Fixing Carbon: the Rubisco Reaction

Life as we know it is based on carbon. All organisms need to have a source of carbon in order to grow and multiply. Animals, such as humans, get their carbon from eating other living things but there are many other species that can assimilate carbon directly from inorganic sources. This process is known as carbon fixation.

In most cases, carbon is derived from carbon dioxide in the atmosphere or dissolved in water. There are dozens of different chemical reactions in which carbon dioxide is taken up and attached to another organic molecule. Humans can do this to limited extent but not enough to support all of our carbon needs. Bacteria, protists, plants and fungi are much better at efficiently incorporating carbon from carbon dioxide.

The reactions of carbon fixation are often expensive because they require an input of energy to drive the assimilation of the newly-fixed carbon into metabolic pathways that are operating inside the cell. Photosynthetic organisms often have an abundant supply of energy so they can take up large amounts of carbon to make organic molecules. In fact, the association between carbon fixation and photosynthesis is so obvious that it's often assumed that the processes are directly coupled.

They aren't. There are many non-photosynthetic species that can efficiently fix carbon from carbon dioxide and there are many organisms that can carry out photosynthesis but they don't fix huge amounts of carbon using the standard pathways.

Nevertheless, there is one major carbon-fixing pathway that is present in most photosynthesizing bacteria, protists, fungi, and especially plants. It's called the Calvin Cycle after its discoverer Melvin Calvin (see photo) [Nobel Laureate 1961]. In modern biochemistry courses we discuss this pathway in the photosynthesis chapter but it's no longer considered to be part of photosynthesis. Photosynthesis ends with the light-driven synthesis of the energy molecules ATP and NADPH.

The first step in this pathway is the most important; it's the step where a carbon dioxide molecule is attached to a five carbon compound and the resulting 6-carbon intermediate is split into two 3-carbon molecules. The 3-carbon molecules then enter various metabolic pathways, including a pathway that recreates the 5-carbon precursor—hence the name "cycle."

The initial reaction is shown in the schematic below where each ball represents a carbon atom. The substrate for the reaction is the 5-carbon compound with the green balls and the blue ball represents the carbon atom in carbon dioxide (CO₂). As you can see, the reaction takes place in two steps. The first step is the actual fixation reaction; it creates a 6-carbon molecule with the incorporated carbon atom from CO₂. In the second step this 6-carbon molecule is cleaved producing two 3-carbon molecules.


The 5-carbon substrate is called ribulose 1,5-bisphosphate [Monday's Molecule #34]. It's related to the ribose in ribonucleic acid (RNA) except that it's the keto form of ribose and it has two phosphate groups attached to the 1 and 5 positions. The final products are called 3-phosphoglycerate. They are common intermediates in many metabolic pathways.

Here's the complete reaction. The enzyme that catalyzes this reaction is the most abundant enzyme on the entire planet. It's called ribulose 1,5-bisphosphate carboxylase-oxygenase, or Rubisco for short.

Mechanism of Rubisco-catalyzed carboxylation of ribulose 1,5-bisphosphate to form two molecules of 3-phosphoglycerate. A proton is abstracted from C-3 of ribulose 1,5 -bisphosphate to create a 2,3 -enediolate intermediate. The nucleophilic enediolate attacks producing 2-carboxy-3-ketoarabinitol 1,5 -bisphosphate, which is hydrated to an unstable gem diol intermediate. The C-2-C-3 bond of the intermediate is immediately cleaved, generating a carbanion and one molecule of 3-phosphoglycerate. Stereospecific protonation of the carbanion yields a second molecule of 3-phosphoglycerate. This step completes the carbon fixation stage of the Calvin cycle—two molecules of 3-phosphoglycerate are formed from CO₂ and the five-carbon sugar ribulose 1,5-bisphosphate.

©Laurence A. Moran and Pearson Prentice Hall 2007

Are IDiots Creationists?

 
I have complained about misuse of the term "Darwinism" by the Intelligent Design Creationists. They seem to be unable to grasp the fact that not all evolutionary biologists are Darwinists.

Having complained about that, it's only fair to consider their complaint that not all Intelligent Design advocates are Creationists. Casey Luskin raises the issue today on the Discovery Institute website [Another Way to Defeat the ID = Creationism MemeM].

Darwinian logic often contends that because a given proportion of ID proponents are creationists, ID must therefore be creationism. It's a twist on the genetic fallacy, one I like to call the Darwinist "Genesis Genetic Argument." As noted, it implies that each any and every argument made by a creationist must be equivalent to arguing for full-blooded creationism. This fallacious argument is easy to defeat on logical grounds by pointing out that some ID proponents are not creationists, and in fact have been persuaded to support ID in the absence of religion. Thus something other than creationism or religion must be fundamental to the set of views underlying ID (big hint: it's the scientific data indicating real design in nature)!

First off, it's ridiculous to pretend that some IDiots view the intelligent designer as anyone other than God. While I've no doubt that they might dig someone like this out of the woodwork, the fact remains that 99.999% of all intelligent design advocates see God as the designer. The term "creationist" refers to someone who postulates a role for a Creator (i.e., God) in creating life. Any IDiot who says they were persuaded to support intelligent design in the absence of belief in a Creator is, well, an idiot. But I repeat myself.

Second, there is no scientific data to indicate real design in nature. In fact, there's plenty of evidence to suggest a lack of "design" in much of nature (e.g., junk DNA). (Admittedly, many evolutionists are reluctant to accept this evidence.) The entire Intelligent Design Creationist movement is dedicated to disproving evolution. That's the extent of their "data." You don't become an Intelligent Design Creationist just because you've been brainwashed into rejecting evolution. You become an Intelligent Design Creationist because you've been brainwashed to believe in a Creator God and that, in turn, leads to the rejection of the other alternative, evolution.

There are many different kinds of creationist. They include Young Earth Creationists, Old Earth Creationists, and Theistic Evolutionists. The Theistic Evolutionists restrict the role of the Creator to setting up natural laws and then operating mostly within these natural laws to guide evolution. The Intelligent Design Creationists are a special group of creationists who argue against evolution and who claim (falsely) to have discovered evidence for supernatural creation (i.e., intelligent design). It is quite legitimate to refer to them as Intelligent Design Creationists because it distinguishes their form of creationism from the other forms of creationism.

Robert Pennock discusses this in his anthology Intelligent Design Creationism and Its Critics.

Dembski chides me for never using the term "intelligent design" without conjoining it to "creationism." He implies (though never explicitly asserts) that he and others in his movement are not creationists and that it is incorrect to discuss them in such terms, suggesting that doing so is merely a rhetorical ploy to "rally the troops." Am I (and the many others who see Dembski's movement in the same way) misrepresenting their position? The basic notion of creationism is the rejection of biological evolution in favor of special creation, where the latter is understood to be supernatural. Beyond this there is considerable variability. Some creationists think the world is young while a fewer number accept that it is ancient.

Pennock then goes on to show that Dembski is a creationist and so are most (all?) of his followers.

In spite of Luskin's whining (and Dembski's) it is quite appropriate to refer to Intelligent Design Creationism since the advocates of this superstitious nonsense are creationists by definition.

Welcome to Springfield

 
The population of Springfield has just increased by one. Meet Sandwalk. Do you see a resemblance? I don't.

Correcting the Bible

 
Read The Atheist Bible. I have a small correction to Book Two, Chapter Two which reads,

The variations in the biological organisms on Earth, described as the changes in a genetic population over time, is best explained in terms of natural selection.

The correct version should be,

The variations in the biological organisms on Earth, described as the changes in the genetics of a population over time, is best explained in terms of evolution.

Don't be shocked. This is, after all, a Bible and Bibles are notoriously inaccurate.

UPDATE: It's a miracle!!!! The atheist Bible has spontaneously mutated to a correct version of evolution. Praise the Lord.

[Hat Tip: Hemant Mehta at FriendlyAtheist.com]

Wellcome Trust Images

 
The Wellcome Trust's extensive library of images in now available through Creative Commons Licence [wellcome images].

Over on Memoirs of a Skepchick we've been challenged to find the coolest image [Something to get geeked about]. Here's my entry ....

Evolutionary Psychologists in Action

 
Alan S. Miller and Satoshi Kanazawa are evolutionary psychologists. They have written an article for Psychology Today that goes a long way toward explaining why this discipline is in such bad shape [Ten Politically Incorrect Truths About Human Nature]. Miller is a professor of social psychology in the Department of Behavioral Science at Hokkaido University, Japan. Kanazawa is a Reader in Management and Research Methodology at the London School of Economics and Political Science.

Did you know that all men prefer women with large breasts? I didn't. If true there must be a lot of very frustrated men in Asia and a lot of small-breasted spinsters wandering around somewhere. Anyway, Miller and Kanazawa have figured out why young American teenagers men like women with large breasts.

Until very recently, it was a mystery to evolutionary psychology why men prefer women with large breasts, since the size of a woman's breasts has no relationship to her ability to lactate. But Harvard anthropologist Frank Marlowe contends that larger, and hence heavier, breasts sag more conspicuously with age than do smaller breasts. Thus they make it easier for men to judge a woman's age (and her reproductive value) by sight—suggesting why men find women with large breasts more attractive.

Boy, you learn something every day from these evolutionary psychologists, don't you?

Now here's a useful bit of information. Do you know why young Muslim men are more violent and prone to suicide missions? The evolutionary psychologists have the answer,

Suicide missions are not always religiously motivated, but according to Oxford University sociologist Diego Gambetta, editor of Making Sense of Suicide Missions, when religion is involved, the attackers are always Muslim. Why? The surprising answer is that Muslim suicide bombing has nothing to do with Islam or the Quran (except for two lines). It has a lot to do with sex, or, in this case, the absence of sex.

What distinguishes Islam from other major religions is that it tolerates polygyny. By allowing some men to monopolize all women and altogether excluding many men from reproductive opportunities, polygyny creates shortages of available women. If 50 percent of men have two wives each, then the other 50 percent don't get any wives at all.

So polygyny increases competitive pressure on men, especially young men of low status. It therefore increases the likelihood that young men resort to violent means to gain access to mates. By doing so, they have little to lose and much to gain compared with men who already have wives. Across all societies, polygyny makes men violent, increasing crimes such as murder and rape, even after controlling for such obvious factors as economic development, economic inequality, population density, the level of democracy, and political factors in the region.

This is useful information. It means that we can settle all of the problems in the Middle East by withdrawing our troops and simply banning polygyny. Did somebody tell Dick Cheney?

There's lots more where this came from. Did you know that rich people have more sons than daughters? Neither did I, but lets not allow facts to interfere with a good just-so story. Here's the evolutionary explanation,

It is commonly believed that whether parents conceive a boy or a girl is up to random chance. Close, but not quite; it is largely up to chance. The normal sex ratio at birth is 105 boys for every 100 girls. But the sex ratio varies slightly in different circumstances and for different families. There are factors that subtly influence the sex of an offspring.

One of the most celebrated principles in evolutionary biology, the Trivers-Willard hypothesis, states that wealthy parents of high status have more sons, while poor parents of low status have more daughters. This is because children generally inherit the wealth and social status of their parents. Throughout history, sons from wealthy families who would themselves become wealthy could expect to have a large number of wives, mistresses and concubines, and produce dozens or hundreds of children, whereas their equally wealthy sisters can have only so many children. So natural selection designs parents to have biased sex ratio at birth depending upon their economic circumstances—more boys if they are wealthy, more girls if they are poor. (The biological mechanism by which this occurs is not yet understood.)

This hypothesis has been documented around the globe. American presidents, vice presidents, and cabinet secretaries have more sons than daughters. Poor Mukogodo herders in East Africa have more daughters than sons. Church parish records from the 17th and 18th centuries show that wealthy landowners in Leezen, Germany, had more sons than daughters, while farm laborers and tradesmen without property had more daughters than sons. In a survey of respondents from 46 nations, wealthy individuals are more likely to indicate a preference for sons if they could only have one child, whereas less wealthy individuals are more likely to indicate a preference for daughters.

If you believe this garbage then please send me an email message expressing your confidence in evolutionary psychology (and adaptationism). I'd like to talk to you about some swampland that I own in Florida. It will make a terrific vacation property.

[Hat Tip: RichardDawkins.net]

What Is Darwinism?

Over on the thread Close, but no cigar we're having a little discussion about the meaning of the term "Darwinian." I explained it as "evolution by natural selection."

Pete Dunkelberg is one of those people who emphasize natural selection in their discussion of evolution and he didn't like my description of Darwinian evolution. Pete said,

Misbegotten terminology. "darwinian processes" is creationist coinage with no meaning.

Talking of "darwinism" in biology is akin to talking of "newtonism" in physics: a bad idea. Aren't you glad physicists don't use terms like that to make polemics against each other?

wolfwalker asks: Larry, what do people mean by [these unneeded terms]? Larry tells him what Larry means. But the terms have no standard meaning. Larry's official ruling is that Darwin never heard of variable rates of morphological evolution and also thought selection was all.

It is patently untrue that the term "Darwinian" has no meaning in biology. Pete's position is that "Darwinist" refers to evolutionary biologists who no longer exist. He seems to think that everyone has become a pluralist these days. I beg to differ.

Core Darwinism, I shall suggest, is the minimal theory that evolution is guided in adaptively nonrandom directions by the nonrandom survival of small hereditary changes.... Adaptive does not imply that all evolution is adaptive, only that core Darwinism's concern is limited to the part of evolution that is.

Dawkins, R. (2003) The Devil's Chaplain p. 81 In physics, everyone knows that Newtonian physics has been extended in the twentieth century so that it's no longer accurate to refer to oneself as a Newtonian physicist since it implies ignorance of relativity. But this is a bad analogy since there are a great many evolutionary biologists (and even more of the other kinds of biologists) who are proud to call themselves Darwinists. Modern Darwinists place a great deal of emphasis on adaptation and natural selection as the main mechanisms of evolution.

Pete is dead wrong when he claims that, "Larry's official ruling is that Darwin never heard of variable rates of morphological evolution and also thought selection was all." I never said any such thing. I'm well aware of the fact that Darwin considered variable rates of natural selection and I'm well aware of the fact that he accepted other mechanisms of evolution, such as a watered down version of Lamarckism. The problem here seems to be that Pete doesn't understand the meaning of gradualism and he doesn't understand that modern Darwinists do not attribute everything in biology to selection.

As for the standard meaning of "Darwinism," Pete is correct to say that there is no universally accepted definition but that shouldn't be a surprise to anyone. There's hardly anything that all biologists can agree on.

However, there is a considerable group of evolutionary biologists who agree with Ernst Mayr when he says ...

After 1859, that is, during the first Darwinian revolution, Darwinism for almost everybody meant explaining the living world by natural processes. As we will see, during and after the evolutionary synthesis the term "Darwinism" unanimously meant adaptive evolutionary change under the influence of natural selection, and variational instead of transformational evolution. These are the only two meaningful concepts of Darwinism, the one ruling in the nineteenth century (and up to about 1930) and the other ruling in the twentieth century (a consensus having been reached during the evolutionary synthesis). Any other use of the term Darwinism by a moder author is bound to be misleading.

Mayr, E. (1991) What Is Darwinism? in One Long Argument p. 107.

See Why I'm Not a Darwinist for an earlier use of this quotation. The point is that the modern meaning of Darwinism is usually taken to mean an emphasis on natural selection.

Mayr explains the standard adaptationist view of random genetic drift by equating it with Neutral Theory and mischaracterizing the entire controversy. (This seems to be a very common trait among the defenders of strict Darwinism.)

The neutralists are reductionists, and for them the gene—more precisely the base pair—is the target of selection. Hence, any fixation of a "neutral" base pair is a case of neutral evolution. For the Darwinian evolutionists, the individual as a whole is the target of selection, and evolution takes place only if the properties of the individual change. A replacement of neutral genes is considered merely evolutionary noise and irrelevant for phenotypic evolution. (ibid p. 152)

I'm not making this up. I'm trying to do my best to represent the standard—but not universal—description of the adaptationist position. It's quite wrong for Pete Dunkelberg to pretend that the definition of Darwinism and the adaptationists is something that I created. (BTW, most pluralists treat the individual as the unit of evolution. They just believe that populations can fix alleles, even alleles with visible phenotypes, by random genetic drift as well as natural selection.)

Mayr continues,

The Darwinian wonders to what extent it is legitimate to designate as evoluton the changes in gene frequencies caused by nonselected random fixation. In some of the older (particularly nineteenth century) literature on evolution, one finds discussions on how to discriminate between evolution and mere change. There it was pointed out that the continuing changes in weather and climate, the sequences of the seasons of the year, the geomorphological changes of an eroding mountain range or a shifting river bed, and similar changes do not qualify as evolution. Interestingly, the changes in nonselected base pairs and genes are more like those nonevolutionary changes than they are like evolution. Perhaps one should not refer to non-Darwinian evolution but rather to non-Darwinian changes during evolution. (ibid p. 153)

While this position may seem extreme by 2007 standards, I believe that there are many evolutionary biologists who tend to dismiss all nonselected evolutionary change as uninteresting and unimportant. They are Darwinists. The extremists among this group attribute all kinds of things to adaptation, including most animal behavior. They are the ultra-Darwinians.

Many books have been written about the controversy in evolutionary biology between the adaptationists and the pluralists. Michael Ruse, for example, tried to explain it all last year (2006) in Darwinism and Its Discontents. Ruse is a firm believer in Darwinism, which he defines as "natural selection as the chief causal process behind all organisms." This is a common definition as explained above. However, one must read between the lines to see how Darwinists interpret that definition. A key point is what they think about random genetic drift. Here's how the Darwinist Ruse treats Sewall Wright's concept of random genetic drift.

Wright's theory is not very Darwinian. Natural selection does not play an overwhelming role. Genetic drift is a key player in Wright's world. However, although many of these ideas were taken up by later thinkers, especially by Theodosius Dobzhansky in the first edition of his influential Genetics and the Origin of Species, drift soon fell right out of fashion, thanks to discoveries that showed that many features formerly considered just random are in fact under tight control of selection (Lewontin, 1981). Today no one would want to say that drift (at the physical level) is a major direct player, although, in America particularly, there has always been a lingering fondness for it.

Michael Ruse is not an evolutionary biologist but he represents the views of Dawkins and, to a lesser extent, E.O. Wilson. They have no use for drift especially when it comes to visible characteristics. That's the hallmark of modern Darwinism.

So, is it true that no evolutionary biologist would want to say that drift is a major player in evolution? Of course not. There are lots of them who say exactly that in spite of what Michale Ruse would have you believe. Does Ruse have an answer to these "discontents?" Yes, he does ...

At the risk of damning myself in the eyes of both scholarship and God, let me be categorical. All of the critics of Darwinism are deeply mistaken,

To which I reply, you took the risk and your scholarship has been discredited. I can't speak for God.

Monday's Molecule #34

 
Today's molecule is very simple. It is well-known to all biochemistry undergraduates—or at least it was well-known at the time they wrote the exam. Let's see how many of you remember it today.

Today we need the formal IUPAC name in order to win the prize. There's an extremely obvious connection between this Monday's Molecule and Wednesday's Nobel Laureate. You will owe me a lunch if you guess the molecule correctly but can't figure out who the Nobel Prizewinner(s) is/are.

The reward (free lunch) goes to the person who correctly identifies the molecule and the Nobel Laureate(s). Previous free lunch winners are ineligible for one month from the time they first collected the prize. There are no ineligible candidates for this Wednesday's reward since many recent winners haven't collected their prize. The prize is a free lunch at the Faculty Club.

Comments will be blocked for 24 hours. Comments are now open.

Stop the Press!!! ... Genes Have Regulatory Sequences!

Ira Flatow interviews John Greally (see photo) on Science Friday. Greally talks about the ENCODE project and junk DNA. You might be surprised to learn that the expression of genes is controlled by ... wait for it ... REGULATORY SEQUENCES! According to Greally the discovery of these regulatory sequences reveals that junk DNA isn't junk at all. Greally says,

It would be a very brave person who would call it junk at this stage.

Count me as a very brave person. I claim that most of the human genome is junk and I'm not alone.

This is just one more example of the hype surrounding the ENCODE project. Read Ryan Gregory's summary at More about ENCODE from Scientific American for a good summary of what the study really says about junk DNA. The study does not say that all junk DNA has a function in spite of what you might gather from the podcast (below). The study does not say that the discovery of regulatory sequences in noncoding DNA is a breakthrough in our understanding of how genes work. In fact, as almost all of you know, the existence of regulatory sequences that control gene expression has been known for four decades. John Greally misses a good opportunity to educate the public about science and instead uses inappropriate framing to hype his own interest in gene expression. Shame.


powered by ODEO

John Greely is the author of the News & Views article that described the original ENCODE work published in the June 14th issue of Nature. In that review he mentioned the role of regulatory sequences but focused much of his attention on the fact that large parts of the genome were transcribed. He expressed some appropriate skepticism of the results in the Nature piece but not when being interviewed on the radio. Is this appropriate? Is it what Nisbet and Mooney are talking about when they say that scientists should do a better job of framing?

[Hat Tip: Eye on DNA]

Mendel's Garden #16

 
The 16th version of Mendel's Garden has just been posted on Eye on DNA [Mendel’s Garden Genetics Blog Carnival #16M].

Socialized Medicine Will Make America Vulnerable to Terrorists

 
Americans are probably confused about socialized medicine after seeing Michael Moore's Sicko. Don't worry. Fox News explains why highly efficient, profit-based. corporate health care will protect America from those Jihadist Muslim doctors who are taking over the anonymous, highly bureaucratic systems in Europe.

Listen for the part about your family doctor. In America you can't have doctors who believe in stupid things because they'll be exposed by their patients and their colleagues. Apparently in socialist countries you don't have family doctors (news to me) so patients never find out what their doctors are really thinking. That's why jihadist doctors can hide out in Europe.

Why isn't there more outrage when idiotic things like this are broadcast on network television?



[Hat Tip: Canadian Cynic]

Close, but no cigar.

 
Over on Post-Darwinist Denyse O'Leary is whining about the fact that so many scientists are non-believers. She quotes from a poll of evolutionists showing that 78% don't believe in God. Having been sensitized to misuse of the word "evolutionist" she adds this at the end of her blog.

(Note for the record: "Evolutionists" here means scientists who believe that gradual Darwinian processes completely account for every aspect of life and that no design whatever is required. It does not mean scientists who merely accept that evolution occurs or that Earth is billions of years old.)

Denyse, it's the word "Darwinian" that's being misused. I'm an evolutionist but I do not believe that "gradual Darwinian processes completely account for every aspect of life." Instead I believe that evolution accounts for life and this evolution includes strict Darwinian processes as well as non-Darwinian processes.

Why do you find this so hard to understand?

I'm a Skeptic

 
I'm a Skeptic and a member of the Board of Consultants of Skeptics Canada. But it's nice to have confirmation ...

You Are Very Skeptical

Your personal motto is: "Prove it." While some ideas, like life after death, may seem nice... You aren't going to believe them simply because it feels good. You let science and facts be your guide... Even if it means you don't share the beliefs of those around you.

How Skeptical Are You?

[Hat Tip: GrrlScientist]

Mutation Rates

Each of us was born with at least 350 new mutations that make our DNA different from that of our parents.

Douglas Futuyma (2005) p. 162Let’s think about the number of mutations that could accumulate in a population over time. A few pages ago we looked at the origin of antibiotic resistance in bacteria in order to prove that mutations occur randomly. Now we’ll consider just how frequency those mutations could arise in bacteria. Then we’ll ask how frequently mutations occur in humans.

Our model bacterium is Esherichia coli the common, and mostly benign, intestinal bacterium. The entire genome was sequenced in 1997 (Blattner et al., 1997) and its size is 4,200,000 base pairs (4.2 × 10⁶ bp). Every time a bacterium divides this amount of DNA has to be replicated; that’s 8,400,000 nucleotides (8.4 × 10⁶).

The most common source of mutation is due to mistakes made during DNA replication when an incorrect nucleotide is incorporated into newly synthesized DNA. The mutation rate due to errors made by the DNA polymerase III replisome is one error for every one hundred million bases (nucleotides) that are incorporated into DNA. This is an error rate of 1/100,000,000, commonly written as 10^-8 in exponential notation. Technically, these aren't mutations; they count as DNA damage until the problem with mismatched bases in the double-stranded DNA has been resolved. The DNA repair mechanism fixes 99% of this damage but 1% escapes repair and becomes a mutation. The error rate of repair is 10^-2 so the overall error rate during DNA replication is 10^-10 nucleotides per replication (10^-8 × 10^-2) (Tago et al., 2005).

Since the overall mutation rate is lower than the size of the E. coli genome, on average there won’t be any mistakes made when the cell divides into two daughter cells. That is, the DNA will usually be replicated error free.

However, one error will occur for every 10 billion nucleotides (10^-10) that are incorporated into DNA. This means one mutation, on average, every 1200 replications (8.4 × 10⁶ × 1200 is about ten billion). This may not seem like much even if the average generation time of E. coli is 24 hours. It would seem to take four months for each mutation. But bacteria divide exponentially so the actual rate of mutation in a growing culture is much faster. Each cell produces two daughter cells so that after two generations there are four cells and after three generations there are eight cells. It takes only eleven generations to get 2048 cells (2¹¹ = 2048). At that point you have 2048 cells dividing and the amount of DNA that is replication in the entire population is enough to ensure at least one error every generation.

In the laboratory experiment the bacteria divided every half hour so after only a few hours the culture was accumulating mutations every time the bacteria divided. This is an unrealistic rate of growth in the real world but even if bacteria only divide every 24 hours there are still so many of them that mutations are abundant. For example, in your intestine there are billions and billions of bacteria. This means that every day these bacteria accumulate millions of mutations. That’s why there’s a great danger of developing drug resistance in a very short time.

Calculating the rate of evolution in terms of nucleotide substitutions seems to give a value so high that many of the mutations must be neutral ones.

Motoo Kimura (1968)I based my estimate of mutation rate on what we know about the properties of the replisome and repair enzymes. Independent measures of mutation rates in bacteria are consistent with this estimate. For example, the measured value for E. coli is 5.4 × 10^-10 per nucleotide per replication (Drake et al., 1998). Many of these mutations are expected to be neutral. The rate of fixation of neutral mutations is equal to the mutation rate so by measuring the accumulation of neutral mutations in various lineages of bacteria you can estimate the mutation rate provided you know the time of divergence and the generation time. (Ochman et al., 1999) have estimated that the mutation rate in bacteria is close to 10^-10 assuming that bacteria divide infrequently.

The mutation rate in eukaryotes should be about the same since the properties of the DNA replication machinery are similar to those in eukaryotes. Measured values of mutation rates in yeast, Caenorhabditis elegans, Drosophila melanogaster, mouse and humans are all close to 10^-10 (Drake et al., 1998).

The haploid human genome is about 3 × 10⁹ base pairs in size. Every time this genome is replicated about 0.3 mutations, on average, will be passed on to one of the daughter cells. We are interested in knowing how many mutations are passed on to the fertilized egg (zygote) from its parents. In order to calculate this number we need to know how many DNA replications there are between the time that one parental zygote was formed and the time that the egg or sperm cell that unite to form the progeny zygote are produced.

In the case of females, this number is about 30, which means that each female egg is the product of 30 cell divisions from the time the zygote was formed (Vogel and Rathenberg, 1975). Human females have about 500 eggs. In males, the number of cell divisions leading to mature sperm in a 30 year old male is about 400 (Vogel and Motulsky, 1997). This means that about 9 mutations (0.3 × 30) accumulate in the egg and about 120 mutations (0.3 × 400) accumulate in a sperm cell. Thus, each newly formed human zygote has approximately 129 new spontaneous mutations. This value is somewhat less than the number in most textbooks where it's common to see 300-350 mutations per genome. The updated value reflects a better estimate of the overall rate of mutation during DNA replication and a better estimate of the number of cell divisions during gametogenesis.

With a population of 6 billion individuals on the planet, there will be 120 × 6 × 10⁹ = 7.2 × 10¹¹ new mutations in the population every generation. This means that every single nucleotide in our genome will be mutated in the human population every 20 years or so.

---

Blattner,F.R., Plunkett,G., Bloch,C.A., Perna,N.T., Burland,V., Riley,M., ColladoVides,J., Glasner,J.D., Rode,C.K., Mayhew,G.F., Gregor,J., Davis,N.W., Kirkpatrick,H.A., Goeden,M.A., Rose,D.J., Mau,B., and Shao,Y. (1997) The complete genome sequence of Escherichia coli K-12. Science 277:1453-1474.

Drake,J.W., Charlesworth,B., Charlesworth,D., and Crow,J.F. (1998) Rates of spontaneous mutation. Genetics 148:1667-1686.

Ochman,H., Elwyn,S., and Moran,N.A. (1999) Calibrating bacterial evolution. Proc. Natl. Acad. Sci. (USA) 96:12638-12643.

Tago,Y., Imai,M., Ihara,M., Atofuji,H., Nagata,Y., and Yamamoto,K. (2005) Escherichia coli mutator Delta polA is defective in base mismatch correction: The nature of in vivo DNA replication errors. J. Mol. Biol. 351:299-308.

Vogel,F. and Motulsky,A. (1997) Human Genetics: Problems and Approaches. (Berlin, New York: Springer-Verlag).

Vogel,F. and Rathenberg,R. (1975) Spontaneous Mutation in Man. Adv. Hum. Genet. 5:223-318.

©Laurence A. Moran (2007)

The Evils of Darwinism in America

 
Over on the Discovery Institute website there's an important announcement [John West's Forthcoming Book] ...

Next Fall ISI Books will release CSC associate director Dr. John West's important book, Darwin Day in America: How Our Politics and Culture Have Been Dehumanized in the Name of Science.

Darwin Day in America tells the disturbing story of scientific expertise run amuck, exposing how an ideological interpretation of Darwinian biology and reductionist science have been used to degrade American culture over the past century through their impact on criminal justice, welfare, business, education, and bioethics.

Fascinating. Given that "Darwinism" has been so fiercely resisted in America its success in degrading American culture is all that more remarkable.

I look forward to Dr. West's exposé of European culture where rationalism has been even more successful than in America. I wonder what he thinks of France?