Otangelo Grasso is a creationist who's convinced he can learn to understand biochemistry by reading what's on the internet and copy-pasting it into his website. He then takes that limited knowledge and concludes that evolution is impossible. He often poses "gotcha" questions based on his flawed understanding.His behavior isn't very different from most other creationists who suffer from Dunning-Kruger Disease but he happens to be someone who I thought could be educated.
I was wrong.
Over the years I've tried to correct a number of errors he's made so we could have an intelligent discussion about evolution. You can't have such a discussion if one side ignores facts and refuses to learn. Here's an example of a previous attempt: Fun and games with Otangelo Grasso about photosynthesis. Here's a post from yesterday showing that I wasted my time: Otangelo Grasso on photosynthesi.
One of my latest failed attempts concerns glycolysis. Otangelo Grasso claims that glycolysis is necessary to make ATP. He then points out that ATP is necessary to make the enzymes of the glycolytic pathway so evolution is impossible. Sandwalk readers will recognize it's difficult to know where to begin because there are so many flaws in this argument. Nevertheless, I decided, once again, to give it a try. I started by pointing out there are bacteria that do not have the standard glycolytic pathway and that gluconeogenesis (synthesis of glucose) undoubtedly evolved before glycolysis.
Where did Glucose come from in a prebiotic world?. What this shows is that Otangelo didn't listen to a thing I said about basic biochemistry and how scientists understand the origin of life.
He didn't like the fact that I have been ignoring him for the last few days so he posted a comment on Sandwalk. I'll try and answer his questions. I don't do this with the hope of teaching him anything. I'm doing it to show you what we are up against when tying to educate creationists. It looks hopeless to me.
Here's what he posted ....
Your explanation does not take into consideration that :I explained all this in previous posts and in the articles I linked to. He could also read my textbook if he really wanted to learn.
at three points, all outside the metabolic pools, do we find reactions in gluconeogenesis that use different enzymes:
(1) the conversion of pyruvate to phosphoenolpyruvate (PEP),
(2) the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate, and
(3) the conversion of hexose phosphate to storage polysaccharide or hexose phosphate to glucose.
Clearly, if cells are to conduct these reactions in the reverse direction, the three reactions must have a different ATP-to- ADP Stoichiometry and accordingly different enzymes are required.
Otangelo, your reasoning is flawed but your facts are mostly correct. The best way to look at it is to assume that gluconeogenesis is the primitive pathway. In most, but not all, species, two or three new enzymes arose to make an efficient glycolysis pathway. The original glycolytic pathway began with glucose-6-phosphate produced from the breakdown of glycogen. The two new activities were phosphofructokinase-1 and pyruvate kinase.
Later on, cells acquired the ability to use free glucose from the external medium by means of a sugar transport system coupled to ATP hydrolysis to make glucose-6-phosphate from glucose. Bacteria have several different transport systems that are capable of this reaction. Animals convert the end product of glycolysis (glucose-6-phosphate) to free glucose that circulates in vessels to other cells. Glucose is taken up by those other cells so they need an enzymes to phosphorylate it. That enzymes is glucokinase and/or hexokinase. That's the third enzyme. It's found in many species but it's absolutely necessary in humans and other animals.
So, Otangelo, your point is correct insofar as there are differences between gluconeogenesis and glycolysis at three steps but you just have the order reversed. The three enzymes arose to facilitate glycolysis, not gluconeogensis. You've been told that before.
Gluconeogenesis (GNG) is a metabolic pathway that results in the generation of glucose from the breakdown of proteins, these substrates include glucogenic amino acids (although not ketogenic amino acids); from breakdown of lipids (such as triglycerides), they include glycerol (although not fatty acids); and from other steps in metabolism they include pyruvate and lactate.This false statement comes from scientists who teach—hand were taught—that human biochemistry/physiology is all there is. The statement applies (partially) to humans but it does us no good when we are trying to understand the origin of biochemical pathways.
Knowledgeable biochemists assume that the first cells made glucose by fixing CO2, just as many bacteria do today. It's pretty silly to assume that the first cells could only make glucose by committing suicide. (The clue to the bias in your information comes from the claim that fatty acid breakdown can't contribute to the synthesis of glucose. That's because animals have lost the glyoxyate pathway. Most other species, including bacteria, are quite capable of interconverting fatty acids and carbohydrates.)
Questions:Chemoautotrophs exist and so do plants. Surely you are aware of the fact that you can grow plants from seeds by only supplying them with water, air, and minerals?
If Gluconeogenesis came first, where did the atp and all other essential products to make enzymes come from to make the enzymes in the gluconeogenesis pathway?
Think about this a little bit. It means there are thousand of species that manage to thrive and reproduce (and make ATP) without external glucose. These include species that are incapable of photosynthesis. What does that mean? It means your question is ridiculous because there are obviously many ways to make ATP that have nothing to do with glycolysis. All you need to do is learn about them.
Prior Glycolysis took over, what other pathway would supposedly have been in place to produce the same substrates as Glycolysis?If you're talking about ATP, see above.
What was in your view the precursors of gluconeogenesis?The main carbon source in my textbook is pyruvate. Here's the overall equation of gluconeogenesis.
Why would Gluconeogenesis be a less chicken egg - catch 22 problem ? Its complexity is basically the same as of Glycolysis.We can't even begin to discuss this issue until you learn a little bit of biochemistry. I understand that no matter how much you learn you will always return to the same point; namely; that you refuse to accept any origin or life scenario that doesn't require gods. That's fine, I just want to stop you from spreading nonsense about biochemistry on the internet. You can reject biochemistry if you like but let's make sure it's correct biochemistry that you are rejecting.
If the problem of Glycolysis first was the fact that no Glucose was readily available on early earth, what makes you think, the above mentioned substrates to feed gluconeogenesis were less a problem?Because there was always a good supply of CO2 on Earth.
Does Gluconeogenesis not depend on mitochondria, the cytoplasm, and the cell membrane amongst other molecules?It certainly doesn't depend on mitochondria! The fact that you ask such a question shows me that you absolutely refuse to listen to anything I say.
If you are willing to accept everything I've said above and correct your Facebook pages and your website pages, then we can discuss the rest of your question. I can't do that knowing that you probably won't listen to anything I say.
Had pyruvate carboxylase and acetyl-CoA not have to be present for gluconeogenesis to start?I suspect that a pyruvate carboxylase activity arose very early in the history of life because it is a carbon fixing reaction that converts a 3-carbon compound (pyruvate) to a four carbon compound (oxaloacetate).
Acetyl-CoA is not a requirement for gluconeogenesis but synthesis of 2-carbon compounds, such as acetate, was necessary in the early history of life. Acetate was then converted to pyruvate.
How did the transition from the 3 enzymes used in Gluconeogenesis to Glycolysis occur, and upon what selective pressures?Originally there were only two new enzymes required since free glucose wasn't present in cells. I don't know how those two enzymes arose.
The selective pressure was the ability to store energy as glucose (glucose-6-phosphate) in the form of glycogen then break it down efficiently in order to recover the energy as ATP and NADH using the pre-existing enzymes of gluconeogenesis as much as possible.
Why would there have been a transition from a supposed precursor system to Glycolysis?See above.