L14. Energy Generation in Mitochondria Flashcards
explain the electrochemical proton gradient and how it generates ATP - stage 1
- high energy e- are transferred along the electron transport chain
- the electron transfers then release energy
- this energy is then used to pump H+ across the membrane
explain the electrochemical proton gradient and how it generates ATP - stage 2
- H+ flows back into the membrane through the ATP synthase
- this generates ATP from ADP and Pi
explain how the mitochondria can undergo binary fission
bc the mitochondria evolved from a prokaryote, it undergoes a fission process similar to bacterial division
how may a mitochondria be localized
cells can have mitochondria fixed in one location where there is high ATP use
explain how mitochondria can form long tubular networks
- mitochondria can fuse together and be diffusely distributed through the cytoplasm
- these networks are dynamic
explain the structure of the mitochondria
- matrix
- inner membrane
- outer membrane
- intermembrane space
mitochondria structure - matrix
contains a highly concentrated mixture of hundreds of enzymes
mitochondria structure - inner membrane
- contains proteins that carry out oxidative phosphorylation
- folded into cristae
mitochondria structure - outer membrane
- contains large channel-forming proteins called prions
- makes the membrane more permeable than the inner membrane
mitochondria structure - intermembrane space
contains enzymes that use ATP passing out of the matrix to phosphorylate other nucleotides
chloroplasts vs mitochondria - what is similar
- inner membrane
- outer membrane (that is more permeable than inner one)
- DNA
- ribosomes
chloroplasts vs mitochondria - what is different
- chloroplasts: stroma and thylakoid membrane
- mitochondria: matrix
how does the mitochondria catalyze energy conversion
- via oxidative phosphorylation
- energy released by oxidizing NADH to NAD+ drives phosphorylation of ADP to ATP
explain how acetyl CoA is produced
- fatty acids and sugars enter the intermembrane space through porins in the outer membrane
- they are then transferred across the inner membrane into the matrix
- here they are converted into acetyl CoA
explain the role of NADH
- it saves energy derived from oxidation within the citric acid cycle
- it then donates electron to the electron transport chain and turns into NAD+
how is electron transfer coupled
- electrons are transferred between the activated carrier to O2
- this step-wise movement of high-energy electrons releases energy
- that energy is then used to pump H+ across the membrane
what are the three respiratory enzyme complexes that transfer electrons
- NADH dehydrogenase complex
- cytochrome c reductase
- cytochrome c oxidase complex
explain the respiratory enzyme complexes
- they contain metal ions and other groups to facilitate electron transfer
- electrons are passed from electron carriers with weaker to stronger affinity electron carriers
- this continues until they combine with a molecule of O2 to form water
respiratory enzyme complex - NADH dehydrogenase complex
it accepts e- from NADH in the form of H+ and 2e-
how can electron transfers move H+
e- transfer can move entire hydrogen atoms bc protons are readily accepts from or donated to water
electron transfer and movement of H+ - molecule is reduced
- acquired e- brings a negative charge that is neutralized by the addition of a H+ from water
- net effect is to transfer an entire hydrogen atom
electron transfer and movement of H+ - molecule is oxidized
- molecule loses an e- from one of its hydrogen atoms
- e- is transferred to an electron carrier and H+ is passed to water
explain why the orientation of the membrane-embedded e- carrier is important
- the orientation allows e- transfer to drive H+ pumping
- it does this through oxidation-reduction reactions
explain how the orientation of the membrane-embedded e- carrier drives H+ pumping
- protein B picks up a H+ from one side as an e- is passed from A
- B releases the H+ on the other side of the membrane as it donates an e- to C
what are quinones
- they carry e- within the lipid bilayer
- within the electron transport chain it is called ubiquinone
- it picks up 1 H+ from the aqueous environment for each e-
- it can carry 2e- as part of the H atoms
- it also has a long hydrophobic tail that is embedded within the inner membrane
explain redox potential along the mitochondrial e- transport chain
- it increases
- from least to most redox potential: NAD dehydrogenase complex -> ubiquinone -> cytochrome c reductase complex -> cytochrome c -> cytochrome c oxidase complex
explain iron-sulfur centers
- they have a low affinity for e- and iron heme groups serve as an e- acceptor
- this makes them prominent e- carriers in the early parts of the chain
- later in the chain, the iron in the heme groups, which are bound to cytochrome centers, are used as e- carriers
respiratory enzyme complex - cytochrome c oxidase
- it catalyzes the reduction of O2
- it is the last e- carrier and has the highest redox potential
- it removes e- from cytochrome c (oxidizing it) and hands them off to O2
- reaction: 4e- + 4H+ + O2 -> 2H2O (4 additional H+ pumped out)
respiratory enzyme complex: cytochrome c oxidase - what happens after handing e- to O2
- it has a special oxygen binding site that contains a heme group and a copper atom that facilitates the final step (conversion to H2O)
- once O2 picks up an e-, it forms the superoxide radical O2-
- the binding site holds the O2- tightly until 4e- are received and converts O2- to H2O
respiratory enzyme complex: cytochrome c oxidase - why must O2- be held
it is dangerously reactive and can damage DNA
explain the ATP synthase motor - forward process
- ATP synthesis
- it is driven by the H+ gradient
- the top part (F0 rotor) spins within the stationary head of the bottom part (F1 ATPase)
explain the ATP synthase motor - backward process
- ATP hydrolysis
- facultative anaerobic bacteria can reverse the flow of H+ when they run out of the cell
- glycolysis-generated ATP is used to pump H+ out of the cell
- creates a H+ gradient for moving other compounds into the cell
explain the electrochemical H+ gradient forces
- the force due to the membrane potential (delta V) is large
- the force due to the [H+] gradient (pH gradient / delta pH) is smaller
- these forces combine to generate the proton-motive force which pulls H+ back into the matrix
how does the electrochemical H+ gradient facilitate coupled transport
- the pH gradient drives phosphate import and pyruvate import (via 2 different transporters)
- the voltage gradient drives ADP-ATP exchange
