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Amino Acid Racemization Dating. Sean D. Pitman M. Last ated: January All living things use proteins as building blocks in the construction of their physical forms. In turn, proteins are composed of folded strands of 20 different smaller subunits called "amino acids".

When a bone is deposited in soil, decomposition of the organic material in the bone begins, and the components in the bone undergo a series of chemical reactions with the material contained in the soil. As the organic material decomposes, it is replaced by the minerals contained in the ground water which seeps through the soil.

Furthermore, the inorganic material in the bone undergoes change or replacement by minerals contained in the soil. These changes, being a function of the material found in the soil, are irregular, and are governed by the local environment, including mineral content, pH, and temperature.

Fossilization, therefore, can occur at greatly differing rates, under circumstances and by processes that vary considerably. The rates of racemization determined by heating dry, fresh bone fragments sealed in glass ampoules could, and most likely would, differ widely from the rates occurring in a bone undergoing fossilization.

Amino acids are especially sensitive to racemization during either the formation of the peptide bond which links the amino acids together, or the breaking of this bond during the hydrolysis of proteins or of peptides peptides are fragments of proteins of much shorter length than the intact protein.

With many years of experience in the synthesis of peptides and in the determination of the structure of proteins, which involves hydrolysis of the protein, the writer can speak from personal experience. In peptide synthesis, which involves the chemical combination of amino acids in chains of varying length, racemization during synthesis is an ever present concern.

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Reviews on peptide synthesis always devote special note to this problem. Amino acids, as noted above, are also sensitive to racemization during the breaking of the peptide bond, or hydrolysis.

Furthermore, the rate of racemization during hydrolysis is strongly affected by pH. Ordinarily, hydrolysis in strong acid results in little racemization, especially in the absence of impurities. Hydrolysis of a protein in strong alkali, on the other hand, which requires only a fraction of the time required for acid hydrolysis, results in complete racemization of all of the amino acids.

Hydrolysis in weak alkali also results in much higher racemization rates compared to hydrolysis at neutral or acid pH. It has been noted that even the rate of conversion of free L-isoleucine to D-alloisoleucine is greatly accelerated in alkaline solution.

It is thus proposed, as has also been suggested by Wehmiller and Hare, 13 that most of the racemization that occurs in amino acids of fossil material occurs during the hydrolysis of the protein. It is further suggested that the rate of this hydrolysis, and especially the rate of racemization, is governed mainly by the chemical environment of the fossil material, especially the pH.

Temperature could thus play a minor role in determining the extent of racemization. This means that the rate of racemization determined by laboratory experiments under some assumed set of conditions would likely have little or no relevance to the rate of racemization occurring in bone or shell during fossilization.

Local increases in pH, even though temporary, could greatly accelerate the rate of hydrolysis and the rate of racemization, and therefore could result in an apparent age in racemization dating methods vastly older than the real age.

Many other chemical effects that occur during fossilization, as yet undetermined, could also have a profound influence on racemization rates.

These same general considerations would apply to fossilization that occurs in marine sediments and in other sites. Bender 16 has recently strongly questioned the reliability of the amino acid racemization dating method. He points out that bones obtained from different levels in the Muleta Cave of Mallorca, when dated by the amino acid racemization method, the radiocarbon method, and by the Thorium method, as reported by Turekian and Bada, 7 gave strongly discordant ages.

He maintains that amino acid racemization rates are extremely sensitive to the environment. In support, he cited the fact that Kvenvolden and Peterson 17 had found that the extent of amino acid racemization in a supposedly 25, year-old bone from a saber-toothed tiger recovered from the LaBrea tar pits hardly exceeded that of modern fresh bone. Bada, 18 in his reply to Bender's criticisms, strongly disagreed that racemization rates in bone are extremely sensitive to the environment. Yet in this same paper, he admits that the results on the material from the tar pits are anomalous, stating p.

The amino acids in these bones were protected from the environmental influences of soil and groundwater, and consequently suffered practically no racemization. It might be expected, on the other hand, that had these bones been subjected to these environmental factors, the rates of racemization of the amino acids contained in these bones would have far exceeded those obtained in laboratory experiments on bone in the absence of such influences.

There is no doubt that proteins in bone and shell and other fossil material undergo hydrolysis and that the amino acids contained in them suffer racemization with increasing age of fossil material. To use rates of racemization as a dating method, however, the entire history of the fossil material would have to be known, including temperature and the entire diagenetic process, especially the chemical environment that contributed to this process, and most especially the pH.

Since all of these factors, most of which accelerate racemization rates, cannot be known, it is suggested that the apparent ages obtained by this method are unreliable and, with few exceptions, are much older than the real ages. Hare and R. Hare and P. Bada, B. Luyendyk, and J. Bada and R. Turekian and J. Bishop and J. Bada, K. Kvenvolden, and E.

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Bada, R. Schroeder, and G. Schroeder and J. Kvenvolden, E.

There is a book by a vertebrate paleontologist on dating methods pertinent to vertebrate paleontologists. It says little about amino acid racemization, but simply dismisses it with the comment that it is of little value to vertebrate paleontology because of its heavy dependence on calibration by carbon - Leonard Brand, paleontologist, LLU, personal letter, December

Peterson, and F. Wehmiller and P. Manning and S. Zervas, Pergamon Press, New York,p. Schroder and K. Lubke, The Peptides, Vol.

Bodanszky and M. Kvenvolden and E. Bada, Dr. Bada Replies, NatureVol. Skip to main content. The D-form tends to revert to the L-form, and eventually an equilibrium is obtained, as illustrated here for alanine: Mixture of equal amounts of the L- and D-forms, The process by which an L-amino acid changes into a mixture of the L- and D-forms or the D-form changes into a mixture of the L- and D-forms is called racemization.

References 1 P. The Latest. Here it is: "It must have happened because amino acids are found in fossils today after hundreds of millions of years". It is not questioned that the geologic column represents hundreds of millions of years, or even billions of years.

So the only option may be that amino acids are able to survive. Others see the impossibility of long age Amino Acid survivability, because of the physics concerning the rate that amino acids break down.

So they think that the amino acids found in fossils must be a contamination, and not from the original organism. In the last few years, this kind of problem has had to be faced by the scientific community all over again, as various researchers are now finding fossil DNA preserved hundreds of millions of years old. Also, various researchers are even finding intact bacterial spores that are still viable after hundreds of millions of years. I think this is an amazing picture of Evolutionists trying to come to terms with a problem concerning age that might not have a good answer!

Have a look at my two pages on these issues. One is on the presence of amino acids in fossilsthe other on the presence of DNA and bacterial spores in fossils. It is my hope, after you view the data, that you will see the possibility that the usual amino acid dates, as recorded in the scientific literature, are probably much too old. This page is dedicated to looking at the problems and also the assumptions needed to make amino acid age determinations.

But first, I will discuss the basics of Amino Acid dating. Amino acids are the building blocks of protein, and protein is the most abundant organic molecule found in cells. They are found in every part of every cell, since they are involved with all cts of cell structure and function. Protein is mainly composed of 20 different amino acids as determined by the genetic code in the genes.

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In addition, some additional amino acids are produced by a different method. These additional amino acids are produced right in the protein, after they are already incorporated into the new protein.

They are produced by enzymatic reactions that modify some of the already existing 20 amino acids into a new modified amino acid. Some protein structures have a high number of these modified amino acids. Other proteins may have few or none of these modified amino acids. We will see examples of these modified amino acids later on, in this web page. Amino Acid dating is based on the stereochemistry a specific kind of shape of the amino acids that are still present in the fossils.

To understand the change that occurs in the amino acids, we will have to learn a little Chemistry.

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I will keep it really simple! I know that Chemistry scares a lot of people. For those who know their Chemistry, please skip the basic Chemistry section. Most of us know that molecules exist. These molecules have specific shapes. Many of us know this as well. Looking at the picture to the left or above we can see that some molecules are straight, some are bent, and some have atoms attached from all directions.

The shapes of molecules are very important to know when talking about Amino Acid Dating. Because over time, Amino Acids change from one shape to another shape.

When Scientists want to determine the age of a specimen, they look at the shapes of the molecules themselves. They measure how many of the molecules have changed from one shape to another. So, we can see that understanding molecular shapes is extremely important.

Let's start exploring to see why molecules have certain shapes. I will keep it as simple as possible. Two basic questions need to be explored: Why do atoms react? Why do atoms come together to form molecules? And why do these molecules take specific shapes. Why are some molecules shaped differently from other molecules? Both molecules have 3 atoms, yet one is straight and one is bent. Why is that? When we ask both of these questions, we can make it really easy. We only have to look at the central atom of a molecule when we determine both the shape and reason for reacting.

So, in the molecules in the picture to the left or abovewe only need to look at the central Carbon atom for both Methane and for Carbon dioxide. Looking at water, we only need to look at the central Oxygen. Electrons hold the key to understanding why atoms react. The atoms that we will be looking at, in this topic, need 8 electrons in the outside electron layer.

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This is called the Octet Rule. Most atoms do not have 8 electrons in its outside electron layer. Usually there are fewer than 8. When there are not enough electrons in the outside electron layer, it makes the atom reactive. An atom will react with other atoms in order to change the number of electrons to the proper amount. When separate atoms come together in a reaction to form a molecule, the formation allows all the different atoms in the molecule to share their electrons with each other.

The sharing of electrons is called a Covalent bond. There can be several, and often there are many, covalent bonds found in a molecule. These covalent bonds hold the molecule together. By sharing electrons in this way through Covalent bonds, every atom in the molecule ends up with the proper number of electrons as dictated by the Octet Rule. So by reacting with each other, these atoms become more stable. We could say that they become more "self-satisfied" because they now have all 8 positions filled in its outside electron layer.

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So what is a Covalent bond? Covalent bonds allow two atoms to share 2 electrons more or less equally with each other. These two electrons, instead of going around one atom, now go around both atoms. So each atom now has 2 electrons where before the covalent bond formed, each atom had only 1 electron. So by sharing it's electron with another atom, it actually gains an extra electron. The two atoms sharing the electrons, have the two electrons from that covalent bond at least part of the time.

That is enough to satisfy the octet requirement. Please realize that this is an extremely simple way to look at atoms. If you choose to look into chemistry at a deeper level, you will know that this explanation works but that it has some deficiencies.

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Carbon 14 Dating. Amino Acid Dating. Other Dating Methods. The Joy of Winning with Christ. World History Time Line.

Aspects of Archaeology: Thermoluminescence Dating

Comparing Genesis 5,11 in Early Manuscripts. Harmony of End Time Prophecy. Disturbing Controversies. Who is Michael the Archangel? What is the Gospel? Prophets and Knowledge. Second coming of Jesus Christ. Where do we go when we Die? Infinity Aircraft. Music of the Renaissance.

Now, let's look at some specific examples. One type of atom that does not normally react is Neon. See the picture to the left.

It already has the correct number of electrons in it's outside electron layer so Neon does not react. Neon, along with Helium and Argon are known as non-reacting gasses because they do not need to react to be stable.

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Other types of atoms such as Hydrogen, Carbon, and Oxygen do not have the correct number of electrons to be stable by itself.

Instead they have to share electrons in molecules to get the correct number of electrons in their outside electron layer. Since we only have to look at the atom that is in the center of the molecule to find out it's shape, we will concentrate only on Carbon and Oxygen. All the molecules illustrated on this page either have a Carbon or an Oxygen as the center atom.

Carbon will especially be of interest since Carbon is the center atom for all the different Amino Acids. Both Carbon and Oxygen have a deficiency. Neither C nor O have the proper number of electrons in their outside electron layer. Because of that, they are not stable by themselves.

They must react with other atoms to get the proper number of electrons in the outside layer. Oxygen is short 2 electrons. So it must form two covalent bonds to obtain 2 more electrons than it normally has by itself.

The picture to the left will help you visually to see how covalent bonds can help increase the number of electrons that an atom can have. Oxygen can either form two single bonds or one double bond. Water is a good example where Oxygen attaches to 2 different atoms, each by a single bond. Carbon dioxide is a good example where Oxygen attaches to just one molecule through a single double bond.

Carbon is short 4 electrons. It must form four covalent bonds in any combination of single and double bonds so that it ends up with 4 extra electrons. Looking at the picture to the left or above we see that Carbon can be satisfied with either 4 single bonds or 2 double bonds. A third alternative is that 1 double bond and 2 single bonds will also work. A double bond allows 4 electrons to be shared. A double bond allows an atom to gain 2 more electrons through sharing. Looking at the picture to the left or above we can see that Carbon usually shares all its electrons with other atoms.

Combining aspartic acid racemization to estimate age at death and enamel bomb pulse dating to estimate DOB provides a means of estimating date of death, if it is unknown. This approach is a powerful tool for forensic pathologists and police investigators to limit possible matches and establish identity in the case of unidentified remains cases. If Amino Acid dating was a predictable process, like other dating techniques with a predictable rate, the points on the chart would align themselves in a horizontal line. That would indicate that the Racemization constant really is a constant. At a widely publicized news conference in August of , Dr. Jeffrey Bada of Scripps Institute of Oceanography announced the "discovery" of a new dating method based on the rate of racemization of amino acids in fossil material. He was quoted as saying that he had discovered the basis of the method in , and that it was so obvious and simple he was amazed it .

It does this because it has to double the number of electrons to get an octet. Oxygen on the other hand shares only two electrons with other atoms.

The other 4 electrons it keeps for itself. Now that we know about covalent bonds and how an atom achieves an octet, we only need one more fact to understand why molecules have specific shapes.

Here it is. All electrons are negatively charged.

What do we know about like charges? They repel each other. We can see the same exact thing happen with magnets. If we have two magnets and we try to push two like poles together Either North with North or South with Southwe see that they push each other away.

That is what the electrons do to each other. They try to get as far away from each other as possible. Now remember, covalent bonds have two electrons.

These two electrons because they are part of the same bond, are forced to be in the same area because they act as a single unit, a covalent bond. So what happens is that each bond tries to get as far away from all the other bonds. They spread apart since they repel each other. In the Water molecule pictured to the left or above we see that it has two pairs of unshared electrons. These behave very much like the electrons in covalent bonds. They stick together in pairs. In the Carbon dioxide molecule, 4 electrons in each double bond are held together.

Since Carbon dioxide has two double bonds, and since a double bond acts as a unit, the two double bonds try to get as far away from each other as possible. What they do is get on the opposite side of the central Carbon from each other.

This molecule is straight! Both Methane and Water have a similar shape. In both structures, we have 4 pairs of electrons trying to get as far away as possible from each other. So they go in all different directions.

Water is a bent molecule because the unshared electrons force the two Hydrogens to come toward each other a little bit. This allows all the electrons to be more or less equally spaced apart. Methane should be very interesting to us because it's structure is just like the Amino Acids that we are going to be looking at.

All four Hydrogens are spread apart as far as they can be from each other. Let's look at the central carbon of an Amino Acid.

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It is called the a Carbon. The a Carbon has the same distribution of electrons as we saw in Methane. The four bonds are spread apart as far as they can be from each other. Often when we draw molecules on paper. We tend to think that the farthest the bonds can get is up, down, right, and left. However we must remember that molecules are not limited by 2 dimensions like what we see on paper.

Instead, the bonds spread out in all 3 dimensions of space. The angle from one covalent bond to another is This shape that the a Carbon bonds take is called a Tetrahedrial Shape. If we were to look at a 3 sided pyramid. In this structure, every covalent bond is angled So, between every two bonds in this structure is an angle of All the angles Equal each other.

An Amino Acid has a central a Carbon that has four groups attach to it. As you can see in the picture to the left or abovethe groups are: An Amino group, a Carboxyl group, a Hydrogen, and a side chain. There are 20 different Amino Acids, In addition there are several other non-standard Amino Acids that are found in various peptides, polypeptides, and proteins.

Each of these different Amino Acids have different side chains. So each Amino Acid has it's own specific structure, and the place where they are different, is the side chain. The side chain is what allows all the different Amino Acids to have their own specific characteristic.

The Amino and Carboxyl groups are also important because they are what allow Amino Acids to link together to form long chains forming peptides, polypeptides, and proteins.

This produces a peptide bond, which allows the two Amino Acids to be attached to each other. This process continues until long chains of Amino Acids can be produced.

So the Amino and Carboxyl groups make up the backbone of protein chains. In physiological condition, meaning the conditions inside the body a Amino Acids form what is called a "Zwitterion".

Most of the Amino Acids have a characteristic of shape that we need to understand. They are Chiralmeaning that they have a structure that cannot be superimposed on its mirror image. We can look at our own body parts to know what this means. If we look at our hands and feet, we can see that they look somewhat identical except that they are backwards from each other.

Racemization

On our right foot, the big toe is on the left side, and on our left foot, the big toe is on the right. They are backwards from each other! They are actually mirror images of each other which do not superimpose. But rather, they look different from each other. They are Nonsuperimposable mirror images. It is easier to look at your hands. There is no way you can make your one hand look like your other hand. You either have your thumbs pointing in opposite directions or you are looking at opposite sides of the hand.

Other objects such as balls, glasses, and baseball bats ignoring abnormalities such as the grain and name plate on the bat, etc. The mirror images will superimpose. There is no such thing as a left-handed bat or a right-handed bat.

They are all the same! So balls, glasses, and baseball bats do not have Chirality. The a Carbon in most Amino Acids is also Chiral. A Chiral Carbon is a carbon atom that is bonded to four different groups. The two Amino Acids on the left or above are mirror images of each other just like our feet and hands. You can not make these two molecules look like each other.

The right and left form of amino acids are Isomers meaning that the two molecules have the same molecular formulas but different structures. In other words, the two molecules have the same atoms, but they only have them arranged differently.

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Any two molecules that have the same atoms are isomers. They do not even have to look like each other, they only have to have the same number of all the same atoms. However, Amino Acids not only form isomers; The right and left form of Amino Acids are actually mirror images of each other.

This fact makes them Enantiomerswhich means they are two molecules that are nonsuperimposable mirror images of each other. These same amino acids are also Stereoisomers which means that the two molecules differ in their three-dimensional shapes only but that they have the same structural formulas.

This means they have the same exact groups attached in the same way.

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Only the three-dimensional orientation of these groups are different. So, 19 of the 20 Amino Acids form isomers that are are both Enantiomers and Stereoisomers because their functional groups only differ in their three-dimensional orientation in such a way that they form nonsuperimposable mirror images of each other. The a Carbon in 19 out of the 20 amino acids is a Chiral Carbon. Hence, 19 out of the 20 amino acids are Enantiomers mirror images of each other. Partly because of this Stereochemistry, these molecules have become important to the Amino Acid dating process.

For the moment, let's look at the Amino Acid that does not have a Chiral carbon in it. It is Glycine. The reason why Glycine does not have a chiral center is because it has two Hydrogens attached to it. The side chain is also a Carbon. Remember the definition of a Chiral Carbon was that four different groups had to be attached to it.

Every one of the four groups has to be different, in order for it to be chiral. In Glycine, only three types of groups are attached to the central a Carbon. Just like the balls, bats and glasses, we can always make one molecule look like the other one. So Glycine does not form Stereoisomers.

In all of the other 19 amino acids, bonds must actually be broken and the molecules be put back together before the two molecules can look like each other.

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This breaking apart of the molecule and putting it back together is exactly what has happened to the amino acids in the fossils. So of course this is the basis that some scientists use amino acids for, in seeing how long fossils have been in the ground.

It is assumed that the rate that the amino acids have changed has been constant enough for it to be used as a dating process. This is an interesting problem. A scientist has to be able to distinguish the different Stereoisomers from each other.

How does he do it? We can easily tell the difference between left and right hands and feet just by looking at them. Hands and feet are chiral just like the amino acids we want to look at.

However left L and right D forms of amino acids can be extremely hard to distinguish if we look at the wrong feature. Stereoisomers, the left L and right D handed forms of amino acids, have essentially the same structures.

They have the same exact chemical structures except that they are mirror images of each other. So they also have both the same exact physical and chemical characteristics! They will boil and freeze etc.



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