Biology Application Brief
University of Houston
The University of Houston is involved with the Human Genome Program
in sequencing DNA. Dr. Dan Davison is involved in characterizing
the human beta-globin complex.
Interest in DNA and how it functions is on the rise. Examples are even
found in popular literature such as Michael Crichton's fictional
Jurassic Park, where recovered dinosaur DNA was used to create new
dinosaurs. The Human Genome Program has made great strides in
sequencing human DNA to achieve a better understanding of our own DNA.
Deoxyribonucleic acid, DNA, consists of four nitrogenous bases, adenine
(A), cytosine (C), guanine (G), and thymine (T). The sequence of these
four bases constitutes the code which enables the DNA to control the
characteristics of a cell or organism.
The human genome consists of seven billion bases in 24 types of
chromosomes made up of DNA. These chromosomes are organized as 23
pairs of chromosomes, with 22 somatic chromosome pairs and a pair of
either two X chromosomes (in females) or one X and one Y chromosome (in
males). Within individual chromosomes are areas where genetic activity
takes place along with areas of inactivity. One task of the Human
Genome Project is to locate and map areas of activity and inactivity.
The active areas contain genes and a coding region, which typically
specify which protein will be fabricated. The coding region regulates
when and how certain proteins are produced.
Discontinous Coding Regions
A DNA sequence contains many levels of structure and information.
Adding to the complexity, the coding regions are sometimes interrupted
and continued further downstream like portions of an article may be
continued on different pages of a newspaper. However, unlike a
newspaper, there are no instructions or markers for where the remaining
portion of the coding region may be found in the DNA. Instead the
cellular machinery manufacturing the protein uses subtle signals from
the DNA to determine where the protein coding region will resume.
Beta-hemoglobin Gene Study
One of the genes being studied is the beta-hemoglobin complex. This
complex is actually a collection of seven genes lying next to each
other that are expressed at different times or stages of development.
There are different versions of the complex expressed in the embryo,
the fetus, and the adult, as well as other variations. The
beta-hemoglobin protein associates with the alpha-hemoglobin protein,
to form hemoglobin. Hemoglobin is a protein contained in red blood
cells that produces the cell's coloration, and is responsible for
carrying oxygen throughout the body.
Structurally DNA must curl around itself forming the famous double
helix (additional curling of this double helix is called supercoiling).
This results in the human genetic blueprint, consisting of billions of
bases, hundreds of millimeters long, being packed into the tiny nucleus
of every single cell. Detection of the levels of organization is
possible because of the long range correlations between bases. Some
correlations are due to protein coding, while others are due to the
helical structure, superhelical structure and chromosome organization.