STAGE 4:ELECTRON TRANSPORT CHAIN (ETC) AND CHEMIOSMOSIS

Recall Glycolysis

DIGESTION

Which was followed by…

So, what do we have at this point?

A small amount of ATP (the useful energy for

cell functions)

and...

LOTS OF REDUCED CARRIERS: NADH and FADH2

• the electrons are the “currency” with which the bulk of the energy is obtained

Now this “currency” (the electrons) need to be exchanged for the “currency” used by cells.....

So....how do we go from

ELECTRONSTO

ATP

Electron Transport Chain

A series of redox reactions moves electrons along the inner membrane of the mitochondria

Components are arranged in order of increasing EN

The Players

Label your diagram…use

different colours!

Electron Transport Chain

NADH gives up 2 e- to the first protein- complex (NADH dehydrogenase)

e- flow is very exergonicThis E is used to pump protons out

of matrix and into intermembrane space

Electron Transport Chain

Oxygen is used to oxidize the last protein (Strips off the 2e- )

With 2 protons (H+) from the matrix, H2O is formed

Where does the oxygen come from?

FADH2 and NADH do not transfer their e- in the same way

NADH passes e- to the first protein complex NADH dehydrogenase (pumps 3 p+)

FADH2 passes e- to Q (pumps 2 p+)

But what about FADH2?

Solution?A shuttle system is used to pass e-

from cytosolic NADH (produced during glycolysis) to the matrix

One more problem…the inner mitochondrial

membrane is impermeable to NADH!

2 Types of Shuttles

Glycerol-Phosphate Shuttle most commonTransfers e- from cytosolic NADH to

FAD to produce FADH2

Aspartate ShuttleTransfers e- to NAD+ forming NADH

Electron Transport Chain

[p+ ] builds up in intermembrane space

p+ are actually Hydrogen ions...so an electrical gradient also exists

the [gradient] and electrical gradient create the force needed to push the protons back into the matrix (called the Proton Motive Force or PMF)

BUT…

the membrane is (mostly) impermeable to ions

How do the protons pass through the

membrane?

through facilitated diffusion through

the centre of an ATP synthase complex

ELECTRON TRANSPORT

Chemiosmosis As H+ moves into the matrix through ATP

synthase, energy is released The energy is used to phosphorylate ADP

to form ATP (oxidative phosphorylation) Newly formed ATP are transported to the

cytoplasm by facilitated diffusion (where they will be used to drive endergonic processes)

Can we get energy from other food sources?