Sunday, June 17, 2007

A Two-Minute Education in Molecular Biology

Most readers of science blogs already have at least some basic knowledge of molecular biology, but in my experience there are many people interested in science, including academics in non-science fields, lawyers, and older physicians, who aren't famliar with the basics. Such people might have a hard time figuring out where to start learning among all of the many technical terms and techniques.

If you learn the following five key terms, I promise you will be able to get at least the gist of most basic biomedical research. When I try to explain my research to people, it's easy if they know these five terms, and nearly impossible if they don't. These five key terms make up what's whimsically called the Central Dogma. You may have heard that there are all sorts of exceptions to the Central Dogma, and there are, but it still forms the core of our understanding of how instructions from our DNA get carried out in the cell. This is the part of molecular biology that absolutely everyone should know - it's as fundamental to biology the idea that matter is made of atoms (which in turn are made up of nuclei of neutrons and protons, surrounded by electrons) is to physics.

DNA - this is of course where the information to build the cell is stored. DNA consists of two winding chains of small chemical units. The most important part of these units is the portion called the base. Four types of base occur in DNA, abbreviated A, T, C, G. In the two winding chains of DNA, bases are always aligned opposite each other in specific pairs: A is always opposite T, and G is always opposite C:

Thus, if you know the sequence of bases of one chain, then you automatically know the sequence of the opposite chain. DNA sequencing is, obviously, the effort to determine the exact sequence of bases in a stretch of DNA. The sequences of these letters code for proteins, as well as many other important elements.

Our DNA is found in 23 pairs of chromosomes, where it is packaged up with lots and lots of protein.

RNA - Just like DNA, except different. RNA generally comes as one chain instead of two, and contains the base 'U' instead of the 'T' in DNA. RNA has many functions, but for our purposes here, RNA reproduces the information-containing DNA sequence in a form that can be carried to the protein-producing machinery of the cell. RNA that does this is called 'messenger RNA', or mRNA.

Transcription is the process by which RNA is produced from the DNA template. In this process the two chains of DNA are unwound, and one strand of DNA serves as a template for synthesizing a brand new strand of RNA, following the base pairing rules I mentioned above - G matches up with C, and A with T - except that in RNA chains, U gets substituted for T. This new strand of RNA can then move away from the DNA to some other part of the cell, where the information contained in the sequence of bases can be used to carry out various functions.

Many of the interesting new discoveries in basic biology involve transcription so it is important to be famliar with this term. When research reports talk about a region of DNA being 'transcribed', it means that RNA strands are made that match the sequence of that given DNA region. Some portions of our DNA are transcribed (and thus the information in that sequence of DNA can potentially be carried to other parts of the cell), while other portions are never transcribed (although that doesn't mean these non-transcribed regions are worthless - many sequences important for regulating transcription are found here.)

Proteins are the primary workhorses of the cell. Like RNA and DNA, proteins are chains consisting of small chemical subunits. In the case of proteins, those small subunits are amino acids. Amino acids, and thus proteins are much, much more chemically diverse than RNA or DNA, which is why proteins do much of the actual work in the cell - the enzymes that metabolize nutrients, and the receptors that sense hormones on the outside of the cell are proteins - as are your hair and finger nails.

Translation is the process by which the information encoded in the sequence of an RNA strand is used to produce a chain of amino acids to make a protein. The reasoning behind the terminology is this: whereas an RNA strand is transcribed from DNA in the same 'language' of bases, proteins are made by translating the language of bases into the language of amino acids. The bases-amino acid dictionary is called the genetic code. A group of three bases codes for one amino acid (below, amino acids are represented by single letters):

In addition to these five key terms, there is one more that I think comes in handy:

Transcription factor is a protein which binds to DNA in a specific place and helps to initiate (or in some cases, prevent) the process of transcription. Transcription factors are critical in controlling many complex processes, such as development of an organism from a single-celled zygote, and the process of cell division.

If you are familiar with these few terms, I guarantee that the stories on biology research you read about on blogs, magazines, and newspapers will be much more clear. If you don't understand these terms, there is no way you can understand the discoveries that are reported in the media.

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