The original high estimate of the number of protein-coding genes in humans was based partly on the number of different known proteins made by the human organism. How can the small number of genes now thought to be present account for this larger number of proteins synthesized by human cells? What observations of vertebrate genes tend to support this possibility?

20. What type of DNA sequence in eukaryotes is most like that found in bacteria and viruses?

The small number of genes in humans can account for the larger number of proteins synthesized by human cells due to a process called alternative splicing. In eukaryotes, including humans, genes are made up of exons and introns. During the process of RNA splicing, introns are removed and exons are joined together to form a mature mRNA molecule that is then translated into a protein.

Alternative splicing refers to the phenomenon where multiple mRNA transcripts can be generated from a single gene by combining different combinations and arrangements of exons. This allows for the production of multiple protein isoforms from a single gene, increasing the diversity of proteins that can be synthesized.

Observations of vertebrate genes support this possibility. Studies have shown that many vertebrate genes can undergo alternative splicing, resulting in the generation of different mRNA isoforms. This allows for the production of different protein variants with distinct functions or properties. By using alternative splicing, vertebrates can generate a larger number of proteins from a relatively small number of genes.

In conclusion, alternative splicing is a mechanism utilized by eukaryotes, including humans, to generate a larger number of proteins from a smaller number of genes. This process increases the diversity and complexity of gene expression and contributes to the synthesis of a wide variety of proteins in human cells.