These Energy-Rich Molecules pass on e- to an Electron Transport Chain Also termed, the Respiratory Chain

Transcription

1 These Energy-Rich Molecules pass on e- to an Electron Transport Chain Also termed, the Respiratory Chain The ETC is a series of proteins embedded in the inner mitochondrial membrane Text pg 125 Electron Transport Chain or Respiratory Chain ETC A. Includes 4 different protein units Labeled as Respiratory Complexes I-IV B. High energy electrons are passed from NADH or FADH 2 to each complex in order and finally to O 2 to form H 2 O C. As e- are passed on, the complex proteins actively pump ions into the intermembrane space.. Chemiosmosis 1

2 The Electron Transport Chain Very little energy has been produced during glycolysis and the Krebs Cycle. Most of the energy locked in the original glucose molecule will be released by an electron transport chain in a process known as oxidative phosphorylation. The electron transport chain is a network of electron-carrying proteins located in the inner membrane of the mitochondrion. These proteins transfer electrons from one to another, down the chain, much in the way a bucket brigade passes buckets of water. The electrons will eventually be added, along with protons, to oxygen, which is the final electron acceptor and produces water. The ATP is produced by a proton motive force. This force is a store of potential energy created by a gradient formed when hydrogens (protons) are moved across the inner membrane. The electron transport chain merely produces a gradient through which ATP can be made (this is known as chemiosmosis). Electron Transport Chain (or: Respiratory Chain) series of electron carrier proteins which transfer electrons from NADH & FADH 2 to oxygen...forming water end result is the production of ATP in a process known as... Oxidative Phosphorylation Text pg 125 & 127 Four molecule types arranged into 4 protein complexes: Respiratory complex I- accepts electrons from NADH, passes to: Complex II- accepts electrons from I (and from FADH2) and then passes to: Complex III- accepts electrons from II, passes to: Complex IV- accepts electrons from III and transfers them to oxygen 2

3 MATRIX ETC NADH FADH 2 H 2 O I Q II III IV O 2 Intermembrane Space Chemiosmosis Process ETC complexes pass electrons along and pumps ions into intermembrane space. ion concentration thus becomes high in intermembrane space and low in matrix. can only get back into matrix by going through protein channels (the F1particles) Chemiosmotic theory Proposed by Mitchell 1961 and proven by about Nobel Prize ATP synthesis is coupled indirectly to electron transport via the Proton Motive Force (PMF). In the chemiosmotic model, each of the membrane protein sites is responsible for extruding protons, so creating a proton concentration gradient across the membrane. The ATP synthase uses this PMF gradient to energize the synthesis of ATP. 3

4 ATP synthase F1 Particles These are the lollipops referred to earlier the ATP synthase proteins! Cristae ADP ATP F1 Matrix II I III IV Cristae F1 Particles = ATP Synthase Protein particles which embed in inner mitochondrial membrane and face matrix Actual site of ATP production in mitochondria F 1 F 0 4

5 The ATP synthase In eubacteria, chloroplasts and mitochondria, the synthesis of ATP is carried out by a molecular machine known as ATP synthase. It sits in the inner membranes where it uses the transmembrane proton motive force (pmf) generated by the oxidation of nutrients. The enzyme has two major structural parts known as F1 and Fo. In the enzyme from mitochondria, the F1 catalytic domain is a globular assembly of five different proteins a, b, g, d and e. ATP Synthase: How it works ATP synthase molecules located within mitochondria stick out of the inner membrane in mushroom-like clusters. The ATP synthase molecule has two parts. Recently, it was discovered that one part, the "mushroom stem," apparently rotates within the "mushroom cap. A Nobel prize was awarded to the researcher who suggested that forming ATP was tied to this rotation. As the "stem" rotates, it creates a powerful internal shifting in each of the coiled sections within the cap. This shifting provides the energy to cause chemical changes. At one site, the "ingredients" for ATP come together. At another site, they assemble as ATP, and at the third site, the rotation readies the fully formed ATP to pop off the synthase molecule, for use throughout the cell. Rotation of the Stem The central stem rotates at about times per second. The rotation is fuelled by the pmf. The rotation of the central stem in the bacterial enzyme has been observed directly by microscopy 5

6 ATP Yield from ETC Within Mitochondria: Each NADH in ETC yields 3 ATPs Each FADH 2 yields 2 ATPs From Cytoplasm: Each NADH in ETC yields 2 ATPs MATRIX ETC NADH FADH 2 H 2 O I Q II III IV O 2 Intermembrane Space H + Gradient produces force for ATP Synthesis ADP ATP F1 II I III IV ATP is made indirectly using the PMF as a source of energy. Each pair of protons yields one ATP. 6

7 Review: Cellular Respiration Total ATP Theoretical Yield Finally: The Total ATP Sum from 1 Glucose 36 ATPs!!! vs. 2 ATPs for glycolysis Do the efficiency math... ~50% 7

8 Next: Photosynthesis Respiration vs. Photosynthesis Photosynthesis and respiration as complementary processes in the living world. Photosynthesis uses the energy of sunlight to produce sugars and other organic molecules. These molecules in turn serve as food. Respiration is a process that uses O2 and forms CO2 from the same carbon atoms that had been taken up as CO2 and converted into sugars by photosynthesis. In respiration, organis ms obtain the energy that they need to survive. Photosynthesis preceded respiration on the earth for probably billions of years before enough O2 was released to create an atmosphere rich in oxygen. (The earth's atmosphere presently contains 20% O2.) 8