Electron Transport Chain: The Final Stage

Question 1

What is remaining of the original glucose molecule after the Kreb’s cycle?

Answer 1

The entire molecule has been oxidized and the six carbons have been turned into CO2 which is released by the cell as waste. All that remains is stored in the form of 4 ATP (2 from glycolysis, 2 from Kreb’s cycle) and 12 recovered coenzymes (10 NADH, 2 FADH2)

Question 2

What happens with the coenzymes from the Kreb’s cycle?

Answer 2

NADH and FADH2 will enter the ETC to get oxidized

Question 3

Describe the ETC

Answer 3

NADH and FADH2 will transfer their H+ atom electrons to a series of compounds/a chain of integral proteins and lastly, along with the protons from the matrix, to O2 to form H2O. Electrons being transferred to these are used to drive their proton pumps (pumps out H+ protons from NADH in the matrix) which forms ATP via chemiosmosis

Question 4

What is the final electron accepter of the ETC and why?

Answer 4

O2 because it is the most electronegative

Question 5

List the electron transfer proteins in order of increasing electronegativity

Answer 5

1. NADH dehydrogenase complex
2. Q (ubiquinone)
3. Cytochrome b-c1 complex
4. Cytochrome oxidase complex

Question 6

How is ATP made in the ETC?

Answer 6

Chemiosmosis uses the energy from the electrochemical gradient and ATP synthase to make ATP (the proton pump)

Question 7

Describe the contributions of NADH in the ETC

Answer 7

NADH pumps three protons into the intermembrane space, therefore three protons enter the pump to create three ATP

Question 8

Describe the contribution of FADH2 in the ETC

Answer 8

FADH2 pumps two protons into the intermembrane space, therefore two protons enter the pump to create two ATP. It only produces two ATP because it skips NADH dehydrogenase and starts the chain at ubiquinone

Question 9

Why does the NADH from glycolysis produces two ATP?

Answer 9

As the NADH moves from the cytoplasm and into the mitochondria it transfers its electrons to FAD to produce FADH2

Question 10

Summarize the ETC

Answer 10

The ETC gets its electrons from the H atom that NADH obtained from glucose. The free energy released by the electrons as they travel through the chain is harnessed by pumping protons into the H+ reservoir, creating an electrochemical gradient (difference in charge, slightly more positive). The energy of the gradient is reduced as the protons pass through the ATP synthase complex back into the matrix. Most of the energy (roughly 60%) is given off as heat but some is captured in the form of ATP

Question 11

What are the total ATP yields from cellular respiration?

Answer 11

Glucose: 2 ATP + 2 NADH converted to FADH2 as it moves from cytoplasm to mitochondria to form 4 ATP = 6 ATP
Pyruvate oxidation: 2 NADH = 6 ATP
Kreb’s cycle: 2 ATP + 6 NADH (18) + 2 FADH2 (4) = 24

6 + 6 + 24 = 36 ATP

Question 12

Describe the efficiency of cellular respiration

Answer 12

36 (31 kJ/mol) ATP x 100 = 38% efficient
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2870 kJ/mol glucose

Question 13

Describe the NADH shuttle used in humans

Answer 13

Glycerol-phosphate shuttle from cytosol

Question 14

Describe the NADH shuttle used in bacteria

Answer 14

Malate-aspartate shuttle for NADH from cytosol. Very efficient and transfers electrons and protons to NAD+ in the matrix. There is no loss of H+

38 (31 kJ/mol) ATP x 100 = 41.0% efficient
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2870 kJ/mol glucose

Question 15

Show a diagram of the ETC

Question 16

What is the goal of the ETC?

Answer 16

To couple energy stored in electron acceptors to a proton gradient that drives ATP synthesis