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27

The answer to this, I reckon, is that they don't. They use molecular oxygen (O2) dissolved in the water for respiration, where it acts as a terminal electron acceptor, just as we use molecular oxygen in the air for respiration. We can speak of the water as being oxygenated. Water is split in photosynthesis, where reducing equivalents from water are used ...


27

The phosphate group in NADPH doesn't affect the redox abilities of the molecule, it is too far away from the part of the molecule involved in the electron transfer. What the phosphate group does is to allow enzymes to discriminate between NADH and NADPH, which allows the cell to regulate both independently. The ratio of NAD+ to NADH inside the cell is high, ...


23

Oxygen is actually highly toxic to cells and organisms – reactive oxygen species cause oxidative stress, essentially cell damage and contributing to cell ageing. A lot of anaerobic organisms have never learned to cope with this and die almost immediately when exposed to oxygen. One classical example of this is C. botulinum. Oxygen is incorporated in several ...


23

Superoxide, O2− is created by the immune system in phagocytes (including neutrophils, monocytes, macrophages, dendritic cells, and mast cells) which use NADPH oxidase to produce it from O2 for use against invading microorganisms. However, under normal conditions, the mitochondrial electron transport chain is a major source of O2−, converting up to perhaps 5% ...


23

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

CO2 is a product of Cellular Respiration, which generally takes Glucose and molecular Oxygen to produce Carbon Dioxide, water, heat, and allows ADP to be regenerated into ATP (or other various oxidation reactions). The Carbon comes from wherever the acetyl-CoA used in the Citric Acid Cycle came from - either carboyhydrates or fatty-acids (saturated carbon ...


16

According to "Resolution of distinct rotational substeps by submillisecond kinetic analysis of F1-ATPase" (Yasuda et al., Nature, 2001), ATPase rotates at 130 revolutions per second when saturated with ATP.


16

No, hydrogen could not replace oxygen because it has entirely different characteristics. The most important one is probably its electronegativity - oxygen 'pulls' electrons much 'stronger' than hydrogen. Basics: Reduction potential Oxygen is the so-called terminal electron acceptor of the electron transport chain in eukaryotes. You can see "reduction ...


16

You probably know by now that cytochrome c oxidase, the last complex of the electron transport chain, belongs to a class of enzymes called oxidoreductases, that use oxygen atoms as electron acceptors. One type of oxidoreductases are oxidases, enzymes that (at least in theory [1]) use molecular oxygen--O2, like in air--as their electron acceptor. From what I ...


15

Mitochondria are very similar to bacteria and are thought to have originated from bacteria. This points you to the answer: bacteria produce ATPs the same way mitochondria do, with the oxidation machinery place in their plasma membrane (analogous to the mitochondrial membrane).


12

Anaerobic respiration is a respiration where the final electron acceptor is different than oxygen. The final acceptor can be a less oxidizing than oxygen, like sulfate (SO42-), nitrate (NO3-), or sulfur (S). For example bacteria that use sulfate are obligate anaerobs. The Krebs cycle cannot take place in the absence of oxygen, although oxygen is not ...


11

Mitochondria are comprised of ~3000 proteins. However, the mitochondrial genome has only 13-14 protein-encoding genes. The remaining 99.6% of mitochondrial proteins are encoded by genes in the nuclear genome. (Wikipedia) Chloroplast genomes are only slightly larger (~100 genes). Gene regulation and signaling between the nucleus and mitochondria (and between ...


10

There is a good review in the Journal of Experimental Biology (Bickler and Donohoe 2002, JEB 205, 3579–3585) I will just summarize for those that do not have access to the review. Neurons use lot of energy to maintain their polarized state, this is not required to other cells. When O2 or blood flow is reduced, the neuronal ATP levels breaks down very fast, ...


10

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 ...


9

Image from wikipedia page on ATP synthase In brief, the addition and release of protons to the structure cause a conformational change that leads to another conformational change. This series of conformational changes occurs in such a way that it induces a rotational motion. The rotation of the central axel that extends through both hemispheres of this ...


9

Here's an illustrated example in neurons: ATP, of course, is generated by aerobic respiration. The critical biochemical reaction in the brain that is halted due to lack of ATP (and therefore O2) is the glutmaine synthetase reaction, which is very important for the metabolism and excretion of nitrogenous wastes: The body uses this reaction to dump excess ...


9

Just to expand slightly on the answer by Jack Aidley: Have a look at this section from Stryer's Biochemistry text book, particularly Fig 10.17, where you can see that haemoglobin has evolved to have a high affinity for oxygen at the O2 concentrations present in the lungs, but a low affinity at the O2 concentrations present in the peripheral tissues. This is ...


9

They do generate heat. They just do not SPEND energy specifically on heating their bodies by raising their metabolisms. This is a form of energy conservation. The metabolic rate they need to live is not nearly enough to heat their bodies. An example of spending energy to heat the body is seen in humans shivering. Here muscle is activated not for its usual ...


8

The overwhelming use of oxygen is to provide us (in combination with food) with energy. We have a great need for energy in our cells, which is why we have these lungs, diaphragms, red blood cells, etc.; they assure we get the oxygen to obtain the energy (via the electron transport chain). The overall metabolism of glucose (C6H12O6) is a representative ...


8

Your question is based on a bit of confusion about electron acceptors that is very common and that drives microbiologists crazy. Energy (as ATP) is generated when electrons are moved from an electron donor to an electron acceptor. In respiration, the electron acceptor is inorganic -- oxygen for aerobic respiration or an inorganic molecule such as sulfate or ...


8

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 ...


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

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 ...


7

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 ...


7

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 ...


6

The textbook version for the regulation of ATP involves a feedback loop with phosphofructokinase (PFK). The relative concentrations of ADP and ATP are characteristic of the energy state of the cell. If the cell is using energy, then there will be an excess of ADP. If not, then ATP. ATP is an inhibitor of PFK, which in turn slows glycolysis (thus reducing ...


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

The ATP is not actually produced from the respiration. It comes from ADP and free phosphate ions. The production of ATP in cellular respiration happens in all parts of a series of chain reactions, and you can read more about those here: https://en.wikipedia.org/wiki/Cellular_respiration#Aerobic_respiration


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 ...


5

Your latter assumption is the best we have so far, to my understanding. Here are a few excerpts from "Early Evolution of Photosynthesis" published in Plant Physiology, October 2010 (emphasis mine): There is suggestive evidence that photosynthetic organisms were present approximately 3.2 to 3.5 billion years ago... Overwhelming evidence indicates ...



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