BRIDGING REACTION STEP 2
description
Transcript of BRIDGING REACTION STEP 2
![Page 1: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/1.jpg)
BRIDGING REACTIONSTEP 2
Fall 2013BIOT 309
![Page 2: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/2.jpg)
TRANSITION OR BRIDGING REACTIONConnects glycolysis to citric acid/Kreb’s Cycle
OVERALL REACTION
2 pyruvate + 2 NAD+ + 2 CoA-SH (coenzyme A)
2 acetyl-CoA + 2 NADH + 2 H+ + 2 CO2
CONNECTION TO OTHER BIOLOGY: Where else is CO2 made?
![Page 3: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/3.jpg)
TRANSITION REACTION
3 carbon
2 carbon
Co A
![Page 4: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/4.jpg)
STEP 3 AEROBIC RESPIRATION:Krebs Cycle
BIOT 309Fall 2013
![Page 5: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/5.jpg)
Tricarboxylic Acid Cycle = Krebs Cycle =
Citric acid Cycle
![Page 6: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/6.jpg)
THE TCA CYCLE
• Converts acetyl CoA (from pyruvate via bridging reaction) to CO2
• Provides small amounts of energy in the form of GTP/ATP
• Collects electrons and stores as NADH and FADH2 Electron Transport Chain (ETC)
• Provides intermediates for other pathways• Occurs in cytoplasm
![Page 7: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/7.jpg)
KREB’S CYCLESummary Reaction:
acetyl-CoA + 3NAD+ + FAD + GDP + Pi + 2H2O
——>
2CO2 + HSCoA + 3NADH + FADH2 + GTP + 2H+
![Page 8: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/8.jpg)
TCA/KREB’S CYCLE
![Page 9: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/9.jpg)
CITRIC ACID CYCLE
![Page 10: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/10.jpg)
![Page 11: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/11.jpg)
CHEMICAL REACTIONS
Key Equation: Δ G0 = -RTlnKeq
• Δ G0 = Gibb’s standard free energy change, distance from equilibrium, (expresses driving force of reaction)
• Keq =[products]/[reactants]; measurable• R= gas constant• T = absolute temperature (Kelvin)
![Page 12: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/12.jpg)
BIOCHEMICAL REACTIONS
• Instead of Δ G0, Δ G0’ is used • Δ G0’ = standard free energy change at pH 7.0
= biochemical standard free energy
![Page 13: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/13.jpg)
Remember: enzymes, cofactors
• Lower activation energy• Accelerate reaction• Organize and control
reaction• Recover energy in new
chemical forms and make it available for other uses
![Page 14: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/14.jpg)
Gibb’s Free Energy
• if Δ G0’ is negative, reaction goes forward spontaneously; - products have less energy than reactants
• if Δ G0’ is ~ 0, reaction is at equilibrium• if Δ G0’ is positive, reaction does not go forward
spontaneously
• Δ G0’ of two or more reactions is calculated by adding reactions and the Δ G0’ of the reactions
• CAVEAT: Δ G0 values shown in next slides will not be true under all circumstances, could be different for prokaryotes and eukaryotes
![Page 15: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/15.jpg)
KREB’S CYCLE, step 1
Citrate SynthaseAldol Condensation, X
2 C 4 C 6 C
![Page 16: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/16.jpg)
KREB’S CYCLE, step 2
AconitaseDehydration, Fe-S
![Page 17: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/17.jpg)
KREB’S CYCLE, step 3
AconitaseHydration, 4Fe-4S
![Page 18: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/18.jpg)
Steps 2 & 3 combinedSTEPS 2 & 3 done by one enzyme
aconitaseObserve that:• Step 2: dehydration generates (double bond)
intermediate (cis-aconitate)• Step 3: dehydration moves position of OH
group
![Page 19: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/19.jpg)
PRINCIPLE & EXAMPLE:
Δ G0’ of overall reaction is calculated by adding reactions and the Δ G0’ of the reactions*:
• Applied to 2 or more reactions, e.g., all of EMP or TCA
Δ G0’ = +2 kcal/mol
Δ G0’ = -0.5 kcal/mol
Δ G0’ = +1.5 kcal/molcitrate isocitrate
citrate cis-aconitatecis-aconitate isocitrate
![Page 20: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/20.jpg)
KREB’S CYCLE, step 4
Isocitrate Dehydrogenase2 step reactionOxidative decarboxylation, Mg2+ or Mn2+
NAD+
NADH, H+
6 C 5 C
SPONTANEOUS
![Page 21: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/21.jpg)
KREB’S CYCLE, step 5
α-Ketoglutarate Dehydrogenase Complex
Oxidative Decarboxylation, TPP, Lipoic Acid, FAD
NAD+ +
CoA-SH
NADH, H+
5 C 4 C
SPONTANEOUS
![Page 22: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/22.jpg)
KREB’S CYCLE, step 6
Succinyl CoA SynthetaseSubstrate Level Phosphorylation, FAD, TPP, Lipoic Acid
GTP converted into ATP by nucleoside diphosphate kinase
![Page 23: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/23.jpg)
KREB’S CYCLE, step 7
Succinate DehydrogenaseOxidation, FAD & FeS
Why FAD? • alkane oxidation poorly
exergonic and can’t reduce NAD+
![Page 24: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/24.jpg)
KREB’S CYCLE, step 8
Fumarate HydrataseHydration, Fe-S
![Page 25: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/25.jpg)
KREB’S CYCLE, step 9
Malate DehydrogenaseOxidation
Δ G0’ = +7 kcal/mol
![Page 26: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/26.jpg)
![Page 27: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/27.jpg)
*
<
>
>
![Page 28: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/28.jpg)
KREB’S CYCLE !!!Summary Reaction:
acetyl-CoA + 3NAD+ + FAD + GDP + Pi + 2H2O
——>
2CO2 + HSCoA + 3NADH + FADH2 + GTP + 2H+
![Page 29: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/29.jpg)
Transition Reaction + Kreb’s Cycle
Summary Reaction:
1 pyruvate + 4 NAD+ + 1 FAD + 1 GDP + 1 Pi
——>
4 CO2 + 4 NADH + 4 H+ + 1 FADH2 + 1 GTP(1 ATP)
![Page 30: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/30.jpg)
EMP + TR + TCA
Summary Reaction:
GLUCOSE + 2H20 + 10 NAD+ 2 FAD + 4 ADP + 4 Pi
——> 6 CO2 + 10 NADH + 10 H+ + 4 ATP + 2FADH2
![Page 31: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/31.jpg)
GLYOXYLATE CYCLEKREBS CYCLE ALTERNATIVE
BIOT 309Fall 2013
![Page 32: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/32.jpg)
GLYOXYLATE SHUNT/CYCLE
• By-passes 2 decarboxylation steps in TCA making possible– net formation of succinate, oxaloacetate, and other cycle
intermediates from acetyl-CoA• Retains the two carbons lost in decarboxylation steps
with each turn of TCA• => net synthesis of oxaloacetate, a four-carbon
molecule, because each turn of the cycle incorporates two molecules of acetyl-CoA– Oxaloacetate used for other purposes
![Page 33: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/33.jpg)
GLYOXYLATE SHUNT/CYCLE
• Allows many bacteria to metabolize two-carbon substrates such as acetate
FOR EXAMPLE:E. coli can be grown in a medium that provides
acetate as the sole carbon source. E. coli synthesize acetyl-CoA, then uses it for energy
production (via the citric acid cycle)
![Page 34: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/34.jpg)
GLYOXYLATE SHUNT/CYCLE
• Some enzymes in common with TCA • BUT has two exclusive enzymes not in TCA
– isocitrate lyase: cleaves D-isocitrate to glyoxylate and succinate
– malate synthase: forms L-malate from glyoxylate and acetyl-CoA
![Page 35: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/35.jpg)
GLYOXYLATE SHUNT/CYCLE
• Used when the principal or sole carbon source is a C2 compound (acetate, ethanol).
• Fat catabolism produces acetyl CoA which feeds into other catabolic reactions and produces energy
![Page 36: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/36.jpg)
![Page 37: BRIDGING REACTION STEP 2](https://reader036.fdocuments.us/reader036/viewer/2022062315/568165dc550346895dd8f3bf/html5/thumbnails/37.jpg)