Some fascinating technical biology.
When we figured out how genes, which are like blueprints in a library, specify how to make proteins which are nanomolecular robots that make the chemical transformations that is life, that act as mini computers to process information that come together to make the mobile scaffolding that builds us... we thought we knew how the sequence of letters in each gene specified the correct sequence of the 20 different amino acids we snap together one after the other, like different tools, to make each robot. This beaded string of amino acid tools then folds into a stiff or flexy chemically active robot.
The code allows for specifying up to 64 different amino acids, but biology, world wide from bacteria to oak tree to human only uses 20. So there is some redundancy in the code. This has been a mystery.
It has also slowly become apparent that we don't understand how the strings of amino acids fold into the right shape. And indeed, under some conditions they don't!
A recent paper describes a clever way this redundancy allows for a gene to not only specify the correct sequence of amino acid tools to build the right protein but also to specify the speed at which the protein is built, which is essential for it folding into the correct functional shape.
New work hints at a reason why the genetic code is redundant! Needs to code not only for sequence of aminos but also the RATE at which the sequence gets translated to get the right shape and right function. Clever! Explainer:
Reading genes with 4 possible bases 3 at a time can lead to 4x4x4 possible words, translated to 64 possible amino acids to build proteins. Yet biology uses only 20! Presently most aminos are represented by 2 to 6 possible base combos. Redundant! or is it?
Protein function is dependent on shape. We knew shape is dependent on amino acid sequence specified in genes. But it's not like computer code, it's also physics, so shape is also dependent on RATE of building a protein. Cells need to regulate THAT. wait for it...
The redundancy in the genetic code allows for this. For each amino, different codons that code for it can have a different tRNA molecule translate the code to amino. Different versions of tRNA for each amino are made in varying amounts.
Needing a tRNA of low abundance will slow down the protein building process. By coding for a rare tRNA or abundant one the genes can also code for the RATE of translation (=building) of the protein and therefore its correct finally folded shape. 4/4
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