Confused?

Me too... but you can be helped by reading my intro post.

Saturday, August 28, 2010

DNA 101


I want to try to blog here once a week – which will probably mean the weekends. All week, I was thinking about what I would write about, and I was all set to explain genetically engineered food products and how, while they certainly need to be regulated and created safely, they aren’t the death threat some critics make them out to be.

In doing a little research for this topic, I came across the 2005 Eurobarometer – a report describing the public opinion of various technologies (including genetic engineering). One survey given was to gauge general ‘textbook’ knowledge about genetics and science. The results from three questions shocked me and gave me a new inspiration for this post. But before we get to that, here are the three questions-in-question:
     1.  True or false: By eating a genetically modified fruit, a person’s genes could also become modified.

     2. True or false: Ordinary tomatoes do not contain genes, while genetically modified tomatoes do.


     3. True or false: Human cells and genes function differently from those in animals and plants.
If you answered false to these questions, you are right! If you didn't, sadly, you are in good company: only 54%, 41%, and 34% of respondents correctly answered each question, respectively.
I did not take this picture.
Well, it is clear that a tutorial is in order before the intricacies of genetic engineering can be discussed. So, I present to you: DNA 101.
DNA = your genes.
DNA is actually an acronym for the technical chemical structure (deoxyribonucleic acid) of all your genetic material. This molecule resides inside the nucleus of every single one of your cells. Not just your cells, but the cells of every single living thing. That means humans and bacteria; plants and animals.
DNA is the chemical that is able to store all your genes in one place, so that it can be replicated (like when a cell divides) and passed on (to your kids through your eggs or sperm) without mistakes and at the proper time. Think of it as the library for the blueprint of your genes: a safe place to store all that genetic information until you need it. Again, this is not something special to humans: everything alive has the same chemical – DNA – for coding their genes!
What do genes look like? On paper, they look like a bunch of letters – As, Ts, Cs and Gs – all in a row. These letters also stand for the chemical names (adenosine, tyrosine, cytosine, and guanidine) of the bits that are connected together to make one long strand of DNA. Just as an example, here is the sequence of the gene that codes for insulin in human beings:
agccctccaggacaggctgcatcagaagaggccatcaagcagatcactgtccttctgccatggccctgtggatgcgcctcctgcccctgctggcgctgctggccctctggggacctgacccagccgcagcctttgtgaaccaacacctgtgcggctcacacctggtggaagctctctacctagtgtgcggggaacgaggcttcttctacacacccaagacccgccgggaggcagaggacctgcaggtggggcaggtggagctgggcgggggccctggtgcaggcagcctgcagcccttggccctggaggggtccctgcagaagcgtggcattgtggaacaatgctgtaccagcatctgctccctctaccagctggagaactactgcaactagacgcagcccgcaggcagccccacacccgccgcctcctgcaccgagagagatggaataaagcccttgaaccagcaaaa

From DNA to a protein
OK, so how does that DNA sequence get from a jumble of letters to insulin?
First, when you (or any living thing) wants a gene to be “on,” it has to take it from its storage state (DNA) to its more active state (RNA, another acronym for ribonucleic acid).
Why this middle-man, RNA? Well, DNA doesn’t stop at the end of one gene. That insulin sequence above is connected to many other genes all on a single chromosome (the packing unit of DNA). But you don’t necessarily want alllll those genes “on” at one time. So, you only make RNA from the parts you want. It’s like making a photocopy of a single chapter from a book in the library; or looking at the details of a single room on a blueprint.
RNA looks a lot like DNA – only instead of the letter T, you have the letter U – just a slightly different chemical, and unless you’re trying to make a gene, it’s not so important.
But it’s still a jumble of letters that looks nothing like insulin.
Insulin is a protein. DNA and RNA are not. How do you make a protein from something that is not a protein? Well, the reason DNA is called the genetic code is because it is just that: it is a code for making protein. If you start at the beginning of a gene, every 3 letters codes for one letter of a protein.
Huh?
Well, just as DNA and RNA can be written on paper as a string of letters, so can proteins. Instead of using just 4 letters, proteins are made up of 20! That is, there are 20 different molecules that can be strung together in different combinations to make every protein in your body – or every protein in a bacteria.
That insulin DNA sequence above gets made into the following protein:
MALWMRLLPLLALLALWGPDPAAAFVNQHLCGSHLVEALYLVCGERGFFYTPKTRREAEDLQVGQVELGGGPGAGSLQPLALEGSLQKRGIVEQCCTSICSLYQLENYCN
Yes, I know what you’re thinking. It’s still a string of letters. But this is a different string of letters! THIS string of letters is made of different molecules, that have different shapes, sizes, and electric charges – all properties that allow this string of letters to fold and look and behave like – insulin!
This structure was solved by researchers in Denmark in 1997.
 And because I know you’re dying to know: this is what it looks like! All those nice spiral ribbons are the backbone – the general arrangement of all those letters in space. The black and gray circles are parts of the molecules that stick out from the backbone and give different chemical properties to the protein. Didn’t know you could do THAT with a bunch of letters, did you?
So, just think about it: every single protein in your body – and in every living thing – starts out as DNA! And every time your body needs a certain protein, it can go to the DNA, copy the gene it needs into RNA, and then decode the RNA to make protein. Pretty amazing, huh?
Obviously, there are some differences in the DNA between you and bacteria, otherwise we’d be bacteria. But it’s really not a huge difference – the basics are the same: bacteria and you both have DNA made up of A, T, C, G; this DNA gets copied to RNA; this RNA gets decoded into the same 20 letters of proteins. Some of these sequences have been changed over evolution. And we obviously don’t need the same genes for say, photosynthesis, that plants do.
Related to the above survey, your genes are strictly regulated – incredibly so. They don’t have minds of their own, and they’re not just moving about, jumping from place to place. (Disclaimer: there are examples of genes moving from one organism to another, but it happens over evolution and very rarely. Nothing for you to worry about). Think of all the bacteria you have living in your gut right at this very instant: their DNA stays with them and your DNA stays with you. When you eat a tomato – even the ordinary ones – the DNA from the tomato doesn’t jump into your cells and turn your skin red.  
So, that’s the basic story of how your genes make YOU. And how bacteria genes make bacteria, tomato genes make tomatoes, etc. I find it remarkable how all these complex organisms can be so diverse and even function at all, from the same four letter code of DNA. Simple is usually best!
I hope you can now pass the survey questions with flying colors.
Nor this one.
While it was a bit depressing to be inspired to write this tutorial, it was kind of fun! I think I’ll be on the lookout for other topics in the future!

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