pairs with thymine, while cytosine pairs with guanine. In DNA, adenine and thymine are connected by two hydrogen bonds, whereas cytosine and guanine are connected by three.
CURSOR → GENTLE MOLECULAR DISPLACEMENTEach DNA strand has a backbone made of alternating deoxyribose and phosphate molecules. Attached to the sugar is one of four nitrogenous bases: A, T, C, or G.
DEOXYRIBOSE / PHOSPHATE / BASEA single copy of the human genome contains approximately 3 billion DNA base pairs, distributed across 23 chromosomes. It is the sequence of these bases that forms the genome's record.
If the DNA from a single human cell were stretched out and laid in a straight line, it would be about 1.8 meters long. Histones and nucleosomes help package it inside the nucleus.
About 150 DNA base pairs wrap around a core of histone proteins, forming a nucleosome — the basic unit of chromatin packaging.
23 pairs of chromosomes. 46 chromosomes in most body cells.
Humans have 22 pairs of autosomes and one pair of sex chromosomes. One chromosome from each pair is inherited from one parent, and the other from the other parent.
The human genome contains about 20,000 protein-coding genes. A gene is a segment of DNA containing the information a cell needs to produce a biological product, often a protein or RNA molecule.
A DNA sequence can contain instructions for protein synthesis. The cell first transcribes the information from DNA into RNA and then uses it during protein synthesis.
Less than 2% of the human genome codes for proteins. Much of the remaining DNA does not code for proteins; some of these sequences serve regulatory functions.
On average, about 99.6% of the human genome sequence agrees with the reference genome when different types of genetic variants are taken into account. A small fraction of differences creates enormous diversity among people.
FACTS ABOUT THE HUMAN GENOME ↗