Contrast the structure of SINE and LINE DNA sequences. Why are LINEs referred to as retrotransposons?

Key Concepts

SINE and LINE Sequences

SINE (Short Interspersed Nuclear Elements) and LINE (Long Interspersed Nuclear Elements) are two types of transposable elements found in eukaryotic genomes. SINEs are typically less than 500 base pairs long and do not encode proteins, relying on other elements for their transposition. In contrast, LINEs are longer, usually over 1,000 base pairs, and can encode proteins necessary for their own mobilization, including reverse transcriptase.

Retrotransposons

Retrotransposons are a class of transposable elements that replicate through an RNA intermediate. LINEs are classified as retrotransposons because they transpose via a process called retrotransposition, where their RNA is reverse transcribed back into DNA and integrated into new genomic locations. This mechanism allows them to increase their copy number within the genome.

Transposition Mechanisms

Transposition refers to the process by which transposable elements move within the genome. SINEs typically use a 'copy-and-paste' mechanism facilitated by the enzymatic activity of LINE-encoded proteins, while LINEs can utilize their own reverse transcriptase to replicate and insert themselves into new sites. Understanding these mechanisms is crucial for studying genome evolution and the role of transposable elements in genetic diversity.