44

One of the main reasons that modern(!) biology uses oxygen as an electron acceptor is availability. Around 2.45 billion years ago, oxygen (O$_2$) started being built up in the atmosphere (which actually killed off a lot of the lifeforms/bacteria at that point). Since then, oxygen consuming lifeforms were able to establish themselves. Before that, most ...


31

Availability and applicability. Availability. In the beginning, there was CO2. It was abundant in the atmosphere, and later, the oceans. Fluorine and neon weren't, and so respiration evolved around what was (and is) available. Ref.: Paeloclimatology / History of the Atmosphere. Applicability. The other point about oxygen is that it works rather ...


28

Oxygen is actually not needed in the Krebs cycle - it is needed in the electron transport chain that is downstream 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 Krebs cycle. However, note that without O2, NADH accumulates and the cycle cannot continue as ...


25

Animals use oxygen as a chemical energy source because oxygen gas can react with many other compounds to form oxides, which releases energy and happen spontaneously. Both carbon and nitrogen can be made to react with oxygen, but otherwise they are pretty inert. So of all the gasses in the air present at over a fraction of a percent, oxygen is the only ...


19

I'd argue that we do "breathe" all those gases. Air that we inhale (at sea level) is about 78% N$_2$, 20.9% O$_2$, 1% argon, and smaller percentages of CO$_2$, neon, methane, etc. So all those gases are going into the lungs with every breath in. We take up oxygen preferentially because we have hemoglobin to bind O$_2$. When hemoglobin binds the oxygen, it ...


14

The atomic radius of fluorine is just slightly larger than that of carbon. When a fluorine atom bonds to a carbon atom that is part of a carbon backbone, the fluorine atom covers up not only the C-F bond but also the adjoining C-C bonds. This makes it impossible for biological enzymes to access these bonds to break them, and is why fluorinated compounds ...


13

You are correct that reduction is simply a gain of electrons. This results in a decrease in oxidation number. You know that NAD+ is reduced by this process because it starts off with a positive charge (+1) and ends up with a neutral charge (0). The reducing agent that is donating the electrons is the hydrogen. More correctly, the electrons come from the ...


13

As far as I can understand your question, you wish to know why a plant cell consumes ATP to produce glucose when it can directly use the ATP as an energy molecule. ATP is an energy currency and is required in different biochemical pathways. However, it is not a good energy storage molecule. Following are the reasons why production of an energy molecule ...


11

Phosphorus is a very common nutrient, found in high levels in proteins, which are in such foods as milk and milk products, meat, beans, lentils, nuts, and grains, especially whole grains. Phosphorus is found in smaller amounts in vegetables and fruit, as well. Adenosine can be found in many of the same foods, both as free ATP/ADP/AMP, and as part of the DNA ...


10

The way we were To understand why you may encounter ATP synthase referred to as ATPase, you need to be aware of the historical context — the experimental work that preceded the knowledge of the structure and function of the enzyme complex that we have today. In a nutshell: Original studies of the components of what we now know to be a complex capable of ...


9

Another small addition There is class of oxidoreductases called oxygenases which incorporate molecular oxygen into the substrates and not just use it as an electron acceptor like in oxidases (note that the terminal enzyme in ETC is an oxidase and there are other such oxidases). In other words, oxygen is not a cofactor but a co-substrate. Oxygenases are ...


9

This is slightly depending on which reaction you want to include into the cycle. I count four: One when Pyruvate is converted to Acetyl-CoA, one when Isocitrate is converted to α-Ketoglutarate, one for the reaction of α-Ketoglutarate to Succinyl-CoA and finally one for the reaction of Malate to Oxaloacetate. If you see the reaction of ...


9

Glycolysis needs a steady supply of NAD+ to happen - this is the driver for the anaerobic oxidation to lactate and ethanol, although this is energetically much less favorable than the complete oxidation. But without oxygen there is no other way to keep the glycolysis active for at least some energy supply. The difference is located in the enzymes available ...


9

Neon just does not work as an electron acceptor. It is that inert that there are currently no known Neon compounds at all. Fluorine would work in principle, but it is rare compared to oxygen and its strong reactivity makes it a very dangerous substance in elementary form. So it seems very natural that life chooses Oxygen and not Fluorine.


7

Nitrogen is much less reactive than oxygen. Indeed, if I haven't totally forgotten my long-ago chemistry courses, most chemical reactions involving N2 are energy-consuming. Thus you get nitrogen compounds produced by lightning, in auto engines, and other places where there's a lot of energy to spare. Oxygen reactions, OTOH, are energy-producing. You ...


7

Aren't there any other alternatives for this acceptor? Not that we're aware of. Every other alternative requires an anaerobic environment - which means small, and often less efficient. Oxygen is already recognized to have several harmful effects to cells - wouldn't another molecule be a better choice? When we're talking about a molecule's fit there are ...


7

Organisms are classified, not by their behavior, but by their phylogeny (evolutionary relationships). Sponges have unique and complex molecules in their intracellular matrix that developed in a common ancestor of sponges, and are shared with sponges and all other animals. These molecules include collagen, proteoglycans, integrin, and adhesive glycoproteins. ...


7

Uncoupling ATP synthesis from the ETC (electron transfer chain; this is where oxidation takes place) by thermogenin or any other method means that the energy used to generate or uphold the proton gradient gets 'lost'. Since physics teaches us that energy is only transferred and never truly lost, the energy consumed by the ETC must most go somewhere - heat / ...


6

Aren't there any other alternatives for this acceptor? Yes, there are multiple other acceptors used by anaerobic bacteria. Iron is probably the most common other acceptor used by a range of organisms in a range of environments but others are used as well, such as sulphur. Aren't there any other alternatives for this acceptor? Oxygen is already recognized ...


6

Pyruvate is negatively charged and quite polar, which makes it unfavourable to diffuse directly through any membrane. The outer mitochondrial membrane contains porins, which allow small molecules, like pyruvate, to passively diffuse through. Specifically, pyruvate uses voltage dependent anion channels. The inner mitochondrial membrane lacks such channels and ...


6

Diffusion, is by definition (Ficks Law) describing movement along or against some gradient (here its concentration) even if the mechanism of transport differ: active, passive, facilitated. The setup of the electrochemical gradient across membrane, like any thermodynamic process is not perfect, there are always entropy losses. In this case, this manifests as ...


6

The Fallacies in the argument The question contains two main fallacies (some would say sleights of hand) in the energetic comparison of glucose synthesis from CO2 in the Calvin cycle and glucose oxidation via glycolysis, the tricarboxylic acid cycle and the electron transport chain: The descriptions of the two reactions are incomplete — important co-...


6

Roughly, half of the CO2 assimilated annually through photosynthesis is released back to the atmosphere by plant respiration (Gifford, 1994; Amthor, 1995). Source: https://academic.oup.com/aob/article/94/5/647/151785/Plant-Respiration-and-Elevated-Atmospheric-CO2 Furthermore, it appears like plant respiration rates do not change much with changing ...


6

There are organisms with anaerobic metabolism that tolerate oxygen: aerotolerant anaerobes. "Anaerobic" refers to the metabolic system. You cannot be sure of oxygen tolerance based solely on metabolic system. Factors influencing the tolerance of anaerobic bacteria to oxygen Here is why this is a facultative anaerobe. This organism does not gain weight ...


6

In short, the difference stems from different values regarding the number of ATP attributed to the electron carriers in the electron transport chain (ETC). My guess is that your class didn't go too far in depth on the subject, and also that your class or text is using mixed sources of information. I have overviewed (general) glucose metabolism here, but ...


5

You haven't directed us to any evidence for your assertion, so it is difficult to evaluate. I'm not a plant physiologist, so I will argue from first principles: photosynthesis consumes CO2 and produces O2: 6CO2 +6H2O -> C6H12O6 + 6O2 respiration consumes O2 and produces CO2: C6H12O6 + 6O2 -> 6CO2 +6H2O Plants do both of these things at the same ...


5

There are some recipes available on the web, my answer is based on this webpage and this information: The process itself is rather easy and you can either use ready bought apple juice, homemade juice or apple cider (basically unfiltered apple juice). You will need some specially cultivated yeast, baker's yeast is generally not recommended since it might ...


5

Yes. But it is incorrect to call mitochondria an organism now. Most of their genes were lost and are now encoded in the nuclear genome It gets most of its metabolites It is not known. See the other post for details. Why membrane: I guess you know that. Why folded: you guessed right. Only ovum donates mitochondria and other cytoplasmic factors. Sperm just ...


5

Oxygen is good for animals because our basic metabolism is this: High energy carbon molecules + O2 → energy + H2O + CO2 Plants do that too at night, but during the day, they mostly do this: High energy photons + H2O + CO2 → High energy carbon molecules + O2 Rubisco, one of the most important enzymes in photosynthesis, can bind to O2, leading to less ...


5

Short answer (A) is a possible answer and is indeed cause for fatigue, as pyruvate is needed for the Krebs cycle to run. The krebs cycle is an essential step in the generation of ATP in aerobic organisms. (B) is incorrect because NADH is never transported into the mitochondria in any organism (it is a nonsense answer). Background NADH is not transported ...


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