1 Chronic bronchitis: A form of COPD characterized by a chronic productive cough. 2  Emphysema: Lung damage allows air to be trapped in the lungs in this form of COPD. 3  Difficulty blowing air out is its hallmark. 4  Acute bronchitis: A sudden infection of the airways, usually by a virus.
There are only 46 DNA molecules ( 23 pairs) in human somatic cell. There are about 22000 genes and close to 3.2 billion base pairs in total.
Structurally, DNA consists of two long strands of smaller molecules called nucleotides, bound together to form a twisted ladder called a double helix (see photo). Every nucleotide contains a phosphate molecule, a sugar molecule and one of four bases: adenine (A), cytosine (C), guanine (G), or thymine (T).