Biochemistry Chapter 10: Carbohydrate Metabolism II Flashcards
Acetyl-CoA
Contains a high energy thioester bond that can be used to drive other reactions when hydrolysis occurs
What can acetyl-CoA be formed from?
pyruvate via pyruvate dehydrogenase complex (a 5-enzyme complex in the mitochondrial matrix that forms and is also inhibited by - acetyl-CoA and NADH)
Pyruvate dehydrogenase
oxidizes pyruvate, creating CO2; it requires thiamine pyrophosphate (vitamin B1, TPP) and Mg2+
Dihydroprpyl 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 when ATP or acetyl-CoA levels are high, turning it off
Pyruvate dehydrogenase phosphatase
dephosphorylates PDH when ADP levels are high, turning it on
Acetyl-CoA can be formed from…
fatty acids, which enter the mitochondria using carriers
How does fatty acid and CoA move into the intermembrane space?
Couples with fatty acid in the cytosol to form fatty acyl-CoA, which moves to the intermembrane space.
How does fatty acid acetyl-CoA cross the inner membrane
acyl is transferred to carnitine to form acyl-carnitine
What is the final step to make acetyl-CoA?
acyl group is transferred to a mitochondrial CoA to re-form fatty acyl-CoA, which can undergo Beta-oxidation to form acetyl-CoA
What can acetyl-CoA be formed from?
the carbon skeletons of ketogenic amino acids, ketone bodies and alcohol.
Where does the citric acid cycle take place?
The mitochondrial matrix
What is the main purpose of the citric acid cycle?
main purpose is to oxidize acetyl-CoA 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.
(-) ATP, NADH, succinyl-CoA and citrate
aconitase
isomerizes citrate to isocitrate
isocitrate dehydrogenase
oxidizes and decarboxylates isocitrate to form alpha-ketoglutarate. This enzyme generates the first CO2 and first NADH of the cycle. As the rate limiting step of the citric acid cycle, it is heavily regulated:
(-) ATP and NADH
(+) ADP and NAD+ are activators
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. It is inhibited by ATP, NADH and succinyl-CoA;
(+) ADP and Ca2+
Succinyl-CoA synthetase
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
Electron transport chain
takes place on the matrix-facing surface of the inner mitochondrial membrane
What donates electrons to the electron transport chain?
NADH
What is the progression of electrons in the ETC?
- Complex I
- Complex II
- Complex III
- Complex IV
Complex I
uses an iron-sulfer cluster to transfer electrons from NADH to flavin mononucleotide (FMN), and then to coenzyme Q, forming CoQH2. Four protons are translocated by complex I.
Complex II
Uses an iron-sulfer cluser to transfer electrons from succinate to FAD, and then to CoQ, forming CoQH2. No proton pumping occurs at Complex II
Complex III
uses an iron-sulfer cluster to transfer electrons from CoQH2 to heme, forming cytochrome c as part of the Q cycle. Four protons are translocated by complex III
Complex IV
uses cytochromes and Cu2+ to transfer electrons in the form of hydride ions (H-) from cytochrome c to oxygen, forming water. Two protons are translocated by complex IV.
glycerol 3-phosphate shuttle
electrons are transferred from NADH to dihydroxyacetone phosphate (DHAP), forming glycerol 3-phosphate. these electrons can then be transferred to mitochondrial FAD, forming FADH2
Malate-Apartate shuttle
electrons are transferred from NADH to oxaloacetate, forming malate. Malate can then cross the inner mitochondrial membrane and transfer the electrons to mitochondrial NAD+, forming NADH.
Proton-motive force
the electrochemical gradient generated by the ETC across the inner mitochondrial membrane.
Chemiosmotic coupling
The utilization of the proton-motive force generated by the electron transport chain to drive ATP synthesis in oxidative phosphorylation.
ATP synthase
the enzyme responsible for generating ATP from ADP and an inorganic phosphate.
F0 portion
ion channel allowing protons to flow down the gradient from the intermembrane space to the matrix
F1 portion
uses the energy released by the gradient to phosphorylate ADP into ATP.
Energy yield of glycolysis
2 NADH and 2 ATP
Energy yield of pyruvate dehydrogenase
1 NADH per molecule of pyruvate. (each glucose has 2 pyruvate molecules)
Energy yield of citric acid cycle
3 NADH, 1 FADH2, and 1 GTP (2 times per glucose)
Energy yield of NADH
2.5 ATP,
Energy yield of FADH2
1.5 ATP
Energy yield of GTP
converted to ATP
How many ATP per glucose molecule total?
25
