ELECTRON TRANSPORT CHAIN

Aerobic Respiration Summary

Glycolysis Glucose + 2ADP + 2Pi + 2NAD+ à 2 pyruvate + 2ATP + 2NADH + 2H+

Pyruvate Oxidation 2 pyruvate + 2NAD+ + 2CoA à 2 acetyl-CoA + 2NADH + 2H+ + 2CO2

Citric Acid Cycle/Krebs Cycle 2 acetyl-CoA + 6NAD+ + 2FAD + 2ADP + 2Pi à 4 CO2 + 6NADH + 6H+ + 2FADH2 + 2 ATP + 2CoA

Electron Transport Chain (ETC) ---

Aerobic Respiration Summary

¨  Most of the potential energy from glucose is transferred to high-energy molecules, NADH and FADH2

Cellular Respiration Energy Molecules Produced

Glycolysis 2 ATP 2 NADH

Pyruvate Oxidation 2 NADH

Krebs Cycle 2 ATP 6 NADH 2 FADH2

Two Methods of ATP Synthesis

¨  Substrate‐level phosphorylation ¤ direct ATP formation through phosphate transfer from

substrate to ADP ¤ Occurs in glycolysis & Kreb cycle

¨  Oxidative phosphorylation ¤  indirect ATP formation through redox reactions involving

O2 as a final electron acceptor ¤ Driven by the electron transport chain

Substrate-level Phosphorylation

¨  Formation of ATP by direct transfer of phosphate group from a substrate to ADP

Oxidative Phosphorylation

Involves 2 processes that occur on the inner mitochondrial membrane (IMM): ¨  Electron Transport Chain:

¤ Energy in electrons of NADH and FADH2 used to drive H+ against its concentration gradient

¤ Electrons fall to oxygen (final electron acceptor)

¨  Chemiosmosis: ¤ Using facilitated diffusion of H+ to drive the synthesis of

ATP

Electron Transport Chain Overview

¨  Occur on the inner mitochondrial membrane ¨  The ETC extracts energy stored in the NADH and

FADH2 molecules and covert it to ATP by: ¤ Move protons against its concentration gradient

creating a proton gradient across the inner mitochondrial membrane (IMM)

¤ Final electron acceptor is oxygen which converts H2O

¨  All reactions are redox reactions

Electron Transport Chain

ETC: Complex I

¨  2 e‐ from NADH are transferred to Complex I

¨  Protons are pumped across the

inner mitochondrial membrane (IMM) by Complex I

ETC: Ubiquinone (Q)

¨  e‐ are transferred from Complex I to ubiquinone (Q)

¨  Q is lipid soluble (hydrophobic molecule)

¨  can move within the phospholipid bilayer

¨  mobile component within the IMM

¨  It shuttles e- from complex I to complex III

ETC: Complex III

¨  e‐ are transferred from Q to Complex III

¨  Protons are pumped across the IMM by Complex III

ETC: Cyt C

¨  e‐ are transferred from Complex III to cytochrome c (cyt c)

¨  cyt c is a mobile component on the surface of IMM (peripheral)

¨  in the intermembrane space ¨  It shuttles e- from complex III

to complex IV

ETC: O2

¨  O2 is the final electron acceptor of the ETC

¨  enough e‐ pass through the ETC to produce full H2O molecules

¨  Protons are pumped across

the IMM by Complex IV

ETC: NADH pathway

NADH e‐ transferred to O2; three proton pumps activated

ETC: FADH2 Pathway

FADH2 e‐ transferred to O2; two proton pumps activated

ETC Components: Complex II

¨  2e‐ are transferred from FADH2 to Complex II

¨  no protons are pumped across

the IMM

¨  e‐ are transferred from Complex II to Q and proceed through the rest of ETC

Driving Force Behind Electron Transport

¨  Each electron transfer step is energetically favorable

¨  Each carrier in the chain has a higher electronegativity than the carrier before it

¨  Electrons from NADH and FADH2 lose energy (pulled downhill) by each electron carrier to pump H+

Driving Force Behind Electron Transport

¨  Final electron acceptor is the very electronegative oxygen

¨  Oxygen drives the entire process of ETC

¨  Lack of oxygen prevents this whole process from occurring

Electrochemical Proton Gradient

High H+

Low H+

Proton Motive Force: Chemiosmosis

¨  The electrochemical gradient produced by the ETC: ¤ High proton concentration in the intermembrane space

¨  Chemiosmosis: facilitated diffusion of proton down the concentration gradient (Passive) ¤ Occurs by coupling passive movement of protons to

produce ATP through the enzyme complex ATP synthase ¤ ATP is produced as protons flow through ATP synthase

ATP Synthase

¨  Fo = rotor ¤ Transmembrane ¤ Proton channel

¨  F1 = knob, rod ¤ Peripheral ¤ catalytic sites that

phosphorylate ADP to ATP

ATPase: http://www.youtube.com/watch?v=PjdPTY1wHdQ&feature=related

Links

ETC ¨  http://highered.mcgraw-hill.com/sites/0072507470/

student_view0/chapter25/animation__electron_transport_system_and_atp_synthesis__quiz_1_.html

¨  http://www.youtube.com/watch?v=lRlTBRPv6xM&feature=related

Proton gradient ¨  http://www.youtube.com/watch?v=3y1dO4nNaKY&

%20feature=related

ATP Production

¨  In general: ¤ 1 NADHà3 ATP molecules ¤ 1 FADH2à2 ATP molecules ¤ The ETC is coupled with ATPsynthesis.

Activity

¨  Calculate total ATP produced from Aerobic Respiration.

ATP Production Summary

¨  Most of the potential energy from glucose is transferred to high-energy molecules, NADH and FADH2

Cellular Respiration Energy Molecules Produced

Glycolysis 2 ATP 2 NADH

2 ATP 4-6 ATP

Pyruvate Oxidation 2 NADH

6 ATP

Krebs Cycle 2 ATP 6 NADH 2 FADH2

2 ATP 18 ATP 4 ATP

Total 36-38 ATP

Question 1

¨  The electrons that are transferred through the electron transport system initially belonged to: A) NADH B) FADH2 C) ATP D) oxygen E) NADH and FADH2

Question 2

¨  The movement of protons through ATP synthase occurs from the A) matrix to the intermembrane space. B) matrix to the cytoplasm. C) intermembrane space to the matrix. D) intermembrane space to the cytoplasm. E) cytoplasm to the intermembrane space

Question 3

¨  When oxygen accepts electrons, water is produced as a byproduct. A)   True B)  False

 

Question 4

¨  The formation of ATP as a result of the activity of the electron transport system is termed substrate-level phosphorylation. A)  True B)  False

 

Question 5

¨  The function of the enzyme ATP synthase is to... A)  accept a proton from inside the cell membrane as it

accepts electrons B)  utilize the energy of the proton motive force to

convert ADP to ATP C)  produce reduced coenzymes like NADH D)  transfer hydrogen to the electron transport chain E)  shuttle electrons from NADH to a terminal electron

acceptor

 

Question 6

¨  When protons are pumped outside the cell membrane  A) water is made B) a proton motive force is created C) NADH gets reduced D) electrons are lost  

Catabolism of various molecules from food

Regulation of Cellular Respiration

Negative Feedback Inhibition