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Aerobic respiration

Aerobic respiration. Mitochondrial structure and function Visible under light microscope Universal in aerobic eukaryotes Have own DNA and ribosomes Number and shape vary widely in different cell types Number: more in cells with higher E requirements

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Aerobic respiration

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  1. Aerobic respiration • Mitochondrial structure and function • Visible under light microscope • Universal in aerobic eukaryotes • Have own DNA and ribosomes • Number and shape vary widely in different cell types • Number: more in cells with higher E requirements • Shape: can undergo fission and fusion to yield typical ‘cylinder’ shape or more complex tubular networks

  2. Aerobic respiration • Mitochondrial structure and function • Membranes • Outer: permeable to many things • Porins, large central pore • Inner: highly impermeable • Channels for pyruvate, ATP, etc

  3. Aerobic respiration • Mitochondrial structure and function • Membranes • Outer: permeable to many things • Porins, large central pore • Inner: highly impermeable • Channels for pyruvate, ATP, etc • Cristae • Complex invaginations of the inner membrane • Functionally distinct • Joined to inner membrane via narrow channels

  4. Aerobic respiration • Mitochondrial structure and function • Intermembrane space • Between inner and outer membranes • Also within the cristae • Acidified ( high [H+] ) by action of the Electron Transport Chain (ETC) • H+ are pumped from matrix into this compartment • ATP synthase lets them back into the matrix

  5. Aerobic respiration • Mitochondrial structure and function • Matrix • Compartment within the inner membrane • Very high protein concentration ~500mg/ml • Contains: • ribosomes and DNA • Enzymes of TCA cycle, enzymes for fatty acid degradation

  6. NADH enters the mitochondria by one of two mechanisms: 1. aspartate-malate shuttle NADH --> NADH 2. glycerol phosphate shuttle NADH --> FADH2 • Pyruvate to TCA

  7. Oxidation-reduction potentials • Reducing agents give up electron share • The lower the affinity for electrons, the stronger the reducing agent • NADH is strong, H2O is weak • Oxidizing agents receive electron share • The higher the affinity for electrons, the stronger the oxidizing agent • O2 is strong, NAD+ is weak • Couples • NAD+ - NADH couple (weak oxidizer, strong reducer) • O2 - H2O couple (strong oxidizer, weak reducer)

  8. NADH is a stronger reducing agent than FADH2 DG = -nFE strong reducing NADH --> H2O G0’= -52kcal/mol 7ATP(max), ~3ATP(real) FADH2 --> H2O G0’= -36kcal/mol 5ATP(max), ~2ATP(real) strong oxidizing

  9. The Tricarboxylic Acid (TCA) cycle (Kreb’s cycle) 2Pyruvate + 8NAD+ + 2FAD + 2GDP + 2Pi --> 6CO2 + 8NADH + 2FADH2 + 2GTP Adding in products of glycolysis, 2NADH + 2ATP Total yield for both: 10NADH + 2FADH2 + 4ATP = 38 ATP How NADH from cytoplasm are counted changes the theoretical yield

  10. Formation of a tricarboxylic acid from pyruvate • In two steps: • A dehydrogenasestep 3C + NAD 2C + CO2 +NADH • Yields Acetyl group bonded to CoenzymeA (CoA) • A synthase step • 2C + 4C(OA) 6C (OA)

  11. The Tricarboxylic Acid (TCA) cycle (Kreb’s cycle) • 2C+4C(OA)6C • 6C+NAD  5C+CO2 • +NADH • 5C  4C+CO2 • +NADH • 4C+GDP  4C+GTP • 4C+FAD  4C+FADH2 • 4C+NAD  4C(OA) • +NADH

  12. Fatty acid catabolism • Enzymes localized to mitochondrial matrix • Fatty acids cross inner membrane and become linked to HS-CoA • Each turn of cycle generates FADH2 + NADH2 + Acetyl-CoA

  13. Amino acid catabolism • Enzymes in mitochondrial matrix • cross inner membrane via specific transporters • Enter TCA at various points

  14. General outline of oxidative phosphorylation

  15. Electron Transport Chain: e- carriers • Electron carriers • Flavoproteins (FMN) • Ubiquinone(Q or UQ) • Cytochromes(b, c1, c, a) • Cu atoms • Fe-S centers • Proton movement driven by complexes I, III, IV coupled to large DE

  16. Electron carriers: Ubiquinone • Lipid soluble • Dissolved within inner mitochondrial membrane • Free radical intermediate • Free radical ‘escape’ from electron transport chain can damage proteins, lipids, RNA, and DNA in a cell UQ Q

  17. Electron Transport Chain • Complex I passes e- from NADH to Q and pumps 4H+ out of matrix • Complex II passes e- from FADH2 to Q • UQ shuttles e- to Complex III

  18. Electron Transport Chain • Complex III passes e- to Cytochrome c and pumps 4H+ out of matrix • Cytochrome c passes e- to Complex IV • Complex IV passes e- to O2 forming H2O and pumps 2H+ out 1 pH unit diff

  19. ATP synthesis: The ATP Synthase enzyme • F1 head/sphere (ATPase) catalyzes ADP + Pi <--> ATP • F0 base embedded in inner membrane (H+ pass through this) • F0 + F1 = ATP synthase • Connected via two additional proteins • Central rod-like gamma subunit • Peripheral complex (abd) holds F1 in a fixed position • Location • Bacteria = plasma mem • Mitochondria = inner mem • Chloroplast = thylakoid ATP matrix Intermembrane space H+

  20. Binding Change mechanism of ATP Synthase • Each F1 active site progresses through three distinct conformations • Open (O) Loose (L)Tight (T) • Conformations differ in affinity for substrates and products • Central gamma () subunit rotates causing conformation changes

  21. Rotational catalysis by ATP synthase • Central gamma () subunit rotation caused by proton (H+) translocation drives the conformation changes 1 pH unit diff

  22. Rotational catalysis by ATP synthase • If true, should be able to run it backwards (ATP --> ADP + Pi) and watch gamma spin like a propeller blade

  23. Rotational catalysis by ATP synthase

  24. Other fxns of electrochemical gradient • E also used for: • Import of ADP + Pi (+H+) and export of ATP • Import of pyruvate (+H+) • Uncoupling sugar oxidation from ATP synthesis • Uncoupling proteins (UCP1-5) • UCP1/thermogenin, shuttles H+ back to matrix (endothermy) • Brown adipose tissue • Present in newborns (lost with age) and hibernating animals • Generates heat • 2,4-dinitrophenol (DNP) • Ionophore that can dissolve in inner membrane and shuttle H+ across • 1930’s stanford diet pill trials: overdose causes a fatal fever

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