Bioenergetics II : lithotrophy, phototrophy, autotrophy

Question 1

what are lithotrophes?

• how do they get electrons

Answer 1

• they get their electrons from rocks
• they follow the “tower of power” to obtain electrons from inorganic molecules (rock eaters)

Question 2

recall: why do we need electrons?

Answer 2

• electrons can be used in the electron transport chain to generate ATP
• most anabolic reactions require reducing power

Question 3

One problem with lithotrophy: NAD(P)H!

Answer 3

• NAD(P)H is required to provide reducing power for most biosynthetic (anabolic) reactions
• if a cell takes electrons from something lower on the Electron Tower than NADH, those electrons can’t be used to reduce NAD+ to NADH (ELECTRONS CANNOT MOVE UP THE TOWER)

Question 4

How do a nitrite-oxidizing bacteria (below NADH) generate NADH?

Answer 4

Reverse electron flow using PMF to generate NADH (reducing power).

Question 5

explain reverse electron flow (going with vs against the electron transport chain)

Answer 5

going down the electron transport chain makes PMF, which can be used to produce ATP

going against the electron transport chain uses PMF

Question 6

two problems with lithotophy

Answer 6

1. reverse electron flow
   - electrons can’t go up the electron transport chain… and NADH is required (reducing power)
2. solubility

Question 7

second problem with lithotrophy: solubility

what are the solutions (2)

Answer 7

• lots of lithotrophic electron donors and terminal electron acceptors are insoluble and cannot pass the cell membrane;

SOLUTIONS
- membrane-bound terminal reductases (rely on direct contact between cell surface and insoluble mineral.

• secretion of soluble electron “shuttles” that “carry” electrons to the insoluble mineral (elusive… not well understood).

Question 8

where do phototrophs get their energy from?

Answer 8

energy from the sunlight