Biomedical Engineering Reference
In-Depth Information
Fig. 1.1
DNA structure
T
CAGGTAG
. . .
. . .
AGTCCATC
1.2.1
Genome
In an organism, the basic unit of life is the cell. Practically all cell function is carried
out by large molecules called
proteins
. There exist many types of proteins, and they
provide most of the cell structure and cell function. Some examples of proteins are
enzymes to promote chemical reactions, signaling molecules for communication
across cells, and molecules with moving parts [
1
], [
2
]. Proteins can have complex
shapes, allowing for many functions. Each protein is made up of a chain of amino
acids as determined by its corresponding gene, and the shape is determined by its
amino acid sequence [
1
], [
2
]. The unique shape of a protein allows it to chemically
bind to other molecules, including other proteins, that match its specific shape.
The genetic information of each living organism is encoded in DNA (Deoxyri-
bonucleic acid). DNA is a molecule consisting of a sequence of 4 nucleotide bases:
adenine, guanine, cytosine, and thymine (often shortened to the letters A, G, C, and
T respectively) [
3
]. The actual sequence of the bases is the property that encodes the
genetic information. The structure of DNA consists of two strands, each providing
a copy of the sequence. The two strands run in parallel and are connected to each
other through base pairing, wherein each base on one strand bonds with only one
type of base on the other strand. There are two types of base pairs, A-T and G-C. An
example of the DNA structure is shown in Fig.
1.1
.
The DNA can be visualized as a string of characters, where each character is one
of the four nucelotide bases.
Genes
are short stretches (chunks) of
DNA
(Fig.
1.2
)
that produce functional molecules proteins and RNA. The linear sequence of bases
in a gene spells out the sequence of amino acids in a protein.
When taken as a whole, the complete set of information in an organism's DNA is
called the genome. Individual “instances” of the same species have small variations
in their genome (which result in variations in characteristics of the human being
for instance). The entire genomes of several model organisms have been
sequenced
,
yielding the entire sequence for those organisms. For instance, the human genome
has been sequenced and has been found to consist of approximately 3.2 billion base
pairs in all and around 30,000 genes.
While is comprised of 4 bases, proteins are an amino acid chain with 20 possible
amino acids. The process of mapping a 4-letter alphabet (DNA) to 20-letter alphabet
DNA
Gene 1
Gene 2
Gene 3
Gene 4
Fig. 1.2
Genes consist of short stretches of DNA
