Carbohydrate Metabolism 1- Glycolysis, Glycogen, Gluconeogenesis, and Pentose Pathway Flashcards
Acetyl-CoA
Contains a high-energy thioester bond that can be used to Reactions of the Citric Acid Cycle
drive other reactions when hydrolysis occurs.
Acetyl-CoA Formation:
Can be formed from fatty acids, which enter the
mitochondria using carriers. The fatty acid coupled with CoA in the cytosol to form fatty acyl-CoA, which moves to the intermembrane space. The acyl (fatty acid) group is transferred to carnitine to form acyl-carnitine, which
crosses the inner membrane. The acyl group is transferred to a mitochondrial CoA to re-form fatty acyl-CoA, which can undergo b-oxidation to form acetyl
Acetyl-CoA Formation
Can also be formed from the carbon skeletons of ketogenic amino acids, ketone bodies, and alcohol.
Pyruvate Dehydrogenase
(PDH):
Oxidizes pyruvate, creating CO2; it requires thiamine pyrophosphate (vitamin B1, TPP) and Mg2+
Dihydrolipoyl
Transacetylase
Oxidizes the remaining two-carbon molecule using lipoic acid, and transfers the resulting acetyl group to CoA, forming acetyl-CoA.
Dihydrolipoyl
Dehydrogenase
Uses FAD to reoxidize lipoic acid, forming FADH2. This FADH2 can later transfer electrons to NAD+, forming NADH that can feed into the electron transport chain.
Pyruvate Dehydrogenase
Kinase
Phosphorylates PDH (pyruvate dehydrogenase) when ATP or acetyl-CoA levels are high, turning it off
Pyruvate Dehydrogenase
Phosphatase
Dephosphorylates PDH (pyruvate dehydrogenase) when ADP levels are high, turning it on.
Acyl Carnitine Translocase
Mechanism for Acyl CoA to enter the mitochondrial matrix. The mitochondrial matrix is where Acyl CoA can undergo b-oxidation to form Acetyl-CoA.
Where does the citric acid cycle take place?
In the mitochondrial matrix
What is the purpose for the citric acid cycle?
Its main purpose is to
oxidize carbons in intermediates to CO2 and generate high-energy electron carriers (NADH and FADH2) and GTP.
Citrate
Synthase
Couples acetyl-CoA to oxaloacetate and then hydrolyzes the
resulting product, forming citrate and CoA-SH
What regulates citrate synthase?
Negative feedback from ATP, NADH, succinyl coA and citrate
Aconitase
Isomerizes citrate to isocitrate
What is the rate limiting step of the citric acid cycle?
Isocitrate dehydrogenase
What are the inhibitors and activators of isocitrate dehydrogenase?
ATP and NADH are inhibitors and ADP and NAD+ are activators
Isocitrate
Dehydrogenase
Oxidizes and decarboxylates isocitrate to form a-ketoglutarate
a-Ketoglutarate
Dehydrogenase
Complex
Acts similarly to PDH complex, metabolizing a-ketoglutarate to form succinyl-CoA.This enzyme generates the second CO2 and
second NADH of the cycle
What inhibits and activates alpha-ketoglutarate dehydrogenase complex?
It is inhibited by ATP, NADH, and
succinyl-CoA; it is activated by ADP and Ca2+
Succinyl-CoA
Synthesis
Hydrolyzes the thioester bond in succinyl-CoA to form succinate
and CoA-SH. This enzyme generates the one GTP generated in the
cycle.
Succinate
Dehydrogenase
Oxidizes succinate to form fumarate. This flavoprotein is anchored
to the inner mitochondrial membrane because it requires FAD,
which is reduced to form the one FADH2 generated in the cycle.
Fumarase
Hydrolyzes the alkene bond of fumarate, forming malate
Malate
Dehydrogenase
Oxidizes malate to oxaloacetate. This enzyme generates the third
and final NADH of the cycle.
Proton-Motive
Force
The electrochemical gradient generated by the electron transport
chain across the inner mitochondrial membrane. The
intermembrane space has a higher concentration of protons than
the matrix; this gradient stores energy, which can be used to form
ATP via chemiosmotic coupling.
