What is the difference in these terms "metabolism: and “respiration”. And, while we’re at it, does “respiration” mean “breathing” to a biologist?
As I understand it, [b[metaboilsm** is the rate we burn sugar to make energy. And, the metabolic rate is the rate at which we burn sugar. Now, to the biologist, respiration is the general name for the process of burning sugar starting with glycolysis which leads into two major categories: aerobic or anaerobic respiration.
So, what’s the difference? Is metabolism a very general term used to talk about the whole act of creating energy without getting into the specifics???
Lastly, does respiration have a different meaning to a biologist than a doctor? Wouldn’t a doctor say that respiration means breathing?
Please help me understand the subtle differences here! Thanx!
Respiration is the exchange of gases. In most animals, this would be the processes involved in keeping the body supplied with oxygen, while ridding it of carbon dioxide. For plants and certain single-celled organisms, the reverse would occur.
Metabolism is, in general, refers to the sum total of cellular chemical reactions. That is, all the controlled and enzyme-mediated chemical reactions by which the cells acquire and use energy. These would be the synthesis, storage, elimination, and break down of any substance that enables the cell to divide and grow.
I’ve never heard a biologist refer to respiration as “the general name for the process of burning sugar starting with glycolysis which leads into two major categories: aerobic or anaerobic respiration.” Ever.
I would think that a doctor is more likely to refer to respiration as “breathing” because they are dealing with humans, i.e., organisms with lungs. That is not an incorrect usage but it is not the strict biological definition, which account for non-animal organisms as well as those without lungs.
Yes, Xcheopis, but the whole reason I ask IS because it IS called aerobic respiration AND anaerobic respiration! This is per any general biology text. But, I agree with you…if it were up to me, it’s be “aerobic metabolism” and “anaerobic metabolism”.
Therefore, in light of this, isn’t respiration more than just a reference to gas exchange??? Especially when respiration doesn’t always require an actual “exchange” of gasses, such as when it’s anaerobic! And so, isn’t the word “metabolism” simply now the overall term for the whole shee-bang of cycles and processes? Simply put, should I think of “metabolism” as a very GENERAL term acting as the tip of the iceberg in the story about how living things breakdown glucose to yield energy?
Metabolism is the sum of all of the biochemical processes that occur in an organism. It can be divided into two forms: (1) catabolism, which is the breakdown of biomolecules such as sugar and amino acids to yield energy (e.g., in the form of ATP), and (2) anabolism, which is the use of energy to synthesize more complex biomolecules from simpler ones. To put it simply:
Respiration is a form of catabolism, that involves some sort of gaseous exchange (i.e., CO[sub]2[/sub] and O[sub]2[/sub]; certain microbes may exchange more exotic gases). Aerobic respiration specifically requires the presence of oxygen. Anaerobic respiration, also known as fermentation, does not require oxygen.
I believe you are thinking of cellular respiration, which is the oxidation of food to carbon dioxide and water. That is, oxygen is exchanged for carbon dioxide. This is a set of reactions that occur as part of the metabolic process and are not the same as the more general respiration, to which you refered in the OP.
Not all organisms must use metabolic processes that require cellular respiration, however. If oxygen is lacking in the cellular environment, an organism can use a fermentation process to generate energy. This is the anerobic process, and is not referred to as respiration.
Some organisms never use oxygen and others can go without if necessary. Yeast can, for example, use alcohol fermentation to generate energy from fuel. Human muscle cells can use lactic acid fermentation in the absence of oxygen. The wonderous diversity of life and so forth.
To reiterate: Cellular respiration is the part of metabolism that uses oxygen and organic fuel to generate energy in the form of ATP, water, and carbon dioxide. Fermentation is a metabolic process that occurs in the absence of oxygen, also produces ATP from glucose but not by the same path, and generally has a characteristic end product, such as ethyl alcohol or lactic acid. Neither of these is to be confused with respiration, the means by which organisms exchange gases with their environment.
Well, the OP specifically asked about anaerobic respiration, which in this context means fermentation. Note that both aerobic and anaerobic respiration produce CO[sub]2[/sub], thus qualifying the latter for the “exchange of gases”. Photosynthesis involves uptake of CO[sub]2[/sub] and release of O[sub]2[/sub], but is not counted as respiration because it involves biosynthesis rather than breakdown.
Metabolism is both catabolism and anabolism, as someone else said.
To a doctor, respiration does mean breathing, the rate at which air (oxygen) is inhaled and exhaled (carbon dioxide). To a biologist, respiration can mean something more, the use of an external (or in cases internal) final electron acceptor in order to further obtain energy from glucose and for the cell (or organism).
The steps for complete glucose breakdown:
Glycolysis- Does not require an external electron acceptor, final product is pyruvate. Net yield is 2 ATPs (Adenosine triphosphates, supply energy to anabolic reactions). Also produces NADH
Pyruvate can then go to anaerobic or aerobic respiration (the use of another electron acceptor). Fermentation is a type of anaerobic respiration, and the final product varies by organism/tissue, from lactic acid to alcohol. NADH is produced by fermentation.
TCA cycle (or Krebs cycle) is the path pyruvate goes to on the way to aerobic respiration, and it releases carbon dioxide. One ATP (or GTP), is produced, plus NADH and FADH[sub]2[/sub] is produced.
All the above processes produce differing amounts of the molecules NADH or FADH[sub]2[/sub]. These molecules go into the electron transport chain, which in aerobic respiration uses oxygen and in anaerobic respiration uses other molecules, and make ATP for the cell (which is the energy storage/currency unit used in anabolic reactions).
This is not correct. While fermentation is an anaerobic process, it
DOES NOT yield ATP. Therefore, an organism cannot use fermentation to generate energy. Fermentation is just a way of disposing of the pyruvic acid created in the last step in glycolysis. Starting with pyruvic acid, the fermentation pathways can either lead to alcoholic fermentation or lactic acid fermentation…neither of which yield ATP.
Overall, Xcheopis, I greatly appreciate your replies. You are correct that the subtle difference is the term really is “cellular” respiration. My biology references fail to note this subtle difference. Likewise, one of my bio refs shows metabolism in parenthesis - next to respiration - implying the two terms are interchangeable.
Along these lines: How does grain alcohol turn into vinegar (acetic acid)? Or, should I start this question a new thread???
Yes, it does. It yields, on average, 2 ATP during glycolysis, just as cellular respiration does. The difference is that, in fermentation, the pyruvate does not enter the citric acid cycle and, by extension, the electron transport system. (Cellular respiration yields about 19 times the amount of ATP as fermentation.)This site may help you with some of the concepts, as might this one.
[QUOTE]
*Originally posted by xcheopis *
**Yes, it does. It yields, on average, 2 ATP during glycolysis, just as cellular respiration does…
Xcheopis, hmm…I’ll check your links, but I think we have a difference in semantics here. I agree that 2 ATPs are yielded by glycolysis, but the fermentation of pyruvic acid is the next step after glycolysis. However, from your description, it sounds like you were taught that glycolysis INCLUDES fermentation, is that correct?
I think of both cellular respiration and fermentation as pathways by which an organism can breakdown fuel and generate energy. Glycolysis is the first part of both pathways for all organisms, and pretty much all cells, after which the pyruvate may follow one of a number of paths.
(Pyruvate does not always immediately follow either respiratory type of pathway, however. For example, it may be stored by the body or used to regenerate glucose. And so on and so forth.)
I didn’t know that! I thought it was a waste product of which the body wants to break down further in order to excrete. (Doesn’t lactic acid eventually get broken down to urea or uric acic?)
It’s strange to me that living organisms can so easily reverse reactions. Why doesn’t this violate some law about entropy? Perhaps we talk about reversal too loosely. While it’s true many reactions are “undone”, new ATP is brought in (or ADP +P), so these reactions are not “reversing”…in the physics sense, anyhow, IMHO…to the best of my knowledge.
Lastly, Xcheopis, how does wine (and such) turn into vinegar? While acetic acid is a step (or two) before aerobic respiration…is it like anaerobic organisms attempt to go down the aerobic pathway? :dubious:
Jinx: Fermentation does give products to produce energy. Read what I wrote, fermentation produced NADH, a molecule that goes into another cycle, the electron transport chain, to produce more ATP!
Eh… most of the reactions that occur in the body can occur both ways. Factors like environmental conditions, enzyme concentrations, enzyme activation, substrate concentrations, etc. determine which reaction pathway occurs.
And yes, many reactions themselves are unfavorable (go against entropy). That’s one reason enzymes and cofactors exist, to help make those reactions go the desired way.
Organisms can be facultative anaerobic, meaning they can grow both with or without the presence of oxygen. So an organism can be anaerobic and use fermentation, or (in presence of oxygen) take the pyruvate and take it to the TCA cycle.
Wow, Karl, it seems there’s some conflicting info out there amongst biology books. Maybe you can clarify something else for me - about TCA: My advanced bio book agrees that one ATP is yielded from the Krebs cycle (or Citric Acid Cycle). And, it does admit that every one glucose molecule results in two “turns” of the Krebs cycle…yielding 2 ATPs, total…in keeping with what you say above.
But, a basic bio book says the Citric Acid Cycle yields 36 ATPs!
This sounds much more impressive than a miniscule 2 ATPs! And, while the basic bio book shows the Citric Acid Cycle, in some detail, it fails to show how they claim we get these 36 ATPs! OK, I’d even wager it’s maybe really 2 turns of the cycle x 18 ATPs = 36 ATPs, but still…where is this coming from? Maybe, you know?
Also, when I say fermentation does not generate energy, I am talking specifically about the synthesis of ATP - directly. I just don’t see ATP being yielded directly from fermentation. (NOTE: I am not including the net gain of 2 ATPs from the process of gylcolysis.)
BTW, what does “TCA” stand for? Curiouser and curiouser…
NADH enters the electron transport system only under aerobic conditions. Under anaerobic conditions, pyruvate is first converted to acetaldehyde by removal of CO[sub]2[/sub]. The acetaldehyde is then reduced to ethanol by NADH. A similar set of reactions, using up NADH, convert pyruvate to lactate. This whole set of reactions from glucose to ethanol or lactate is usually called fermentation.
The missng ATP comes from the aforementioned NADH, which feeds into the electron transport system (ETS). Oversimplifying, the ETS converts the energy stored in NADH into 3 ATP. One glucose molecule produces two pyruvates, 2 ATP, and 2 NADH (= 6 ATP). Conversion of a pyruvate to acetyl-CoA also yields 1 NADH; since there are two pyruvates from 1 glucose, this is a total of 6 ATP from this step. Krebs cycle produces 3 NADH (= 9 ATP), 1 FADH (= 2 ATP), and 1 GTP (= 1 ATP). This is a total of 12 ATP from one turn of the cycle or 24 ATP total from Krebs cycle. Summing everything up:
Glycolysis
2 ATP = 2 ATP
2 NADH = 6 ATP
Pyruvate -> acetyl-CoA
(1 NADH = 3 ATP) x 2 = 6 ATP
Krebs cycle
(3 NADH = 9 ATP) x 2 = 18 ATP
(1 FADH = 2 ATP) x 2 = 4 ATP
(1 GTP = 1 ATP) x 2 = 2 ATP
-------
38 ATP
For aerobic respiration, ETS requires the presence of oxygen to accept the protons coming from NADH and FADH. This splits the O[sub]2[/sub] molecule and produces water.
It appears I was mistaken when I said that fermentation = anaerobic respiration. According to this site, anaerobic respiration occurs when the terminal electron acceptor in ETS is some compound aside from oxygen such as nitrate, sulfate, or carbonate. This is very common in the microbial realm.
I don’t know what levels of biology and chemistry you’ve had, so I’ve hesitated in discussing anything beyond what might be found in a freshman biology course. Demonstrating my knowledge of technical jargon doesn’t answer your question. Still, you asked and now you’ll be sorry.
First, pyruvate is not a waste product; without it there is no TCA cycle/electron transport system for those organisms that mainly rely on the cellular respiration pathway, and no fermentation for those that don’t. It is an end product of glycolysis, which is not the same thing as waste. It is not excreted, it is converted or stored.
For example, in humans, the conversion of pyruvate to acetyl-CoA acts as a signal for energy production. (While pyruvate is not the only source of acetyl-CoA, it is a common one. The acetyl-CoA itself is used in other biochemical reactions outside the TCA (Tricarboxcylic Acid) cycle.) If acetyl-CoA enters the TCA cycle, then further reactions lead to the regneration of important co-enzymes such as NAD+, the release of CO[SUB]2[/SUB] which is used in other reactions, helps maintain the homeostasis of blood and regulate breathing, generation of ATP and GTP, and uses byproducts of other pathways to generate oxaloacetate.
Second, urea is formed in the Urea cycle (in the liver) and is the means by which the human body rids itself of excess nitrogen, which result from increase in amino acid catabolism, i.e., more protein was eaten that you actually needed. Lactate formed in muscle cells is transported by the blood to the liver, where it reacts with pyruvate in a process called gluconeogenesis (making new glucose.)
**
The number of biochemical reactions that are reversible is huge. If they weren’t, all reactions would quickly go to completion and you would die. A living organism is not a closed system and no reaction takes place that is not energetically favourable (think Gibbs Energy), so no thermodynamic laws are broken. Enzymes only speed up reactions that are already energetically favourable but not thermodynamically favourable. An excellent example is the reaction of glucose with oxygen to produce cargon dioxide, water, and energy. Leave glucose laying about and it may eventually react with oxygen in the air but don’t bet your life on it. However, the reaction can and does take place at a remarkable rate within cells via enzyme catalysis.
Remember that it is the maintenance of a homeostasis that is important in survival, which means reversible reactions. For example, hemoglobin binding of oxygen and carbon dioxide must be reversible or those gases would never leave the heme domain and diffuse into/out of the cells. Reactions that are irreversible are almost always heavily regulated.
Also, ATP is not the only useful product of either pathway. Most of the byproducts are used in other reaction pathways and the regeneration of coenzymes, substrates, etc. helps to keep down the number of new molecules that must be synthesized by the body.
**
Well, my focus is biochemistry/cell biology not organic chemistry, so I don’t know much about alcohol fermentation. However, I took O-chem with a young woman who planned to go into wine making and she mentioned a few things. If I remember aright, vinegar is the result of a secondary fermentation by a bacteria that is common in the environment, especially fruit. It’s named acetae or aceti or some such. The bacteria converts alcohol to acid by oxidation and uses ethanol and acetate as carbon sources.
I apologize for the lateness of the response but I have classes all day.
The alcohol (ethanol) in fermented grape juice is produced by the yeast Saccharomyces cerevisiae. The bacterium Acetobacter aceti then oxidizes the ethanol into acetic acid.
Yeast is a facultative anaerobe, meaning it can survive with or without the presence of oxygen. It does this by switching the fate of pyruvate. If oxygen is present, pyruvate is converted to acetyl-CoA that then enters the Krebs cycle. In the absence of oxygen, pyruvate is converted to ethanol which is excreted as a waste product. Do not confuse acetyl-CoA with acetic acid; they are (vast oversimplification) different compounds.
