38 human, protein coding genes are mainly organized “exons” and “introns’’. There are intergenic regions that transcribe into various types of non-coding RNA (nottranslating into protein). Some introns may harbor also transcription units, which are
(1) always other protein coding genes
(2) protein coding gene and RNA coding genes
(3) always RNA coding genes
(4) pseudo genes
Introduction
Human protein-coding genes are primarily organized into exons and introns, with exons encoding the protein sequences and introns traditionally considered non-coding intervening sequences. However, recent research reveals that introns are not merely “junk” DNA but can contain transcription units that produce various RNA molecules. These transcription units can be either protein-coding or RNA-coding, contributing to the complexity of gene regulation and genome function. This article discusses the nature of transcription units found within introns and their biological significance.
Organization of Human Protein-Coding Genes
Protein-coding genes in humans consist of:
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Exons: Sequences that code for proteins, joined together after splicing to form mature mRNA.
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Introns: Non-coding sequences removed during mRNA processing but can contain regulatory elements and transcription units.
Between genes lie intergenic regions, which also transcribe various types of non-coding RNAs involved in gene regulation.
Transcription Units Within Introns
Introns can harbor transcription units that are:
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Protein-coding genes: Some introns contain nested genes that encode proteins distinct from the host gene.
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RNA-coding genes: Many intronic transcription units produce non-coding RNAs such as microRNAs (miRNAs), small nucleolar RNAs (snoRNAs), and long non-coding RNAs (lncRNAs).
This dual nature of intronic transcription units expands the functional repertoire of the genome beyond the primary protein-coding function.
Biological Significance
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Gene Regulation: Intronic RNA-coding genes can regulate the expression of their host genes or other genes, influencing developmental and cellular processes.
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Genomic Efficiency: Embedding multiple transcription units within introns maximizes the coding potential of the genome.
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Complexity of Transcriptome: The presence of both protein-coding and RNA-coding genes within introns contributes to the diversity of transcripts and regulatory networks in human cells.
Why Other Options Are Incorrect
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Always other protein-coding genes: Introns do not exclusively contain protein-coding genes; many transcription units are RNA-coding.
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Always RNA-coding genes: Introns can also contain protein-coding genes, not only RNA-coding ones.
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Pseudogenes: While pseudogenes exist in the genome, they are not specifically or exclusively located within introns as transcription units.
Conclusion
Introns in human protein-coding genes are versatile genomic regions that can contain transcription units producing both protein-coding and RNA-coding genes. This arrangement enhances the complexity and regulatory capacity of the genome, underscoring the intricate organization of human genetic material.
Answer:
The correct option is (2) protein coding gene and RNA coding genes.
