DNA = You (Or, How to assemble a human)Posted: January 16, 2013
Many of you may know that DNA is the code that is stored in tightly-wrapped bundles in our cells; you may also know that our genes are what is being coded for by our DNA; you may even know that genes are important to us because they determine how we are made. But do you know how to get from DNA to you?
If your body was a program, DNA would be kind of like computer code; to figure out the program, first you need to know how the coding language works. Scientists have figured this out a long time ago; the DNA code is very simple, and only made up of four letters (called bases) – A for Adenosine, T for Thymine, G for Guanine and C for Cytosine. Each ‘word’ in DNA, also known as a codon, is made up of three letters; for example, you could have TAC, ATC, ACT or ATT. These all make itty-bitty pieces of your body’s cells, which will eventually end up as you.
However, your cells can’t read DNA directly; what they can read is a similar language called RNA (ribonucleic acid). RNA is made up of four letters too – A, G, C and instead of T, RNA has U for Uracil. This process of converting DNA to RNA is called transcription, and is carried out by a protein called RNA polymerase. The DNA words above would then be read as UAC, AUC, ACU or AUU. Or would they?
One thing about the bases A, T, G and C is that they bind with one another to form two different sets of base pairs – A always binds to T or vice versa, and G always binds to C or vice versa. (In the case of RNA, just substitute U for T and you won’t go wrong!)
When DNA is converted into RNA, RNA polymerase makes use of this base pairing to carry out its transcription work – in other words, G in DNA is transcribed into C in RNA, and vice versa; T in DNA is transcribed into A in RNA, but A in DNA is transcribed into U in RNA. (See – just substitute U for T in RNA!) So the DNA words transcribed into RNA would be AUG, UAG, UGA or UAA. Easy, isn’t it?
So now we have:
After transcribing DNA into RNA, we need to translate RNA into amino acids, which can then be assembled into proteins; in order to do so, we need the help of a protein molecule known as a ribosome.
If we think of RNA as kind of like an IKEA instruction manual, the ribosome then acts a little like a very meticulous person putting together a piece of IKEA furniture. It reads the RNA code, and makes sure that each amino acid that corresponds to each RNA codon is present. The ribosome then assembles a protein molecule out of the amino acids according to the RNA code, but unlike some people who put together IKEA furniture in any old order, the ribosome puts the protein together in a sequential manner, reading off one codon after another.
A special molecule (also made up of RNA) called transfer RNA brings different amino acids to the ribosome, kind of like a friend or a trained monkey bringing different parts of the IKEA furniture to the very meticulous person.
Because both tRNA and the RNA code (also known as memory RNA, or mRNA) are both made up of RNA, they are able to form complementary base pairings with each other. So like the trained monkey being able to match the shape of a screw in the IKEA manual to an actual screw, a tRNA is able to match the RNA codon to the amino acid it has bound to, and hands it to the ribosome, which attaches the new amino acid to the previous amino acid.
Proteins are made up of long sequences of amino acids, folded into different configurations. (For more information, I will soon release a post on protein folding. Soon.) Different sequences of amino acids yield different proteins; different proteins then come together with lipids and carbohydrates to make cells. Many cells are put together, and thus make up organs, which when assembled together in the proper fashion, become you. And me.
Et voila, one human, fresh off the assembly line.