Respiration: Electron Transport Systems

how much NADH is produced by glycolysis?

2 NADH

How much ATP is produced by glycolysis?

2 ATP

How much NADH is produced by pruvate to acetyl coa?

2 NADHs

How many molecules of reduced coenzymes are produced by the Krebs cycle?

6 NADH and 2 FADH2

how many ATP is produced by the Krebs cycle?

2 ATP

where does all the NADH and FADH2 go during the oxidation of glucose?

their electrons are donated to bacterial ETS to generate ATP by oxidative phosphorylation

what are the three components of the respiratory ETS in some bacteria and E. coli?

initial substrate oxidoreductase

quinone pool

terminal oxidase

initial substrate oxidoreductase

receives a pair of electrons from an organic substrate such as NADH

the two electrons from NADH enter as an ETS protein complex embedded in the membrane

NADH donates e'- to NADH dehydrogenase

quinone pool

can receive 2 electrons from the substrate oxidoreductase, along with 2 H+ from solution to balance the negative charges yielding a quinol

the quinols diffuse within the membrane and carry reduction energy to the other ETS components

after transferring 2 e- to the next protein complex, the quinol releases its 2 H+

terminal oxidase

receives electrons from quinol and transfers them to a terminal electron acceptor such as oxygen

the complex usually includes a cytochrome that accepts electrons from quinols

aerobic respiration

microorganisms that can grow in the presence of molecular oxygen use it as a terminal electron acceptor in the electron transport chain\

common to all three domains

aerobic vs. anaerobic respiration in the domains

aerobic respiration is common to all three domains while anaerobic respiration is unique to prokaryotes

proton motive force

electrochemical gradient of protons

stores energy for most microbes and for the mitochondria of animals and plants

drives many forces, such as ATP synthesis and flagellar rotation

The PMF includes the electrical potential and the pH difference

when protons are pumped across the membrane, the PMF stores energy in the separation of charge (electrical potential) and the gradient of H+ concentration (pH difference)

reduction potential

ability to gain electrons

how many H+ is pumped across the membrane for each NADH oxidized in E. coli?

8-10 H+

how many H+ are pumped across the membrane for each FADH2 oxidized in E. coli ?

6-8 H+

how does mitochondrial ETS differ from that of E. coli?

1. it posseses an intermediate ubiquinol: cytochrome c oxidoreductase (complex III) for the transfer of electrons

2. Mitochondrial ETS pumps 12H+ per NADH, 2 more than E. coli

chemiosmotic theory

the transfer of H+ through a proton pump generates a proton motive force. this drives the conversion of ADP to ATP through ATP synthase

ATP synthase

harvest energy from PMF to synthesize ATP

it is a protein complex highly conserved in the bacterial cell membrane, the mitochondrial inner membrane, and the chloroplast thylakoid membrane

composed of two complexes: F0 and F1

F₀ ATP Synthase

translocates H+ across the membrane

F₁ ATP Synthase

consists of 6 alternating subunits of alpha and beta surrounding a gamma subunit which drives the F1 complex to rotate one third of a turn

each third of the F1 complex interconverts ADP+ Pi with ATP+H2O

how many protons are pumped out of ATP synthase per NADH?

10 protons

how many ATP does one NADH produce in ATP synthase?

3 molecules of ATP

How many protons are pumped out of ATP synthase per FADH?

6 protons

how many molecules of ATP does 1 FADH2 produce when pumped through ATP synthase?

2 molecules of ATP

electron transport in bacteria

protons pumped from the cytosolic face to the exoplasmic face

electron transport in mitochondrion

protons pumped from matrix to intermembrane space

electron transport in chloroplast

protons pumped from stroma to thylakoid lumen

Peter Mitchell

won Nobel Prize for his contribution to the discovery of chemiosmotic theory

Anaerobic respiration

prokaryotes can use other terminal electron acceptors besides oxygen including metals, and oxidized ions of nitrogen and sulfur

anaerobic respiration occurs in environments where oxygen is scarce

wetland soil and the human digestive tract

electron acceptors and donors in anaerobic respiration

some use nitrate

• nitrate reduced to nitrite (NO₃^- → NO₂^- )

some use sulfur compounds

• sulfate reduced to sulfite (SO₄^2- → SO₃ ^2- )