MITOCHONDRIA

1. MITOCHONDRIA Speaker: 陳玉怜 Apr. 26, 2006

2. eukaryotic cells • the specialized membranes inside energy-converting organellesare employed for the production of ATP. • The membrane-enclosed organelles are mitochondria, which are present in the cells of virtually all eukaryotic organisms.

3. mitochondrion • mitochondria • occupy a substantial portion of the cytoplasmic volume of eukaryotic cells • the metabolism of sugars is completed: the pyruvate is imported into the mitochondrion and oxidized by O2to CO2 and H2O. (This allows 15 times more ATP to be made than that produced by glycolysis alone).

5. * stiff, elongated cylinders with a diameter of 0.5-1 m. • * are remarkably mobile and plastic organelles, constantly changing their shape and even fusing with one another and then separating again. • * As they move about in the cytoplasm, they often seem to be associated with microtubules. • In others they remain fixed in one position where they provide ATP directly to a site of unusually high ATP consumption — • packed between adjacent myofibrils in a cardiac muscle cell; wrapped rightly around the flagellum in a sperm.

6. Mitochondrial • Plasticity • time-lapse • microcinematography • - rapid changes of shape in a living cell

7. Dynamic mitochondrial reticulum • Form a continuous reticulum underlying the plasma membrane • A balance of fission and fusion determines the arrangement of the mitochondria • Shape change, • the network is constantly remodeled by fission and fusion.

8. Mitochondrial fission and fusion - Involve both outer and inner mitochondrial membrane

9. The relationship between mitochondria and microtubules Mitochondria  microtubules  The mitochondria tend to be aligned along microtubules.

10. Localization of mitochondria near sites of high ATP utilization in cardiac muscle and a sperm tail

11. The mitochondrion: *an outer membrane *an inner membrane *two internal compartments (matrix and intermembrane space)

12. Biochemical fractionation of purified mitochondria into separate components

14. The outer membrane • a transport protein called- porin, which forms large aqueous channels through the lipid bilayer. • This membrane thus resembles a sieve that is permeable to all molecules of 5000 daltons or less, including small proteins. Such molecules can enter the intermembrane space, but most of them cannot pass the impermeable inner membrane.

15. the inner membrane Its lipid bilayer contains a high proportion of the "double" phospholipid cardiolipin, which has four fatty acids rather than two and may help to make the membrane especially impermeable to ions.

16. Inner membrane - contains a variety of transport proteins that make it selectively permeable to those small molecules that are metabolized or required by the many mitochondrial enzymes concentrated in the matrix. - enzymes of the respiratory chain, are essential to the process of oxidative phosphorylation, which generates most of the animal cell's ATP.

17. cristae • * The inner membrane is usually highly convoluted, forming a series ofinfoldingsthat project into the matrix. • increase the area of the inner membrane • * a liver cell: constitutes about one-third of the total cell membrane. • * cardiac muscle cells- many cristae

18. Matrix The matrix enzymes include those that metabolize pyruvate and fatty acids to produce acetyl CoA and those that oxidize acetyl CoA in the citric acid cycle.

22. THE GENETIC SYSTEMS OF MITOCHONDRIA -contain their own genomes, as well as their own biosynthetic machinery for making RNA and organelle proteins. Red: nuclear genome Bright yellow spots: mitochondrial genome Green: mitochondrial matrix space

23. Mitochondria Contain Complete Genetic Systems Most of the proteins in mitochondria are encoded by the nucleus and must be imported from the cytosol.

24. An electron micrograph of an animal mitochondrial DNA molecule caught during the process of DNA replication

25. Why Do Mitochondria Have Their Own Genetic Systems?

26. Mitochondria grow in a coordinated process that requires the contribution of two separate genetic systems —one in the organelle and one in the cell nucleus. Most of the proteins in these organelles are encoded by nuclear DNA, synthesized in the cytosol, and then imported individually into the organelle. Some organelle proteins and RNAs are encoded by the organelle DNA and are synthesized in the organelle itself. The human mitochondrial genome contains about 16,500 nucleotides and encodes 2 ribosomal RNAs, 22 transfer RNAs, and 13 different polypeptide chains.

27. Chemiosmotic coupling * the chemical bond-forming reactions that generate ATP ("chemi") * membrane-transport processes ("osmotic"). * The coupling process occurs in two linked stages, both of which are performed by protein complexes embedded in a membrane

28. Harnessing energy for life

29. Chemiosmotic coupling Electrochemical proton gradient-drive other mem-embedded protein machines Special proteins couple the “downhill” H+ flow to the transport of specific metabolites into and out of the organelles Electrochemical proton gradient- Rapid rotation of the bacterial flagellum

30. electron transport chain = the entire set of proteins in mem+ small molecules in electron transfer

32. High-Energy Electrons Are Generated via the Citric Acid Cycle glucose is converted to pyruvate by glycolysis Mitochondria can use both pyruvate and fatty acids as fuel. Pyruvate- comes from glucose and other sugars Fatty acids-come from fats Both of these fuel molecules are transported across the inner mitochondrial membrane and then converted to the crucial metabolic intermediate acetyl CoA by enzymes located in the mitochondrial matrix. The acetyl groups in acetyl CoA are then oxidized in the matrix via the citric acid cycle.

33. Energy –generating metabolism in mitochondria

34. Pyruvate+HS-CoA+NAD+ →acetyl CoA+CO2+NADH+H+ decarboxylation

35. How electrons are donated by NADH A hydride ion (H- a hydrogen atom and extra electron) NADH: reduced nicotinamide adenine dinucleotide NAD+: nicotinamide adenine dinucleotide

36. The tricarboxylic acid cycle Acetyl CoA+2H2O+FAD+3NAD++GDP+Pi→ 2CO2+FADH2+3NADH+3H++GTP+HS-CoA

37. A Chemiosmotic Process Converts Oxidation Energy into ATP These electrons, carried by NADH and FADH2, are then combined with O2 by means of the respiratory chain embedded in the inner mitochondrial membrane. The large amount of energy released is harnessed by the inner membrane to drive the conversion of ADP + Pi to ATP (oxidative phosphorylation).

38. The major net energy conversion catalyzed by the mitochondrion

39. Electrons Are Transferred from NADH to Oxygen Through Three Large Respiratory Enzyme Complexes H2+1/2 O2→H2O The hydrogen atoms are first separated into protons and electrons. The electrons pass through a series of electron carriers in the inner mitochondrial membrane. When the electrons reach the end of the electron-transport chain are the protons returned permanently, when they are used to neutralize the negative charges created by the final addition of the electrons to the oxygen molecule.

40. The process of electron transport - The hydride ion is removed from NADH (to regenerate NAD+) and is converted into a proton and two electrons (H-H+ + 2e-). - Each of these ions being tightly bound to a protein molecule that alters the electron affinity of the metal ion. Most of the proteins involved are grouped into three large respiratory enzyme complexes.

42. As Electrons Move Along the Respiratory Chain, Energy Stored as an Electrochemical Proton Gradient Across the Inner Membrane • *It generates a pH gradient/across the inner mitochondrial membrane, with the pH higher in the matrix than in the cytosol, where the pH is generally to 7. • *It generates a voltage gradient (membrane potential) across the inner mitochondrial membrane, with the inside negative and the outside positive (as a result of the net outflow of positive ions). the ∆pH and the ∆V- constitute electrochemical proton gradient

44. How the Proton Gradient Drives ATP Synthesis The electrochemical proton gradient across the inner mitochondrial membrane is used to drive ATP synthesis in the critical process of oxidative phosphorylation.

45. Spectroscopic Methods Have Been Used to Identify Many Electron Carriers in the Respiratory Chain @ the cytochromes - identified by their distinctive absorption spectra and designated cytochromes a, b, and c. The cytochromes constitute a family of colored proteins that are related by the presence of a bound heme group, whose iron atom changes from the ferric oxidation state (Fe 3+ ) to the ferrous oxidation state (Fe 2+ ) whenever it accepts an electron. The heme group consists of a porphyrin ring with a tightly bound iron atom held by four nitrogen atoms at the corners.

46. @ Iron-sulfur proteins either two or four iron atoms are bound to an equal number of sulfur atoms and to cysteine side chains, forming an iron-sulfur centeron the protein.

47. @ ubiquinone The simplest of the electron carriers in the respiratory chain—and the only one that is not part of a protein—is a small hydrophobic molecule that is freely mobile in the lipid bilayer A quinone (Q) can pick up or donate either one or two electrons; upon reduction, it picks up a proton from the medium along with each electron it carries.

48. Redox potential changes along the mitochondrial electron-transport chain

50. The Respiratory Chain Includes Three Large Enzyme Complexes Embedded in the Inner Membrane • The NADH dehydrogenase complex (complex I) is the largest of the respiratory enzyme complexes, containing more than 40 polypeptide chains. It accepts electrons from NADH and passes them through a flavin and at least seven iron-sulfur centers to ubiquinone. Ubiquinone then transfers its electrons to a second respiratory enzyme complex, the cytochrome b-c1complex. • The cytochrome b-c1complexcontains at least 11 different polypeptide chains and functions as a dimer. Each monomer contains three hemes bound to cytochromes and an iron-sulfur protein. The complex accepts electrons from ubiquinone and passes them on to cytochrome c, which carries its electron to the cytochrome oxidase complex. • 3.The cytochrome oxidase complexalso functions as a dimer; each monomer contains 13 different polypeptide chains, including two cytochromes and two copper atoms. The complex accepts one electron at a time from cytochrome c and passes them four at a time to oxygen.