ELECTRON TRANSPORT CHAIN

Stage 4:

How far have we come?

• We began with our simple glucose molecule• Through the processes of...– GLYCOLYSIS– PYRUVATE OXIDATION– KREBS CYCLE

...we have used the energy stored in the C-C bonds of glucose to help ATP

• Directly (substrate-level phosphorylation)• Indirectly (oxidative phosphorylation)

Energy Totals • GLYCOLYSIS

• PYRUVATE OXIDATION

• KREBS CYCLE

ATP USED ATP produced

NADH produced

FADH2

produced

2 6 10 2

ATP USED ATP produced

NADH produced

FADH2

produced

2 4 4 0

ATP USED

ATP produced

NADH produced

FADH2

produced

2 4 2 0

So what’s the deal with ATP??

• C6H12O6 + 6O2 6CO2 + 6H2O + 36 ATP

• We need to produce 36 ATP in Cell. Resp.• After 3 stages, we have only produced 6 ATP

through substrate-level oxidation• Thus, there are 30 ATP left to create– We produce the remaining 30 ATP through

oxidative phosphorylation in the ETC

ELECTRON-TRANSPORT-CHAIN

• In this step, we will utilize the energy provided by the electron carriers NADH and FADH2

•Extremely EXERGONIC∆G = -2870 kJ/Mol

How it works• NADH + FADH2 eventually transfer the electrons they carry to a

series of proteins that are located in the inner membrane

• The components of the ETCare arranged in order of increasing electronegativity

• Thus, allowing the electrons toflow, or BE TRANSPORTED, between the compounds

• Every step involves oxidationand reduction rxns.

How it works• Every time an electron moves from one molecule to the next,

free energy is released

• The free energy is used to pump H+ ions, or PROTONS, from the mitochondrial matrix into theINTERMEMBRANE SPACE

• The ETC needs a highly electronegative compound to oxidize the last protein– OXYGEN is used here, as it is one

of the most electronegative compounds on earth

How it works• An oxygen atom removes two é from the final protein complex • Oxygen then combines with 2 protons (H+) in the mitochondrial

matrix to form an H2O molecule

Diagram• The red path shows the path

that é travel through the ETC• KNOW NAMES OF THESE

MOLECULES

How it works

NADH DEHYDROGENASE

CYTOCHROME b-c1 COMPLEX

CYTOCHROME OXIDASE COMPLEX

UBIQUINONE (Q) cytochrome C

NADH + FADH2... Not so similar• NADH passes its electrons to the first protein complex

– NADH DEHYDROGENASE

• FADH2 passes its electrons to Q (or ubiquinone)

• This distinction means that:– NADH = 3 H+ pumped out– FADH2 = 2 H+ pumped out

• SO...

– NADH produces 3 ATP– FADH2 produces 2 ATP

NADH + FADH2... Not so similar• The NADH you produced in glycolysis works differently than the

NADH produced in pyruvate oxidation and Krebs cycle– Why?

• Glycolysis occurs in the cytoplasm, thus NADH has to travel through the double membrane of mitochondria– it can’t pass the inner membrane

• NADH passes its é through a protein transport to FAD thus forming FADH2

ATP PRODUCTION• Electrochemical Gradient: A concentration gradient created by

pumping ions into a space surrounded by a membrane that is impermeable to the ions– This is exactly what we are doing when we pump H+ ions into the

intermembrane space using the ETC– Thus, the inner membrane becomes a H+ reservoir – An potential difference, or VOLTAGE, is created across the

membrane• +ve charge in the intermembrane space • –ve charge in the mitochondria matrix +

-------

-

ATP PRODUCTION• H+ ions can not diffuse back through the innermembrane • They need to be pumped back by the transport protein

ATP SYNTHASE• As H+ ions are passed through

ATP SYNTHASE, the free energy of the gradient is reduced, thus releasing enough energy to produce ATP

• ADP + Pi ATP

ATP PRODUCTION• This process was coined: CHEMIOSMOSIS• ATP synthesized was caused by the ‘osmosis of H+ ions’

• Chemiosmosis is said to be COUPLED to the ETC

Final Energy Tally

Theoretical Yield vs. Actual Yield

• It is possible that we will not always obtain 36 ATP for every glucose molecule that we used

• 2 reasons:1. Some H+ ions may make it through the inner mitochondrial

membrane reducing the number of H+ ions that pass through ATP synthase.

2. Some of the protons in the H+ reservoir might get used up in other cellular reactions