Understanding the Code of Life is important to understanding how our bodies function and how they are evolving. This scond post in a series explains the Code of Life.
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 2 - the code of life (below)
Part 3 - why they're similar
Part 4 - and why that's significant
The Code of Life
This is a eukaryotic cell (image from gene therapy review):
The human body contains about 10,000,000,000,000 of them, each one is only 0.01 mm in length but it contains an immensely varied chemical soup. Everything the human body does is controlled by the way the cells move or the chemicals the cells release; and that's determined by which chemicals in the soup react with each other.
The cell controls which reactions happen in two ways. Firstly it uses membranes to divide the cell into different 'reaction chambers'. And secondly it uses proteins as catalysts. Each specific catalyst has a dented surface that exactly matches the particular chemicals in the soup that it wants to react. Without the catalyst the chemicals bump together at random, only reacting if they happen to hit each other facing in exactly the right direction. With the catalyst the correct orientation happens every time, and the speed of the reaction is increased by a factor of a million or even a billion.
But it wasn't until 1953 that we cracked the code of how the cell decides which protein catalysts to make, or where it stores the information.
Locating the Code
It was known that the nucleus of the cell contained structures called chromosomes (chromosome images from Wikipedia):
Humans have 23 pairs of them:
In 1953, James Watson and Francis Crick discovered that our chromosomes are made up of DeoxyriboNucleic Acid (DNA), arranged in a double-helix structure (image from Wikipedia). Read more about Watson & Crick, the basics of DNA and how it "does it's thing" in these past journal posts.
And that genetic information is encoded in this twisted ladder using the sequence of 'base pairs' that make up the rungs of the ladder. There are 4 base pairs, which are known by their initial letters: T, C, A & G.
Chromosomes vary in length, but average about 100,000,000 base pairs in length (source). Each base pair is about 0.34 nanometers long, which means that the DNA in each cell, if fully unwound, would stretch almost 2 meters high.
Cracking the Code
In 1961, Francis Crick and Sydney Brenner demonstrated that these base pairs are arranged into groups of three, known as "codons", such as: TGG or CTA, each of which corresponds to a particular amino acid (image from NASA):
Actually working out which codon corresponded to which amino acid was done in a massive race by labs around the world, triggered by Crick and Brenner's announcement. Each lab synthesised a sequence of base pairs, such as "CCC-CCC-CCC-CCC" and then fed it into the right part of a cell, to see which amino acid then got produced.
Not all the codons correspond to an amino acid. Some combinations are interpreted as "START SEQUENCE" and "STOP SEQUENCE". These START and STOP signals are used to divide the chromosome into regions called "genes", each gene sequence corresponding to a particular sequence of amino acids that forms a specific protein catalyst.
(If you'd like to know more about the code, and how it was discovered, I recommend as a good starting place this Introduction to the subject. )
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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