Which one of the following statements about LINEs present in the human genome is TRUE?
LINEs preferentially localize to AT-rich DNA.
LINEs in the Human Genome
LINEs, or Long Interspersed Nuclear Elements, are a type of retrotransposon found in eukaryotic genomes, including the human genome. They are capable of replicating and inserting themselves into new positions in the DNA. Let's examine the given statements about LINEs in the human genome to determine which one is true.
Analyzing Statements about LINEs
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Statement 1: LINEs preferentially localize to AT-rich DNA.
Studies on the insertion preferences of LINE-1 (L1), the most abundant LINE in humans, have shown that while L1 inserts throughout the genome, there can be a preference for AT-rich regions or specific genomic features often associated with AT content. These regions can include euchromatin where active transcription occurs, though L1 activity can disrupt genes. Therefore, this statement is considered true based on observed insertion biases.
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Statement 2: LINEs cannot transpose independently.
This statement is false. LINEs, specifically autonomous LINEs like L1, encode the proteins necessary for their own retrotransposition: an RNA-binding protein and a protein with both endonuclease and reverse transcriptase activity. This machinery allows them to transpose independently.
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Statement 3: By parasitizing on the SINE element transposition machinery, LINEs can attain very high copy number.
This statement is false and reverses the actual parasitic relationship. SINEs (Short Interspersed Nuclear Elements), such as the Alu family, do not encode their own transposition machinery. Instead, they rely on the machinery provided by autonomous retrotransposons, primarily the reverse transcriptase and endonuclease encoded by LINE-1 elements, to transpose. SINEs parasitize LINEs, not the other way around.
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Statement 4: The Alu family is the most prominent LINE family in terms of copy number.
This statement is false. The Alu family is the most prominent and abundant family of SINEs in the human genome, not LINEs. While Alu elements are the most numerous transposable elements overall in humans, the most prominent LINE family is L1 (LINE-1). L1 has a very high copy number (around 500,000 copies), but Alu has an even higher copy number (over 1 million copies).
Conclusion on LINEs
Based on the analysis of each statement regarding LINEs in the human genome, only the statement that LINEs preferentially localize to AT-rich DNA aligns with the known characteristics and observed insertion patterns of these retrotransposons.
Important Questions from Genes and chromosomes
Readers of histone modifications include:
The amino acid side chains of the four histones in the nucleosome are subjected to remarkable variety of post-translation modifications such as phosphorylation, acetylation and methylation. Which one of the following post-translational marks on histone tails is usually associated with transcriptional repression?
In context of DNA methylation, which one of the following statements is FALSE?
The nucleosome is the fundamental subunit of chromatin in eukaryotes. Following statements are made about nucleosome:
A. Generally, a typical nucleosome contains ~ 200bp of DNA and two copies of each histone (H2A, H2B, H3 and H4)
B. 146 bp length of DNA per nucleosome core particle is strictly maintained across the organisms
C. The histone octamers are not conserved during/after replication, however, H32-H42 tetramers are.
D. Variants have been identified for all core histones except histone H3
E. While wrapping around the core histones, the structure of DNA is altered at the middle of the nucleosome core particle and exhibits increased number of base pairs per turn
Which one of the following combination of statements is most appropriate?
Which one of the following statements about Short Interspersed Nuclear Elements (SINEs) is TRUE?
