Lecture 11 - Electron Transport Chain

Question 1

How does the TCA cycle fuel the ETC?

Answer 1

the end products, NADH and FADH2 are electron carriers in the electron transport chain

Question 2

What is the goal of the electron transport chain?

Answer 2

to use NADH and FADH2 to concentrate H+ protons in the intermembrane space of the mitochondria

• this proton gradient is used to fuel ATP synthesis

Question 3

Where do the 3 metabolism pathways we talked about occur?

Answer 3

Glycolysis: cytoplasm
Krebs cycle: matrix of mitochondria
Electron transport chain: across the inner mitochondrial membrane

Question 4

What provides the energy for the ETC?

Answer 4

the oxidation of NADH into NAD
- the hydride ion is removed from NADH (to regenerate NAD+) and is converted into a proton and 2 electrons (H- => H+ + 2e-)

• instead of ATP, the ETC uses electrons from NADH or FADH2

Question 5

True or false: electrons lose energy as they pass along the chain?

Answer 5

True

Question 6

What is the final destination for electrons?

Answer 6

oxygen

Question 7

What are electron carriers?

Answer 7

prosthetic groups => large non-protein molecules embedded in the protein, have complicated chemical structures not possible with amino acids

• they are used to help proteins carry out reactions

examples:
- iron-sulfur clusters -> sulfur binds to cysteine
- flavin mononucleotide

Question 8

Complex 1

Answer 8

receives 2 electrons from NADH and passes them to CoQ
- energy is used to pump 4 H+

Question 9

Coenzyme Q (CoQ)

Answer 9

a lipid-like carrier (goes through inner membrane so must be hydrophobic)

Question 10

Complex 2

Answer 10

receives 2 electrons from succinate and passes them directly to FADH2 and then into CoQ
- does not pump H+

Question 11

Complex 3

Answer 11

receives 2 electrons from CoQ and passes them to Cytochrome C
- energy is used to pump 4 H+

Question 12

Cytochrome C

Answer 12

a small protein that serves as an electron carrier
- moves electrons from complex 3 to 4
- has a heme prosthetic group/ cofactor
- heme is the electron carrier

Question 13

Complex 4

Answer 13

receives 2 electrons from cytochrome C and passes them to oxygen, which is reduced to water
- energy is used to pump 2 H+

Question 14

Why do electrons not just jump to oxygen?

Answer 14

because the redox centres (electron carriers) are arranged from low to high electron affinity, with oxygen having the highest

Question 15

What is the path of electrons from NADH?

Answer 15

Complex I => CoQ => Complex III => Cyt C => Complex IV => oxygen

Question 16

What is the path of electrons from FADH2

Answer 16

Complex II => CoQ => Complex III => Cyt C => Complex IV => oxygen

Question 17

True or false: the redox centres and H+ pumps are together in a complex?

Answer 17

False

Question 18

How do H+ ions get pumped?

Answer 18

a structural change in the complex (i.e., electrons passing) direct H+ to move through translocation half-channels which align with structural changes

Question 19

Why are all of the complexes clustered together? What is the assembly of complexes called?

Answer 19

ensures electrons never get the chance to jump straight to oxygen

called: supramolecular assemblies or supercomplexes

Question 20

How is ATP synthesis powered?

Answer 20

power source for ATP synthase is a difference in the concentration of H+ on opposite sides of the inner mitochondrial membrane

• the ATP synthase uses flow of H+ to move the first motor, then moves the second motor to squeeze ATP together

ATP = ADP + Pi + squeezing force