In this chapter, Carroll introduces a group of organisms called the Archaea and makes a good point about how the study of these obscure dwellers of hot springs has lead to a revolution in molecular biology and biotechnology, spawning a multi billion pound industry.
Part of the chapter deals with the basics of the genetic code (see here for more) and makes the point that some genes are shared between all major groups of organisms. These genes (about 500) are called immortal genes. Within the proteins encoded by
these genes, there are some “immortal” letters. These are basically amino specific amino acid residues that don’t vary and indicates a selective pressure to maintain these amino acids. He introduced a historical belief that by today’s standards seems obviously absurd – that it was once thought that mutation would rewrite the gene sequence over time. There reason that does not happen is because the functions of proteins are dictated by the chemical and physical properties of the amino acids that make them up. Some amino acids for example are essential for accepting or donating electrons or forming covalent bonds with other molecules. Similarly, some amino acids like proline are essential for sharp turns in the protein structure. So, the fact that some amino acids must not vary is not surprising. Because there is more than one way for DNA to encode a specific amino acid (see here), there is more mutational freedom in the DNA sequence than the protein sequence, and this can give a better idea of the relatedness of organisms.
Carroll ends the chapter by presenting evidence that the conventional view of life branching from a single common ancestor may not be true. He proposes that the Eukaryota (the group we belong to) probably arose from a fusion of the geneomes of a bacterial and an Archaean ancestor. He cites other examples of genome mixing such as horizontal gene transfer (a way to introduce new genetic information into organisms) and the endosymbiotic relationship between eukaryotic cells chloroplasts and mitochondria. Whether the bacteria Archaea have independent origins is still debatable though.
Part of the chapter deals with the basics of the genetic code (see here for more) and makes the point that some genes are shared between all major groups of organisms. These genes (about 500) are called immortal genes. Within the proteins encoded by
these genes, there are some “immortal” letters. These are basically amino specific amino acid residues that don’t vary and indicates a selective pressure to maintain these amino acids. He introduced a historical belief that by today’s standards seems obviously absurd – that it was once thought that mutation would rewrite the gene sequence over time. There reason that does not happen is because the functions of proteins are dictated by the chemical and physical properties of the amino acids that make them up. Some amino acids for example are essential for accepting or donating electrons or forming covalent bonds with other molecules. Similarly, some amino acids like proline are essential for sharp turns in the protein structure. So, the fact that some amino acids must not vary is not surprising. Because there is more than one way for DNA to encode a specific amino acid (see here), there is more mutational freedom in the DNA sequence than the protein sequence, and this can give a better idea of the relatedness of organisms.
Carroll ends the chapter by presenting evidence that the conventional view of life branching from a single common ancestor may not be true. He proposes that the Eukaryota (the group we belong to) probably arose from a fusion of the geneomes of a bacterial and an Archaean ancestor. He cites other examples of genome mixing such as horizontal gene transfer (a way to introduce new genetic information into organisms) and the endosymbiotic relationship between eukaryotic cells chloroplasts and mitochondria. Whether the bacteria Archaea have independent origins is still debatable though.
2 comments:
Bugger... I've got behind on my reading. Damn and Damn
I said I was a slow reader
Lee,
Reminds me of the Two Ronnie's (?) joke:
Ronnie B: "I've just spent a month in France finishing my latest novel."
Ronnie C: "Really?"
Ronnie B: "Yes, I'm a very slow reader..."
To be fair, I'm not quite there yet, either, but I will be by the weekend. To be fair, speaking as a novice at this, and someone who's always capable of confusing myself, I did like Carroll's explanation of the necessary A, C, G, T business...
Mark_W
Post a Comment