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22

Before I restrict the answer to human metabolism, I recon it is important to mention that CO2 is the source of the carbon atoms of glucose in photosynthesis (in the Calvin cycle). [In photosynthesis CO2 is 'fixed']. Even with the above restriction, I am certain I cannnot do justice to every helpful aspect of CO2 in mammalian metabolism, and I'll restrict ...


22

Nice question! Oxygen is actually not needed in the Krebs cycle - it is needed in the electron transport chain that is upstream of the Krebs cycle to regenerate NAD+ from NADH. NAD+ is a co-enzyme and acts as an electron carrier in oxidizing reactions at various positions in the Crebs cycle. However, note that without O2, NADH accumulates and the cycle ...


20

A coupled biochemical reaction is one where the free energy of a thermodynamically favourable reaction (such as the hydrolysis of ATP) is used to 'drive' a thermodynamically unfavourable one, by coupling or 'mechanistically joining' the two reactions. To put it another way, two (or more) reactions may be combined by an enzyme (for example) such that a ...


16

Gasoline toxicity through ingestions seems to be a topic where there's not a great deal of in-depth information available. I don't know how this works for chronic use, as most literature refers to acute scenarios. Either way, orally ingested, 30-50g is said to be toxic to humans while 350g can be fatal.[3]. So... Gasoline's Constituents A lot of ...


16

Short answer Birds emit infrared. Background Objects with a temperature higher than the background emit detectable infrared (IR). Endothermic (warmblooded) animals keep their body temperatures at around 37oC and given the relatively cool temperatures at the earth's surface, endotherms generally emit more IR than the background. Endothermic animals include ...


15

The cost of transcribing and translating a hypothetical average gene in yeast has been calculated as 551 activated phosphate bonds ~P per second (Wagner, 2005). The median length of a yeast RNA molecule is 1,474 nucleotides, and the median cost of precursor synthesis per nucleotide (derived from the base composition of yeast-coding regions) is 49.3 ...


15

It's pretty simple. A reaction occurs that releases energy (like ATP losing a phosphate to become ADP + Pi). If this is uncoupled, the energy will merely turn into heat. If it is coupled, then it can be used to fuel some other process. For instance, if you couple the ATP -> ADP reaction to a certain protein, the energy can be used to modify the shape of that ...


13

Gluconeogenesis is not the reversal of the glycolysis, but the generation of glucose from non-carbohydrate precursors (like odd chain fatty acids and proteins). The reason why we have this process is because some organs and tissues can only use glucose as their energy source. These include the brain (although ketone bodies can be used here as well), ...


12

All organisms recycle their waste internally. Every cell of every living organisms is constantly breaking things down and re-using the components so produced. But you're presumably wondering about things such as carbon dioxide, urine and faeces? These are not recycled because the benefits of doing so are not worth the costs. Let's consider carbon dioxide as ...


11

There are some very general answers to your question. Definitely, there is a lot of magical thinking. We as humans are very prone to anecdotical evidence and extrapolations from incomplete data, even more so when we are drunk. As an interesting "proof" is the fact that the German counterpart of the saying "beer after wine and you'll feel fine, wine after ...


11

First of all, we should specify that there is no such thing as "HDL-cholesterols" and "LDL-cholesterols". On the same note there is no such thing as "good cholesterol" and "bad cholesterol": cholesterol is just one molecule, with this chemical structure What blood tests generally report is HDL-C and LDL-C, that is the amount of cholesterol in HDL or LDL ...


10

Fat uptake means cells eating fat. I'll try to keep it simple, so forget the many approximations. You need first to consider that most fat circulates in the blood under the form of triglycerides (TG). TG are not soluble in water, so how do they circulate? They are hidden inside cargo vehicles called lipoproteins. When a circulating lipoprotein touches a ...


10

For the most part they are not used. there are amino acid racemases, which interconvert L- and D- forms of some specific amino acids, which may be used in some particular biosynthetic or metabolic pathways. In particular I'm thinking of firefly luciferase which uses D-Cysteine as a re-dox reagent to regenerate the luciferin substrate that the light - ...


10

does the microbiome affect food metabolism? Most definitely (and not surprisingly). The Arumugam paper [1] notes that The drivers of [enterotype 1] seem to derive energy primarily from carbohydrates and proteins through fermentation, … because genes encoding enzymes involved in the degradation of these substrates (galactosidases, hexosaminidases, ...


10

During putrefaction of animal tissue, lysine is decarboxylated into cadaverine and arginine is decarboxylated into putrescine. These compounds are deemed to be toxic. A serving of meat contains 8 g of protein, corresponding to 640 mg lysine and a little bit less of arginine. Let's go straight and say that a spoiled meat serving contains 640 mg cadaverine ...


10

In the case of red blood cells: human erythrocytes (red blood cells) have no mitochondria. Since the mitochondria are the cellular site for oxidative metabolism of fatty acids, erythrocytes cannot oxidise fatty acids to release energy. The erythrocytes also cannot fully oxidise glucose (to carbon dioxide and water) because this is also a mitochondrial ...


10

Some additional points about role of bicarbonate (which is directly formed from carbon dioxide as described by TomD): Helps is neutralizing the acidic chyme when it enters intestine. Formation of shells in invertebrates and eggshells in birds and reptiles. Shells are formed by deposition of calcite (calcium carbonate) which primarily happens by increased ...


9

No; the problem is, as you pointed out, that no organism will manage to multiply, grow or even sustain itself without absorbing matter to create new cells and fill metabolic losses. Even photoautotrophic organisms which get energy from light (which is in fact an E-M wave, so pretty close to electricity) collect matter from the environment -- plants for ...


9

First, the hormonal and hemodynamic changes seen in hangover are distinct from those seen in alcohol withdrawal, so the advice to drink more is not good, even if some symptoms are in fact improved. See tables 2/3 in the cited review. It appears the molecular mechanism of veisalgia (HA, a new word) is not well known. 1. acetaldehyde Part of it may be ...


9

Halsey & White (2012) Comparative energetics of mammalian locomotion: Humans are not different. Journal of Human Evolution 63:718–722 This paper presents a comparison of the metabolic cost of walking and running in humans, Australopithecus and other mammals. They use a parameter NCOT (net cost of transport), whose units are ml O2 consumed m-1. The ...


9

This question asks about the urinary excretion of THC. Before answering the question I think you're getting at, I'll first note that cannabinoids (of which THC is one) are primarily metabolized by hepatic cytochromes rather than being excreted directly. This article is a classical pharmacokinetic paper on the topic if you’re able to access it; this one is a ...


8

Just to add an answer to the 'how does the body process gasoline?' portion of the question, the liver and kidney would be doing most of the work of removing the stuff from the system once it was absorbed in the digestive tract. The liver does most of the processing of toxins and their removal from the blood and would tend to do the most work in removing ...


8

That book was likely crap, but in short the answer is yes, probably there is a genetic basis in the metabolism, with human 'types' that could benefit from a personalized nutrition. The discipline studying these relationship is called nutrigenomics, and the main concept is similar to what is being told for personalized medicine. The bad news is that ...


8

The brain and heart can take advantage of ketone bodies when the amount of glucose is low. These are byproducts of fat metabolism and can be converted to acetyl-coA via the citric acid cycle. Overproduction of these products can cause pathological conditions: When the rate of synthesis of ketone bodies exceeds the rate of utilization ,their ...


8

Perhaps the question may also be phrased, "Why is it common for plants to produce chemicals that possess pharmacological or toxicological effects in man and animals?", and to that question it is often reasoned that plants, being sessile and otherwise defenceless food sources for predators, produce compounds that affect the physiology of animals in such a way ...


8

The blood pH is tightly controlled since variations are quite dangerous for us. Under normal circumstances the pH is 7.4 (with a normal range between 7.35 and 7.45). Below that we are talking about acidosis, above it about alkalosis. If the blood pH goes about 7.8 or below 6.8, death will occur. This pH is maintained by the Bicarbonate-buffering system, for ...


8

The term "irreversible" means that the reverse reaction occurs so rarely that it is considered negligible. This means that you do not have to consider equilibrium, as you have to for reversible reactions. Instead, you can assume that all of the reactants will eventually become product. As you stated, this is true for reactions that have a very negative ...


7

Yes, the microbiome affects food metabolism and the diet affects the composition of the microbiome. +1 to Konrad for his response. This is an area of research in which I and colleagues are engaged. Frankly, it is easier to assess the changes to the microbiome based on diet rather than looking at the fecal material to determine (unused) metabolic energy or ...


7

You may also be interested in D-amino-acid oxidase (EC 1.4.3.3), a flavoprotein (FAD) highly specific for the D-form of amino acids, which was discovered by Hans Krebs in 1935 (see here), and which has a wide distribution (including in humans). The enzyme has been very thoroughly investigated, in particular by Massey & co-workers (see here for ...



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