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.
able. Researchers already knew that DNA was a relatively simple molecule. It seemed to consist of an un-remarkable chain of phosphates and sugars, in some way attached to a set of ring-shaped molecules called nitrogenous bases. These bases come in four âflavorsâ: adenine (A), thymine (T), cytosine (C), and guanine (G) (Fig. 4).