Questions tagged [metabolism]

Metabolism is the set of defined biochemical transformations occuring within the cells of living organisms.

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How much energy does a spider expend per day just waiting for its web to vibrate?

Roughly speaking, a small, complex electronic circuit or IC might sit in "sleep mode" using a current of roughly 1 µA (e.g. 1, 2), thereby using roughly $3\times 10^{-6}$ Watts, and that ...
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Kinetic mathematical model of glycolysis?

I am looking for papers containing kinetic mathematical models of glycolysis, hopefully in mammalian cells (or as close as possible, say yeast). The papers I have found do qualitative analysis (...
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Food Intake versus ability to flee among birds, particularly the hummingbird?

Logically speaking, if a hummingbird drinks too much nectar, it will be temporarily overweight and less able or unable to fly to escape danger. However if the same hummingbird doesn't drink enough ...
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What's the lowest atmospheric pressure a tardigrade can remain active in?

I'm not asking what atmospheric pressures they can survive (we now they can survive the vacuum of space) I'm wondering at what point a deficit of atmospheric pressure would cause them to enter one of ...
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How does anaerobic bacteria produce ATP for it's own cellular activities?

Anaerobic bacteria utilise glycolysis: Glucose + 2 P + 2 NAD+ => 2 ATP + 2 H + 2 NADH + 2 H2O + 2 Pyruvate followed by fermentation: Pyruvate + NADH => Lactate + NAD+ The resultant NAD+ formed ...
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In ketogenesis, why is acetacetyl-CoA not directly hydrolized to acetoacetate in ketogenesis?

Ketogenesis pathway maps show acetoacetyl-CoA converted to HMG-CoA and only then to the first ketone body acetoacetate. Why this detour instead of directly hydrolyzing off the CoA to get there in a ...
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293 views

Affinity for oxygen and carbon dioxide in animals

I'm currently reading Treatise on Invertebrate Paleontology (A) and don't understand the following fragment: The affinity for oxygen in lower animals is many times that in higher ones, whereas ...
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If your body can slow down your metabolism, why doesn't it do that all the time?

I've read that in cases such as in anorexia or a lack of food, the body slows down the metabolism to preserve the little food it does get. If it can do this, though, why doesn't it keep your ...
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Regulation of the concentration of precursors of DNA and RNA synthesis

What is the specific cellular process for regulating the amount of the four DNA bases (adenine, thymine, cytosine, and guanine) that are present in the cytoplasm of a cell? Basically, how do the cell'...
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101 views

Are there animals that can deliberately manipulate their metabolism, apart from hibernation?

Are there animals that can slow down their metabolism deliberately? I know that hibernation would be one mechanism, and maybe being cold-blooded, but I was wondering if there was maybe an animal that ...
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What is the function of CETP?

I read up that CETP transfers cholesterol from HDL, which collected it from tissues, to VLDL. This VLDL is then sent back to the tissues, ultimately forming LDL internalised by cells. What is the ...
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277 views

Does the metabolic rate determine how fast the telomeres shorten?

In many papers one can read that telomeres may play an important role in longevity. According to Calado et al.1 the telomeres of mice are much longer than the telomeres of humans. However, mice have ...
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Are there any enzymes synthesised by humans that specifically catalyse the hydrolysis of non-cyclic Imides?

Imides or dicarbonyl amides are an interesting class of compounds that includes the pharmaceuticals thalidomide, aniracetam and a few other drugs. These compounds, however, are cyclic and I'm ...
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Could certain drugs enable one to consistently eat above TDEE or BMR without fat gains?

I heard anabolic steroids and stuff like DNP and ephedrine and etc. can somewhat enable one to eat more and get away with it without much or any fat gain, despite eating more than the body would ...
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Is there a relationship between HDL-C and LDL-C?

For a gentle introduction to cholesterol and its functions, see a great answer on SE Biology Whenever I read about how to deal with cholesterol level, the rule is to keep a low LDL fraction, ad a ...
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Is homocysteine converted to glutathione during oxidative stress?

From the paper titled "The basis for folinic acid treatment in neuro-psychiatric disorders" by Ramaekers et al., 2016: On the left side of the figure, the purine metabolite GTP serves as the ...
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Why does pyruvate from lactate and pyruvate from other sources follow different pathways in gluconeogenesis?

My teacher taught me in a lecture that PEP forms from Pyruvate by two ways, based on their sources, that is - 1. If the Pyruvate was from lactate (by lactate dehydrogenase action), it gets shuttled ...
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Is gut bacteria Succinivibrionaceae's low methanogenesis understood well enough for GM of cattle gut bacteria to be considered?

After watching the Periodic Table of Videos episode linked in this question I watched the episode Wallabies and Methane where Sir Poliakoff says (a bit after 02:00):...
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Why does GLUT2 (With a high Km), bind less glucose at a lower glucose concentration (below Km)?

A text I am reading says "GLUT2 is a low-affinity transporter in hepatocytes and pancreatic cells. After a meal, blood travels through the hepatic portal vein and GLUT 2 captures excess glucose for ...
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How can you gain 1 lb of bodyweight from eating less than 1 lb of food surplus?

A commonly referenced "fact" is that a caloric surplus of 3500 kcal is equivalent to a 1 lb gain in bodyweight. But I'm confused. If you get 3500 kcal worth of, say, fatty acids, which are 9 kcal per ...
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Is the amount of cholesterol the body produces affected by how much cholesterol you take in with food?

In the past I've been told multiple times that if you don't eat foods containing cholesterol, your body will increase its production of cholesterol to balance out the lack of nutritional cholesterol. ...
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Validity of measurements of respiration in isolated mitochondria

I've recently read a couple of papers on exercise and mitochondria, in which state 4 and state 3 respiration rates and ROS production are assessed in vitro after exercise has been performed (i.e., rat ...
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What is the rationale behind reverse cholesterol transport?

Reverse cholesterol transport is transport of cholesterol from the tissues back to liver/VLDL. My question is why do the tissues have this extra cholesterol in the first place? Why would you ...
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Why lactate inhibits growth (or enhances death rate)?

Extracellular lactate tends to inhibit cellular growth or enhance cell death. This happens in the vicinity of tumors and in cell cultures. See for example this reference: Ozturk, Sadettin S., Mark R....
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Is there a way to quantify in vivo cholesterol transport rates?

I have always had trouble grasping the physiology of lipoprotein cholesterol transport. The "standard" description found in the literature is that liver synthesizes cholesterol which is carried in "...
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469 views

How much energy would it cost to synthesize all cholesterol requirements de novo?

Imagine a scenario in which some person is unable to absorb any dietary cholesterol because of some intestinal mutation (for example). Thus, they have no cholesterol available from their diet for ...
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Metabolic control theory: proof of the summation theorem?

I'm looking for a rigorous proof of the summation theorem of metabolic control theory. The only sources I find are the original papers by Kacser and Burns 1973 and Heinrich and Rapoport 1974, both of ...
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Which Lactobacillales (Lactic acid bacteria — LAB) strains are capable of degrading starch?

I've been researching bacteria strains but am having trouble finding amylolytic LAB strains with amylolytic and lactic acid producing character. The only species I've found, that are capable of ...
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Why doesn't the body optimize how many fatty acids it burns?

Ketone bodies are produced due to an excess of fatty acids being burned (accumulation of acetyl-CoA) so my question is: Why doesn't the body simply regulate how many fats it burns so it doesn't have ...
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Which biosynthetic pathways take place in the plastid and were are they located?

I know that the isoprenoid, jasmonate, glucosinolate, fatty acids, chlorophyll, starch, and aromatic amino acid syntheses are located in the plastid. But I don't know if they are located in the ...
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Is body energy production and consumption cyclical?

If we look into how energy is produced by the humans, it always involves some kind of periodicity: fuel combustion rotates engines, water rotates turbines, nuclear chain reactions heat up water, which ...
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Can you change your gut microbiota by changing your diet? Would that affect calorie uptake?

I have seen peer-reviewed papers mentioning the daily changes in gut microbiota composition according to dietary changes. See for example this paper: http://genomebiology.com/2014/15/7/R89 My ...
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Regulation of Cra protein level in E coli

Catabolite Activator/Repressor, Cra protein (formerly known as Fructure Repressor FruR) plays a significant role in central carbon metabolism of E coli. Its activity is inhibited by fructose-1,6-...
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Why is a nicotinamide-tryptophan combination used to treat affective episodes in a few older clinical trials?

At least one of the journal articles that reported on such clinical trials allured to the nicotinamide-tryptophan pathway that I assume must be related to the metabolism of tryptophan into serotonin ...
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Are simple esters like those used as flavouring agents metabolised into their constituent carboxylic acids and alcohols in the human body?

By this I mean to ask whether say ethyl butanoate is hydrolysed in humans into ethanol and butyric (butanoic) acid. This is of interest to me as a pharmacology researcher because butyric acid, for ...
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How is Saccharomyces cerevisiae grown on acetate and ammonium able to produce TCA intermediates?

I am working with a metabolic model of Saccharomyces cerevisiae and I am studying its growth on acetate and ammonia. I am performing Flux Balance Analysis to compute the growth rate and then I am ...
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What's the lowest temperature a tardigrade can remain active at?

There's a lot of information floating around the net about how tough they are & what they can survive, like "We now know that some tardigrades can tolerate being frozen to -272.8 °C". But any ...
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Where is ethanol detoxified? peroxisomes or smooth ER? Or both?

I am reading the textbook Biology (Campbell et al, 2005), and I am confused. In Chapter 6.4, on page 104, it says that "In the smooth ER, other enzymes help detoxify drugs <...>", and alcohol is ...
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How cells determine how many enzymes are needed for digestion

How do pancreatic cells, epithelial cells of the stomach and intestinal epithelium cells determine the right amount of enzymes for digesting carbohydrates, proteins, fats? How does the pancreas ...
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What waste products do cells secrete in culture, and at what rate?

I am designing microfluidic chips for mammalian cell culture. One aspect I am interested in modeling is the rate at which I must renew media to ensure that: Cells receive enough nutrients Cytotoxic ...
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Bacteria utilize short chain fatty acid as energy source

I'm doing research about the short chain fatty acid producing bacteria. I studied 7 short chain fatty acid (acetic propionic butyric isobutyric valeric isovaleric and captionic). and I found that the ...
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What happens to lipoprotein lipase after a sugar only diet?

Insulin increases the activity of lipoprotein lipase thay allows cells to take in lipids from chylomicrons in the blood. If a person takes a sugar only meal like drinking coke, insulin is released. ...
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Simplest known form of aerobic glycolysis

What is the simplest known way that an organism performs aerobic glycolysis? In other words, what is the simplest known way known to convert glucose into $\ce{H2O}$ and $\ce{CO2}$, other than by ...
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Contribution of major nutrients to energy in the human body

What is the contribution of the major nutrients -- glucose, fat and protein -- to the human body's energy requirements, in normal conditions? For some tissues, the fuel preference is known ...
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310 views

Entropy increase or decrease in an reaction

My question is how would you tell if the product of an reaction has more or less entropy than the reactants? For example, in glycolysis, when glyceraldehyde-3-phosphate becomes 1-3 ...
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What are the chemical characteristics of cofactors that functionally differentiate them from the side chains of amino acids?

Cofactors are essential for the function of many enzymes, such as NAD+ in the glycolytic pathway - I was wondering how the chemical properties of these cofactors allow them to fulfil their function ...
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How do marine mammals stay hydrated?

This is a question that has always bothered me. A quick internet search yields "metabolic processes" as the reason for how marine mammals obtain water, but what are those processes and why don't land ...
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How is the human oxygen absorption dependent on the concentration of oxygen in respiratory air?

I just wanted to calculate the theoretical time span in which I could survive (conscious) in my apartment without letting the air on the inside exchange oxygen/carbon dioxide with fresh air. During my ...
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Does hunger necessarily mean that we should eat?

People feel hunger sooner after they eat food that consists mostly of carbohydrates. For example, if someone eats a good portion of rice then most likely they will be hungry after a couple of hours. ...
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Why does lactate build up prevent a further increase in the speed of an athlete?

This question was triggered by an exam question that I was doing on the following paper (Q2 part (b)(i)): http://qualifications.pearson.com/content/dam/pdf/A%20Level/Biology/2013/Exam%20materials/...