Lambda phage consists of a virus particle including a head (also known as a capsid), a tail and tail fibres. The head contains the phage's double-stranded circular DNA genome. The phage particle recognises and binds to its host E.coli causing DNA in the head of the phage to be ejected through the tail into the cytoplasm of the bacterial cell. Lambda phage DNA is commonly used as a DNA molecular weight marker. Digestion of the lambda phage genome with HindIII produces a set of 8 fragments consisting of 125, 560, 2000, 2300, 4300, 9400, and 23000 base pairs.