AP Biology

✔ ✔

“Linking reaction”

AP Biology 2006-2007

Cellular RespirationStage 2 & 3:

Oxidation of PyruvateKrebs Cycle

In the 1930s, some physicians prescribed low doses of a compound called dinitrophenol (DNP) to help patients lose weight. This unsafe method was abandoned after some patients died. DNP uncouples the chemiosmotic machinery by making the lipid bilayer of the inner mitochondrial membranes leaky to H+. Explain how this could cause both weight loss and death.

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pyruvate ®®®®®® CO2

Glycolysis is only the start:§ Glycolysis

§ Pyruvate has more energy to yieldu 3 more C to strip off (to oxidize)u if O2 is available, pyruvate enters mitochondriau enzymes of Krebs cycle complete the full

oxidation of sugar to CO2

2x6C 3Cglucose ®®®®® pyruvate

3C 1C

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Cellular respiration:

Linking reaction

AP Biology

intermembranespace inner

membrane

outermembrane

matrixcristae

Mitochondria — Structure:§ Double membrane energy harvesting organelle

u smooth outer membraneu highly folded inner membrane

§ cristaeu intermembrane space

§ fluid-filled space between membranesu matrix

§ inner fluid-filled spaceu DNA, ribosomesu enzymes

§ free in matrix & membrane-bound

mitochondrialDNA

What cells would have a lot of mitochondria?

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Mitochondria – Function:

What does this tell us about the evolution of eukaryotes?Endosymbiosis!

Dividing mitochondriaWho else divides like that?

Advantage of highly folded inner membrane?More surface area for membrane-bound enzymes & permeases

Membrane-bound proteinsEnzymes & permeases(membrane transport proteins)

Oooooh!Form fits function!

bacteria!

What cells would have a lot of mitochondria? Why?

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pyruvate ®®® acetyl CoA + CO2

Oxidation of pyruvate:

NAD3C 2C 1C[2x ]

§ Pyruvate enters mitochondrial matrix

u 3 step oxidation processu releases 2 CO2 (count the carbons!)

u reduces 2 NAD ® 2 NADH (moves e-)u produces 2 acetyl CoA

§ Acetyl CoA enters Krebs cycle

Wheredoes theCO2 go?Exhale!

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✔ ✔

“Linking reaction”

AP Biology

“Linking” glycolysis to Krebs Cycle: Pyruvate is oxidized to Acetyl CoA

Yield = 2C sugar + NADH + CO2

reduction

oxidation

Coenzyme APyruvate Acetyl CoA

C-C-C C-CCO2

NAD+

2 x [ ]2 Pyruvate → 2 acetyl Co-A + 2CO2 + 2NADH

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Krebs Cycle, (aka. Citric Acid Cycle):u in mitochondrial matrixu 8 step pathway

§ each catalyzed by specific enzyme§ step-wise catabolism of 6C citrate molecule

§ Evolved later than glycolysisu does that make evolutionary sense?

§ bacteria ®3.5 billion years ago (glycolysis)§ free O2 ®2.7 billion years ago (photosynthesis)§ eukaryotes ®1.5 billion years ago (aerobic

respiration = organelles ® mitochondria)

1937 | 1953

Hans Krebs1900-1981

2 acetyl Co-A → 4 CO2 + 2 ATP + 6 NADH + 2 FADH2

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4C

6C

4C

4C

4C

2C

6C

5C

4C

CO2

CO2

citrate

acetyl CoACount the carbons!

3Cpyruvate

x2

oxidationof sugars

This happens twice for each glucose molecule!

AP Biology

4C

6C

4C

4C

4C

2C

6C

5C

4C

CO2

CO2

citrate

acetyl CoACount the electron carriers!

3Cpyruvate

reductionof electron

carriers

This happens twice for each glucose molecule!

x2

CO2

NADH

NADH

NADHNADH

FADH2

ATP

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So we fully oxidized glucose

C6H12O6

¯CO2

& ended up with 4 ATP!

Whassup?

What’s the point?

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§ Krebs cycle produces large quantities of electron carriers

u NADH – yields 3 ATP’s/electronu FADH2 – yields 2 ATP’s/electron

u go to Electron Transport Chain!

Electron Carriers = Hydrogen Carriers:

What’s so

important about

electron carrie

rs?

H+

H+ H+

H+

H+ H+H+H+

H+

ATP

ADP+ Pi

AP Biology

Energy accounting of Krebs cycle:

Net gain = 2 ATP= 6 NADH + 2 FADH2

1 ADP 1 ATPATP

2x

2 NAD + 1 FAD 3 NADH + 1 FADH2

pyruvate ®®®®®®®®® CO23C 3x 1C

AP Biology

§ If the yield is only 2 ATP then how was the Krebs cycle an adaptation?u value of NADH & FADH2

§ electron carriers & H carriersw reduced molecules move electronsw reduced molecules move H+ ions

§ to be used in the Electron Transport Chain

like $$in the bank

Value of Krebs cycle?

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What’s thepoint? To build a

proton gradient in the Mitochondria.

Then makeATP!

ATP

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H+

H+ H+

H+

H+ H+

H+H+H+And how do we do that?

ATPBut… Have we done that yet?

P+

§ ATP synthaseu set up a H+ gradientu allow H+ to flow

through ATP synthaseu powers bonding

of Pi to ADP

ADP + Pi ® ATP ADP