[Music] [Music] in this lecture we're going to talk about microbial metabolism and that's generation or production of energy as well as utilization of energy in both the prokaryotic cells and the eukaryotic cells so organisms in carbon it depends as we discussed earlier on whether or not the organism can utilize directly carbon dioxide or if organisms rely on the production from of carbon from other organisms so the autotrophs are the organisms that engage in photosynthesis and they use carbon dioxide from the atmosphere as their source of carbon and they're they're able to produce glucose from the atmospheric carbon in the presence of sunlight so most autotrophs are photosynthetic and they actually obtain their energy from the Sun now the heterotrophs on the other hand those are the organisms that rely on the production of glucose from or the production of carbon for that matter from other organisms that is they cannot use atmospheric carbon dioxide they must obtain their carbon from the environment mostly in the form of complex organic molecules called glucose those are the simple form of carbohydrate and they must so they're by definition they subsist on the products of other organisms so carbon hydrogen oxygen and water are constantly cycled between the heterotopic and the autotrophic worlds and in this slide you can say that basically both are dependent on one another so the autotrophs cannot produce glucose unless they have carbon dioxide that is expired or during respiration we all exhale carbon dioxide and that is what is used by the autotrophs to produce oxygen and glucose so for instance with the global warming crisis one of the drivers of the possibility that we are undergoing global warming is the cutting down of all these forests so when we remove the capacity to produce oxygen of course then that's a serious problem and the plants also they're dependent on the carbon dioxide that's produced by the heterotrophs and we certainly have an overabundance of carbon dioxide because the cars produce carbon dioxide as well so metabolism now just so that we get our terms understood metabolism is the sum of all chemical transformations that occur in a cell or in an organism and that these chemical reactions are all if not or most if not all driven by a series of enzyme catalyzed reaction and that these reactions constitute the metabolic pathway now catabolism is the degradation or the breakdown of metabolism where organic nutrient molecules are converted into smaller and simpler end products and the process of catabolism releases energy the term anabolism is the opposite of catabolism and that's synthesis so that's actually taking small molecules and building them up into larger more calm flex ones and as we have been learning throughout the lectures the three biomolecular groups of molecules the lipids proteins and carbohydrates all start out in simpler forms and then go through anabolism where energy is required for these simpler molecules to become more complex so cellular respiration is defined as the production of ATP and ATP is utilized in terms of producing energy so when ATP first of all when ATP is broken down into ADP we get energy so in order to produce ATP from ADP it requires energy so we're constantly cycling back and forth between these two forms of energy molecules and when they're broken down energy is released and when they're built up when that extra phosphate is added to ADP then that requires energy so aerobic respiration is occurs in bacteria that live in environments with oxygen so they live in oxygenated environments and in order for this energy production to occur oxygen is required and the reason for that is at the end of the reaction oxygen is the electron acceptor now anaerobic respiration occurs in bacteria that live in environments without oxygen and in fact oxygen will kill or eradicate these anaerobic bacteria so the final electron acceptor for those bacteria is an inorganic not a molecule that is not oxygen so glucose is the most important energy carbohydrate molecule I call it a currency molecule it's the molecule that's exchanged between plants and animals it's the molecule that flows in our bloodstream and provides energy to all of our cells and it it is the molecule as I explained that is also the building block molecule in plants so glucose has three major outcomes it can be stored it can be glucose can be oxidized and now oxidized is another word for being broken down and it can be oxidized or broken down into pyruvate and that process is called glycolysis we'll have a little more in-depth discussion about that and ultimately glucose will be turned into ATP and then other metabolic intermediates glucose can be oxidized by the pentose phosphate pathway now you're wondering what is that well actually that's the pathway that produces the nucleic acids now during our discussion about the DNA and RNA the backbone of the DNA molecule remember DNA has like a ladder so the backbone of that molecule are all ribose which are sugar molecules and in order to produce those molecules we need to go through this pentose phosphate pathway so basically this is a synthesis of what I just said which is glucose can get stored and in animals it's stored in the form of glycogen and in plants it's stored in the form of star okay now glucose can also go down and be oxidized or broken down into pyruvate or glucose can be oxidized via the pentose phosphate pathway now it's important to get a clear sense about terminology so remember we talked about catabolism earlier so catabolism is just another word for oxidation okay and anabolism is another word for synthesis which is another word for being broken down or for being built up so I like to make sure that students understand that these terms can are basically mean very similar things and sometimes that one can get confused by it all and and the intention isn't to do that it's just the way in which terms are used now the other that reminds me the other word for anabolism is reduction and that's used in a more chemical sense so reduction is actually the opposite of oxidation okay so also the glucose pathway can further go into glycolysis and the citric acid cycle so here there are three directions so to speak that glucose can go through in terms of being broken down so glucose can be fermented into ethanol in yeast it can actually undergo anaerobic respiration over here or glucose can undergo aerobic respiration now the Arabic pathways the more common one and this pathway generally produces much more ATP than the anaerobic pathway and the reason for this is very complex biochemically and we'll review that in another lecture but basically pyruvate goes through the glycolysis or glucose goes through glycolysis to pyruvate which then goes through the citric acid cycle and then oxidative phosphorylation until we get to our ultimate end product which again is member co2 and water so aerobic metabolism to really review these two more specifically occurs in three stages there's glycolysis which is glucose going to pyruvate there's citric acid cycle where we get formation of a settle Cowen's i'm a and then the final stage is oxidative phosphorylation so in summary this is what we have we have glucose plus oxygen being produced to yield carbon dioxide and water now here's another picture in more detail of aerobic metabolism so you'll see again that we go through this process called glycolysis and we produce pyruvate then pyruvate gets turned into a settle Cowen's i'm a and the settle coenzyme a travels through the citric acid cycle which then ultimately yields or comes to this oxidative phosphorylation stage some people call it the respiratory electron transport chain and this is the part where ATP is produced now everything below this place here this process all occurs in the mitochondria whereas the glycolysis process occurs in the cytoplasm and as I said before this process is a lot more direct and produces a much larger amount of ATP so it's a much more efficient way to produce energy now this is a picture of respiration and fermentation in terms of bacteria and yeast so remember yeast can produce energy through fermentation and through fermentation we get these other types of products where pyruvate is our Peruvian is carried by NADH which is an electron transporter from glycolysis into fermentation in products and that that is different from respiration which occurs in the presence of oxygen and here we get the various processes where we end up with the electron transport chain which as you can see right here requires oxygen to produce water so this is actually at the very end stage and here is our production of ATP now in terms of thinking about carbohydrate catabolism in terms of the different eukaryotic and prokaryotic cells that glycolysis occurs in the cytoplasm of both types of cells the intermediate acetylcholine a step occurs in the cytoplasm of both cells the Krebs or citric acid cycle as some other people call it the Krebs cycle or citric acid cycle occurs in the mitochondria of periodic cells but occurs in the cytoplasm of prokaryotes and this is a short abbreviation for the electron transport chain that occurs in the mitochondrial inner membrane but occurs in the plasma membrane of the prokaryotic cells so anaerobic metabolism on the other hand remembers remember does not require oxygen and the byproduct of lactic of our anaerobic metabolism is lactic acid now in humans that lactic acid can actually be recycled back by the liver but in terms of the bacteria they just produce lactic acid and they go through their various types of conversions but remember they don't have a liver okay so they can't undergo the same kind of process but certainly they can exist in an anaerobic environment and you know the truth is humans for a very short time can also undergo movement and energy production and utilization also without oxygen but we don't last very long the example there is sprinters essentially mostly rely on anaerobic metabolism but they can only undergo anaerobic metabolism for a very short time so here are the different types of are the different ways in which ATP can be produced so we can produce ATP through photosynthesis or photosynthetic pigments in combination with light we can start with glucose over here we generate ATP and depending on the type of metabolism that occurs we can have the electron carriers at the end or nad p or nad or fa and then we end up with oxygen or we require oxygen in terms of that final electron acceptor for aerobic respiration we can exist on other molecules for anaerobic or fermentation we have an organic compound so our first example which cellular respiration pathway is the most efficient at producing ATP is an aerobic anaerobic or fermentation well the answer is as we talked about throughout the discussion today the answer is aerobic but we can certainly produce ATP by these other pathways we just don't get as much of it what kinds of human tissue do you think anaerobic bacteria live in so to answer this question you really need to think about what parts of the human body are not exposed to oxygen well how about an example great example there is the human bladder so we have bacteria so for instance if we have a urinary tract infection that bacteria is often anaerobic if you can imagine bacteria living in human bladder that bacteria is not going to get exposed to oxygen at all really but what about aerobic bacteria well that one isn't as challenging to think about number one what is the tissue exposed to oxygen number one is the respiratory tract well guess what pneumonia I think what do you think I think pneumonia is an aerobic bacteria so sometimes with these questions you may not remember the exact bacteria whether it's anaerobic or aerobic but you can think about what tissue does it infect and what tissue doesn't live in and lo and behold maybe you can take a very educated guess so the third example has to do with where does the electron transport chain occur in the eukaryotic cell well the eukaryotic cell is very lucky because it has this wonderful organelle called the mitochondria now remember we've talked about the mitochondria several times in these lectures and not only does the mitochondria have this wonderful outer membrane but it also has an inner compartments or compartments and there is an inner space and actually that last stage is occurring on the inner mitochondrial membrane now unfortunately the prokaryotic cell is not that lucky and that cell has to have that same function go on in the plasma membrane so here in the prokaryotic cell the actual last stage that oxidative phosphorylation electron transport occurs in the inner lining of the plasma membrane so that concludes our discussion about microbial metabolism thank you very much for visiting educator com