| MadSci Network: Biochemistry |
Rich: I am not entirely certain what you are interested in when you are
asking for the molecular formula of 'Human DNA.' The human genome, recently
sequenced contains several billion base pairs of DNA, either, and adenine,
guanine, cytosine, or thymine. Each of these base pairs is supported by a
sugar-phosphate backbone, and the double-helix of these base pairs, iterated
to the nth, makes up the genome. An individual set of base pairs, A-T, or
G-C, has a molecular weight of about 600. The structure of the four
(five) base pairs can be found in any biology, genetics or biochemistry
textbook. Gene V, VI, or VII, by Benjamin Lewin is a good place to start. Human
DNA is dynamic, however, and its molecular formula is constantly changing,
as DNA is cut, nicked, extended or digested, methylated etc. But at rough
approximation, 600 Daltons per base pair time 4 billion base pairs, means
that the human genome has a molecular weight of approximately 2.4 trillion
Daltons. As a comparison H2O, Water, has a mass of 18 Daltons. The chemical formula of the various base pairs and sugars can also be
found in the textbook, but I will list them below also: Adenine: C5H5N5 Guanine: C5H5N5O Cytosine: C4H5N3O Thymine: C5H5N2O2 Phosphate: PO4 2-deoxyribose: C5H9O4 A more useful piece of information might be to mention some of the
experiments that led to the ability to sequence the base pairs of DNA, and
how we determined what we know about it. DNA as the genetic material was determined by Griffith in 1928. He
observed that one could
(Click here for information on transformation, I have convered it entensively before) a harmless bacteria into a lethal one in mice by mixing the two. Years later, Oswald Avery found the transformable material to be deoxyribonucleic acid. As for the chemical, DNA was first isolated and identified by Johann Miescher in 1869, and was already being called DNA by the turn of the Century. Although, the complete molecular formula was largely determined by Phoebus Levine and Alexander Todd in the 1950's. In the 1940's, Erwin Chargaff observed that in any double strand of DNA, the ratio of A to T was 1:1 and G to C was also 1:1. Essentially that there is one T for every A, and a C for every G. This helped develop the base-pairing model we accept today, that A pairs with T, and G with C. The chemistry of why this occurs has since been determined, but is not warranted here.
The nature of the repication of DNA, with one strand serving as a template for the synthesis of a new one was elucidated by Meselson & Stahl in 1958, and the 3-D structure/model of DNA was determined by Francis Watson and James Crick in 1953, due to efforts by Maurice Wilkins and Rosalind Franklin.
The sequencing of DNA had two major advancements, one of which was dideoxy sequencing pioneered by Fred Sanger, where you replicate a chain of DNA, and it stops every pabe pair, generating a ladder that can be read, and the development of PCR, by Kerry Mullis in the 80's, which allows us to amplify large amounts of DNA in a test tube and use it to sequence, modify, mutate or work with. This, in addition to restriction enzymes is one the most important technologies we have today for manipulating genetic material. Restriction enzymes are proteins that cut DNA. The ones we utilize tend to cut DNA vey specifically, at only a certain set of base pairs, and this allows us to fragment and move pieces of DNA very precisely.
This week in Science & Nature, (Two Journals) the human genome is being unveiled. Science is presenting the privately funded genome sequenced by Celera Corp. (Craig Venter) and Nature is presenting a public funded genome performed by multipel groups around the world. The genome issue of Science is free on-line, and contains entensive notes and data on the gene organization, base pair content, coding and non-coding regions etc. etc. I encourage you to check it out, as it is extremely fact-filled and useful. You can access Science on-line here.
Science Magazin I hope this helps answer your questions, let us know if you need anything else. Thanks for writing to MadSci Network-Matt-
Try the links in the MadSci Library for more information on Biochemistry.