chapter 17: the citric acid cycle aka krebs cycle

the mitochondrion is the

site for the citric acid cycle and oxidative phosphorylation

outer membrane

permeable to small molecules and ions through porins

inner membrane

the location of the electron transport chain and ATP synthase, highly impermeable.

intermembrane space

the proton gradient is established here, the space between the outer and inner membrane

matrix

the location of the pyruve dehydrogenase complex and the citric acid cycle, the internal compartment of the mitochondrion

the link between glycolysis (cytosol) and the citric acid cycle (mirochondrial matrix) is the conversion of 

pyruvate to acetyl coenzyme A 

overall conversion of pyruvate to acetyl CoA 

pyruvate (3 carbons) is converted to Acetyl CoA (2 carbons) and CO2.

the conversion of pyruvate to Acetyl CoA is catalyzed by

pyruvate dehydrogenase complex

the conversion of pytuvate to acetyl CoA is an

irreversible oxidative decarboxylation

process 1: pyruvate loses

a carboxyl group as CO2

process 2: the remaning two-carbox acetly unit is linked 

to coenzyme A forming acetly CoA which forms acetyl CoA

process 3: NAD+ is reduced to

NADH ( oxidation)

acetly CoA is the primary fuel for

the citric acid cycle

acetyl CoA enters the cycle by combining its two carbon acetyl groups with

four carbon compound oxaloacetate to form the six-carbon compound citrate.. 

step 1 of citric acid cycle

occurs in the mitochondrial matrix and begins with the entry of the two carbon unit acetyl CoA

the cycle starts when

citrate synthase catalyzes the condensation of acetyl CoA with the four-carbon oxaloacetate to form citrate (6C)

step 2 of citric acid cycle part 1 

isocitrate dehydrogenase converts isocitrate to produce the first molecule of NADH and releases the first CO2 molecule 

step 2 of citric acid cycle part 2

the a-ketoglutarate dehydrogenase complex acts on a-ketoglutarate which generates the second NADH an releases the second and final CO2 for the cycle. 

step 3 of citric acid cycle

succinly CoA is cleaved by succinyl CoA synthetase to generate GTP (which is readily convertible to ATP through substrate-level phosphorylation

after succinly CoA is cleaved to generate GTP 

the 4C molecule, succinate, is then oxidized by succinate dehydrogenase

succinate dehydrogenase is embedded

in the inner mitochondrial membrane

succinly CoA undergoes oxidization to produce

FADH2.

malate dehydrogenaase would then oxidized the 4C chain once more

generating the third and FINAL NADH

NADH can regenerate into

oxaloacetate

citric acid cycle generates a total of

3 NADH, 1 FADH and 1 GTP

ATP or GTP is produced directly in

STEP 5 via substrate level phosphorylation, catalyzed by succinyl COa synthetase 

NADH is created in steps

3,4,8

FADH2 is created in step

6

one molecule of

acetyl CoA enters the cycle

one glucose yields

two pyruvates

two acetyl CoA’s would yield 

from glucose double the amount 

the citric acid cycle is controlled by these four irreversible steps 

1. pyruvate dehydoogenase complex 

2. citrate synthase

3. isocitrate dehydrogenase

4. a-ketoglutarate dehydrogenase complex 

phyruvate dehydrogenase complex is inhibited by

ATP, Acetyl CoA, and NADH 

pyruvate dehydrogenase complex is stimulated by

ADP, NAD+, CA2+

citrate synthase is inhibited by

ATP,NADH, and succinyl CoA

isocitrate dehydrogenase is inhibited by

ATP and NADH

isocitrate dehydrogenase is stimulated by

ADP and Ca2+

alpha-ketoglutarate dehydrogenase complex is inhibited by

ATP, NADH, and succinyl CoA

alpha-ketoglutarate dehydrogenase complex is stimulated by

Ca2+