The statements below attempt to describe a few characteristics of Alu repeats found in the human genome A. Alu elements are a class of short interspersed elements (SINEs). B. SINES are autonomous transposons. C. Alu repeat originated from cDNA copies of 7SL RNA. D. Alu repeats have a relatively high AT content. E. They are preferentially located in the gene-poor G chromosome bands. Which one of the following options shows combination of all correct statements?
A and C only
Let's evaluate each statement regarding Alu repeats found in the human genome to determine which ones are correct.
Alu Repeats: Characteristics Analysis
We will analyze each statement individually:
- Statement A: Alu elements are a class of short interspersed elements (SINEs).
This statement is correct. Alu elements are indeed the most abundant SINEs in the human genome.
- Statement B: SINEs are autonomous transposons.
This statement is incorrect. SINEs are non-autonomous retrotransposons. They do not encode the necessary proteins (like reverse transcriptase) for their own transposition. Instead, they rely on the machinery provided by autonomous elements, primarily LINE-1 elements, to move within the genome.
- Statement C: Alu repeat originated from cDNA copies of 7SL RNA.
This statement is correct. Alu elements are thought to have originated from the gene encoding the 7SL RNA component of the Signal Recognition Particle (SRP). They are reverse transcripts (cDNA) of this RNA.
- Statement D: Alu repeats have a relatively high AT content.
This statement is incorrect. Alu elements are known to be relatively GC-rich, particularly in their linker region and the 3' end of the right monomer.
- Statement E: They are preferentially located in the gene-poor G chromosome bands.
This statement is incorrect. Alu elements are typically found preferentially in gene-rich, GC-rich R chromosome bands, which are generally lighter staining with Giemsa stain compared to the gene-poor, AT-rich G bands where LINE elements are more concentrated.
Identifying Correct Alu Statements
Based on the analysis above, the correct statements are A and C.
Therefore, the combination of all correct statements is A and C only.
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?
