Our cells are incredible machines that provide for a variety of specialized functions, such as respiration, motion, digestion and more. Almost every cell in the body holds the individual's genome and uses it to make protiens to support thos emany functions. To understand how it's done, and how this relates to human evolution, read on........
Scientists predicted, based on a vestigial organ in the human body, that the human genome should contain a broken version of a particular reptile gene. This predicted gene has now been discovered, in the hidden 'comment' lines of the human genetic code.
Part 1 - the code of computers
Part 2 - the code of life
Part 3 - why they're similar
Part 4 - and why that's significant
I hope, in this part, to say why the code of computers and the code of life are similar so, if you missed the first two parts you might want to go skim them first before reading on...
How we use the Code of Life
To understand some of the similarities between the code of computer and the code of life, we're going to have to look at the actual machinery in the cell by which we start off with base pairs, and end up with proteins,
The process can be broken down into steps:
1. Transcribe the DNA into RNA
2. Modify the RNA
3. Translate the RNA into a chain of amino acids
4. Modify the chain of amino acids
(with a bit of transport happening between steps to take things to the right parts of the cell.)
Step 1 - Transcribe the DNA into RNA
This is the RNAP enzyme, which is responsible for hooking apart a small section of DNA in the cell's nucleus then coping the information from it onto a messanger strand of RNA which can be moved around the cell. The image is from Wikipedia.
Step 2 - Modify the RNA
This is the spliceosome (image from an Biologische Fakultat) which removes bits of the RNA and just throws them away. We call the bits it keeps "exons" and the bits it throws away "introns". The process is known as "splicing" (image from Wikipedia):
Step 3 - Translate the RNA into a chain of amino acids
This is the ribosome, and it translates the messanger RNA into a chain of amino acids known as a "peptide" (image from Wikipedia).
Step 4 - Modify the chain of amino acids
This is a chaperone enzyme, responsible for creating proteins from peptide chains by doing things like folding, making bridges, adding groups, cutting them in half, and so on. Think of it as a tailor doing a final fitting and accessorising. The image is from Wikipedia.
If the sequence of base pairs between the START and the STOP signs
are the equivalent of a single computer program, then the introns are
the equivalents of comment lines.
A boss can tell a programmer "We no longer need to have your web browser be able to send email." and the programmer responds by commenting out the bits of code that allow email sending. In just the same way, if a fish starts adapting to living in deep caves with no light, the bit of genetic code that gives the fish eyes may get 'commented out' by a random mutation that turns the previously active code into an intron, giving you a blind fish that doesn't need to expend energy on growing an organ it no longer has a use for.
These 'non-coding' regions of DNA are also subject to bit rot in just the same way as computer programs are. A retrovirus is an RNA virus that is replicated in a host cell via the enzyme reverse transcriptase to produce DNA from its RNA genome. The DNA is then incorporated into the host's genome by an integrase enzyme. The virus thereafter replicates as part of the host cell's DNA. An endogenous retroviruses is one which affects the germline cells in the eggs or sperm, which mean the changes made in the hosts DNA are not restricted to a single cell, they are passed on to all the host's descendants.
These 'markers' are left in the DNA at a random but steady rate, and these remain untouched when the markers fall within the introns, slowly degrading the unused functionality in successive generations of the creature.
In just the same way that we can estimate how long ago a piece of computer code went inactive, by how many of the commented out lines have accumulated mistakes, we can estimate how long ago a feature in a creature became vestigial, by comparing the 'commented out' version of a gene with a clean working copy of the gene from a related species (such as a fish that remained on the surface and still uses eyes).
A huge thanks to Clairwil for this special series that will walk us through using human genetics to establish ancestry of our species. For more from Clairwil, or discussion on the topic of evolution, see her new group Debate Evolution vs Creationsim. It's not just for debate - by reading, you'll learn alot about evolution, genetics and what's new in our scientific understanding of where we came from.
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