hello and welcome back to the prentice-hall biology textbook today we'll be covering chapter 9 cellular respiration okay section 9 - one chemical pathways so chemical energy and food we need to first learn about chemical energy in food so one gram of of the sugar glucose when burned in the presence of oxygen releases 3811 calories of heat energy and a calorie is the amount of energy needed to raise the temperature of one gram of water one degree Celsius and that's a calorie with a lowercase C a calorie with an uppercase C is 1,000 calories now our cells don't burn the glucose they have they gradually release energy from it and other food compounds and that process begins with glycolysis so glycolysis recent releases only a small amount of energy and if oxygen is present glycolysis will lead down down the Krebs cycle to the electron transport chain and if oxygen is not present it leads to fermentation okay a quick overview of cellular respiration in the presence of oxygen glycolysis is followed by Krebs cycle and the electron transport chain like I just said and those three processes make up a the make up cellular respiration and cellular respiration is defined as the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen and the equation for cellular respiration is six oxygen molecules plus one glucose will are turned into six carbon dioxide molecules six water molecules and energy and this isn't one step it is that equation is the equation for all three of the process okay so glycolysis got qualit glycolysis is the process in which one molecule of glucose is broken in half producing two molecules of pyruvic acid a 3-carbon compound and the electrons go to the electron transport chain while the pyruvic asked to go to the krebs cycle so the ATP in that is used and produced in glycolysis is relatively small it takes two ATP molecules to start the glycolysis cycle and at the end it produces four ATP molecules for a net gain of two ATP now this doesn't sound like a lot of ATP but cells can produce thousands of ATP molecules in just a few milliseconds however the other product the other molecule needed nad plus it the cells run out of it fairly quickly so the NADH production that is one reaction will remove four high-energy electrons and passes them to an electron carrier called nad Plus which is nicotinamide adenine dinucleotide and that transforms it to NADH which is a high energy electron carrier so if they had an abundance of nad plus cells could run glycolysis forever and produce massive amounts of energy but on but it runs out as I said earlier in a few seconds okay so fermentation is what happens when there is no oxygen present after glycolysis and it's considered an anaerobic process which means without oxygen so fermentation releases energy from food molecules by producing ATP in the absence of oxygen these cells convert NADH the high the high energy electron carrier to nad plus by passing high-energy electrons back to the pyruvic acid so there are two main types of fermentation there's alcoholic fermentation and lactic acid fermentation alcoholic fermentation is used by yeast and a few other microorganisms and it forms ethyl alcohol and carbon dioxide and the equation for that is pyruvic acid plus NADH is turned into alcohol carbon dioxide and nad plus then there's lactic acid fermentation so that converts pyruvic acid into lactic acid and this regenerates nad plus so glycolysis can continue the equation for that is pyruvic acid plus NADH turns into lactic acid and nad plus so this is lactic acid is what happens in your in the muscle cells during exercise your muscle cells produce an excess of lactic acid because they're starved for oxygen when you are exercising ok 9 - to the Krebs cycle and electron transport so this is the aerobic pathway for glycolysis this is when there is oxygen present the next step would be the Krebs cycle followed by the electron transport chain so at the end of glycolysis about 90% of the chemical energy that was available in glucose is still unused and to extract the rest the cells must use oxygen so the cells start with the Krebs cycle and this is the second stage of cellular respiration it's named after Hans Krebs the British biochemist who demonstrated its existence in 1937 during the krebs cycle pyruvic acid is broken down into carbon dioxide in a series of energy extracting reactions and there are two main steps citric acid production and energy extraction so these are a lot so make sure you follow along closely so for citric acid production as the pyruvic acid enters the mitochondria a carbon is removed forming co2 which is then released into the air later the electrons are removed and change NADH to nad or nad plus use me two NADH the coenzyme a joins the two carbon molecule forming acetyl co a an acetal Co a then adds to carbon groups - a four carbon compound forming citric acid so after that we have energy extraction an energy extraction is the citric acid is broken down into a five carbon compound then into four common count four carbon compound along the way two more molecules of co2 are released and the electrons join nadh and fadh2 Avi n-- addenda nine dinucleotide forming nadh and fadh2 so f ad and fadh2 are just similar electron carry our electron carriers similar to NAD+ and NADH and then in addition to this one molecule of ATP is generated the energy from the molecule of pyruvic acid is four NADH one fadh2 and one molecule of ATP so here we can see the graph we start our we can see some of the the products we have the co2 here the NAD+ changed into the NADH here and here ADP is given another phosphate group and turned into ATP FA B is turned into fadh2 fadh2 and the same with nad + is turned into NH NADH there again okay the electron transport chain so this is the next step in the cellular respiration and the electric chain the electrons carried by nadh and fadh2 are passed to the electron transport chain we can see that here the electron transport chain uses the higher energy electrons from the krebs cycle to convert ADP to ATP so there are three main steps electron transport hydrogen ion movement and ATP production so electron transport the high-energy electrons are passed along the electron transport system in eukaryotes the electron transport system is composed of a series of carrier proteins located in the inner membrane of the mitochondria in prokaryotes the same chain is in the cell membrane so high-energy electrons are passed from one carrier protein to an the next and at the end an enzyme combines these electrons with hydrogen ions and oxygen to form water so oxygen serves as the final electron acceptor of the electron transport chain and it's also essential for getting rid of low energy electrons and hydrogen ions the waste of cellular respiration next we have the hydrogen ion movement so every time two high-energy electrons are transported down the electron transport chain their energy is used to transport hydrogen ions across the membrane so during electron transport the hydrogen ions build up in the intermembrane space making it positively charged while the other side becomes negative so ATP production the third and final step the inner membrane of the mitochondria contains protein spheres called ATP synthase which we discussed in an earlier chapter as the hydrogen ions escape through the ATP synthase it spins or it rotates and each time it rotates the it grabs a low energy P attaches a phosphate and forms ATP we can see that here these would be this would be the ATP synthase and as the hydrogen ions escape it grabs an ADP as the phosphate group to form ATP the energy final energy product okay so the totals of this so glycolysis produces just two ATP molecules per molecule of glucose however the Krebs cycle and the electron transport chain produced 36 ATP per glucose molecule 18 more than can be generated without oxygen so it's not just glucose they take large complex carbohydrates that are eaten and then are broken down into simple sugars however the 36 ATP represents only 38 percent of the total energy of glucose the other 62 percent is released as heat and is unable to be produced or turned into ATP so energy and exercise so we use the ATP for energy there's quick energy which is when we use up the stored energy we have in a few quick seconds that is quick energy and then muscle cells start lactic acid fermentation to produce more energy and this lasts for about 90 seconds so you could run hypothetically 400 meters using lactic acid fermentation and this then produces lactic acid as a byproduct which requires extra oxygen to remove from your body this is why you see runners breathing heavily the more oxygen they get the quicker the lactic acid buildup is dispersed and then long-term energy so the body stores glycogen which is a glucose carbohydrate and then by breaking that down it can uh it will produce a that breaking it down produces glucose which is then put into the cellular respiration however this can this doesn't last for very long either and then after the body uses up its stores of glycogen it breaks down fats and other molecules in the body for energy okay let's compare photosynthesis and cellular respiration as we can see from the diagram photosynthesis takes in light water and co2 and produces oxygen and glucose now we see in cellular respiration it takes glucose oxygen and it produces is co2 water heat and ATP so we can see that the two processes are very closely linked it's easy to think of it as photosynthesis deposits energy while the cellular respiration withdraws the energy okay let's go to key concepts so the key concepts for chapter 9 describe the process of cellular respiration what are the products of glycolysis name the two main types of fermentation what happens to pyruvic acid during the Krebs cycle and how does the electron transport chain use high-energy electrons from the Krebs cycle alright that's it for chapter 9