can view a 3-D rotatable image of DNA here...
hereditary material of all multi-cellular organisms
is the famous double helix of deoxyribonucleic acid
(DNA). This contains all of our genes. DNA, itself is
made up of four chemical bases, pairs of which form
the "rungs" of the twisted, ladder-shaped DNA molecules.
These four molecules are adenine (A), thymine (T), cytosine
(C), and guanine (G).
genes are made up of stretches of these four bases
(arranged in different ways and in different lengths).
National Institute of Health
critical feature of DNA is the ability of the nucleotides
to make specific pairs: . Adenine pairs with Thymine
and Cytosine pairs with Guanine. We say A is complementary
to T (and U) and C is complementary to G
double helical structure of DNA, is due largely to
hydrogen bonding between the base pairs (shown as
green dotted lines in image to left), which link one
complementary strand to the other
bonds between guanine and cytosine
human genome of Homo sapiens is stored on 23 chromosome
pairs. 22 of these are autosomal chromosome pairs,
while the remaining pair is sex-determining. The haploid
human genome occupies a total of just over 3 billion
DNA base pairs that means 6 billion base pairs per
Human Genome Project (HGP) was one of the great
feats of exploration in history - an inward voyage
of discovery rather than an outward exploration
of the planet or the cosmos; an international
research effort to sequence and map all of the
genes - together known as the genome - of members
of our species, --Homo Sapiens"--genome.gov
many genes does the Human Genome contain?
Human Genome Project has revealed that there are probably
about 20,000-25,000 'haploid' protein coding genes. The
completed human sequence can now identify their locations.
But only about 1.5% of the genome codes for proteins, while
the rest consists of non-coding RNA genes, regulatory sequences,
introns, and noncoding DNA (once known as "junk DNA").
the number of human genes seems to be less than a factor
of two greater than that of many much simpler organisms,
such as the roundworm and the fruit fly -- see table showing
number of genes for different organisms.
many genes do other organisms have?
3.3 x 109
though have on average three times as many kinds of proteins
as the fly or worm because of mRNA transcript "alternative
splicing" and chemical modifications to the proteins. This
process can yield different protein products from the same
gene. --------Fruit flies share nearly 60% of human genes
and are studied by
do genes actually do?
genes get a lot of attention, itís the proteins that perform
most life functions and even make up the majority of cellular
structures. Proteins are large, complex molecules made up
of smaller subunits called amino acids. Chemical properties
that distinguish the 20 different amino acids cause the
protein chains to fold up into specific three-dimensional
structures that define their particular functions in the
ribosome is the component of a biological cell that
creates proteins from all amino acids and RNA representing
human mitochondrial genome, while usually not included when
referring to the "human genome", is of tremendous interest
to geneticists, since it undoubtedly plays a role in mitochondrial
disease. It also sheds light on human evolution; for example,
analysis of variation in the human mitochondrial genome
has led to the postulation of a recent common ancestor for
all humans on the maternal line of descent.
different is the human genome from one person to the next?
have identified about 1.4 million locations where single-base
DNA differences (SNPs) occur in humans. This information
promises to revolutionize the processes of finding chromosomal
locations for disease-associated sequences and tracing human