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17

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 ...


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

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 (see link). However, note that without O2 NADH accumulates and the cycle cannot continue as it needs NAD+ to run.


15

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 ...


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 ...


14

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 ...


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 ...


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

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

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 ...


9

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 - ...


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 ...


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

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 ...


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

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 ...


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

I can't speak to the causes of hypotension, but you are indeed correct, caffeine is a stimulant. As a stimulant, there is a well documented acute period of hypertension that lasts for up to 4 hours. Interestingly, there is no causal link established between caffiene consumption and chronic hypertension leading to cardiovascular disease (see here and here). ...


7

I speak only for the U.S. regulations: the calorie labels on wrappers refer to the energy released when burned. Sometimes these are inaccurate. Many dieticians recommend calculating the calories based on weights of protein, carbohydrates and fats in the serving: 4 kcal in each gram of protein and carbohydrate and 9 kcal in each gram of fat in your food. ...


7

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 ...


7

There are metabolic processes in which ATP is synthesised without the involvement of ATP synthase. The best examples are, in fact, two steps in the glycolytic pathway, catalysed by phosphoglycerate kinase and pyruvate kinase. This is why, in the absence of any aerobic metabolism, many organisms (like yeast for example) can grow quite happily, producing two ...


7

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 ...


6

In general the answer is yes. However, the degree in which this is true and the degree in which the human body can adjust and adapt to new food types is larger misjudged. I am of the opinion that metabolism is largely controlled by the microbiome. It is largely recognized that the gut biome does adjust depending on diet and will also vary depending on drug ...


6

The question is not too broad, just involves a fair bit of work to both do the research and compose a response. I'll do the latter, but in brief. The strings of the four nucleotides encode genes. Sometimes these genes are broken into protein-coding portions (exons) and sometimes intervening, non-coding regions (introns). Bacteria, for example do not have ...


6

I thought this was a great question. In particular because it hints at two questions. The first is 'why carbohydrates are used to store energy' in general. The second being 'why glucose rather than other carbohydrates?' in particular. Glucose metabolism (and glycogen storage) is a core gene pathway - its found in bacteria archaea and eukaryotes. So ...


6

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 ...


6

Having done an inordinate number of rather mind-numbing A.S. practicals involving milk and enzymes the year before last, in my experience lactase always began breaking down the lactose immediately and converting a boiling tube worth of milk in less than 50 minutes at below room temperature. To further allay your concerns, this website suggests that most ...


6

Adenosine triphosphate (ATP) is often thought of as the energy currency of cells. It is not "used up" per se, but energy is released from the conversion of ATP to ADP (adenosine diphosphate), and yet more can be obtained by removing another phosphate to make AMP (adenosine monophosphate). Here's a chemical schematic of ATP, you can see the three phosphates ...


6

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 ...


6

Rudolf Shoenheimer and David Rittenberg were key figures in introducing the isotopic tracer technique to biology. This technique, which may be dated to the discovery of deuterium by Urey in 1933, produced a revolution in biological thought. Much of the early work was done at the Department of Biological Chemistry at Columbia University under the ...



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