Cellular Respiration Stage 2:Oxidation of Pyruvate Stage 3: Krebs Cycle Stage 4: ETC 2006-2007

Cellular respiration

Mitochondria Structure Double membrane highly folded inner membrane called cristae Importance: increases surface area Fluid filled interior called “matrix” DNA, ribosomes, enzymes Site of the Krebs Cycle intermembrane space inner membrane outer matrix cristae mitochondrial DNA

Mitochondria – Form fits Function Divide like bacteria Supports endosymbiosis Membrane-bound proteins passive & active transport Almost all eukaryotic cells have mitochondria there may be 1 very large mitochondrion or 100s to 1000s of individual mitochondria number of mitochondria is correlated with aerobic metabolic activity more activity = more energy needed = more mitochondria What cells would have a lot of mitochondria? Active cells: • muscle cells • nerve cells Internal folds Advantage = more surface area

Stage 2: Oxidation of pyruvate Pyruvate enters mitochondria Pyruvate OXIDIZED and forms acetyl CoA releases 1 CO2 reduces 2 NAD+  2 NADH [ 2x ] pyruvate    acetyl CoA + CO2 3C NAD 2C 1C CO2 is fully oxidized carbon == can’t get any more energy out it CH4 is a fully reduced carbon == good fuel!!!

Stage 3: Krebs Cycle Aka citric acid cycle What? oxidation/reduction process that forms CO2 and H2O [wastes] Where? Matrix of mitochondria Significance  evolved later than glycolysis, but fundamental to aerobic respiration

OXIDATION – in the presence of O2 - aerobic Produces: CO2 and H2O energy carriers [8 NADH and 2 FADH2] 2 net ATP

Electron Carriers = Hydrogen Carriers NADH FADH2 go to Electron Transport Chain ADP + Pi ATP

Energy accounting of Krebs cycle 2x 4 NAD + 1 FAD 4 NADH + 1 FADH2 pyruvate          CO2 1 ADP 1 ATP 3C 3x 1C ATP Net gain = 2 ATP = 8 NADH + 2 FADH2

Electron carriers are important because they … Set up a H+ gradient allow H+ to flow through ATP synthase ADP + Pi  ATP ADP P + ATP

Stage 4: Electron Transport Chain

ETC transport proteins and enzymes are built into inner mitochondrial membrane [cristae] transport electrons down ETC using protons donated by energy carriers (NADH, FADH) yields ~34 ATP from 1 glucose only in presence of O2 (aerobic respiration) O2

Time to break open the bank! glucose Krebs cycle Glycolysis PGAL 8 NADH 2 FADH2 Time to break open the bank!

Electron Transport Chain Building proton gradient! NADH  NAD+ + H p e intermembrane space H+ H+ H+ inner mitochondrial membrane H  e- + H+ C Q e– e– e– H FADH2 FAD H 1 2 NADH 2H+ + O2 H2O NAD+ NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex mitochondrial matrix

Stripping H from Electron Carriers NADH and FADH pass electrons to ETC electrons stripped from H atoms  H+ (protons) electrons passed from one electron carrier to next in mitochondrial membrane (ETC) transport proteins in membrane pump H+ (protons) across inner membrane to intermembrane space NAD+ Q C NADH H2O H+ e– 2H+ + O2 FADH2 1 2 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD H+ Oxidation refers to the loss of electrons to any electron acceptor, not just to oxygen. Uses exergonic flow of electrons through ETC to pump H+ across membrane. ADP + Pi ATP

O2 is 2 oxygen atoms both looking for electrons But what “pulls” the electrons down the ETC? Pumping H+ across membrane … what is energy to fuel that? Can’t be ATP! that would cost you what you want to make! Its like cutting off your leg to buy a new pair of shoes. :-( Flow of electrons powers pumping of H+ O2 is 2 oxygen atoms both looking for electrons O2 oxidative phosphorylation

Oxidative phosphorylation is the process in which ATP is formed as a result of the transfer of electrons from NADH or FADH 2 to O 2 by a series of electron carriers. This process, which takes place in mitochondria, is the major source of ATP in aerobic organisms

Electrons flow downhill Electrons move from carrier to carrier downhill to O2 each carrier more electronegative controlled oxidation controlled release of energy Electrons move from molecule to molecule until they combine with O & H ions to form H2O It’s like pumping water behind a dam -- if released, it can do work

H+ gradient Allows protons to flow through ATP synthase ADP + Pi Allows protons to flow through ATP synthase Synthesizes ATP ADP + Pi  ATP ATP

Chemiosmosis links the Electron Transport Chain to ATP synthesis The diffusion of ions across a membrane build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP Chemiosmosis links the Electron Transport Chain to ATP synthesis Chemiosmosis is the diffusion of ions across a membrane. More specifically, it relates to the generation of ATP by the movement of hydrogen ions across a membrane. Hydrogen ions (protons) will diffuse from an area of high proton concentration to an area of lower proton concentration. Peter Mitchell proposed that an electrochemical concentration gradient of protons across a membrane could be harnessed to make ATP. He likened this process to osmosis, the diffusion of water across a membrane, which is why it is called chemiosmosis.

Pyruvate from cytoplasm synthase Krebs cycle Mitochondrial matrix + Q C 32 ATP 2 Pyruvate from cytoplasm Electron transport system synthase H2O CO2 Krebs cycle Intermembrane space Inner mitochondrial membrane 1. Electrons are harvested and carried to the transport system. 2. Electrons provide energy to pump protons across the membrane. 3. Oxygen joins with protons to form water. 2H+ NADH Acetyl-CoA FADH2 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. Mitochondrial matrix 1 e-

Cellular respiration + + 2 ATP 2 ATP ~34 ATP