Multiple Choice
Which of the following elements is a transposable element in Drosophila?
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16. Transposable Elements
Transposable Elements in Eukaryotes
1:30 minutesProblem 16
Textbook Question
Contrast the structure of SINE and LINE DNA sequences. Why are LINEs referred to as retrotransposons?
Verified step by step guidance1
Understand the basic structure of SINE (Short Interspersed Nuclear Elements) and LINE (Long Interspersed Nuclear Elements). SINEs are shorter sequences, typically less than 500 base pairs, and do not encode proteins. LINEs are longer sequences, often exceeding 6,000 base pairs, and contain genes that encode proteins necessary for their own replication.
Recognize that SINEs rely on LINEs for their replication. SINEs are non-autonomous elements, meaning they cannot replicate independently and use the enzymatic machinery provided by LINEs, such as reverse transcriptase.
Examine the structure of LINEs to understand why they are referred to as retrotransposons. LINEs contain an internal promoter, two open reading frames (ORFs), and a poly-A tail. The ORFs encode proteins, including reverse transcriptase and endonuclease, which are essential for their replication and movement within the genome.
Learn the mechanism of retrotransposition. LINEs are referred to as retrotransposons because they use an RNA intermediate during their replication process. The DNA sequence of the LINE is transcribed into RNA, which is then reverse-transcribed back into DNA by the reverse transcriptase enzyme encoded by the LINE itself.
Understand the significance of retrotransposons in the genome. LINEs and SINEs are classified as transposable elements, and their ability to move within the genome can contribute to genetic diversity, but also to mutations and genomic instability in some cases.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
SINE and LINE Sequences
SINE (Short Interspersed Nuclear Elements) and LINE (Long Interspersed Nuclear Elements) are two types of transposable elements found in the genome. SINEs are typically less than 500 base pairs long and do not encode proteins, relying on other elements for their mobilization. In contrast, LINEs are longer, usually over 1,000 base pairs, and can encode proteins necessary for their own replication and insertion into the genome.
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Sequencing Difficulties
Retrotransposons
Retrotransposons are a class of transposable elements that replicate through an RNA intermediate. LINEs are classified as retrotransposons because they transcribe their DNA into RNA, which is then reverse-transcribed back into DNA and inserted into a new location in the genome. This mechanism of replication is similar to that of retroviruses, hence the name 'retrotransposon.'
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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 replicate themselves through a 'cut-and-paste' or 'copy-and-paste' mechanism involving reverse transcription. Understanding these mechanisms is crucial for grasping how these elements contribute to genetic diversity and evolution.
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