AEROBIC RESPIRATION Chapter 8
AEROBIC RESPIRATION Aerobic respiration is the next step after Glycolysis if the cell can obtain oxygen. We won t need it until the last step but we still need it. Remember that the final product of Glycolysis is pyruvate. Aerobic respiration takes place in the mitochondria The first step is an intermediate reaction to prepare the pyruvate for the citric acid cycle (The intermediate step is only one step, and it s not technically part of Glycolysis OR aerobic respiration. It s just a preparatory step.) The pyruvate gives off a carbon as CO 2, donates a H to form NADH, and the final molecule is an acetyl-coa molecule
CITRIC ACID CYCLE The citric acid cycle takes place in the matrix of the mitochondria **Remember: each step in aerobic respiration happens TWICE once for each PGAL formed in Glycolysis Step 1 Acetyl CoA (2-carbon molecule) bonds with an oxaloacetate (4- carbon molecule) to form citric acid (6-carbon molecule)
CITRIC ACID CYCLE Step 2 Citric acid gives off a CO 2 The molecule now contains 5-carbons CO 2 is not needed by the cell, so it is expelled out into the blood stream. Citric acid donates a hydrogen to an NADH Citric acid reforms to an alpha-ketoglutarate
CITRIC ACID CYCLE Step 3 Alpha-ketogluterate gives off a CO 2, a hydrogen for an NADH, and a phosphate for ATP The molecule then forms a succinate The molecule is now back to the 4-carbon molecule that the cycle started with
CITRIC ACID CYCLE Step 4 Succinate donates a hydrogen for an FADH 2 molecule. The succinate then rearranges to form a molecule of fumerate
CITRIC ACID CYCLE Step 5 The fumerate rearranges to form a molecule called malate
CITRIC ACID CYCLE Step 6 The malate donates a hydrogen to form NADH The malate then reforms to the original oxaloacetate molecule The oxaloacetate begins the cycle over again.
CITRIC ACID CYCLE SUMMARY Inputs per cycle, (per glucose) Acetyl CoA 1 (2) Outputs ATP 1 (2) FADH 2 1 (2) CO 2 2 (4) NADH 3 (6)
ELECTRON CARRIERS A hydrogen is simply one proton and one electron. So, when a hydrogen is donated, it is also appropriate to say an electron is donated Electron carriers are molecules that transport a hydrogen from one location to another Typically, the electron of the hydrogen will be used as a cofactor for an enzyme NADH and FADH 2 have been synthesized multiple times so far in cellular respiration. All will finally be used in the electron transport chain as reactants
ELECTRON TRANSPORT CHAIN The electron transport chain follows glycolysis and the citric acid cycle. It is taking place at the same time as glycolysis and citric acid cycle, but it uses the products of glycolysis and the citric acid cycle as reactants The ETC takes place in the inner membrane of the mitochondria. The ETC is powered thanks to the concept of diffusion and equilibrium Important fact to remember: diffusion and osmosis naturally occur in the universe, which means that these processes happen for free.
ELECTRON TRANSPORT CHAIN The ETC is a series of protein channels embedded in the cristae (inner mitochondrial membrane). The NADH and FADH 2 give off their electron, which powers each protein channel in sequence.* The NAD + and FAD + then return to pick up another electron *REMEMBER: If we can t do this step, then the cell has to do fermentation instead. These proteins move hydrogen atoms from inside the membrane to outside the membrane, against the concentration gradient. The energy for this comes from the NADH and FADH 2 electrons. The hydrogen that cross the membrane are already present. They never leave. This creates an unequal ratio of hydrogen atoms along the membrane (more are outside than inside). The membrane is NOT in equilibrium
ATP SYNTHASE The only way for the hydrogen atoms to get back across the membrane (and reach equilibrium) is through a specific channel enzyme called ATP synthase. ATP synthase looks like an upside-down light bulb. As the hydrogen atoms pass through the ATP synthase from the outside of the membrane to the inside, they provide kinetic energy to the enzyme. With this energy, ATP synthase attaches phosphates to ADP molecules in the bulb part, building an ATP molecule.
ATP PRODUCTION Each molecule of NADH powers the ETC enough to build 3 molecules of ATP FADH gives a little less power and can build only 2 ATP This means the ETC can produce a total of 32-34 ATP per glucose molecule. Add that to the four ATP already produced in glycolysis and the citric acid cycle, you have a maximum-possible net gain of 36-38 ATP molecules from 1 molecule of glucose. With fermentation: it s two. To remove the electron from the ETC, the cell bonds it with a molecule of oxygen and forms H 2 O This is why you need to breathe. This is what the oxygen is used for.
ETC SUMMARY Inputs (per molecule of glucose) 10 NADH 2 FADH 2 O 2 Outputs 28-30 ATP from NADH 4 ATP from FADH 2 NAD + FAD + H 2 O
CELL RESPIRATION SUMMARY C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + Energy C 6 H 12 O 6 : For glycolysis 6 O 2 : To collect the electron in the ETC 6 CO 2 : Given off in intermediate step and Citric Acid Cycle 6 H 2 O : Given off in the ETC Energy : In the form of ATP