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AP Biology Unit 2 The Cell (Cellular Respiration)

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Aerobic Respiration
Cellular respiration in the presence of Oxygen
Glycolysis
1st step of cellular respiration. Takes place in the cytosol. A 6-carbon glucose is split into two 3-carbon pyruvates. Two electrons and two protons are released by one of the intermediates in the pathway. Two of the electrons and one of the protons are transferred to NAD , reducing it to NADH. This is the oxidation step. ATP is produced by substrate level phosphorylation. Two ATP are used in glycolysis and four are produced. Net gain of 2 ATP (Summary: Takes 1 glucose and turns it into 2 pyruvate, 2 NADH. Net gain of 2 ATP)
Acetyl CoA formation
2nd step of cellular respiration. Occurs in matrix of mitochondria. Pyruvate loses two electrons, two protons, and one carbon. The two electrons and one proton are accepted by NAD , reducing it to NADH. The carbon diffuse out of the cell as CO2. The remaining 2-carbon acetyl group attaches to CoA. Because 2 pyruvates result from one glucose, pyruvate oxidation will occur twice. (Summary: Pyruvate combines with coenzyme A, to produce acetyl CoA. 1 NADH and 1 CO2 are also produced.)
Citric Acid Cycle (Krebs Cycle)
3rd step in cellular respiration. Occurs in matrix of mitochondria. Also called Citric Acid Cycle because acetyl unit combines with oxaloacetate to form citrate in first step. Decarboxylation occurs at two steps (input of 2 carbons from acetyl unit is balanced by loss of 2 carbons as CO2) Oxidation occurs in four steps. In three of these, NAD is the electron acceptor. In the fourth, FAD is the electron acceptor, reducing it to FADH2. ATP is generated at one point by substrate level phosphorylation. 6. Oxaloacetate is regenerated to complete the cycle and ready it to begin again. It takes two turns of the cycle to metabolize both acetyl units generated by one glucose. (Final products: 3NADH, 1FADH2, 1ATP, CO2)
Electron Transport System
Occurs in inner mitochondrial membrane. System consists of series of electron carriers that can exist in either oxidized or reduced state. NADH and FADH deliver the electrons to the chain which delivers them to the final electron acceptor, oxygen. As electrons flow through the chain, hydrogen ions are pumped from the matrix into the intermembrane space. This gradient provides the energy necessary for ATP synthesis. The carriers all return to the oxidized state. H2O is a final product. For each electron pair from NADH, 3 ATP are produced. For each electron pair from FADH2 , 2 ATP are produced.
Oxidative Phosphorylation
Occurs in cristae of mitochondria. The electrochemical gradient set up by the ETS drives the enzymatic synthesis of ATP. Protons in the intermembrane space move through the ATP Synthase, causing a conformational change which activates it and results in formation of ATP. Known as the chemiosmotic model. (Summary of ETS and OP: Electrons from NADH and FADH2 pass along an electron transport chain. The chain consists of proteins that pass these electrons from one carrier protein to the next. Along each step of the chain, the electrons give up energy used to phosphorylate ADP to ATP. The final electron acceptor of the electron transport chain is oxygen. O2 accepts the two electrons and combines with H+ to form H20. Proton flow activates ATP synthase which begins producing ATP)
Outermembrane of the Mitochondria
consists of a double layer of phospholipids
Intermembrane space
This is the narrow area between the inner and outer membranes. H+ ions (protons) accumulate
Inner membrane of the Mitochondria
Double phospholipid bilayer, has many folds called cristae. Oxidative phosphorylation occurs here.
Matrix
fluid material that fills the area inside the inner membrane. Krebs Cycle and conversion of pyruvate to Acetyl CoA occur here.
Chemiosmosis
mechanism of ATP generation that occurs when energy is stored in the form of a proton concentration gradient across a membrane
ATP Synthase
Channel protein in the inner membrane. Allows protons in intermembrane space to flow into the matrix. Movement of protons through the channel generate the energy for ATP synthase to produce ATP.
Substrate-Level Phosphorylation
occurs when a phosphate group and its associated energy is transferred to ADP to form ATP. Occurs during glycolysis.
Anaerobic Respiration
Process cells use when oxygen is not present
Alcohol Fermentation
A type of anaerobic respiration. For each pyruvate, 1 CO2 and 1 acetaldehyde are produced. For each acetaldehyde, 1 ethanol is made and 1 NAD+ is produced. The release some NAD+ for use by glycolysis to produce 2ATP.
Lactic Acid Fermentation
A pyruvate is converted to lactate (or lactic acid). NADH gives up its electrons to form NAD+. NAD+ can now be used for glycolysis.
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