Biology Reference
In-Depth Information
are listed in Fig. 4.2. The continuing success of the discipline of molecular biol-
ogy is only possible because of this basic similarity between all organisms. It is the
unity of biochemistry that enables genetic engineers to take a gene from one type
of organism and get it to work inside a quite different organism. For example, the
production of human insulin by both bacteria and yeast has been achieved by iso-
lating the genes for this vital hormone from human cells and inserting them into
bacterial and yeast cells. These methods of production have now replaced the origi-
nal method of isolating insulin from the pancreas of pigs and cows for the treatment
of human diabetes.
The most detailed information about the diversity and relatedness of organisms
available today is provided by determining the base sequence of the DNA found in
different organisms. The total DNA sequence of each species is called its genome,
and it is the collection of genes in this genome that contains the information to
build and operate that species. Due to advances in sequencing technology, it is
now possible to determine the total DNA sequence of say, a new type of bac-
terium, in 24 hours. In recent years, increasing number of total genome sequences
have been determined, mostly for bacteria, but including some plants and animals,
including humans, chimpanzees, dogs, cats, fish, worms, flies, rice and maize. These
sequences show directly that, for example, we share almost all our genes with chim-
panzees, and thus chimpanzees are regarded as our closest relatives. But we also
share many of our genes with bacteria and plants - all organisms are genetically
related. None of these similarities is predicted by hypotheses that organisms have
been separately created.
The Principles of Molecular Biology
To help you understand how the DNA sequence in the genome specifies the entire
organism, Fig. 4.3 reminds you of the basic principles of molecular biology.
The modern view about the nature of life is that organisms are self-assembling
chemical machines programmed by their genes. The term “self-assembling” is used
because organisms grow, develop and reproduce by taking in chemicals from the
environment, and converting them into the huge range of other chemicals necessary
to build cells. The sum of all these processes is called metabolism. All the informa-
tion for metabolism is contained within the collection of genes that each organism
inherits from its parents. This information is internal to the organism and requires
no external directing agency for it to operate - in other words, organisms assemble
themselves.
Organisms are described as “machines” to describe the idea that the proper-
ties of organisms are due to the interactions of their component parts, in just the
same way that the properties of a motorcar result from the interactions between the
parts that it contains. This approach to thinking about organisms is called “hierar-
chical reductionism” and the important aspect of this definition is its hierarchical
nature. The properties of a complex system are explained in terms of the inter-
actions between the parts which form the next level of complexity down in the
