“Linking reaction”shaunab.info/AP Biology/Unit 3/Lectures/Chapter 9...AP Biology Energy...
Transcript of “Linking reaction”shaunab.info/AP Biology/Unit 3/Lectures/Chapter 9...AP Biology Energy...
AP Biology
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“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
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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
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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