Are We Hollow?

We are used to thinking of our human bodies as solid, and that everything that lies beneath our skin belongs to an inside world. It would be more correct to say that we are hollow. The design of the human body is much more interesting, and artistic than you may or dare think.

Running through the middle of the body is a log tunnel, the digestive tract. The space inside this tunnel (the lumen, from the Latin for light or opening inside a tubular structure), bordered by the inner layers of the mucosa, carries substances that don't belong to you. This strange exterior world flows inside you, transporting foods, liquids, substances, chemicals, and bacteria ー everything that you have swallowed and consumed. The digestive tract controls the passage of all these foreign substances, as they pass through your body from the mouth to the anus during digestion. En route, the foods you eat are assimilated and become the building blocks that make up your body, they become you. 

The digestive mucosa is the human body's customs service: a "high-intelligence service of the state." You depend on its work for your health and your life. The digestion and absorption of nutrients that it undertakes are vital functions, as essential as breathing and the beating of the heart. A bad digestion should be given equal importance to poor respiration or a cadiac condition.

Looked at in a certain way, you really are hollow. Your essence and continuity to interrupted by the lumen of this tube that runs through you carrying foreign substances; this tube is in charge of the vital functions of defence, strength, nutrition, energy, growth, construction of new tissues, and detoxification. 

Water balance regulation

The human body uses and loses water every day.

 

How does the body regulate its water balance?

 

The maintenance of a correct water balance
(the net difference between water gain and
water losses) is essential to good health.
It is all the more essential as there is no real
water storage in the body: the water we lose
needs be replaced, and humans cannot survive more
than a few days without water.^1,2

We lose water on a daily basis.

• Through the respiratory tract (by breathing)
• Through the gastro-intestinal tract (faeces)
• Through the skin (perspiration and sweating)
• Through the kidneys (urine excretion)

Lifestyle and environmental conditions have
a significant impact on an individual’s own
level of water loss, but on average, a typical
adult loses about 2.6 litres (L) per day.³

Table: Average daily water loss from different organs in adults³
 

Additional water losses via sweat will be induced by physical exercise and/or a hot environment and could contribute to water losses of up to several litres.
We gain water through fluid and food intake and metabolic water production mainly through food nutrient utilization by the body. Metabolic water production represents 0.3 L per day, on average, and water from foods can vary greatly according to dietary habits. Our remaining requirement needs to be provided by fluids.

References

1. Institute of Medicine (IOM). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: National Academies Press,2004.
2. EFSA. Scientific Opinion on Dietary Reference Values for water. Available at: http://www.efsa.europa.eu/en/scdocs/scdoc/1459.htm. Accessed April 2010.
3. Shirreffs SM. Markers of hydration status. J Sports Med Phys Fitness 2000;40:80-4.
4. Bouby N, Fernandes S. Mild dehydration, vasopressin and the kidney: animal and human studies. Eur J ClinNutr. 2003;57:S39-46.
5. Armstrong LE. Hydration assessment techniques. Nutr Rev. 2005;63:S40-54.

Steps of cellular respiration

Cellular respiration is a metabolic pathway that breaks down glucose and produces ATP. The stages of cellular respiration include glycolysis, pyruvate oxidation, the citric acid or Krebs cycle, and oxidative phosphorylation.

Introduction
Cellular respiration is one of the most elegant, majestic, and fascinating metabolic pathways on earth. At the same time, it’s also one of the most complicated. When I learned about it for the first time, I felt like I had tripped and fallen into a can of organic-chemistry-flavored alphabet soup!

Luckily, cellular respiration is not so scary once you get to know it. Let's start by looking at cellular respiration at a high level, walking through the four major stages and tracing how they connect up to one another.

Steps of cellular respiration

Overview of the steps of cellular respiration.



During cellular respiration, a glucose molecule is gradually broken down into carbon dioxide and water. Along the way, some ATP is produced directly in the reactions that transform glucose. Much more ATP, however, is produced later in a process called oxidative phosphorylation. Oxidative phosphorylation is powered by the movement of electrons through the electron transport chain, a series of proteins embedded in the inner membrane of the mitochondrion.

These electrons come originally from glucose and are shuttled to the electron transport chain by electron-carriers form:

NAD+ + 2e-  + 2H+ → NADH + H+
​
​FAD + 2e- + 2H+ → FADH2
plus $2 \text H^+$ $\tex$
To see how a glucose molecule is converted into carbon dioxide and how its energy is harvested as ATP and NADH/FADH2 in one of your body's cells, let’s walk step by step through the four stages of cellular respiration.

1. Glycolysis. In glycolysis, glucose—a six-carbon sugar—undergoes a series of chemical transformations. In the end, it gets converted into two molecules of pyruvate, a three-carbon organic molecule. In these reactions, ATP is made, andNAD+
 is converted to NADH.

2. Pyruvate oxidation. Each pyruvate from glycolysis goes into the mitochondrial matrix—the innermost compartment of mitochondria. There, it’s converted into a two-carbon molecule bound to Coenzyme A, known as acetyl CoA. Carbon dioxide is released and NADHN generated.

3. Citric acid cycle. The acetyl CoA made in the last step combines with a four-carbon molecule and goes through a cycle of reactions, ultimately regenerating the four-carbon starting molecule. ATP, NADHN, and FADH​2​​  are produced, and carbon dioxide is released.

4. Oxidative phosphorylation. The NADH and FADH​2 made in other steps deposit their electrons in the electron transport chain, turning back into their "empty" forms (NAD​+ and FAD). As electrons move down the chain, energy is released and used to pump protons out of the matrix, forming a gradient. Protons flow back into the matrix through an enzyme called ATP synthase, making ATP. At the end of the electron transport chain, oxygen accepts electrons and takes up protons to form water.

Glycolysis can take place without oxygen in a process called fermentation. The other three stages of cellular respiration—pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation—require oxygen in order to occur. Only oxidative phosphorylation uses oxygen directly, but the other two stages can't run without oxidative phosphorylation.

Questions & Reply (Q&R)

Q: How did you get the coenzymes NADH and FADH in the cellular respiration overview.

R: The NADH resulted from the reduction (gaining of electrons) of NAD+ (nicotinamide adenine dinucleotide). NAD+ is synthesized in other metabolic pathways. The FADH2 was made from adding a hydrogen to FADH. FADH was reduced from FAD (flavin adenine dinucleotide), which was synthesized in the cytosol and mitochondria.
I hope this helps a little. I am still trying to understand this as well.


Q: What is the role of NAD+ in cellular respiration. Why is the role NAD+ plays so important in our ability to use the energy we take in?

R1:  NAD+ is an electron transport molecule inside the cristae of a cell's mitochondria. In glycolysis, the beginning process of all types of cellular respiration, two molecules of ATP are used to attach 2 phosphate groups to a glucose molecule, which is broken down into 2 separate 3-carbon PGAL molecules. PGAL releases electrons and hydrogen ions to the electron carrier molecule NADP+. Each PGAL molecule has a phosphate group added to it, forming a new 3-carbon compound. These phosphate groups and the phosphate groups from the first step are then added to adenosine diphosphate or ADP, forming 4 ATP molecules. This also produces 2 molecules of pyruvic acid.

R2: To continue on with R1 answer, the NAD+ then goes on to oxidative phosphorylation, where it will deposit the electron it gained into the cascade of proteins. The electron will jump from protein to protein, letting it pump H+ (protons) from the mitochondrial matrix out into the intermembrane space between the inner and outer membrane of the mitochondria, and will eventually reach water. The H+ floating around will want to move into the mitochondrial matrix because there is a low concentration of H+ inside and a high concentration in the intramembrane space. The only way it goes inside is through ATP synthase, which will then create ATP using the H+ movement. That ATP goes on to power other cellular processes, and that is the energy that we use every day.


Q: If glycolysis requires ATP to start how did the first glycolysis in history happen?

R: Although ATP synthesis is a process that uses a lot of energy, it can occur randomly, but it isn't very probable. You'll need a lot of ADPs and Phosphate groups in order to get a very small portion of them to bind and become ATPs.
As much as I understand, it isn't very different from the idea of "how life began?". If there is a process that occurs an infinite amount of times, every possible result will occur, even the least probable.


Q: When it states in "4. Oxidative phosphorylation" that the NADH and the FADH2 return to their "empty" forms NAD+ FADH2, the author meant FAD when referring to the "empty" forms, right?

R: I believe so, may be a typo.


Q: In the Citric Acid Cycle (Krebs Cycle), would the four-carbon molecule that combines with Acetyl CoA be Oxaloacetic acid?

R: Yes. Acetyl CoA and Oxaloacetic Acid combine to form a six-carbon molecule called Citric Acid (Citrate).

Q: After oxidative phosphorylation, the ATP created is in the mitochondrial matrix, right? If so, how does it get out of the mitochondrion to go be used as energy?

R: Just like the cell membrane, the mitochondrion membranes have transport proteins imbedded in them that bring in and push out materials.

Q: WHEN does your body go through cellular respiration? I know what happens and why it does, but when does your body do it? When you are exercising? All the time?

R1: Cellular respiration is always happening, but goes at a faster rate when exercising.

R2: Cellular Respiration is very important to the body and as you stated it is occurring all the time. Similar to what R1 said it goes at a faster rate when you are exercising but there are also many other processes going on in your body such as fermentation when undergoing strenuous activity. Hope this helps!

Q: I have a question... Which part of the body will most likely use the cellular respiration? Is it lungs?

R1: No, its your brain.

R2: Cellular Respiration happens in your cells and you entire body is made up of cells, it goes on all throughout your body including your lungs and brain.


Q: What are the inputs of Glucose Oxidation? Because in the book its very specific on the outputs but the inputs are kind of hard to identfy?

R:  Depends on your syllabus! Respiration is very complex so different textbooks shorted it in different ways. Glucose is the main starting material, and various enzymes alter its shape to turn it into pyruvate. Here is a short summary of what is happening: http://bio-notesa2.tumblr.com/post/74615599611/stage-one-glucose-is-phosphorylated-by-adding-2


Q: How many ATP'S are produced in each step of cellular respiration?

R1: Glycolysis: Net production of 2 ATPs
Krebs Cycle: Production of 2 ATPs
Electron Transport Chain: Production of 34 ATPs (theoretically at highest efficiency)
This adds up to a total maximum of 38 ATP molecules produced as a result of cellular respiration.

R2: I'm almost sure these are the correct amounts:
Glycolysis produces 2 ATP,
Preparatory Reaction produces 2 NADH and 2 Acetyl CoA (and releases 2 carbons- CO2)
Citric Acid Cycle produces 2 ATP 6 NADH and 2 FADH2 (and releases 4 carbons- CO2)
Electron Transport Chain produces 32-34 ATP.

R3: During cellular respiration the mitochondria produces 36 Adenosine triphosphate.
R3.1: Actually due to energy loss it's most likely to be around 28-30 ATP It has a 36% efficiency rate which is exceptionally high for chemical reactions.


Q: Why is FADH2 used as an electron carrier in complex II of oxidative phosphorylation? Why not NADH since it yields more ATP than FADH2?

R: Because FADH2 has a higher electronegativty and the complex's of oxidative phosphorylation are in order of increasing electronegativty therefor skips the first one.


Q: In my textbook it says glycolysis occurs in the cytoplasm of the cell. What is the difference between the cytoplasm and the cytosol?

R: The cytosol is the gel-like fluid that the nucleus and organelles are suspended in & the cytoplasm includes everything in the cell (aside from the nucleus) plus the cytosol itself. So basically the cytosol is just a portion of the cytoplasm.


Q: Is the kreb cycle another name for the citric acid cycle?
R: Yes, it is either Krebs cycle (named after the leading scientist), citrate acid cycle or even tricarboxylic acid (TCA)cycle.

Q: Water is produced during which step in cellular respiration?

R:  Oxidative Phosphorylation. Self explains where the water comes from at 2:09 in the following video:

https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/oxidative-phosphorylation/v/oxidative-phosphorylation-and-the-electon-transport-chain

Q: What are the capacities of the lungs?

R1:  Maximum capacities of lungs in to in/out is 5 litres

R2: The maximum volume (total lung capacity) is approximately 6 liters but you typically only breathe in/out approximately 0.5 liters per breath.

Q: What is the H2O at the end of the oxidation phosphorylation used for?

R: It is released into the organism and taken up by cells, as it is an output of cellular respiration. Excess water present in the organism, which is produced by oxidation phosphorylation, can be released via urine.

https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/overview-of-cellular-respiration-steps/a/steps-of-cellular-respiration

Overview of cellular respiration

[Voiceover] So what I wanna do in this video is give ourselves an overview of cellular respiration. It can be a pretty involved process, and even the way I'm gonna do it, as messy as it looks, is going to be cleaner than actually what goes on inside of your cells, and other organs themselves, because I'm going to show clearly from going from glucose, and then see how we can produce ATP through glycolysis, and the Krebs cycle, and oxidative phosphorylation, but in reality, all sorts of molecules can jump in at different parts of the chain, and then jump out at different parts of the chain, to go along other pathways. But I'll show, kind of the traditional narrative. So we're gonna start off, for this narrative, we're gonna start off with glucose. We have a six-carbon-chain right over here. And we have the process of glycosis, which is occurring in the cytosol, the cytosol of our cells. So if this is a cell right over here, you can imagine, well the glycolysis, the glycolysis could be occurring right over there. And that process of glycolysis is essentially splitting up this six-carbon glucose molecule into two three-carbon molecules, and these three-carbon molecules, we go into detail in another video, we call these pyruvate. Pyruvate. And in the process of doing so, and this is, I guess you could say, the point of glycolysis, we're able to, on a net basis, produce two ATP's. We actually produce four, but we have to use two, so on a net basis, we produce two ATP's. I'm gonna keep a little table here, to keep track. So we produce two ATP's, and we are also, we're also, in the process of that, we reduce two NAD molecules to NADH. Remember, reduction is gaining of electrons. And you see over here, this is positively charged, this is neutrally charged, it essentially gains a hydride. So this is reduction. Reduction. And if we go all the way through the pathway, all the way to oxidative phosphorylation, the electronic transport chain, these NADH's, the reduced form of NAD, they can be, then, oxidized, and in doing so, more energy is provided to produce even more ATP's, but we'll get to that. So you're also gonna get two NADH's. Two NADH's get produced. Now at that point, you could kind of think of it as a little bit of a decision point. If there's no oxygen around, or if you're the type of organism that doesn't want to continue, for some reason, with cellular respiration, or doesn't know how, this pyruvate can be used for fermentation. We have videos on fermentation, lactic acid fermentation, alcohol fermentation, and fermentation is all about using the pyruvates to oxidize your NADH back into NAD, so it could be re-used again, for glycolysis. So even though the NADH has energy that could eventually be converted into ATP, and even though pyruvates have energy that could eventually be converted into ATP, when you do fermentation, you kinda give up on that, and you just view them as waste products, and you use the pyruvate to convert the NADH back into NAD, And then, glycolysis can occur again. But let's assume we're not gonna go down the fermentation pathway, and we're gonna continue with traditional aerobic cellular respiration, using oxygen. Well, the next thing that's going to happen, is that the carboxyl group, and and everything I'm going to show now, it's going to happen for each of these pyruvates. So, you can imagine these things all happening twice. So I'm gonna multiply a bunch of things, times two. But what happens in the next step, is this carboxyl group, this carboxyl group is stripped off of the pyruvate, and it, essentially, is going to be released as carbon dioxide. So this is our carbon dioxide being released here, and then the rest of our pyruvate, which is, essentially, an acetyl group, that latches onto coenzyme A. And you'll hear a lot about coenzyme A. Sometimes I'll write just CoA, like this. Sometimes I'll do CoA, and then the sulfur, bonded to the hyrdrogen. And the reason why they'll draw the sulfur part, is because the sulfur is what bonds with the acetyl group, right over here. So, you have the carbon dioxide being released, and then the acetyl group, bonding with that sulfur, and by doing that, you form acetyl-CoA. And acetyl-CoA, just so you know, you only see three letters here, but this is actually a fairly involved molecule. This is actually a picture of acetyl-CoA, I know it's really small, but hopefully you'll appreciate that it's a more involved molecule. That, the acetyl group that we're talking about is just this part, right over here, and it's a coenzyme. It's really acting to transfer that acetyl group, and we'll see that in a second. But it's also fun to look at these molecules, because once again, we see these patterns over and over again in biology or biochemistry. Acetyl-CoA, you have an adenine right over here. It's hard to see, but you have a ribose, and you also have two phosphate groups. So this end of the acetyl-CoA is essentially, is essentially an ADP. But it's used as a coenzyme. Everything that I'm talking about, this is all going to be facilitated by enzymes, and the enzymes will have cofactors, coenzymes, if we're talking about organic cofactors, that are gonna help facilitate things along. And as we see, the acetyl group joins on to the coenzyme A, forming acetyl-CoA, but that's just a temporary attachment. The acetyl-CoA is, essentially, gonna transfer the acetyl group over to, and now we're going to enter into the citric acid cycle. It's gonna transfer these two carbons over to oxaloacetic acid, to form citric acid. So it's gonna transfer these two carbons to this one, two, three, four carbon molecule, to form a one, two, three, four, five, six carbon molecule. But before we go into the depths of the citric acid cycle, I wanna make sure that I don't lose track of my accounting, because, even that step right over here, where we decarboxylated the pyruvate, we went from pyruvate to acetyl-CoA, that also reduced some NAD to NADH. Now, this is gonna happen once for each pyruvate, but we're gonna- all the accounting we're gonna say, is for one glucose molecule. So for one glucose molecule, it's gonna happen for each of the pyruvates. So this is going to be times- This is going to be times two. So we're gonna produce two, two NADH's in this step, going from pyruvate to acetyl-CoA. Now, the bulk of, I guess you could say, the catabolism, of the carbons, or the things that are eventually going to produce our ATP's, are going to happen in what we call the citric acid, or the Kreb cycle. It's called the citric acid cycle because, when we transferred the acetyl group from the coenzyme A to the oxaloacetic acid, we formed citric acid. And citric acid, this is the thing that you have in lemons, or orange juice. It is this molecule right over here. And the citric acid cycle, it's also called the Kreb cycle, when you first learn it, seems very, very complex, and some could argue that it is quite complex. But I'm just gonna give you an overview of what's going on. The citric acid, once again, six-carboned, it keeps getting broken down, through multiple steps, and I'm really not showing all of the detail here, all the way back to oxaloacetic acid, where, then, it can accept the two carbons again. And just to be clear, once the two carbons are released by the coenzyme A, then that coenzyme A can be used again, to decarboxylate some pyruvates. So there's a bunch of cycles going on. But the important take-away, is as we go through the citric acid cycle, as we go from one intermediary to the next, we keep reducing NAD to NADH, in fact, we do this three times for each cycle of the citric acid cycle, but remember, we're gonna do this for each acetyl-CoA. For each pyruvate. So all of this stuff is going to happen twice. So we're going to go through it twice for each original glucose molecule. So, here we have one, two, three NADH's being produced, but since we're going to go through it twice, and we're gonna be accounting for the original glucose molecule, we could say that we have six six NADH's, or you could say, six NAD's get reduced to NADH. Now, you also, in the process, as you're breaking down, going from the six-carbon molecule to four-carbon molecule, you're releasing carbon, as carbon dioxide, and you also have, traditionally GDP being converted into GTP, or sometimes ADP converted into ATP, but functionally, it's equivalent to ATP, either way. So, we could also say that we're gonna directly- Remember, we're gonna do all of this stuff twice. So, we could say that two, I'll just say two ATP's, to make it simple. We could say GTP, but I'll say two ATP's. Because once again, this happens once in each cycle, but we're gonna do two cycles, for each glucose. And then, we have this other coenzyme right over here, FAD, that gets reduced to FADH2, but that stays covalently attached to the enzymes that are facilitating it, so eventually, that's being used to reduce . coenzyme Q to QH2. So I'm just gonna write the QH2 here, but once again, you're gonna get two of these. So two QH2's. Now let's think about what the net product, over here, is going to be. And to think about it, we should just, we'll just- I'll do a little bit of a shorthand. We'll go into more detail in future videos. These coenzymes, the NADH, the QH2, these are going to be oxidized, during oxidative phosphorylation, and the electron transport chain, to create a proton gradient across the inner membrane of mitochondria. We're gonna go into much more detail in the future, but that proton gradient is going to be used to produce more ATP. And one way to think about it, is each NADH is going to produce, and I've seen accounts, it depends on the efficiency, and where the NADH is actually going to be produced, but it's going to produce anywhere between two and three ATP's. Each of the reduced coenzyme Q's, so QH2, that's going to each produce about one and a half ATP's. And people are still getting a good handle on exactly how this is happening. It depends on the efficiency of the cell, and what the cell is actually trying to do. So, using these ranges, actually I'll say one and a half to two ATP's. And these are approximate numbers. So let's think about what our total accounting is. So if we just count up the ATP or the GTP's, we're gonna get two there, two there. So we're gonna have four direct, or very close to direct, ATP's net, being created. And then how many NADH's? We have two, four, and then we add six. We have ten NADH's. Ten NADH's. And then, we have two of the coenzyme Q's. Two QH2's. So that's gonna be four ATP's, this is going to be between- this is going to be between 20 and 30 NADH's. Sorry, 20 and 30 ATP's. 20 to 30 ATP's. And then, this is going to be three to four. Three to four ATP's. So if you add them all together, if you add the low ends of the range, you get, let's see, 20 plus three, plus four. That's 27 ATP's. 27 ATP's. And the high end of the range, let's see. You have four plus 30 plus four. You have 38. 38 ATP's. And 38 ATP's is currently considered to become the theoretical maximum, but when we actually observe things in cells, it looks like it comes right at around 29 to 30 ATP's. And once again, it depends what the cell's trying to do, the type of cells, and the type of efficiency. But all of this is happening through cellular respiration. And just to get a better sense of where all of this is occurring. Where all of this is occuring, we said glycolosis is occurring in the cytosol. The citric acid cycle, this is occurring in the matrix of the mytochondria. So this space right over here, that is the citric acid cycle, in that little magenta space that I've drawn. So that's the matrix. In the video on mitochondria, we go into much more detail on that. And then, the actual conversion of the coenzymes, of the electron transport chain, that's occurring across the membrane of the crista. And the crista are these folds, these kind of, inner membrane folds, of our mitochondria. So, it's occurring across the membranes of those, actually the plural is cristi. Crista is the singular of the cristi. And we'll go into more detail into that, in other videos.

Questions & Replies.


Q:What is the QH2 that Sal was talking about? In my classes, we only learned about FADH2, not about QH2. Is it important that we know this?

R:Q is the coenzyme Q, an antioxidant called ubiquinone with vitamin-like properties, and QH2 is the reduced form of the coenzyme. I have to acknowledge that Sal is right in using QH2 as the electron carrier. Although textbooks teach that FADH2 does this, it is not correct. FADH2 remains bound to the Succinate dehydrogenase (complex II) and as such it does not carry the electrons to the next complex III (cytochrome bc1); QH2 does. Therefore, QH2 is the "true" electron carrier. Regarding what you have to learn? Keep in mind that you need to pass the exam, thus, it would be better to use FADH2 as your answer, but remember that it is wrong until the AP college board changes its thinking. There is an excellent discussion on using QH2 instead of FADH2: http://sandwalk.blogspot.com/2007/06/cellular-respiration-ninja-enzymes.html


Q: What is GTP and GDP??

R: Excellent question!
GTP stands for Guanine Triphosphate, and GDP for guanine diphosphate. These function in a very similar way to ATP and ADP, and most of the GTP produced in the krebs cycle is used to turn ADP into ATP. GTP and GDP also play a role in other cellular functions, though, such as g-protein coupled receptors.
ATP (and GTP) are like a fully charged battery. Lots of energy for a cell to use. ADP (and GDP) are like partially charged batteries. They still contain some energy in the remaining phosphate bond, but not as much energy as in ATP, which has a second high energy bond.


Q: How can you have 1.5 atp's?

R1: Maybe because the number of H ions that specific electron carrier(QH2) can pump via the electron transport chain into the reserve are more than required to make one complete ATP and less than the number of protons required to make 2 ATP.

R2: I believe its an approximation because they probably calculated that an average between 1-2 ATP gets produced.
R2.1: That still isn't clear. You can't have half a molecule. They need to be whole numbers.


Q: So a muscle cell in an environment with a large amount of oxygen available would produce a number of ATP closer to the maximum 38 ATP versus a skin cell in an environment with less oxygen available?

R: Yes. More oxygen (and the mere presence of it) defiantly increase ATP production, although there is a threshold above which more oxygen will not increase ATP production.


Q: Do every cell in our body produce the exact same amount of ATP by completely oxidizing glucose?

R: I'm not sure, but I think the answer is yes. The mitochondria in your cells are more or less the same, and all of your cells undergo the same process of cellular respiration (that is, the ones that undergo it. Some cells, such as red blood cells or cells that are part of the urethra do not have mitochondria and don't perform cellular respiration.


Q:  NAD+ --> NADH. Where does the proton come from? Is it just floating around in the cytosol?

R1: Hmm... well, this might be a bit late, but to explain in the best way I can, there's a lot of H+ (hydrogen ions) that are drifting around. They're the reason why the electron transport chain is needed in the first place, in order to bring in more hydrogen ions against the concentration gradient. The hydrogen ions are very high-energy, so they react with NAD+ to make it become NADH.
I'm very sorry if that didn't help, I'm rather new to this topic myself. I just hope it helped a little. 

R2: No, that makes sense. Thanks!

Q: What is the difference between NADH and NADPH?

R: The difference between NADH and NADPH is that NADPH has an extra phosphate group. While NADH is used to power cellular reactions such as glycolysis, during which molecules are broken down, NADPH is used to power photosynthesis.

Q: If cellular respiration produces 10 x NADH molecules then where do the NAD+ come from to reduce into NADH?

R1: Every time NADH drops off the electrons in the ETC, it becomes NAD+ again and can be recycled.

R2: There is always a big pool of both NAD+ and NADH around as the reaction can go in both directions.

Also NAD+ can be made by the cell directly, either from scratch starting with the amino acid tryptophan or breaking up other molecules like Niacin/vitamin B3 (which has to be taken up via food first).

Q: What is an acetyl?

R: In organic chemistry, acetyl is a functional group, the acyl with chemical formula COCH3.


Q: If oxygen is present what is the sequence of processes that occur in cell respiration?

R: If oxygen is present, the sequence of processes that occur in cellular respiration are:
1. Glycolysis -> 2. Pyruvate Oxidation -> 3. Citric acid cycle (a.k.a Kreb's cycle) -> 4. Oxidative phosphorylation (a.k.a Electron transport chain). These processes combined produce 38~ net ATPs.
However, if oxygen is not present, only Glycolysis can occur.


Q: Where does oxygen come into play during the Kreb's cycle? All I know is that it's required (because otherwise, fermentation) but I don't see it anywhere here.

R: Oxygen is needed for the electron transport chain.


Q: What does "pi" mean(ATP turns to ADP+pi+energy)?

R: It's an Inorganic phosphate.


Q: How does FAD reduce into FADH2? It should be just FADH right?

R: Well, yes Q is the coenzyme Q, an antioxidant called ubiquinone with vitamin-like properties, and QH2 is the reduced form of the coenzyme. I have to acknowledge that Sal is right in using QH2 as the electron carrier. Although textbooks teach that FADH2 does this, it is not correct. FADH2 remains bound to the Succinate dehydrogenase (complex II) and as such it does not carry the electrons to the next complex III (cytochrome bc1); QH2 does. Therefore, QH2 is the "true" electron carrier.


Q: How does GDP/ADP become GTP/ATP?
R: With an inorganic free phosphate group.

Q: Is cytoplasm and cytosol same?
R: No. cytoplasm is jelly like matter in cell where all organelles reside but cytosol is the soluble part of cytoplasm.

Q: Where did the O2 go?
R1: The O2 is not released in the Krebs cycle nor it is a waste product of cellular respiration. CO2 is.
R2: The O2 is usually just a waste product of Cellular Respiration. It will most probably be used else where in the body.


Q: Why does the cell not want to make as many ATP's as possible? I have heard that sometimes the cell does not fully maximize Cellular Respiration. Even though the cell has the capability to make 38 ATP, it chooses not to and instead makes less. Why is this?

R1: Not all the energy released in the exergonic reactions of cellular respiration goes into making ATP - there are other kinds of work the cell can perform using it.

R2: Not sure about making less per cycle, but they don't over make it so there is no waste for the amount of work that was put in to make it!


Q: So in glycolysis, the number of hydrogen atoms are less than what was to begin with. I can understand that two hydrogen protons are used to reduce the NADH, but we start out with 12 hydrogen and only end up with 6. What happens to the other six?

R: Glycolysis is actually ridiculously complex: https://www.google.co.uk/search?q=glycolysis&espv=2&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjV9rjxxIvMAhXExRQKHe7ZDlAQ_AUIBygB&biw=1439&bih=778#imgrc=_ 

If you follow that through you should find out where the missing hydrogens are going, but I'm not sure you want to.


Q: What is the purpose (goal) of cellular respiration?

R: To convert glucose, a sugar, into ATP, energy that cells can use (they can't use glucose directly!).


Q: Does NAD gain two hydrogen or one?

R1: Once NAD is reduced to NADH it receives one hydrogen proton.

R2: NAD is reduced and become positive electrode. Then according to biologic point of view, it tends to relieve or gain one hydrogen atom being NADH. Hope that helps.

Cellular Respiration

Contents

About

Introduction to cellular respiration

Steps of cellular respiration

Glycolysis

Pyruvate oxidation and the citric acid cycle

Oxidative phosphorylation

Variations on cellular respiration

How do your cells extract energy from the food that you eat? As it turns out, cells have a network of elegant metabolic pathways dedicated to just this task. Learn more about cellular respiration, fermentation, and other processes that extract energy from fuel molecules like glucose.

Introduction to cellular respiration

How does your body get usable energy from the snack you just ate? Learn the basics of how cells extract energy from fuel molecules, including what redox reactions are and why they are important in the breakdown of fuels.

ATP: Adenosine triphosphate

Introduction to cellular respiration

Video transcript:

 ATP or adenosine triposphate is often referred to as the currency of energy, or the energy store, adenosine, the energy store in biological systems. What I want to do in this video is get a better appreciation of why that is. Adenosine triposphate. At first this seems like a fairly complicated term, adenosine triphosphate, and even when we look at its molecular structure it seems quite involved, but if we break it down into its constituent parts it becomes a little bit more understandable and we'll begin to appreciate why, how it is a store of energy in biological systems. The first part is to break down this molecule between the part that is adenosine and the part that is the triphosphates, or the three phosphoryl groups. The adenosine is this part of the molecule, let me do it in that same color. This part right over here is adenosine, and it's an adenine connected to a ribose right over there, that's the adenosine part. And then you have three phosphoryl groups, and when they break off they can turn into a phosphate. The triphosphate part you have, triphosphate, you have one phosphoryl group, two phosphoryl groups, two phosphoryl groups and three phosphoryl groups. One way that you can conceptualize this molecule which will make it a little bit easier to understand how it's a store of energy in biological systems is to represent this whole adenosine group, let's just represent that as an A. Actually let's make that an Ad. Then let's just show it bonded to the three phosphoryl groups. I'll make those with a P and a circle around it. You can do it like that, or sometimes you'll see it actually depicted, instead of just drawing these straight horizontal lines you'll see it depicted with essentially higher energy bonds. You'll see something like that to show that these bonds have a lot of energy. But I'll just do it this way for the sake of this video. These are high energy bonds. What does that mean, what does that mean that these are high energy bonds? It means that the electrons in this bond are in a high energy state, and if somehow this bond could be broken these electrons are going to go into a more comfortable state, into a lower energy state. As they go from a higher energy state into a lower, more comfortable energy state they are going to release energy. One way to think about it is if I'm in a plane and I'm about to jump out I'm at a high energy state, I have a high potential energy. I just have to do a little thing and I'm going to fall through, I'm going to fall down, and as I fall down I can release energy. There will be friction with the air, or eventually when I hit the ground that will release energy. I can compress a spring or I can move a turbine, or who knows what I can do. But then when I'm sitting on my couch I'm in a low energy, I'm comfortable. It's not obvious how I could go to a lower energy state. I guess I could fall asleep or something like that. These metaphors break down at some point. That's one way to think about what's going on here. The electrons in this bond, if you can give them just the right circumstances they can come out of that bond and go into a lower energy state and release energy. One way to think about it, you start with ATP, adenosine triphosphate. And one possibility, you put it in the presence of water and then hydrolysis will take place, and what you're going to end up with is one of these things are going to be essentially, one of these phosphoryl groups are going to be popped off and turn into a phosphate molecule. You're going to have adenosine, since you don't have three phosphoryl groups anymore, you're only going to have two phosphoryl groups, you're going to have adenosine diphosphate, often known as ADP. Let me write this down. This is ATP, this is ATP right over here. And this right over here is ADP, di for two, two phosphoryl groups, adenosine diphosphate. Then this one got plucked off, this one gets plucked off or it pops off and it's now bonded to the oxygen and one of the hydrogens from the water molecule. Then you can have another hydrogen proton. The really important part of this I have not drawn yet, the really important part of it, as the electrons in this bond right over here go into a lower energy state they are going to release energy. So plus, plus energy. Here, this side of the reaction, energy released, energy released. And this side of the interaction you see energy, energy stored. As you study biochemistry you will see time and time again energy being used in order to go from ADP and a phosphate to ADP, so that stores the energy. You'll see that in things like photosynthesis where you use light energy to essentially, eventually get to a point where this P is put back on, using energy putting this P back on to the ADP to get ATP. Then you'll see when biological systems need to use energy that they'll use the ATP and essentially hydrolysis will take place and they'll release that energy. Sometimes that energy could be used just to generate heat, and sometimes it can be used to actually forward some other reaction or change the confirmation of a protein somehow, whatever might be the case.

Up Next; ATP hydrolysis mechanism

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Medical Studies that Prove Cannabis Can Cure Mouth and Throat Cancer (10) :

Cannabinoids inhibit cellular respiration of human oral cancer cells.

Abstract

BACKGROUND AND PURPOSE:

The primary cannabinoids, Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and Delta(8)-tetrahydrocannabinol (Delta(8)-THC) are known to disturb the mitochondrial function and possess antitumor activities. These observations prompted us to investigate their effects on the mitochondrial O(2) consumption in human oral cancer cells (Tu183). This epithelial cell line overexpresses bcl-2 and is highly resistant to anticancer drugs.

EXPERIMENTAL APPROACH:

A phosphorescence analyzer that measures the time-dependence of O(2) concentration in cellular or mitochondrial suspensions was used for this purpose.

KEY RESULTS:

A rapid decline in the rate of respiration was observed when Delta(9)-THC or Delta(8)-THC was added to the cells. The inhibition was concentration-dependent, and Delta(9)-THC was the more potent of the two compounds. Anandamide (an endocannabinoid) was ineffective; suggesting the effects of Delta(9)-THC and Delta(8)-THC were not mediated by the cannabinoidreceptors. Inhibition of O(2) consumption by cyanide confirmed the oxidations occurred in the mitochondrial respiratory chain. Delta(9)-THC inhibited the respiration of isolated mitochondria from beef heart.

CONCLUSIONS AND IMPLICATIONS:

These results show the cannabinoids are potent inhibitors of Tu183 cellular respiration and are toxic to this highly malignant tumor.

 

Whyte DA¹, Al-Hammadi S, Balhaj G, Brown OM, Penefsky HS, Souid AK.

Author information

• ¹Department of Pediatricsy, State University of New York, Upstate Medical University, Syracuse, NY, USA.