L14. Energy Generation in Mitochondria

Question 1

explain the electrochemical proton gradient and how it generates ATP - stage 1

Answer 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

Question 2

explain the electrochemical proton gradient and how it generates ATP - stage 2

Answer 2

• H+ flows back into the membrane through the ATP synthase
• this generates ATP from ADP and Pi

Question 3

explain how the mitochondria can undergo binary fission

Answer 3

bc the mitochondria evolved from a prokaryote, it undergoes a fission process similar to bacterial division

Question 4

how may a mitochondria be localized

Answer 4

cells can have mitochondria fixed in one location where there is high ATP use

Question 5

explain how mitochondria can form long tubular networks

Answer 5

• mitochondria can fuse together and be diffusely distributed through the cytoplasm
• these networks are dynamic

Question 6

explain the structure of the mitochondria

Answer 6

• matrix
• inner membrane
• outer membrane
• intermembrane space

Question 7

mitochondria structure - matrix

Answer 7

contains a highly concentrated mixture of hundreds of enzymes

Question 8

mitochondria structure - inner membrane

Answer 8

• contains proteins that carry out oxidative phosphorylation
• folded into cristae

Question 9

mitochondria structure - outer membrane

Answer 9

• contains large channel-forming proteins called prions
• makes the membrane more permeable than the inner membrane

Question 10

mitochondria structure - intermembrane space

Answer 10

contains enzymes that use ATP passing out of the matrix to phosphorylate other nucleotides

Question 11

chloroplasts vs mitochondria - what is similar

Answer 11

• inner membrane
• outer membrane (that is more permeable than inner one)
• DNA
• ribosomes

Question 12

chloroplasts vs mitochondria - what is different

Answer 12

• chloroplasts: stroma and thylakoid membrane
• mitochondria: matrix

Question 13

how does the mitochondria catalyze energy conversion

Answer 13

• via oxidative phosphorylation
• energy released by oxidizing NADH to NAD+ drives phosphorylation of ADP to ATP

Question 14

explain how acetyl CoA is produced

Answer 14

• 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

Question 15

explain the role of NADH

Answer 15

• it saves energy derived from oxidation within the citric acid cycle
• it then donates electron to the electron transport chain and turns into NAD+

Question 16

how is electron transfer coupled

Answer 16

• 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

Question 17

what are the three respiratory enzyme complexes that transfer electrons

Answer 17

• NADH dehydrogenase complex
• cytochrome c reductase
• cytochrome c oxidase complex

Question 18

explain the respiratory enzyme complexes

Answer 18

• 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

Question 19

respiratory enzyme complex - NADH dehydrogenase complex

Answer 19

it accepts e- from NADH in the form of H+ and 2e-

Question 20

how can electron transfers move H+

Answer 20

e- transfer can move entire hydrogen atoms bc protons are readily accepts from or donated to water

Question 21

electron transfer and movement of H+ - molecule is reduced

Answer 21

• 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

Question 22

electron transfer and movement of H+ - molecule is oxidized

Answer 22

• molecule loses an e- from one of its hydrogen atoms
• e- is transferred to an electron carrier and H+ is passed to water

Question 23

explain why the orientation of the membrane-embedded e- carrier is important

Answer 23

• the orientation allows e- transfer to drive H+ pumping
• it does this through oxidation-reduction reactions

Question 24

explain how the orientation of the membrane-embedded e- carrier drives H+ pumping

Answer 24

• 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

Question 25

what are quinones

Answer 25

• 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

Question 26

explain redox potential along the mitochondrial e- transport chain

Answer 26

• it increases
• from least to most redox potential: NAD dehydrogenase complex -> ubiquinone -> cytochrome c reductase complex -> cytochrome c -> cytochrome c oxidase complex

Question 27

explain iron-sulfur centers

Answer 27

• 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

Question 28

respiratory enzyme complex - cytochrome c oxidase

Answer 28

• 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)

Question 29

respiratory enzyme complex: cytochrome c oxidase - what happens after handing e- to O2

Answer 29

• 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

Question 30

respiratory enzyme complex: cytochrome c oxidase - why must O2- be held

Answer 30

it is dangerously reactive and can damage DNA

Question 31

explain the ATP synthase motor - forward process

Answer 31

• 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)

Question 32

explain the ATP synthase motor - backward process

Answer 32

• 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

Question 33

explain the electrochemical H+ gradient forces

Answer 33

• 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

Question 34

how does the electrochemical H+ gradient facilitate coupled transport

Answer 34

• the pH gradient drives phosphate import and pyruvate import (via 2 different transporters)
• the voltage gradient drives ADP-ATP exchange