Download 04 Transition reaction and Krebs cycle

Cellular Respiration
Part 2: The Transition Reaction
Part 3: Krebs Cycle
Part 2: Transition Reaction
• Remember, glycolysis took a 6 carbon glucose
molecule and produced two 3 carbon
pyruvates, a net of 2 ATP molecules, H2O and
NADH
• In this step the end products of glycolysis, the
2 pyruvate molecules, are moved from the
cytoplasm into the mitochondria for further
energy “harvesting”.
TRANSITION
REACTION
-this occurs across
both the outer and
inner mitochondrial
membranes
-Decarboxylation
-NAD+ reduced to
energized NADH + H+
- coenzyme A added to
pyruvate forming
AcetylCoA
Part 3: Krebs Cycle
• This is also called the Citric Acid Cycle or the
Tricarboxylic Acid Cycle (TCA)
• The purpose is to slowly oxidize a pyruvate
molecule and “harvest” the bond energy in
small amounts
• The energy released in the catabolism of the
pyruvate is stored in NADH, FADH2 and ATP via
GTP (guanine triphosphate)
1. KREBS CYCLE starts
-acetyl CoA bonds to
4C oxaloacetate
forming a 6C citrate
- a water is required
- the coenzyme A is
released to be reused
2. Isomerization
- This happens so
the next reaction
requires less energy
3. Harvest Energy
-Decarboxylation
-an NAD+ is reduced
to an energized
NADH + H+
-this is from the
energy “harvested”
during the
decarboxylation and
oxidation of
isocitrate
4. More Energy is
“Harvested”
-Decarboxylation
-another NAD+ is
reduced to NADH + H+
-this is from the
energy “harvested”
during the
decarboxylation and
the oxidation of
 keto glutarate
- note again the
addition of a
coenzyme A to the
product
5. Harvest More Energy
-The release of the
coenzyme A and the
isomerization provides
energy to
phosphorylate a GDP to
a GTP
-The GTP is used to
phosphorylate an ADP
to an ATP
- these are both
examples of substrate
level phosphorylation,
where the
phosphorylation energy
comes from breaking
the bonds of another
molecule
6. It’s all about the
energy STOOPID!!
-FAD is reduced to
an energized FADH2
-the energy comes
from oxidation of
succinate
-another coupled
redox reaction!!
7. What Energy?
- adding a water
hydrolyses the
double bond
8. Yeah – More
Energy!!
-again an NAD+ is
reduced to energized
NADH + H+
- the 4 carbon
oxaloacetate molecule
is regenerated
-Note that of the 3 CO2
molecules generated
only the first one
actually removed a
carbon from the
original pyruvate
-The 2nd and 3rd
carbons removed were
from previous
pyruvate molecules
Transition Reaction and Krebs Cycle SUMMARY
For each molecule of pyruvate the Krebs Cycle
turned once and:
• Required 2 H2O and CoA
• Generated 1 ATP, 4 NADH, 1 FADH2, 4H+ and
released 3 CO2
Double all these products for a glucose!
Finally,
For a test you will be given the Krebs Cycle with
the main molecules and you will have to name
reactions and complete all the molecules on
the coupled reaction arrows.
Next, how does the cell get ATP energy from the
energized NADH and FADH2?