Stage 4: Electron Transport and Chemiosmosis

Angel Gu, Samantha Wong, Linda Yang, Angel Zhang

What is the electron transport chain?

A chain of protein complexes embedded in the inner mitochondrial membrane. Transports electrons and pumps hydrogen ions into the intermembrane space to create a gradient.

Components of the electron transport chain (ETC)

• • • • • • NADH dehydrogenase Ubiquinone (Q) Succinate dehydrogenase Cytochrome b-c

1

Cytochrome c Cytochrome oxidase • Arranged in order of increasing electronegativity (weakest to strongest)

NADH produced from glycolysis

VS VS

NADH produced from Krebs cycle

• NADH produced in the cytoplasm by glycolysis: CAN diffuse from

outer mitochondrial membrane to intermembrane space.

CANNOT diffuse from

inner membrane to matrix.

• NADH produced from Krebs cycle: Already in the matrix.

• •

What to do?

Cytosolic NADH (NADH that are produced by glycolysis) Pass electrons to shuttles • • Glycerol-phosphate shuttle: Transfers electrons from cytosolic NADH to FAD to produce FADH 2 Aspartate shuttle: Transfers electrons from cytosolic NADH to NAD + to produce NADH

Complex I: NADH dehydrogenase

• NADH dehydrogenase oxides NADH

NAD

H

+

H + 

NAD

+ back to NAD+

+

2H +

+

2e • The electrons are transferred to flavin mononucleotide ( FMN ) which reduces to FMNH 2

FMN +

2H +

+

2e 

FMNH

2 • The electrons are then passed to iron-sulphur proteins (FeS) located in NADH dehydrogenase

Complex I Continued…

• Electrons are accepted by Fe 3+

2Fe

3+

+

2e  which is reduced to Fe 2+

2Fe

2+ • • These two electrons are then given to ubiquinone ( Q ) The two hydrogen ions are pumped into the intermembrane space *One hydrogen ion is pumped per electron transferred

Ubiquinone (Q)

• A mobile electron carrier

2Fe

2+

gives 2e

-

to Q Q is reduced to

QH 2

2Fe

2+

is oxidized

2Fe

(ubiquinol) and

3+ • Carries electrons to complex III, cytochrome b-c

1

Interactive Animation:

http://www.brookscole.com/chemistry_d/templates/student_re sources/shared_resources/animations/oxidative/oxidativephosp horylation.html

Complex II: Succinate Dehydrogenase

• oxidation of succinate from Krebs cycle to fumarate Succinate + FAD  Fumarate + FADH 2 • FADH 2 then tries to oxidize back into FAD by passing its electrons to 2 Fe 3+ , which is reduced to 2 Fe 2+ (Like in Complex 1)

2Fe

3+

+

2e 

2Fe

2+

Complex II Continued...

• These electrons from 2Fe 2+ are then stolen by ubiquinone (Q), which carries them to complex III. Q + 2Fe 2+ 

2Fe

3+

+

QH 2 • *Unlike complex I, complex II doesn’t have enough free energy for active transport of the hydrogen ions (protons) from FADH 2 across the intermembrane . This is why oxidation of FADH 2 only yields 2 ATP molecules instead of 3 ATP molecules like NADH.

Complex III: cytochrome b-c

1

• • • Contains cytochrome b, cytochrome c

1

, and FeS proteins.

QH 2 passes two electrons to cytochrome b causing Fe reduce to Fe 2+ 3+ to Same way from cyt b to FeS protein and then to cyt c

1

Cytochrome C (c)

• I’m a protein and like Q...

• I am also a water soluble mobile electron carrier. I transport electrons one at a time from complex III to complex IV.

Complex IV:

Cytochrome Oxidase (The End of the Line) • • This is the end of the line for electrons from NADH or succinate.

Oxygen (breathed in) is reduced and when combined with these electrons, they form...

WATER

½ O 2 (g) + 2H + + 2e  H 2 O (l) THIS REACTION IS EXPLOSIVE! It’s highly exergonic, releasing large amounts of energy.

Electrochemical gradient

• • • A concentration gradient created by pumping ions into a space surrounded by a membrane that is impermeable to the ions.

Two components: electrical and chemical Proton-motive force (PMF) moves protons through an ATPase complex on account of the free energy stored in the form of an electrochemical gradient of protons across a biological membrane.

Chemiosmosis

• • • • Peter Mitchell – Nobel Prize in Chemistry in 1978 A process for synthesizing ATP using the energy of an electrochemical gradient and the ATP synthase enzyme. “osmosis” After chemiosmosis, ATP molecules are transported through both mitochondrial membranes.

Connections!

• • • Electrons from NADH and FADH 2 ETC were passed down the • As the electrons move down, energy released moves protons to create electrochemical gradient Protons move through proton channels, and release energy to synthesize ATP from ADP and P i The many processes of ATP synthesis are all continuous

Respiration

• • C 6 H 12 O 6 + 6O 2  6H 2 O + 6CO 2 The oxygen is necessary to take away the electrons from the ETC so the new electrons can keep flowing. Only oxygen is electronegative enough • • The ETC cannot get clogged up by electrons Oxygen takes two electrons and two protons from the matrix, and forms water • Glucose provides electrons and energy in its bonds for the body.

Oxidative Phosphorylation

• • Each step of ATP synthesis is completely dependent on its previous step Glycolysis  Pyruvate Oxidation  The Krebs Cycle  Electron Transport Chain and Chemiosmosis • Each step depends on the step before for the correct molecules and energy to work

Bibliography

• • • • • Highered Mcgraw Hill. Electron Transport System and ATP Synthesis. October 26, 2011. Interactive Animations. Oxidative Phosphorylation. October 26, 2011. Leeds Lecture. Electron Transport Chain. October 26, 2011. Nelson Biology 12. Chapter 2 Cellular Respiration. Pages 103-108.

Thomson Brooks/Cole. The Mitochondrion. October 26, 2011.

Bibliography continued…

• • • • • Brooks, Dr. S. J.. "Electron Transport Chain." University of Leeds. N.p., n.d. Web. 19 Oct. 2011. .

Carlson, Rebecca. "Hey Soul Sister/Electron Transport Chain." YouTube. N.p., n.d. Web. 18 Oct. 2011.

=DNReloT3QYU>.

Cengage. "Oxidative Phosphorylation." Thomson Books. N.p., n.d. Web. 18 Oct. 2011. .

Khan Academy. "Electron Transport Chain." YouTube. N.p., n.d. Web. 18 Oct. 2011. .

Wiley, John. "Concepts in Biochemistry - Interactive Animations." Wiley College . N.p., n.d. Web. 19 Oct. 2011. .