Natural Selection and Macromolecules
DNA
The larger organic molecules found in living
organisms are called macromolecules because of their large size. They are primarily proteins, carbohydrates,
and nucleic acids. Many of them function
within the cells where they were formed.
But the most important or central one to biology and evolution is DNA, a
nucleic acid.
The long, linear double-stranded molecules of DNA
are coiled in helices of chromosomes enclosed within the nucleus of animal and
plant cells. How the purine and
pyrimidine base combinations along the molecule function, to duplicate the DNA
sequence and form RNA and proteins to do the work of the cell, was a mystery
until the code units were first determined by Watson and Crick in the mid
1950’s.
Determining the DNA code of humans then became a
major priority for geneticists and molecular biologists throughout the
world. Francis Collins was a leader
among those heading the Human Genome Project, which with others determined the
sequence. Along the way of his
scientific journey he made a transition from atheism to belief in God. He describes many aspects of the journey in
his 2006 book, The Language of God*.
When I read the book in 2007 I thought he had
written the book I was trying to write.
He also finds evolution by means of natural selection a basically true
scientific explanation. He does a good
job of refuting creationist arguments.
He does a much better job explaining the molecular side of evolution in
the genetics area than I could possibly do.
If you want to know that, please read his book. If you don’t want the details, please read
the introduction and first chapter of his book.
It is great food for thought.
Macromolecules
in cells
Some macromolecules have an important structural
function outside of cells. The protein,
collagen, functions as a connective tissue fiber in tendons, ligaments, and
separate fibers of loose connective
tissue of many animals such as ourselves.
It, and the spongin fibers in sponge tissue, are similar proteins and
are the only proteins that release the amino acid hydroxyproline when
hydrolyzed. The collagen fiber networks in bone
are the primary protein portion strengthening the crystallized calcium compounds of mineralized
bone.
Keratin is a protein important in hair, nails, and
horns of some mammals. Chitin is a
polymer of acetyl glucosamine, the structural protein of insect and other
arthropod exoskeletons.
Within the cells, DNA has functions demonstrating many
of the potential functions cell molecules may have. Slight changes in function can be eliminated
or incorporated in subsequent generations depending on accompanying rates of
survival.
Localization. The DNA can keep functional parts (genes) in
close association. Then necessary
interactions can be accomplished efficiently.
It provides a better opportunity for functional clusters to be passed on
to offspring during reproduction.
Retention. They are easily retained by the cell as well
as by the nucleus.
Storage. The information coded can be kept and then
passed on to subsequent generations. The
individual’s DNA cannot be effectively built up and depleted, like carbohydrate
and fat nutrient reserves, except through cell division or cell death.
Reduced
osmotic impact. The approximately four
dozen molecules of DNA in each human cell have less osmotic impact than most other
major components of the fluid portion of the cell that do not readily permeate
the cell membrane.
Reduced
chemical reactivity. Relative to size, reactivity
of DNA is far below that of most small organic compounds.
Diversity. We are each unique in our DNA, as are most
species.
Reproduction. DNA contains the information needed to
develop within a functioning cell the machinery to duplicate itself and make
the other changes necessary for reproduction of the species. The plan is there. All it needs is a functioning organism and a
favorable environment.
Evolution
A variety of glitches in the mechanism for
duplicating itself can rearrange one or more portions of the DNA molecule. If it is a serious enough change the organism
or the offspring getting the change may die or be incapable of
reproduction. A minor change will
usually be passed on with little effect if it is a region of the DNA not active
in producing necessary products.
But those changes or rearrangements of sequences may
in rare instances be beneficial to survival of the offspring. Over time, it may contribute to better
reproductive and survival success and the new form will eventually replace the
original form. That is the simplified
version of the development of the diverse community of species living on earth.
So what is good for survival? Whatever works best! A heavy fur coat if you live in the arctic, a
skimpy or missing coat of fur if you live in the tropics. A trim body may help if food is abundant and
the environment is comfortable. Abundant
fat may help you survive if you face long winters or times without food. Migrate to another environment and your
offspring will eventually be quite different from those that didn’t migrate.
The story of evolution is in the DNA. But it is often easier to find the story in
conjunction with the details of the organisms when the intermediate forms are
extinct.
*Collins,
Francis S. 2006. The Language of God – A Scientist Presents Evidence for Belief. Free Press, New York. 294 pp.
Joseph G. Engemann May 2, 2014
No comments:
Post a Comment