Practice question

Long interspersed nuclear elements LINEs are autonomous non-LTR retrotransposons about six kilobases that encode proteins required for retrotransposition. Human LINE-1 features internal RNA polymerase II promoter in 5' UTR and two open reading frames ORF1 encoding RNA-binding chaperone and ORF2 encoding endonuclease plus reverse transcriptase. Despite lacking long terminal repeats, LINEs terminate with poly-A tail and mobilize via target-primed reverse transcription providing trans machinery also used by SINEs. Few LINE-1 copies remain active driving human insertional diversity and disease. This principle illustrates essential molecular mechanisms governing replication fidelity and mutation fixation relevant for exam interpretation.