Cellular Respiration Third Step

Road Map of Cellular Respiration

This is the end of the road for our process of breaking down or manipulating the carbon chain.  At this point there’s nothing really left in our carbon chain.  We’ve excused all of the carbon dioxide that we can and we’ve retained those final 4 carbons that we need to restart the citric acid cycleseries of enzyme-catalyzed chemical reactions of central importance in all living cells for extracti. 

Take a look again at our overview of cellular respirationThe process of gas exchange, including ventilation, external and internal respiration..  The white arrows that lead from glycolysisprocess of breaking glucose into two three-carbon molecules with the production of ATP and NADH to grooming of pyruvatethree-carbon sugar that can be decarboxylated and oxidized to make acetyl CoA, which enters the citr and into the citric acidA substance that releases hydrogen ions (H⁺) in solution. cycle are the pathway of the carbon chain.  There is no connection of those white arrows to that third step cellular respiration as we’re done with breaking down the carbon chain.  We’ve produced all of the carbon dioxide that will be produced from the breakdown of the carbon chain. 

We have also produced all of the ATPThe energy currency of cells used for muscle contraction. that will be produced by substrate level phosphorylationaddition of a high-energy phosphate to a compound, usually a metabolic intermediate, a protein, or A. 

The most important things that we have produced are a lot of electron taxis.  You can see these electron taxis are the connection from the first 2 steps to the last step.  These electronsNegatively charged subatomic particles found in atoms. were produced by stripping them from the carbon chain and they carry that energyThe capacity to do work or cause change. that glucoseA simple sugar that is the main source of energy for cells. provides as food.  We’ve converted some of that energy to ATP, but we’ve banked a lot of it into the electron taxis NADH.  These electrons will finally make their way to our last step of cellular respiration and help us create a lot of ATP using oxygen in the process. 

Electron Transport Chains

Before we get into the process of oxidative phosphorylationproduction of ATP using the process of chemiosmosis in the presence of oxygen which is the third and last step of cellular respiration we need to understand the anatomyThe study of the structure of the human body. or the proteinsLarge molecules made of amino acids with various functions in the body. that are involved in the process.  First proteins involved in the process are a series of proteins embedded in the inner mitochondrial membrane.  This collection of proteins is called the electron transport chain which is commonly abbreviated E TC.  I think they kinda look like teeth, right?   Take a moment and think about where we are.  We have a cell, within the cell is a mitochondrion, and within the mitochondrion is an inner membrane. That’s where these proteins are embedded.  Different resources include more or less detail of electron transport chains, including more proteins with higher levels of learning.  At our level, it is common to see three or five proteins involved in an electron transport chain.   We’re going to go with five.  Three of these proteins are locked in position in the ETC, like the three big proteins you can see here, and two of these proteins are known as mobile electron carriersMembrane proteins that transport substances across a cell membrane. that can move through the membrane, carrying an electron from one of those fixed proteins to the next. 

ATP Synthase

The last and most significant protein is called ATP synthasemembrane-embedded protein complex that adds a phosphate to ADP with energy from protons diffusing th and is just awesome.  Check this thing out.  ATP synthase looks complicated but it is not.  ATP synthase has one part that is a channel protein that allows protons move from their area of high concentration their area of low concentration, like in facilitated diffusionPassive movement of molecules from areas of high to low concentration..  The other part of ATP synthase is a rotor.  Think of ATP synthase like a paddlewheel at an old mill.  Water or in this case protons run down their own gradient causing motion in the rotor.  The motion turns this internal rod that then turns this catalytic knob of ATP synthase.  This catalytic knob is capable of converting the energy of rotational motion into the bond that binds that last phosphate group to create ATP.  Another good analogy is a dam.  Water flows through the dam and is converted into electricity, something that can be used by humans.  In general, we’re doing the same, converting energy of motion into something that can be used by your cellsThe basic structural and functional units of life.: ATP. 

ATP Synthase

I want you to understand the magnitude of the ATP synthase proteins in your cells.  This picture here is a picture of ATP synthase imbedded in the my inner mitochondrial membrane.  Take one mitochondria in one of yourself and peel away the outer membrane.  There isn’t one ATP synthase there aren’t some ATP synthase there are thousands of ATP synthase in one mitochondria.  This is the magnitude of ATP conversion that is required to fuel you, and it is immense.  Your electron transport chains and ATP synthase require an input of oxygen and glucose to create the ATP required for your life.  You have only about a 5 minute supply of ATP.  Once you are deprived of oxygen, depriving your electron transport chains and ATP synthase of the molecule they need to create the ATP, you only have about 5 minutes to live. 

You must watch videos of this process.

Now that we’ve described the anatomical players of this third step of cellular respiration let’s try to put it into motion.  Orient yourself to this diagram.  We can identify the 5 proteins of the electron transport chain, ATP synthase, some electron carriers, ATP, oxygen, waterThe universal solvent essential for life., and some protons.  When we put this in motion we’re going to see a game of hot potato.  Think of the electrons as the potato and the proteins are the people playing the game.  As the first person grabs the potato, it burns their hands, emitting a little energy as it does, and the person passes it to the next in line.  The people in the game are the proteins in the electron transport chain.  We can think of the electrons as the hot potato. 

All of the electron carriers that we’ve been loading throughout the first and second step are finally going to off load their electrons into the electron transport chain.  Take a look at the pathway of electrons here.  Look how NADH offloads its electrons to the first protein in the ETC, and FADH2 offloads to one of the mobile electron carriers.  Once offloaded the electrons hop their way through the remaining proteins in the electron transport chain and then are offloaded from the chain by oxygen.  Take a look oxygen is the molecule that is accepting the electrons from this electron transport chain.  Oxygen is the final electron acceptor, getting reduced to water in this process.  Remember that we’ve already accounted for the waste product of carbon dioxide from cellular respiration now we’re counting for the waste product of water. 

Electrons don’t move through ATP synthase; they only move through the chain.

 Remember as we’ve been transporting the electrons that were stripped from moleculesGroups of atoms bonded together. the protons have been coming along and now we’re going to use all of those protons.  These protons have been building up in the matrix of the mitochondria.  Instead of leaving them there were going to actively pump them into the inter membrane space which, as you remember, is the space that is between the outer and inner membrane of the mitochondria.  Every time an electron gets passed from one protein to another that protein pumps a proton from the matrix to the inter membrane space.  Recall our game of hot potato where the potato releases a small amount of heat into the hands of each person that is playing.  Our potato or our electrons transfer a small amount of energy to each protein and that protein uses that energy to pump the proton. 

We are now accumulating a high concentration of protons in the inter membrane space.  Just similar to our analogy of a damn holding back water the inner membrane is that dam trapping the proton gradient in the intermembrane space.  With a dam, we open the locks of the dam allowing the water to flow through and converting that kinetic energyEnergy of motion. of water movementA fundamental property of life involving motion of the body or its parts. into the potential energy of electricity.  In our case we are going to allow our protons to flow through ATP synthase and we will trap the kinetic energy of the moving protons into ATP.  This is the process of oxidative phosphorylation.  We are making ATP and we are using oxygen in the process.  Unlike the substrate phosphorylation we’ve seen in glycolysis and the citric acid cycle, we are making 36 ATP per glucose input whereas the substrate only made two ATP. 

You really have to watch this in motion there are so many videos on line just choose one and watch it don’t just watch it once be like Teletubbies watch it again and again and again by the third time you watch it you’ll finally get some of the processes.  The first time you watch it you should focus on the movement of electrons the dropping off and the movement through the electron transport chain and the picking up.  The second time you watch it you should watch the movement of protons moving from the matrix to the intermembrane space and then back again to the matrix through ATP synthase.

Disrupting Oxidative Phosphorylation

When I teach human anatomy and Physiology we discussed many practices that happened in your body but then we discussed the diseases that can disrupt them.  This diagram shows toxins that can disrupt the electron transport chain and ATP synthase.  The first we have is rotenone which seems to affect the first protein in the electron transport chain.  If you can’t drop off your electrons you can’t make that proton gradient.  The next disruptors we see are cyanide and carbon monoxide which also disrupt the electron transport chain.  However they do it at the final protein instead of the first protein.  Carbon monoxide basically sits on the last protein preventing the electrons from being offloaded.  This causes a back up at the electron transport chain and then again you can’t build your proton gradient.  DNP, which is basically a pesticide, pokes holes in the inner mitochondrial membrane, diffusing the proton gradient.  The protons lost into these holes doesn’t diffuse through ATP synthase.  Although the gradient is created, it can’t be used by ATP synthase and no ATP is created.  Oligomycin is another toxic chemical which pretty much sits right on the channel of ATP synthase preventing any of the protons from diffusing from the intermembrane space to the matrix.  Again, the proton gradient is made, but can’t be used by ATP synthase and no ATP is made.

This is a tough concept.  Think of what type of learner you are.  Do you need to draw this out?  Do you need to listen to it again?  Do you need to watch videos?  Do it.  Understanding this process is incredibly important because we use the components here in the next module when we cover photosynthesis.  Don’t skimp on your understanding here.  You will regret it during the quiz we will have on photosynthesis.  Whatever type of learner you are, I strongly suggest printing out the last two slides in this powerpoint.  They are the road map of cellular respiration and the up-close diagram of oxidative phosphorylation without any labels on them.  Sometimes solidifying the anatomy makes the physiologyThe study of how the body functions. come out clearer.