The ribosome is a nanomolecular factory that uses genetic instructions and amino acids to build proteins. If the previous understanding of the functions of the ribosome were not enough evidence for design, new technology has enabled researchers capture nanoscale movements inside the structure and found that the functioning of the ribosome was complicated than previously thought.1
In the protein manufacturing process, the genetic code – or instruction manual – for making proteins lies inside a cell’s double-stranded DNA. When the cell needs to produce more proteins, the DNA unzips into two separate strands, exposing the protein code so it can be duplicated by single-stranded messenger RNA (mRNA). The mRNA dutifully delivers that code to the ribosome, which somehow reads the instructions, or “data tape,” as each amino acid is added to a growing protein chain.
At the same time, other RNA molecules, called transfer RNA (tRNA), bring to the ribosome amino acids, the raw building blocks needed for protein construction.
To help elucidate the ribosome’s movements as it interacts with mRNA and tRNA, the researchers used X-ray crystallography to obtain a highly detailed picture of the ribosome – a mere 21 nanometers wide – from an Escherichia coli bacterium. In addition to revealing atomic level detail, the technique allowed the researchers to capture the ribosome mid-action, a challenge because it acts fast, adding 20 new amino acids to a protein chain every second.
“Scientists used to think that the ribosome made a simple two-stage ratcheting motion by rotating back and forth as it interacts with mRNA and tRNA,” said Cate, who is also a member of the California Institute for Quantitative Biomedical Research (QB3) at UC Berkeley. “What we captured were images of the ribosome in intermediate stages between the rotations, showing that there are at least four steps in this ratcheting mechanism.”
“We suspect that the ribosome changes its conformation in so many steps to allow it to interact with relatively big tRNAs while keeping the two segments of the ribosome from flying apart,” said Cate. “It’s much more complicated than the simple ratcheting mechanism in a socket wrench.”
Cate said that while this study marked a major accomplishment in cracking open the “black box” of ribosomal function, there are far more details yet to be revealed. Advances in imaging techniques over the next decade should allow researchers to go beyond the snapshots taken in this study to high-resolution movies of a ribosome’s movements, he said. (emphasis mine)
1 New Images Capture Cell’s Ribosomes At Work, ScienceDaily, 8/23/09