Cellular Respiration PDF

00:00:04 everyday activities require energy humans like all living organisms need to fuel their actions similar to the way a car requires fuel to run to fuel all this physical work our bodies break down food molecules and extract their energy we rely on this process called cellular respiratio...

00:00:04 everyday activities require energy humans like all living organisms need to fuel their actions similar to the way a car requires fuel to run to fuel all this physical work our bodies break down food molecules and extract their energy we rely on this process called cellular respiration to run smoothly so that we'll have the energy needed to exert ourselves or just relax in cellular respiration plants animals and all other living organisms Harvest energy by breaking down energy-rich molecules in this example a Bison 00:00:44 ingests Grass digests the food and delivers food molecules to cells of its body as energy is released by the reactions of cellular respiration cells capture and store the energy in the bonds of ATP molecules the chief energy currency of the cell this plentiful readily available stored energy in ATP can then be used as needed to fuel the activities of the organism cellular respiration requires oxygen which the animal inhales and releases carbon dioxide which the animal exhales water is also released during 00:01:21 these reactions cellular respiration is a bit like photosynthesis in Reverse note that in photosynthesis oxygen and sugar are products of the reaction while they are inputs in cellular respiration in cellular respiration carbon dioxide and water are products of the reaction while in photosynthesis they are inputs in photosynthesis the sun provides the energy to power the reactions while in cellular respiration the released energy is stored in the bonds of ATP cellular respiration occurs in three 00:01:59 basic steps G olysis the citric acid cycle and the electron transport chain during these processes food molecules such as glucose are gradually broken down and their energy is used to produce ATP 00:00:04 glycolysis is a series of chemical reactions in the cytoplasm of a cell in which glucose is essentially split in half in the process a small amount of energy is released and captured in ATP for many organisms glycolysis is just the first of three steps together called cellular respiration in which glucose is completely broken down and used to produce a much larger amount ount of ATP glycolysis has two distinct phases an uphill Preparatory phase and a downhill payoff phase one way to understand the two 00:00:43 phases of glycolysis is to compare the process to a downhill bike ride glucose has a lot of potential energy a cyclist at an uphill starting spot has a lot of potential energy too with little effort the rider Taps the potential energy and coasts to the downhill spot but sometimes to reach a downhill spot the cyclist must first go uphill investing energy to get to the top of the hill but on the way down the cyclist gets back most of that energy investment along with the reward of a longer ride glycolysis is similar although 00:01:22 glucose is packed with energy the energy is not readily released unless energy from ATP is first added when ATP is added to the reaction the resulting sugar molecule now has two phosphate groups which make it less stable than before and ripe for chemical breakdown in the payoff phase three reactions now yield energy in one reaction each of the halves from glucose is attached to a high energy phosphate group and each donates high energy electrons along with protons also called hydrogen ions to electron carriers 00:01:59 called an nad+ the resulting nadh molecules are high energy electron carriers that are used later in cellular respiration for an even greater energy payoff the essential difference between nad+ and nadh is that nadh carries one additional proton and two additional high energy electrons as glycolysis continues and more bonds from the two halves of glucose are broken the energy released is quickly recaptured by attaching phosphate groups to molecules of ADP creating energy-rich ATP molecules two molecules of water are 00:02:41 also produced during glycolysis near the end of glycolysis two ADP molecules take the remaining phosphate groups forming two additional ATP molecules by the end of glycolysis a molecule of glucose has been broken down into two molecules of Pyro rate glycolysis results in the production of two nadh and four ATP molecules however two ATP molecules were originally invested represented by the two remaining ADP molecules so glycolysis Nets 2 ATP and two nadh molecules per molecule of glucose however much more energy Still Remains 00:03:27 in the pyruvate molecules cells get much more energy bang for their food Buck if they now perform the citric acid cycle and the electron transport chain 00:00:04 the second step in cellular respiration called the citric acid cycle picks up where glycolysis left off recall that in glycolysis glucose is split into two molecules of pyruvate note that these two pyruvate molecules retain the original six carbon atoms from glucose as well as most of glucose's energy before the citric acid cycle can begin the pyruvate molecules must be transported from the cytoplasm where glycolysis occurs into mitochondria where the citric acid cycle takes place to prepare for the citric acid cycle 00:00:39 pyruvate is modified in three quick steps involving nad+ and another molecule called co-enzyme a in one of these modifications carbon dioxide is released from pyruvate and eventually exhaled from the body in the other modifications the two carbon molecule that remains is attached to co-enzyme a while a proton also called a hydrogen ion and high energy electrons are donated to nad+ yielding the high energy electron carrier nadh the new molecule is called acetal COA because two pyruvate molecules 00:01:16 emerged from glycolysis two acetal COA molecules and two nadh are now formed note that two of the six carbon atoms from glucose are now in the form of two carbon dioxide molecules acetal COA enters the citric acid cycle where the remaining four carbon atoms that originated from glucose will soon be released as carbon dioxide in the first step of this pathway acetal COA combines with water and a molecule called oxaloacetate the first outcome of the citric acid cycle is the production of a molecule with six carbon 00:01:55 atoms four from oxaloacetate and two that are originated from glucose this six carbon molecule is rearranged by the removal and then the addition of water another important outcome of the citric acid cycle occurs next when the molecule is stripped of two molecules of carbon dioxide which are exhaled at the same time high energy electrons and protons are donated to molecules of nad+ creating nadh molecules another important outcome of the citric acid occurs in the next reaction which draws energy from the 00:02:34 remaining molecule to join inorganic phosphate and ADP into a molecule of ATP in addition to nad+ another molecule called fad plays a role as a high energy electron carrier the four carbon molecule donates protons and high energy electrons to these carriers the molecule then becomes slightly rearranged by the addition of water after which more electrons and a proton join with nad+ to form nadh the final outcome of the citric acid cycle is the Reformation of the Cycle's starting molecule oxaloacetate the entire cycle occurs 00:03:14 again with the second acetal COA molecule as the second round continues more nadh more carbon dioxide more ATP and more fadh2 molecules result if these molecules are added to those made from the preparation reactions we can see that all six of the carbon atoms from glucose have been released in the form of carbon dioxide although a small amount of ATP has been formed in the citric acid cycle it is the nadh and fadh2 molecules that represent the most energy for the cell these electron carriers enter the 00:03:50 next phase of cellular respiration called the electron transport chain nadh and fadh2 molecules must give up their extra elect electrons to the electron transport chain so that they may revert back to NAD plus and fad and help in the citric acid cycle again the electron transport chain uses the energy from the electrons to produce a large number of ATP molecules note that the electron transport chain absolutely requires oxygen to operate because the citric acid cycle relies on a functioning electron transport chain to accept 00:04:27 electrons from nadh and fad H2 the citric acid cycle will shut down along with the electron transport chain if oxygen disappears aerobic training can cause our bodies to produce more mitochondria in muscle cells why might this be beneficial an increase in mitochondria means that the cell has more cellular Machinery to perform the citric acid cycle and the electron transport chain because so much at p is produced in the electron transport chain such an increase in mitochondria can provide the cell with more energy to sustain 00:05:07 physical activity provided oxygen is available 00:00:04 the last step in cellular respiration called the electron transport chain takes place in mitochondria this step is essential for producing enough ATP for animals and many other organisms to survive the first two steps in cellular respiration glycolysis and the citric acid cycle produced a small amount of ATP from the breakdown of glucose these steps also produced nadh and fadh2 molecules through the electron transport chain the cell can now use the energy and nadh and fadh2 molecules to make many more 00:00:42 molecules of ATP the mitochondrian has two membranes an outer membrane and an inner membrane and is essentially a bag within a bag the proteins of the electron transport chain reside in the inner membrane both nadh and fad dh2 donate electrons to the chain we will use nadh as an example as electrons move from one complex to another in the chain they transfer some of their energy to proteins that pump protons also known as hydrogen ions across the membrane with each transfer the electrons lose energy 00:01:21 which is used to pump more protons the process of electron transfer results in a difference in the concentration of protons on the two sides of the membr bra this concentration difference called a gradient is a form of potential energy the oxygen that we breathe is essential for electron transport oxygen is exceptionally electron greedy and snatches electrons from the end of the electron transport chain after grabbing electrons it combines with protons to form water from the operation of the electron 00:01:56 transport chain a concentration gradient of protons form forms across the membrane like water held behind a dam given the opportunity the protons will tend to flow across the membrane barrier a complex in the membrane provides a passageway for the protons and uses the energy from the proton flow to power the production of ATP the protons will tend to flow in this direction until the concentrations are the same on both sides of the membrane that is until the gradient disappears if the electron transport 00:02:28 chain stops for any reason such as a lack of oxygen to capture electrons at the end of the chain the gradient will quickly disappear turning off ATP production the nad+ molecules left over from the electron transport chain are later recycled back to glycolysis and the citric acid cycle where they will capture more high energy electrons from food molecules ATP produced in plenty during this last stage of cellular resp spiration contains energy that had its origin in a molecule of glucose along the way the energy took many forms 00:03:08 including the energy held by electron carriers the energy released by transporting electrons in the electron transport chain and the energy stored in a concentration gradient across a membrane in the form of ATP the energy originally in the bonds of glucose can be used to fuel cellular work why is cyanide such a deadly poison cyanide is a deadly poison because it cripples the electron transport chain cyanide binds to the last complex in the chain and in so doing blocks oxygen from binding recall that during the operation 00:03:48 of the electron transport chain nadh donates electrons to the beginning of the chain the process of electron transport fuels the pumping of protons across the membrane however with cyanide already bound oxygen cannot grab the electrons at the end of the chain therefore no new electrons from nadh can be added at the beginning under these conditions electron transport and proton pumping grind to a halt without the active pumping of protons to one side of the membrane the proton concentrations on both sides soon 00:04:21 equalize no longer do protons rush through the ATP producing complex and no more ATP is produced cells can't live long on the small quantity of ATP made by glycolysis so without the ATP that comes from the electron transport chain cells die