About Chris Expertise Will answer mouse and human molecular genetics, as well as basic undergrad genetics queries; will also try for other organisms. Microarray technology questions are also welcome.
Experience BSc biochem; PhD candidate in molecular genetics involving microarrays
Question What roles do DNA play in cells and how does the sturcture of DNA consistent with those roles?
My book went over it, but i didn't understand it. it wasnt english. :)
Answer Hey Angie, let me see if I can rephrase this stuff - in English :-)
DNA is the "stuff" our genes are made of. It's like a scroll that contains the instructions to make all the bits and pieces for a cell. A cell is quite a complicated little thing, and it carries out a lot of functions - most of them chemical. It has a maintained structure, uses fuel, gets rid of waste, creates and uses substances it needs, communicates with its environment, etc. In order to perform all these tasks, it needs tools - and these are primarily proteins. The DNA encodes the instructions for making these proteins. In fact, it contains the instructions to make *any* protein in our bodies. Cells don't require all these proteins, so they pick and choose the instructions relevant to them.
Now, if you have instructions, they must be written down in some code or alphabet that makes sense. The DNA alphabet is four letters long - A, G, C, T. Proteins are made up of 20 possible bricks, or amino acids, so the instructions in DNA have to be such that they can specify which one of these aminoacids they mean. It turns out that you get enough combinations with three letter DNA "words" - all the combinations of ACGT (there are actually 64 combos, so more than one can stand for an aminoacid). So DNA has instructions in three letter words, which specify the sequence of aminoacids that has to be strung together to make a protein.
So DNA's structure is consistent with its role, because this simple alphabet can encode "words" to get its job done.
Ok, slightly more scientifically now, we say that genes are expressed when the instructions are used - they get copied into messenger, or mRNA, which is then used as a template to make protein. Only relevant genes are expressed in any cell type. DNA is a very long molecule, and must therefore be packaged very well in order to fit into a cell.It has a natural twist anyway (the double helix structure), so it gets super coiled (see the note at the end). Obviously, this presents a problem - you can't read a gene which is in a piece of DNA in deep storage! So the cell has to be very careful in handling its DNA to avoid such traps.
NOTE: to see how super coiling works, get a rubber band, and start twisting it. It becomes a helix; as you continue twisting, the twisted parts twis again, over themselves. That's supercoiling.
