Energy Conversion

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Author:
mnvang321
ID:
302027
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Energy Conversion
Updated:
2015-05-03 22:34:37
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cellbio
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cellbio
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Chapter 14
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  1. 2 forms of energy are needed by cells 
    -Chemical bond energy = ATP
    -Reducing equivalents = NADH+H / FADH2

    Principally 3 ways to derive energy (ATP)
    -Substrate level phosphorylation
    -Oxidative phosphorylation
    -Photo-phosphorylation 


    Reducing equivalents are derived from 
    -Chemical runs (all aerobes)
    -Photosynthesis (makes NADPH)
    -Reverse e- flows (uses ATP) *

    Location of energy conversion 
    -Prokaryotes--> plasma membrane 
    -Heterotrophic euk--> mitochondria
    -Autotrophic euk--> mitochondria / plastids
    Energy Conversion
  2. -Generate ATP 

    - 4rm membrane transport processes (-osmotic)
    Chemiosmotic coupling
  3. Membrane proteins 

    Small molecules 

    Used to harness 'electric current' to pump H+/Na+


    Movement of e-'s to ETC is mediated by carriers
             - NAD + 2e- <->NADH
             - NADP + 2e- <-> NADPH
    The Electron Transport Chain (ETC)
  4. -Without euks would only be able to do substrate level phosphorylation (2 ATP / glucose) - (30 with)

    -TCA cycle rxns --> NADH

    NADH -> inner mitochondrial membrane -> e- transport 

    - 0.5-1 um

    -move around cell

    -plasticity in shape 

    -can fuse with other mitochondria / split 

    -associated with cytoskeleton (microtubules)

    -short lifetime
    Mitochondria
  5. Often localized where they're needed 

    -in btwn myofibrils (muscle tissue)

    -around flagella (motility)

    -minimized ATP diffusion distance
    Mitochondria
  6. 2 specialized membranes
    -diff functions 
    -diff protein content 
    -crates diff spaces : matrix/inter-membrane space 
    *most mitochondrial proteins are nuclear encodent

    Outer membrane 
    -many porins 
    -resembles 5000 Da sieve 
    -porins // B-barrels 

    Inter-membrane space 
    -chemically equivalent to cytosol 
    -sieving or OM creates unique protein complement

    Inner membrane
    -contains 'cardiolipin' -- lipid
    -transport proteins for metabolized small molecules 
    -respiratory chain
    -H+ gradient and ATP synthesis 

    Cristae 
    -Folding of inner membrane 
    -increases surface area => greater ATP generation capacity
    Mitochondria
  7. -Thought to enhance ion permeability barrier 
             ex: derease permeability 

    purpose: impermeable to protons
    Cardiolipin
  8. 2 components 

    ΔV
         -acts on any cation
         -160-170 mV

    ΔpH
         -selective force for H+ ions 
         -0.3-0.5 pH units (60mV/pH)
    The electrochemical proton gradient
  9. -500kDA
    -100 ATP synthesized/ sec
    -3 ATP per revolution
    -3 protons trans-located / ATP
    -F1
          -6 subunits 
          -binds ADP + Pi -> ATP
    -F0 
          -14 subunits 
          -H+ carrier 
          -Spins F1
    The F0F1 ATPase
  10. - Cost energy
    Proton gradient drives transport
  11. Aerobically 
    - 2.5 ATP per NADH (after subtracting transport)
    -1.5 ATP per FADH2
    - => 1 glucose => 30 ATP

    Anaerobically 
    -euks can only do substrate level phosphorylation
          ~NADH is regenerated via fermentation => ethanol
          ~2 ATP/ Glucose 

    -prokaryotes can use other e- acceptors 
          ~less energy than O2
          ~yield depends of acceptor
    Proton motive force produces most of cellular ATP
  12. Free energy of ATP hydrolysis depends on 
         -ATP
         -ADP
         -Pi

    A negative free energy denotes a favorable rxn

    if delta G positive rxn can run in reverse

    If ATP synthesis runs in reverse depends on 
    -Delta G of ATP synthesis 
    -Chemiosmotic gradient
    ATP
  13. -hydrogen delay 

    -on -NH2 groups of AA side chains
    How to move a proton thru a protein
  14. -EoRED - EoOx < 0 
       => ΔF <0°
       => Favorable 

    released energy used by ETC to pump 

    NADH <-> NAD  -320 mV 
    Ferridoxin ~ -420 mV
    The Electron Tower
  15. Cytochromes
    -All 3 domains of life 
    -designations as a,b, and c depends on absorption spectra; not functionally imp.
    -protons bound to heme-group
         -Porphyrin ring 
         -Bound to Fe
         -Fe+3 <-> Fe+2 allows accepting e-

    Iron sulfur proteins 
    -iron sulfur center
    -sulfur used to covalently bond Fe 
    -accept one e- at a time 
    -more ISP than cytochromes in ETC

    BOTH functional groups bound to cysteines
    Protein Electron Carrier
  16. - adds (-) charge
    - usually balanced with H+ 
    - e- transport is therefore naturally related to H+ movement 


    In biochemical rxns:
    -if 1 molecule is oxidized, another is always reduced 
    -spontaneous if ΔG<0
    -likelihood of oxidizing another molecule: redox potential 
    Passing an e-
  17. AKA 'coenzyme Q'

    -hydrophobic 
    -dissolved in lipid portion of membrane 
          ~freely mobile 
          ~e- carrier NADH dehydrogenase -> cytochrom b-c1
    -can pick up or donate 1 or 2 e-
    Ubiquinone
  18. made up of 3 main complexes 
    -6 heme containing proteins 
    -7 iron sulfur clusters
    -2 copper containing proteins 
        ~total of > 60 proteins involved
    ETC
  19. 3 large enzyme complex embedded in inner membrane 


    NADH dehydrogenase complex (AKA complex I)

    -largest of the respiratory enzyme complexes(REC)

    -has more than 40 polypeptide chains.

    -accepts e-'s from NADH and passes them thru a flavin and at least 7 iron-sulfur centers to unbiquinone. => then transfers its e-'s to 2nd REC, cytochrome b-c1 complex.


    Cytochrome b-c1 complex
    -11 diff poypeptide chains

    -functions as a dimer 

    -each monomer contains 3 hemes bound to cytochromes and an iron-sulfur protein 

    -accepts e-'s from ubiquinone =>passes them to cytochrome c, => which carries its e-'s to cytochrome oxidase complex


    Cytochrome Oxidase Complex
    -functions as dimer also 

    -contains 13 diff. polypeptide chains, including 2 cytochromes and 2 copper atoms 

    -complex accepts 1 e- at a time 4rm cytochrome and passes them 4 at a time to oxygen 

    -bimetallic center holds superoxide radical (O2-)

    -cyanide prevents e- transport 



    -e-'s carriers are insulted so e-'s are donated in desired seq 

    -ubiquinone and cytochrome c diffuse freely carrying e-'s btwn these 3 complexes 
    *do not want to lose energy (hungry for energy)
    Respiratory Chain
  20. Spectroscopy 
    -characteristic absorptions spectra for each complex
    -spectra change: OX vs RED 

    color=oxidized
    Determining path of e-'s in the ETC
  21. -Weak hydrophobic agents

    -E-'s move normally 

    -Protons are pumped normally 

    -H+ gradient is decoupled 


    -2,4-dinitrophenol
            -freely diffusible
            -can accept proton and carry it 4rm one face to another


    -Occurs naturally in brown adipose tissue
            -heat generation
            -"uncoupling proteins"
    Uncoupling agents
  22. -capture light energy 

    -synthesize ATP

    -fix carbon

    -photosynthetic rxn center

    -ATPase

    -calvin cycle
    Chloroplasts
  23. Mitochondria
    -mainly due to H+ gradient 

    Thylakoid 
    -mainly due to pH
    Voltage
  24. Key enzymes 
    -phosphoribulokinase 
    -ribulose 1,5 bisphosphate carboxylase/oxygenase 
           ~up to 50% of chloroplast protein
           ~most abundant protein on earth
    The Calvin Cycle
  25. -Carbon concentrating mechanism

    -Nitrogen fixation

    -Syntrophic interactions
    Cell can work together in same pathway
  26. -difficult to test 

    -early earth 
           ~no o2 
           ~geochemically produced org. molecules 

    => first rxns likely similar 

    -fermentation: a metabolic process whereby e-'s released 4rm nutrients are ultimately transferred to molecules obtained 4rm breakdown of those same nutrients. Typically organic acids and alcohols.
             ~formate,acetate,propionate,butyrate
             ~succinate
             ~methanol,ethanol,propanol,butanol

    -Disproportional: 1 substrate is both the e- donor as well as the e- acceptor, producing 2 end products with distinct oxidation states, one higher, and one lower.
             ~ S° -> H3SO2 + H2S
    ETC evolve

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