Transcript Krebs and ETC

Pyruvate Oxidation or Oxidative
Decarboxylation
(if oxygen is present…)
The following occurs for each pyruvate:
1. CO2 removed.
2. NAD+ reduced to NADH and the
2-carbon compound becomes acetic
acid.
3. Coenzyme A (CoA) attaches to acetic
acid to form acetyl-CoA.
Pyruvate Oxidation or
Oxidative Decarboxylation
Pyruvate Oxidation or
Oxidative Decarboxylation
Energy Yield & Products:
2 NADH
2 acetyl-CoA
2 CO2 (released as waste)
Acetyl-CoA






CoA comes from vitamin B5
Proteins, lipids, and carbohydrates are catabolized to
‘acetyl-CoA’
It can be used to make fat or ATP
[ATP] determines what pathway this molecule takes
If O2 is present, ‘acetyl CoA’ moves to the Kreb’s Cycle
(aerobic respiration)
If O2 is NOT present, ‘acetyl CoA’ becomes ‘lactate’
(anaerobic respiration / fermentation)
Krebs cycle - overview



8 step process, with each step catalyzed by
a specific enzyme
It is a ‘cycle’ because oxaloacetate is the
product of step 8, and the reactant in step 1
REMEMBER: Two acetyl-CoA molecules
enter, so the Krebs Cycle must happen
TWICE for every one molecule of glucose
that begins glycolysis
The Krebs Cycle
Occurs twice for each molecule of glucose, 1 for each acetyl-CoA.
The Krebs Cycle – Key Features
1.
2.
3.
4.
5.
6.
In step 1, acetyl-CoA combines with oxaloacetate to
form citrate.
NAD+ is reduced to NADH in steps 3, 4 and 8.
FAD is reduced to FADH2 in step 6.
ATP if formed in step 5 by substrate-level
phosphorylation. The phosphate group from succinylCoA is transferred to GDP, forming GTP, which then
forms ATP.
In step 8, oxaloacetate is formed from malate, which
is used as a reactant in step 1.
CO2 is released in steps 3 and 4.
The Krebs Cycle
Energy Yield & Products:
2 ATP
6 NADH
2 FADH2
4 CO2 (released as waste)
NADH and FADH2 carry electrons to the electron transport
chain for further production of ATP by oxidative
phosphorylation.
Cellular Respiration so far has produced…

Glycolysis
2 ATP (net)
 2 NADH, converted to 2 FADH2


Pyruvate Oxidation


2 NADH
Krebs Cycle
2 ATP
 6 NADH
 2 FADH2

E.T.C. - Structure




A series of electron acceptors (proteins) are
embedded in the inner mitochondrial membrane.
These proteins are arranged in order of
increasing electronegativity.
The weakest attractor of electrons (NADH
dehydrogenase) is at the start of the chain and
the strongest (cytochrome oxidase) is at the end.
Since the mitochondrial membrane is highly
folded, there are multiple copies of the ETC
across the membrane
Electron Transport Chain - Overview





NADH and FADH2 transfer electrons to proteins
in the inner mitochondrial membrane
The weakest electron attractors are at the start,
and the strongest are at the end
Each component is REDUCED, and then
subsequently OXIDIZED
Oxygen (highly electronegative) oxidizes the last
ETC component
The energy released, moves H+ atoms (i.e.
protons) across mitochondrial membrane
Electrochemical gradient is created, with a lot of H+ outside
Sets the rate of this process…
The energy stored in the [] gradient will be used in the
second part of the ETC to power ATP synthesis