LECTURE 11 - Alternative Oxidase and Uncoupling reactions in Photosynthesis

Question 1

ETC

Answer 1

Electron transport chain
Complex I recieves electrons from NADH
–> passes to coenzyme Q (ubiquinone)
Complex II recieves electrons from succinate
–> passes to coenzyme Q (ubiquinone)

coenzyme Q (ubiquinone)
–> passes electrons to Complex III

Complex III
–> passes electrons cytochrome c

cytochrome c
–> passes electrons to Complex IV

Complex IV
–> O2 + 4e- + 4H+ –> 2H2O

Complex I, III, IV pumps H+ mitochondrial inner membrane, creating a proton gradient.

Question 2

chemiosmosis

Answer 2

The high concentration of H+ in the inner mitochondrial membrane flows back in ATP synthase

ATP synthase (Complex V) has two parts :
F0
–> allows H+ to flow through
–> powers the rotation of a central stalk (part of the F1 subunit).

F1
–> rotation is critical for the synthesis of ATP in the F1 subunit

Question 3

Uncoupling Protein (UCP)

Answer 3

it also allows H+ to flow through,
instead of making ATP, it generates heat

–> essential to maintain internal temperature

Question 4

Alternative oxidase

Answer 4

Skips Complex I, III, IV
electrons go straight coenzyme Q (Ubiquinone) –> O2

Question 5

Alternative oxidases Function

Answer 5

1) H+ is not pumped into the inner membrane
[H+ flowing into the inner membrane can increase electron leakage occur within the ETC when electrons escape from their normal carriers and interactions. Instead of reaching Complex IV, where they would combine with oxygen (O2 )and the formation of reactive oxygen species (ROS)]

2) Quick pathway, straight to coenzyme Q so NADH etc are not accumulating up and reduces “electron pressure”

mainly, ROS = oxidative stress, and electron pressure :)