Supporting Evidence 1

When does life begin?

What is life?

There is no easy definition for life. According to the Reader's Digest Great Illustrated Dictionary, p.979, life is defined as:

"The property or quality manifested in functions such as metabolism, growth, response to stimulation, and reproduction, by which living organisms are distinguished from dead organisms or from inanimate matter."

Technically this is definition could be applied to a piece of crystal as it can grow over time as if it is alive, break apart as if reproducing, and continue the growth. Does this mean all matter can be considered alive?

Russian biochemist, Dr Alexandr Ivanovich Oparin (1894-1980), a former professor at Moscow University, kept the definition of life simple and elegant when he said as early as 1924:

"There is no fundamental difference between a living organism and lifeless matter. The complex combination of manifestations and properties so characteristic of life must have arisen in the process of the evolution of matter." (1)

By Oparin's standards this would mean life is unimaginably common indeed and our question of "Are we alone?" would already have been answered. However, scientists don't like to make this discussion the shortest in history. Instead scientists prefer to mention the accepted point at which life begins.

Deoxyribonucleic Acid (DNA)

Lying within the nucleus of every living cell is a special molecule considered crucial to the development and evolution of life on Earth. On Earth, the scientists call it Deoxyribonucleic Acid (DNA). Most commonly found in the wrapped up state as a rigid and compact rod-like structure known as a chromosome, DNA in the unwrapped state is an extremely long and thin thread-like molecule designed to hold a great deal of biochemical and genetic information over the long-term as needed to replicate itself (genetic) and how to cope with its environment (biochemical). As Murray Gell-Mann of the California Institute of Technology said:

"In biological evolution, experience of the past is compressed in the genetic message encoded in DNA." (2)

How is information encoded in DNA?

Genetic and biochemical information is encoded along active segments of the DNA as a long sequence of nucleic acid bases that attach themselves to a very strong backbone of phosphates and deoxyribose sugar support structures. The nucleic acid bases are broadly composed of two types: purine and pyridimine bases. The names given to the purine bases are adenine and guanine, while the pyridimine bases are cytosine and thymine. For simplicity sake, scientists tend to use the letters A, C, T and G to represent these nucleic acid bases. The entire phosphate-sugar-base subunit is termed a nucleotide. Thus there are only four fundamental nucleotides that make up the code of life here on Earth:

Adenine (A)
Cytosine (C)
Thymine (T)
Guanine (G)

And any active segment of the DNA carrying instructions of how to build a protein is termed a gene.

Thus the complete set of genes running along various active sections of the DNA (or active sequences of nucleotides, wherever they might be) determines not only the species of animal or plant that will develop into a living thing, but also the individuality of the living thing within a species. This means that any changes made to any active sequence of purine and pyridimine bases (or nucleotides), for whatever reason, constitutes a mutation, which may alter, gain or completely lose, the original function", shape and/or behaviour of the living organism.

How do cells know what to do?

Every living cell in an organism contains an exact DNA replica or "blueprint" of the code of life. What makes a group of cells perform differently from another group within the body of a living organism are the range of different proteins produced from specific active sections along the DNA which tell the cell how to do things. However to avoid cells getting mixed up in their functions, the DNA is able to switch off specific genes and allow other genes to create the relevant proteins needed to control the cell.

Keep in the mind that proteins are chains of amino acids of which only 22 different types of amino acids are used by life on Earth as shown in the following table (3):.

Amino Acid

Symbol

Chemical Formula

Alanine

Ala

C3H7NO2

Arginine

Arg

C6H14N4O2

Asparagine

Asn

C4H8N2O3

Aspartic Acid

Asp

C4H7NO4

Cysteine

Cys

C3H7NO2S

Glutamic Acid

Glu

C5H9NO4

Glutamine

Gln

C5H10N2O3

Glycine

Gly

C2H5O2

Histidine

His

C6H9N3O2

Hydroxyproline

Hyp

C5H9NO3

Isoleucine

Ile

C6H13NO2

Leucine

Leu

C6H13NO2

Lysine

Lys

C6H14N2O2

Methionine

Met

C5H11NO2S

Phenylalanine

Phe

C9H11NO2

Proline

Pro

C5H9NO2

Pyroglutamatic Acid

Glp

C5H7NO3

Serine

Ser

C3H7NO3

Threonine

Thr

C4H9NO3

Tryptophan

Trp

C11H12N2O2

Tyrosine

Tyr

C9H11NO3

Valine

Val

C5H11NO2

Knowing how important these active coding sequences are to the healthy functioning of the cells and the living organism, DNA has found a way to maximize preservation of this information through the use of dummy or nonsense coding sequences. Also called introns or just plain "junk DNA", these non-active coding segments are thought to play a role in providing adequate separation between active sequences (called exons) and to further protect the relevant active codes when DNA is properly wrapped up into its more rigid rod-like structure as well as to handle vulnerabilities to DNA in the rigid form

What does DNA look like?

DNA is a double helix meaning it looks like a twisted or spiralling ladder. The sides of the ladder are the phosphates and sugars, whereas the rungs of the ladder are the location for the nucleic acid bases. The then 25 year old American biologist James D. Watson working with Francis H. Crick, an English physicist at the University of Cambridge, are credited with establishing the structure of DNA using the process of x-ray crystallography in 1953. Further details can be found in the original article (4) published by Watson and Crick titled "Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid" in the British journal Nature.

How is DNA information read?

For the information to be read, DNA has to undergo a delicate operation of unzipping or portion of the code. Then a smaller and more agile version of itself called messenger Ribonucleic Acid (mRNA) passes through the membrane of the nucleus and reads the coding sequence on DNA where it is transcribed into its own nucleic acid bases. Once the information is obtained, it runs back to tell the "ribosomes" how to assemble the amino acids to form a protein.

There isn't a great deal of difference between DNA and mRNA structurally speaking other than mRNA being a smaller single strand of the DNA. However, mRNA does not use thymine. Instead another nucleic acid base called uracil (U) replaces the thymine.

When an active coding sequence is read, mRNA is able to grab up to 3 nucleotides of information at any one time and keeps reading further sets of 3 nucleotides until the entire sequence of amino acids for the protein are determined. For example, a potentially complete active sequence of three nucleotides on DNA represented by the letters ATG and read by mRNA as AUG (remember, uracil is used instead of thymine) are sent to the ribosome where it assembles the amino acid known as methionine. If mRNA grabs the complete coding sequence from DNA consisting of nucleotides forming the letters TGT TGC (or UGU UGC from the perspective of mRNA), it is enough information for the ribosome to produce the amino acid called cysteine.

TTT

Phe

TCT

Ser

TAT

Tyr

TGT

Cys

TTC

TCC

TAC

TGC

TTA

Leu

TCA

TAA

Stop

TGA

Stop

TTG

TCG

TAG

TGG

Trp

CTT

Leu

CCT

Pro

CAT

His

CGT

Arg

CTC

CCC

CAC

CGC

CTA

CCA

CAA

Gln

CGA

CTG

CCG

CAG

CGG

ATT

Ile

ACT

Thr

AAT

Asn

AGT

Ser

ATC

ACC

AAC

AGC

ATA

ACA

AAA

Lys

AGA

Arg

ATG

Met

ACG

AAG

AGG

GTT

Val

GCT

Ala

GAT

Asp

GGT

Gly

GTC

GCC

GAC

GGC

GTA

GCA

GAA

Glu

GGA

GTG

GCG

GAG

GGG

But as many functions of a cell require proteins, numerous amino acids usually have to be assembled in a chain. It means the active coding sequence of DNA to produce a protein can be potentially very long.

Fortunately, not all physical characteristics of a living organism require complex proteins to control them. There are some characteristics that can be controlled by just a handful of selected amino acids arranged in a certain combination to help produce the right protein. The table below gives an example of how the hair colour of a human is changed by a handful of amino acids:

AMINO ACID CHAIN COLOUR

Met - Ser - Thr - Gln - Phe

Red hair

Met - Ser - Thr - His - Leu

Blonde hair

Met - Pro - Thr - His - Phe

Black hair

Met - Pro - Thur - Gln - Leu

Brown hair

Met = Methionine; Ser = Serine; Pro = Proline; Thr = Threonine; His = Histidine; Phe = Phenylalanine; Lau = Leucine; Gln = Glutamine.

Why must DNA replicate itself?

To understand why DNA undergoes self-replication, it is necessary to explain how the environment plays a crucial role in this process.

Imagine we lived in a universe containing no radiation. Assuming matter could exist in this environment, we would discover one interesting fact: nothing would move. In other words, there would be no collisions. While there are no collisions, complex molecules would never be produced. In a universe free of radiation, the genetic code and DNA itself would simply not exist.

However, something interesting happens when we turn on the radiation. Matter is suddenly created and it starts to move with the radiation, and potentially quite significantly. Life, on the other hand, prefers not to change in order to survive for a long time, Fortunately, certain environments help provide the protection from radiation to minimise the amount of change exerted on matter.

Rocky planets are truly a godsend for atoms and molecules needing to attain stability and preservation of their chemical structures. The great piece of rock in space composed mostly of iron constitutes an excellent radiation shield and reduces the number of collisions with molecules and atoms to a significant degree. Not only this but so to do the atmospheres of these planets provide further protection to the atoms and molecules.

Nevertheless radiation from space and other matter will concentrate around a rocky planet and continue to fall into it. Should the radiation or other matter be sufficiently energetic, electrons may be stripped off atoms, and molecules may break apart by losing one or more atoms to form what are known as free radicals. Fortunately there will be regular brief moments when the energy dissipates allowing these free radicals to quickly reassemble to form larger and more complex organic molecules.

Should these molecules enter tiny raindrops or fall closer to the surface of the planet, greater protection can be experienced. Fewer collisions within these protected regions will see larger molecules survive for longer.

Still the radiation persists and sometimes reach the surface of the planet. Molecules on the surface will continue to be enticed to form more complex structures as the best solution to becoming stable again.

A more substantial supply of water by way of shallow seas do help to increase the protection for developing and highly complex organic molecules. Hang around near the surfaces of clays and molecules can inadvertently receive greater protection. Then suddenly the molecules grow long chains on these surfaces. Some molecules use the extra chain length to wrap itself for further protection. Some other chains also develop a spiralling structure with its backbone of atoms acting as a barrier against radiation and other matter as it protects something important in the centre to help further achieve its goal of greater stability (sounds familiar?).

Water provides further protection forming tiny bubbles. The molecules held inside them can survive longer than without the bubbles. Add a spherical membrane to hold the water inside and it is possible to carry this bit of watery protection from the radiation around with you to different locations, even in the event where water in the environment has dried up. Here we have the first single cell organism.

Another membrane within a membrane provides extra protection in what we know of as the nucleus of the cell where the DNA resides.

In fact, DNA is often found inside the spherical cell as if trying to protect itself from something. This tells us DNA is designed to preserve its information by developing proteins to act as a barrier from radiation and other foreign objects and give the organism the required brain, arms and legs, eyes, ears and so on to help make it easier for the organism to protect itself for long enough until the DNA is able to reproduce itself.

DNA is a selfish gene. In order to survive, it must reproduce itself. But it has to do it incessantly because of one factor: radiation.

This brings us to the fundamental reason why DNA must replicate itself and do it all the time. It has to do with the intrinsic nature of the universe we call change instigated by the forces of radiation that causes interference to the purpose of DNA. You see, self-replication is a natural and direct response to the constant changes by rebuilding, repairing and ultimately preserving the genetic information it has acquired over billions of year on the Earth.

What are mutations?

Despite the power of self-replication, or even setting up the barriers by DNA or the organism to protect itself, nothing is ever perfect in a universe filled with radiation and while the organism's understanding of this fact remains limited. At some point the organism must be exposed to such changes in the environment in order to gain enough experiences so as to help it understand the knowledge of how to survive better in the environment. DNA may have discovered an almost perfect system for handling changes in the environment. However, the relentless collisions and interference by other matter including radiation itself will eventually affect this self-replication process for DNA. It is during these rather precarious moments when DNA is in the process of self-replication or when it must provide the biochemical information of how to build proteins where it can be forced to record slight changes in the genetic code known as mutations..

Not all mutations are bad. Some mutations may improve the ability of the organism to better handle the environment and hence survive for longer. But other mutations may not be useful. It is here in these latter mutations where natural selection tends to eliminate the propagation of the wrong or non-beneficial mutations.

When does life begin?

We have gone to some considerable detail in explaining DNA. You may be wondering why the emphasis? It is all because DNA is the moment when scientists are certain life will definitely appear.

In other words, the sequence of purine and pyridimine bases forming this all-important self-replicating macromolecule called DNA is where scientists believe all the essential amino acids, enzymes and other vital chemicals needed to build the very stuff of life are brought together to produce a living organism here on Earth.

Scientists think the same must be true of life throughout the universe. If life on another planet is to learn from its environment and find ways to protect itself and keep the information retained for future generations, ETs must use a DNA-like molecule in its alien cells. ETs may not use the exact coding sequence or even the use of specific purine and pyrimidine bases in its biological cells. But scientists are confident a DNA-like molecule should exist.

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