Ch. 11

Question 1

What is chemiosmosis?

Answer 1

• Proton gradient is established across the mitochondrial inner membrane
• H+ travels from high to low
• Energy from H+ gradient is used to generate ATP

Question 2

What does oxidative phosphorylation do for the cell?

Answer 2

• Generates ATP from the oxidation of metabolic fuels
• Accounts for 28 of 32 ATP obtained from glucose breakdown

Question 3

What is the electron transport chain?

Answer 3

• Series of redox reactions that occur in a set of protein complexes embedded in the inner mitochondrial membranes

Start:
- NADH is oxidized into NAD+
- Citrate cycle is source of NADH

End:
- O2 reduced to H2O

Question 4

What are the complexes in oxidative phosphorylation and what do they do?

Answer 4

Question 5

What is the net reaction of oxidative phosphorylation?

Answer 5

2 NADH + 2 H⁺ + 5 ADP + 5 P_i + O₂ –> 2 NAD⁺ + 5 ATP + 2 H₂O

Question 6

What are the key enzymes of oxidative phosphorylation?

Answer 6

• NADH–ubiquinone oxidoreductase (Complex I: oxidation of NADH and the reduction of FMN –> translocation of 4 H⁺ across the inner mitochondrial membrane)
• Ubiquinone–cytochrome c oxidoreductase (Complex III: oxidation of ubiquinol)
• Cytochrome c oxidase (Complex IV: accepts electrons from cytochrome c and donates them to O₂ to form water

Question 7

Where does NADH oxidation occur?

Answer 7

Complex I
- Takes place on matrix side of inner mitochondrial matrix
- Two electrons initiate multiple Redox reactions
- O2 ends up being reduced to water
- Two electrons enter ET system through FADH2 oxidation
- Electron flow facilitated by sequential arrangement of electron carriers

Question 8

How do electrons influence translocation of protons in the transport system?

Answer 8

• 2e- from NADH = 10 H+ translocated
• 2e- from FADH2 = 6H+ translocated
• Two new electron carriers
  
  • Q-QH2
  • Cytochrome C (ox-red)

Question 9

What happens in Complex I?

Answer 9

• Protein: NADH-Ubiquinone oxido-reductase
• NADH is oxidized while Coenzyme Q is reduced
• Largest complex
• Covalently bound to Flavin (FMN)
• FMN accepts 2e- from NADH

Question 10

What is the function of Fe-S clusters?

Answer 10

Complex I
- Exchange 1 e-
Fe3+ ⇋ Fe2+

Question 11

What is coenzyme Q and what does it do?

Answer 11

• Coenzyme Q acts as a mobile electron carrier and transports electrons from Complex I to Complex III
• Ubiquinone (Q) is reduced to ubiquinol (QH2)
• 4 H+ are translocated from the matrix side of the membrane to the intermembrane space

Question 12

How do electrons bind to form QH2?

Answer 12

1. NADH transfers 2e- to FMN
2. 2e- Transferred from carrier to carrier
3. 2e- +2H+ bind to Q making QH2

Question 13

What does Complex II do?

Answer 13

• Protein: succinate dehydrogenase
  
  • citrate cycle: catalyze oxidation reduction of succinate to fumarate
• Coupled redox reaction using FAD
• Reduces coenzyme Q to QH2

FADH2 + Q –> FAD+ + QH2
(no hydrogen translocation)

Question 14

What does Complex III do?

Answer 14

• Protein: Ubiquinone-cytochrome C oxidoreductase
• Reduces cytochrome c and translocates 4 H+
• Docking site for QH2 and Cytochrome c
• Contains binding sites for ubiquinone (Qp and Qn)
• Transfers e- through an iron sulfur cluster center
• Contains 11 different protein subunits

Question 15

What is the Q cycle?

Answer 15

• Complex III
• Translocates 4 H⁺
• Passes 1 electron per Cyt C (there are 2 Cyt C so 2 electrons total)

Question 16

What does Complex IV do?

Answer 16

• Protein: Cytochrome c Oxidase
• Accepts electrons one at a time
  -cytochrome C is oxidized while O2 is reduced
  -2 copper center
• Cu2+ <–> Cu+
• 2H+ are translocated across the membrane
• Forms H2O

2 cytochrome c (red) + 4 HN+ + ½ O2 → 2 cytochrome c (ox) + 2HP+ + H2O

Question 17

How many protons are required to synthesize 7 ATP?

Answer 17

10 protons

Question 18

1 NADH = ? ATP

Answer 18

2.5 ATP

Question 19

What is the balanced equation of the ETS?

Answer 19

2 NADH + 2 H+ + 5 ADP + 5 Pi + O2 → 2 NAD+ + 5 ATP + 2 H2O

Question 20

How many large structural components are there in ATP Synthase complex and what do they do?

Answer 20

F1- encodes catalytic activity
Fo - acts as protein channel crossing the inner mitochondrial membrane

Question 21

What type of conditions favor ATP hydrolysis?

Answer 21

High ATP/ADP ratio

Question 22

How is ADP + Pi imported into mitochondrial matrix?

Answer 22

Translocase proteins located in inner mitochondrial matrix

Question 23

What does ATP/ADP translocase do?

Answer 23

• Exports 1 ATP for every ADP imported
• Antiport
• Switch between cytosolic and matrix states

Question 24

What does phosphate translocase do?

Answer 24

• Translocates 1 Pi and H+ into the matrix
• Can be symporter or antiporter
• Resembles a channel

Question 25

What is the malate-aspartate shuttle?

Answer 25

- Primary shuttle in liver, kidney, and heart - All reactions are reversible - NADH will not be imported into the matrix - Electrons find another way into matrix - Supply of NAD+ is maintained

Question 26

Outline the four steps in the malate aspartate shuttle.

Answer 26

1. Oxaloacetate + NADH + H+ is reduced by cytosolic malate dehydrogenase to form Malate and NAD+ 2. Malate is transported into mitochondrial matrix and oxidized by mitochondrial malate dehydrogenase with NAD+ to form oxaloacetate and NADH + H+ 3. Transamination of Oxaloacetate by mitochondrial aspartate aminotransferase and glutamate to formAlpha ketoglutarate and aspartate which is shuttled across the membrane 4. Transamination of aspartate in the cytosol by cytosolic aspartate aminotransferase and Alpha ketoglutarate to form oxaloacetate and glutamate

Question 27

What is glycerol-3-phosphate shuttle?

Answer 27

- In skeletal muscle and brain - **Delivers electrons from NADH to the mitochondrial matrix using FAD** - Electrons from NADH2 go via FADH2 into electron transport system through coenzyme Q - Consists of two isozymes of glycerol-3-phosphate dehydrogenase

Question 28

Outline the three steps of the glycerol-3-phosphate shuttle.

Answer 28

1. Glycolytic intermediate (dihydroxyacetone phosphate) in cytosol is reduced forming glyerol-3-phosphate which diffuses across outer mitochondrial membrane through porin channels 2. Glycerol-3-phosphate is reoxidized in intermembrane space forming dihydroxyacetone phosphate, 2e- are transfered to FAD in mitochondrial glycerol-3-phosphate dehydrogenase (regenerates dihydroxyacetone phosphate is recycled via porin channels) 3. 2e- passed to Q which transfers them one at a time to complex III via Q cycle

Question 29

How much ATP is generated by one glucose in liver cells via malate-aspartate shuttle? How about glycerol-3-phosphate shuttle in muscle cells?

Answer 29

32 in liver cells 30 in muscle cells

Question 30

What do ADP/ATP and NADH/NAD+ ratios regulate?

Answer 30

ADP/ATP: Control aerobic respiration NADH/NAD+: in mitochondrial matrix control steps in the citrate cycle

Question 31

What happens to O2 consumption and ATP synthesis when inhibitors of ETS are added?

Answer 31

O2 consumption and ATP production shut down

Question 32

Where does cyanide bind in ETS and what happens

Answer 32

Binds to complex IV and causes no electron transfer to O2 which stops ATP synthesis

Question 33

What does oligomycin do?

Answer 33

Blocks H+ flow in ATP synthesis

Question 34

What does 2,4-dinitrophenol do?

Answer 34

Transports H+ across the membrane uncoupling the ETS and ATP synthesis