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.
There are four bases in DNA, and each one is different than the others, making four 'letters.' Amazingly, this is enough variety to spell out all the genes in all living things! The related molecule RNA also has four bases: three are the same as in DNA and one is different. Let's meet the different nitrogenous bases.