Lecture 12 -- Electron Transport and Proton Motive Force

Question 1

• continuous re-oxidation of cofactors

- separation of charge across membrane generating proton motive force

Answer 1

definition of electron transport

Question 2

• primary dehydrogenases or
• terminal oxidases/reductases
• linked by lipoquinones

Answer 2

What are respiratory transport systems mainly made up of?

Question 3

• Flavoprotiens
• Lipoquinones
• Iron-sulfur (Fe-S) protiens
• Cytochromes

Answer 3

What are the four components that can accept and transfer electrons and protons

Question 4

• contain nucleic acid derivative of riboflavin (FAD or FMN)

Answer 4

Flavoprotiens

Question 5

• can only carry one electron (no protons)

- typically associated with cystine (covalently linked to protien)

Answer 5

Iron-Sulfur Protiens

Question 6

• classification based on heme type (iron), cyanide sensitivity, spectroscopy, and redox potential
• 1 electron carriers (no proton)
• often form complexes in electron transport
• often have tetrapyrrole ring systems for prosthetic groups

Answer 6

Cytochromes

Question 7

Heme-copper
- pump protons

Alternative oxidase (AOX)
- does not pump protons

Cytochrome bd
- generates PMF by charge separation but does not pump protons

Answer 7

cytochrome families and their main functions

Question 8

• specific dehydrogenases, non-specific cytochromes, final electron acceptors are oxygen
  vs.
• specific dehydrogenases and specific reductases (for electron acceptor that is not oxygen)

Answer 8

General notes for aerobic respiration and anaerobic respiration electron transport pathways

Question 9

Flavoprotiens, Ubiquinone, Menaquinone

Answer 9

hydrogen carriers

Question 10

Cytochromes, Iron-sulfur protiens

Answer 10

electron carriers

Question 11

They are arranged in an alternating sequence, asymmetrically so proton consumption results in translocation and electron flow to oxygen

Answer 11

How are hydrogen carriers and electron carriers arranged in the chain?

Question 12

H+ is pumped to the outside of the membrane

- oxygen is most electronegative (has most positive reduction potential, so it is final acceptor)

Answer 12

How is charge separated?

Question 13

• many dehydrogenases and terminal oxidases/reductases linked by 2 lipoquinones
• modular/modules are determined by environmental cues (oxygen tension & nutrient availability)

Answer 13

Important things to note about E. coli’s respiratory flexibility

Question 14

= deltaw (charge across membrane) - 59deltapH (H+ concentration)

Answer 14

What does proton motive force depend on

Question 15

• generates chemical energy (ATP)
• generates mechanical energy (flagellar rotation)
• solute transport (symport, antiport –> nutrients in, waste out)

Answer 15

ultimate effect of proton motive force

Question 16

• low pH outside, positively charged
• high pH inside, negatively charged
• chemiosmotic potential –> kinetic –> chemical
• passive process along concentration gradient through ATP synthase

Answer 16

Chemiosmotic theory

Question 17

• 3H+ for 1ATP
• rotation generates ATP
• reversible

Answer 17

ATP synthase

Question 18

• symport of cations as fermentation product leaves
• light absorbed by bacteriorhodopsin
• decarboxylation of a dicarboxylic acid

Answer 18

examples of charge generating PMF

Question 19

• use oxalate –> convert to formate to establish net negative charge inside membrane

Answer 19

how to enteric anaerobes generate PMF?

Question 20

dependent on:

• electron donor
• acceptor
• components of electron transport system
• efficiency of ATP synthase
• the species
• the environment

Answer 20

What is responsible for the different yields per mole of NADH in bacteria?

Question 21

hydrophobic tails can keep structure close to membrane, keytones have high redox potentials

Answer 21

lipoquinones