krebs cycle the meat and potatoes of cellular respiration
TRANSCRIPT
KREBS CYCLE
The Meat and Potatoes of Cellular Respiration
Last class... GLYCOLYSIS- We have converted glucose into two 3-
carbon molecules, PYRUVATE that will be further converted
GLYCOLYSIS ENERGY TALLYATP USED
ATP produced
NADH produced
FADH2
produced
2 4 2 0
PYRUVATE OXIDATION
Steps: 1. CO2 is removed from PYRUVATE to form an acetyl group 2. NAD+ removes 2 e + 1p from pyruvate to form NADH + H+
3. CoA combines to the remaining molecule to form ACETYL-CoA*Co-enzyme A is used to shuttle the acetyl group across the membrane
Where are we now?ATP USED ATP produced
2 4
NADH produced FADH2
produced
4 0
Today, we explore KREBS CYCLE
Krebs Cycle
• Named after the biochemist, Hans Krebs• Discovered this series of metabolic rxn’s in 1937
• An 8-step process, each catalyzed by a specific enzyme
• CYCLIC PROCESS, as the product in step 8 is actually the reactant in step 1! – OXALOACETATE (4-carbon)
• THE MAIN SOURCE OF NADH and FADH2
Krebs Cycle: Step 1
• The Acetyl-CoA product from Pyruvate Oxidation combines with OXALOACETATE
• Forming CITRATE– 2 carbons + 4 carbons = 6!
• Notice that Coenzyme A is released at this point. – It was only used to transport
the 2-C acetyl molecule across the mitochondrial membrane
Krebs Cycle: Step 2
• CITRATE (6C) isomerizes to form ISOCITRATE (6C)
• Notice that the –OH group moves from the 3rd carbon to the 2nd carbon
Krebs Cycle: Step 3
• ISOCITRATE (6C) loses a carbon as a CO2 group forming ∞-KETOGLUTARATE (5C)
• NAD + takes 2 more electrons and 1 proton– NAD+ NADH + H+
– Oxidative Phosphorylation
Krebs Cycle: Step 4
• ∞-KETOGLUTARATE (5C) loses a carbon as a CO2 group, but attaches to CoA formingSUCCINYL-CoA (4C)
* ALL Carbons have been used up
• NAD + takes 2 more electrons and 1 proton– NAD+ NADH + H+
– Oxidative Phosphorylation
Krebs Cycle: Step 5
SUCCINYL-CoA(4C) loses its CoA group forming SUCCINATE (4C)
ATP is produced here via a coupled reaction with GTP
GTP GDP + Pi + energy
This energy is used to catalyze ADP + Pi ATP
Krebs Cycle: Step 6
SUCCINATE(4C) is reduced to via FAD to FUMARATE (4C) Notice the C=C bond
• FAD takes 2 electrons and 2 protons– FAD FADH2
– Oxidative Phosphorylation
Krebs Cycle: Step 7
• FUMARATE (4C) has its C=C react with an incoming H2O molecule to form MALATE (4C)
• Remember that we lost a water in Glycolysis! – We use one here.
Krebs Cycle: Step 8
• MALATE(4C) is reduced by NAD+ to reformOXALOACETATE (4C)
• NAD + takes 2 more electrons and 1 proton– NAD+ NADH + H+
– Oxidative Phosphorylation
KREBS CYCLE SUMMARY• Through a series of 8 reactions we have
converted the remaining energy of C-C bonds in our original glucose using NAD+ and FAD carrier molecules
• C6H12O6 + 6O2 6CO2 + 6H2O + 36 ATP– We produced the remaining 4 CO2 molecules – 2 ATP
ATP USED ATP produced NADH produced FADH2
produced
2 6 10 2