week 3 citric acid cycle & terminal respiration (revised)

Question 1

where does the citric acid cycle occur

Answer 1

• mitochondrial matrix

Question 2

what is the point in the citric acid cycle

Answer 2

• removes electron and passes them on to form NADH and FADH2

- these then pass electrons onto the electron transport chain which creatives a force which drives ATP synthase

Question 3

how is acetyl coA formed

Answer 3

• pyruvate > acetyl coA , via pyruvate dehydrogenase
• series of reactions involving decarboxylation of pyruvate, then oxidation, followed by transfer of coA complex
• decarboxylation step releases two electrons which can pass to oxygen to form ATP through NADH intermediates

Question 4

what does acetyl coA do

Answer 4

allows different intermediates into the citric acid cycle

Question 5

what is the stucture of pyruvate dehydrogenase

Answer 5

• made up of three subunits called E1, E2 E3

- each subunit catalyses a different part of the reaction to convert pyruvate to acetyl coA

Question 6

what does subunit E1 of pyruvate dehydrogenase do

Answer 6

• catalyses the first decarboxylation of pyruvate

Question 7

what does subunit E2 of pyruvate dehydrogenase do

Answer 7

• transfers the acetyl group to coA

Question 8

what does subunit E3 of pyruvate dehydrogenase do

Answer 8

• recycles the lipoyllysine through the reduction of FAD, which is recycled by passing electrons to NAD

Question 9

what happens at each turn of the citric acid cycle

Answer 9

• at each turn 2 carbons (acetyl coA) enter
• 2 different carbons exit the cycle in the form of 2x CO2
• 3 NADH and 1 FADH2 also leave

Question 10

how is entry into citric acid cycle controlled

Answer 10

pyruvate dehydrogenase is regulated

• inhibited by ATP if the cell has enough energy
• activated by ADP + Pi if the cell needs energy

Question 11

what are the two points of control in the citric acid cycle

Answer 11

1. iso citrate > alpha-ketoglutarate, via isocitrate dehydrogenase
   - inhibited by ATP and NADH
   - activated by ADP
2. alpha-ketoglutarate > succinyl coA, via alpha-ketoglutarate dehydrogenase
   - inhibited by ATP, NADH and succinyl coA

Question 12

what does inhibition of isocitrate dehydrogenase in citric acid cycle cause

Answer 12

• citrate build up which shuttles citrate into cytoplasm causing phosphofructokinase to stop glycolysis

Question 13

what does inhibition of alpha-ketoglutarate dehydrogenase in the citric acid cycle cause

Answer 13

• causes alpha-ketoglutarate build up which switches its use to production of amino acids

Question 14

what do they mean by saying that the citric acid cycle is amphibolic

Answer 14

• it is anabolic and catabolic

Question 15

where does terminal respiration (electron transport chain) occur

Answer 15

• on the inner mitochondrial membrane

Question 16

what electron carrying molecules do you get from glycolysis

Answer 16

• NADH + H+

- ATP

Question 17

what electron carrying molecules do you get from pyruvate > acetyl coA reaction

Answer 17

• NADH + H+

Question 18

what electron carrying molecules do you get from each turn of citric acid cycle

Answer 18

• 3 NADH + H+
• 1 FADH2
• 1 GTP

Question 19

what electron carrying molecules do you get from beta oxidation of fatty acids

Answer 19

• 1 NADH + H+

- 1 FADH2

Question 20

what is the job of the glycerol phosphate shuffle

Answer 20

• NADH can’t get through outer membrane to electron transport chain so FADH2 passes the electrons on for it, this is the glycerol phosphate shuffle
• majority of NADH and FADH2 is formed in the mitochondrial matrix, it has to be there to be oxidised, but some of NADH is formed in the cytoplasm so FADH2 transports its electrons for it since it can’t cross

Question 21

what are the steps in the glycerol phosphate shuffle

Answer 21

• NADH + H+ > NAD+ as it loses electrons
• dihydroxy acetone phosphate becomes glycerol 3 phosphate as it holds the electrons from NADH + H+
• glycerol 3 phosphate passes the electrons to FAD which becomes FADH2 at the outer mito. membrane
• FADH2 passes electrons to electrons transport chain on the inner mitochondrial membrane

Question 22

what is the downside to the glycerol phosphate shuffle

Answer 22

• oxidation of FADH2 in electron transport chain generates, per mol, less ATP than NADH
• this energetic ‘price’ is paid for using cytosolic reduced co-substrates in terminal respiration

Question 23

what is the order of the complexes in the electron transport chain

Answer 23

complex 1 = NADH-Q oxidoreductase
complex 2 = succinate-Q reductase
- then ubiquinone/Q pool (but this isn’t a complex, becomes ubiquinol once it has electrons passed to it)
complex 3 = Q cytochrome c oxidoreductase
complex 4 = cytochrome c oxidase

Question 24

what happens at complex 1 (NADH-Q oxidoreductase) of the electron transport chain

Answer 24

• oxidises NADH
• passes the electrons to ubiquinone which becomes ubiquinol (QH2)
• utilises Fe-S centres and FVM
• pumps H+ into intermembrane space

Question 25

what happens at complex 2 (succinate-Q reductase) of the electron transport chain

Answer 25

• oxidises FADH2
• passes electrons to ubiquinone becoming ubiquinol (QH2)
• utilises Fe-S centres to channel electrons
• (doesn’t pump H+)

Question 26

what happens at complex 3 (Q-cytochrome c oxidoreductase) of the electron transport chain

Answer 26

• takes electrons from ubiquinol and passes them to cytochrome c
• pumps H+ into the inter membrane space

Question 27

what happens at complex 4 (cytochrome c oxidase) of the electron transport chain

Answer 27

• takes electrons from cytochrome c and passes them to O2 (O2 > H2O)
• electrons channeled through Fe-Cu centre
• pumps H+ into the inter membrane space

Question 28

what is the electron motive force

Answer 28

• the concentration gradient generated by the complexes of the electron transport chain pumping H+ into the intermembrane space
• high [H+] in intermembrane space

Question 29

what drives ATP synthase

Answer 29

• the electron motive force

- (the concentration gradient created by the electron transport chain)

Question 30

what is chemiosmosis

Answer 30

• the electrons pass through the complexes of the electron transport chain and at the same time H+ is pumped into the intermembrane space, this is called chemiosmosis

Question 31

how does ATP synthase work

Answer 31

• H+ flows down its concentration gradient, through ATPase to get back into the matrix
• as this happens the energy stored in the gradient is used to convert ADP + Pi to ATP

Question 32

what is the structure of ATP synthase

Answer 32

2 parts
F0 - membrane bound proton conducting unit (10 subunits)
F1 - protrudes into mitochondrial matrix, acts as catalyst for ATP synthase
- ADP + Pi enters beta subunit of F1
- rotation of F0 cylinder and conformation changes in beta subunits of F1
- conformational changes catalyse ADP > ATP and release ATP

Question 33

what is the stoichiometry of oxidative phosphorylation

Answer 33

• complexes 1,3,4 of electron transport chain move total of 8 H+ from matrix to outside membrane
• ATP synthase produces 1 ATP for every 3 H+ moved back into matrix
• approx. 2.5 and 1.5 mol of ATP are generated per mol of NADH and FADH2 respectively
• overall oxidative phosphorylation produces 32 ATP (30 if using cytosolic NADH)

Question 34

what is coupling and uncoupling of electron transport chain and ATP synthesis

Answer 34

• electron transport chain and ATP synthesis are said to be coupled
• if the inner mitochondrial membrane became permeable to H+ then you would not get the proton gradient, electron transport would still occur and O2>H2O, but no ATP would be made, so process would be uncoupled
• energy released from electrons would be released as heat instead of making ATP

Question 35

what is malignant hyperthermia

Answer 35

• occurs when the electron transport chain and ATP synthesis processes become uncoupled
• caused by leaky mitochondrial membrane
• brown fat in babies