The Electron Transport Chain

Overview

• Review Glycolysis• Review Krebs Cycle• Where does the ETC occur?

– Inner membrane of the mitochondria

• What goes to the ETC?– Our electron carriers! NADH and FADH2

• Where do the electron carriers come from? – Glycolysis and the Krebs Cycle

A Lil’ Bit About those electron shuttles (NADH and FADH2)

• FADH2 makes 2 ATPs

• NADH from glycolysis makes 2 ATPs– Occurs cytoplasm

• NADH from Krebs cycle make 3 ATPs– Occurs in matrix

• Why the difference in #s?– The NADH made in glycolysis has to use a

little bit of energy to get into the mitochondria

A Lil’ Bit About the ETC

• What is the inner mitochondrial membrane like?– Phospholipid bilayer

• What makes up the ETC?– A series of protein complexes that pass these high E electrons

along• Why do we need to pass the electrons along?

– To pump those hydrogen ions (that tagged along) across the inner membrane to make a GRADIENT

– Every time an electron is passed down the chain, one H+ ionis pumped across the membrane

– What is a gradient?• When there is a high concentration of something on one side of a

membrane and a low concentration on the other side, THEREFORE diffusion occurs

vcell.ndsu.nodak.edu/animations/etc/first.htm

So who are these guys that make up the ETC?

• #1 Big Protein NADH dehydrogenase• #2 Big Protein Cytochrome b-c1• #3 Big Protein Cytochrome Oxidase• #4 Big Protein (most important!) ATP Synthase• We have 2 smaller protein shuttles that are

involved as well:– Ubiquinone (You-bic-win-own)

• Carries two electrons from #1 big protein to #2 big protein

– Cytochrome c• Carries one electron at a time from #2 big protein to #3 big

protein

The Job of the #3 Big Protein: Cytochrome Oxidase (the matchmaker)

• Look at the name…what do you think is involved here? (remember, we are almost to the end of the ETC)– OXYGEN!!

• #3 big protein waits for 4 electrons to enter• When that happens, 8 H+ ions come into with O2

(2 atoms of oxygen)…• Time to mix and mingle!

– 2 e-, 2 H+, and an oxygen join together to make H2O

– This happens again with the other oxygen– These 2 water molecules are released as

products (of cellular respiration)– But who is left by themselves in the #3 Big

Protein?• 4 H+ ion…the party is over, no more e- or

oxygen to pick up, they leave :o( (get pumped across membrane)

Uh Oh…its getting a little crowded…

• By this time, we have way too many H+ ions on one side (there is a gradient=lots of pot. E)

• The ions will diffuse and get pumped back to the less crowded side

• Who allows these ions to cross back?– ATP Synthase

• Every time an H+ goes thru, ATP synthase turns, attaching an ADP to an inorganic phosphate making…

• ATP!!!

vcell.ndsu.nodak.edu/animations/etc/first.htm

• Now the Cell has energy to do work! What types?– Mechanical– Molecular– Transport

• If there is no H+ ion concentration gradient, ATP synthase will NOT turn, and if it does not turn, no ATP is made= NO ENERGY!! (very BAD)

Cellular Respiration Totals For 1 Glucose Molecule

• Glycolysis– 2 NADH to the ETC to make 4 ATP (2x2)– 4 ATP – 2 ATPs used= 2ATP – 2 pyruvates coverted to 2 acetyl CoA 2 NADH to go

to the ETC to make 6 ATPs (2x3)• Krebs cycle

– 2 ATPs– 6 NADH x 3 atp per NADH= 18 ATPs– 2 FADH2 x 2 atp per FADH2= 4 ATPs

• Net Total: 36 ATPs

Tid Bits

• 36 ATPs is 38% of the total energy contained in glucose• What about the other 62%?

– It’s is released as heat– Imagine all use cells working hard giving off heat…

that is why you are hot after exercising!• Each molecule of ATP/ADP travels between the

mitochondria and the cytoplasm approximately once a minute

• Each day, 2 x 1016 molecules of ADP are phosphorylated in our bodies: 160kg/day.

• Each ATP Synthase complex can phosphorylate up to 100 molecules of ADP per second.

vcell.ndsu.nodak.edu/animations/etc/first.htm

http://vcell.ndsu.nodak.edu/animations/etc/first.htm