Concept 26 RNA was the first genetic molecule.
Stanley Miller and Harold Urey demonstrate that organic molecules can be synthesized under prebiotic conditions, and Thomas Cech and Sidney Altman show that RNA can have enzymatic activities.
Hi, I'm Stanley Miller. As a graduate student in the '50s, I worked with Harold Urey on a very basic problem — the origins of life. Billions of years ago, Earth was an inhospitable place. There were plenty of volcanic eruptions, acid rain, little or no breathable oxygen, and no ozone layer to protect against ultraviolet rays. Our best guess was that the atmosphere contained ammonia, methane, carbon dioxide, and hydrogen gases, very much like Jupiter's atmosphere. Roll over chemical representations to see gases. In the early '50s, Urey and I designed a system that simulated the pre-life, pre-biotic conditions on Earth. This is a recirculating system. The gases are in the upper chamber, the "atmosphere," and can condense and dissolve in the water in the lower chamber, the "ocean." Products can vaporize out of the lower chamber, and reenter the upper chamber in gaseous form. This is a recirculating system. The gases are in the upper chamber, the "atmosphere," and can condense and dissolve in the water in the lower chamber, the "ocean." Products can vaporize out of the lower chamber, and re-enter the upper chamber in gaseous form. The gases in the upper chamber get hit by electrical discharges, like lightning in the early Earth's atmosphere. This provides the energy for any possible chemical reactions. Later, energy in the form of UV radiation or heat was used and found to be just as effective in similar experiments. Within hours of circulation, simple organic molecules like hydrogen cyanide, formaldehyde, and acetaldehyde were found in the atmospheric chamber. These molecules accumulated in the lower oceanic chamber and interacted to make a number of amino acids, and other organic acids. These molecules accumulated in the lower oceanic chamber and interacted to make a number of amino acids and other organic acids. Eventually, we also found nucleotides, sugars, and other organic molecules in the mix. Basically, all the building blocks of life can be made in this chamber apparatus. Amino acids can join to form longer chains. Nucleotides can also bond and form longer chains. I'm Tom Cech. Miller and Urey's experiments show that organic molecules can be made in the pre-life conditions of Earth. But it's a long way from molecules bumping into each other to form short chains to the long-chain molecules that carry hereditary information. RNA was very likely the first molecule to be able to replicate itself. In the primordial soup, a single-stranded RNA molecule could be a template. Single nucleotides could base-pair to the template, and then bind to form longer RNA molecules. The process can be repeated and a copy of the original RNA molecule is made. The RNA has replicated. This type of self-replication is one reason why RNA could be the first genetic molecule. RNA is also very versatile; it acts as a structural component of ribosomes and most importantly, I found that it could act as an enzyme. I isolated a specific type of RNA from Tetrahymena thermophila, a single-celled protozoan. This RNA is the precursor of one of the ribosomal RNAs and has a 400 base intron that must be spliced out. Much to my surprise, the RNA spliced itself, with no help from any proteins. The only necessary ingredient is the nucleotide guanine with a free 3' hydroxyl group. I radiolabeled the guanine, and was able to track the reaction. The free 3' hydroxyl group of guanine "attacks" and links to the 5' end of the intron. The 3' hydroxyl group of exon A then links to the 5' end of exon B. This splices out the intron. The transfer of hydroxyl groups seems to be simultaneous with no net loss or gain of metabolic energy. RNA acts as its own catalyst. By studying ribonuclease P of E. coli, my colleague Sidney Altman independently showed a catalytic function for RNA. The two of us shared the 1989 Nobel Prize for Chemistry for our work. Our discoveries changed the central dogma. RNA is not just the transmitter of genetic information, RNA can also act as enzymes. These are now called ribozymes.
Amino acids and other organic molecules have spatial orientations. Some molecules are mirror images of each other and these are known as L- and D-forms.
All the amino acids used by living organisms on earth are in the L-form. Why?