Human beings have a large-sized 'proteome'. The principal and more significant reason for this is-
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This allows high cellular and tissue-specific complexity without needing a massive number of individual genes.
- Humans have an extremely large genome.
- An individual gene of the human genome may encode many different polypeptides.
- Humans are the most complex living organism.
- The human genome contains millions of different genes.
The Correct Option is B
Solution and Explanation
The "genome" is the complete set of DNA in an organism, whereas the "proteome" is the entire set of expressed proteins.
The human genome contains about \(20,000\) to \(25,000\) protein-coding genes, but expresses hundreds of thousands of proteins.
Step 3: Detailed Explanation:
This difference in size between the genome and the proteome is explained by post-transcriptional mechanisms.
The most significant of these mechanisms is alternative pre-mRNA splicing.
Human genes contain coding regions (exons) interspersed with non-coding regions (introns).
During transcription, the spliceosome removes introns and joins exons in different combinations.
This allows a single pre-mRNA transcript to generate several distinct mature mRNA variants.
Each unique mature mRNA is then translated into a different polypeptide isoform.
Other contributing factors include:
1. Alternative promoters: Initiating transcription at different start sites within a single gene.
2. Alternative polyadenylation: Splicing and terminating transcripts at different end sites.
3. Post-translational modifications (PTMs): Adding chemical groups (like phosphates or sugars) to proteins after translation.
Let us evaluate the other options:
Options (A) and (D) are incorrect because the human genome contains only about \(20,000\text{--}25,000\) genes, not millions.
Additionally, many plants and amphibians have genomes that are much larger than the human genome.
Option (C) is a subjective statement that does not provide a biological explanation for proteomic complexity.
Step 4: Final Answer:
The primary reason for the large proteome size is that single genes can encode multiple polypeptides, matching Option (B).
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