BMP: TCA cycle and ETC Flashcards
- What are alternative names to the TCA cycle?
- Where does this process occur?
- What is utilised and where does this come from
- Krebs or citric acid
- Mtocondria of eukaroytes and cytosol of prokaryotes
- Utilises acetyl coA - the immediate precurosr of acetyl coA from carbohydrate metabolism is pyruvate
How does pyruvate enter the mitocondria?
What happens to it?
Under aerobic conditions pyruvate enters via a specific H+ transporter and undergoes further oxidation to CO2 and H20
- What happens to acetyl coA
- What is the outcomes of the TCA?
- IT is completely oxidised
- At the end of the cycle, 2 Carbons from the 6 carbons of citrate leave as CO2 to ultimately yield the 4 carbon oxaloacetate, which is used again in the first step of the next cycle
What does every molecule of acetyl coA produce?
- 3 NADH
- 1 FADH2 (flavin adenine dinucleotide)
- 1GTP (ATP equivalent)
- Co2
But remeber 1 glucose = 2 pyruvaye = 2 acetyl coenzyme A (therefore this will be doubled)
What molecules are required for TCA?
- Acetyl (in the form of acetyl coA)
- Citrate
- consumed and then regenerated
- Coenzymes
- FAD and NAP+
- GDP
- H2O
What are products of TCA?
- GTP (ATP equivalent)
- CO2 (waste product)
- CoA
- Reduced coenzymes
- later undergo oxidative phosphorylation (ETC)
Before the TCA cycle can begin, pyruvate must be converted to the intermediate acetyl coA for TCA.
- How does this happen?
- Pyruvate under goes oxidative metabolism to acetyl coA via oxidative decarboxylation
- This is catalysed by pyruvate dehydrogenase complex (PDC)
(NAD+ is also converted to NADH)
What regulates the activity of PDC?
- PDC kinase (conversion to inactive form)
- PDC phosphatase (conversion to active form)
What is the first step of TCA cycle?
- Condensation
- Transfer of a 2-carbon acetyl group from acetyl CoA to the 4-carbon oxaloacetate to form a 6-carbon compound (citrate)
- This is catalysed by Citrate synthase
What is the 2nd step?
- Isomerisation
- The citrate is dehydrated to cis-aconitase via the enzyme aconitase
- It is then rehydrated by the same enzyme to form isocitrate
- This isomerisim is reversible
What is the 3rd step?
Isocitrate dehydrogenase catalayses the oxidation of isocitrate to oxalosuccinate. NADH is also produced
What is the 4th step?
- Decarboxylation
- Decarboxylation of oxalosuccinate to a-ketoglutartate (5C) by oxalosuccinate decarboxylase
- This is the rate limiting step and is irreversible
What is the 5th step?
- Oxidative decarboxylation
- Oxadative decarboxylation of a-ketoglutartate by a-ketoglutartate to succinyl-coA (4C) and one molecule of NADH.
- This step is irreversible
What is step 6?
- Hydrolysis/ GTP synthase
- Hydrolysis of succiny-CoA to succinate via succinyl-CoA synthase and producing one moleculr of GTP
- –GTP generation driven by hydrolysis of high energy thioester bond
- •Condensation of GDP + Pi
What happens in stage 7?
Oxidation of Succinate by succinic dehydrogenase to fumarate and one molecule of FADH2
FAD —> FADH2 genertes equivalent of 2ATP
What happens in stage 8?
- Hydration
- Hydration of fumarate to malate by fumarase
What happens in stage 9?
Oxidation of malate by malate dehydrogenase to oxaloaxetate and one molecule of NADH
Describe sources of energy from TCA
- •TCA cycle produces
- Reduced co-enzymes (NADH or FADH2) generated by action of four dehydrogenase enzymes
- GTP produced by one thiokinase enzyme
- Used to produce ATP (GTP + ADP → GDP + ATP)
- Energy produced per molecule pyruvate
- 3 NADH
- 1 FADH2
- 1 GTP
What is the net reaction for TCA cycle?
What is the energy yield per cycle?
What is the ATP count so far?
- •Per molecule of glucose
- –2 ATP from glycolysis
- –2 ATP from TCA cycle
- •Life requires far more than 4 ATP!!!
What is the electron transport chain?
Couples electron transfer between an electon donor (NADH) and an electron acceptor (O2) with the transfer of a H+ (Proton)
Series of molecules build into the inner mitocondrial membrane
How much energy is produced?
34 ATP from 1 glucose
What coditions are required?
aerobic - O2
What is the purpose of ETC?
To create an protein gradient between the inside and outside of the innermitocondiral membrane which ATP synthase uses to create ATP
What is the process by which the mitocondria produces ATP?
Oxidative phosphorylation
“The generation of ATP from ADP through the oxidation of metabolic products (food) to CO2”
What happens to energy during biological oxidation
Not just released - transducted to a more useful form - ATP
What does protein complex 1 do?
Protons from NADH associate with proton complex I. Complex I (NADH dehydrogenase) removes 2 electrons from NADH and transferred to the lipid soluble carrier protein ubiquinone. Complex I translocates 4 protons across the innermembrane producing a proton gradient.
Complex 1 is a major site of premature electron leakage to O2 occurs
What happens in complex II?
Electrons carried as FADH2 are passed to complex II. Complex II (succinate dehydrogenase) is a parellel electron transport pw to complex 1, but unlike complex 1 doesnt transport protons into the intermembrane space. This means it contributes less energy overall to the ETC process
What does complex III do?
Hydrogen ions are transolcated into the intermembrane space by interaction with complex III (cytochrome bc1 complex) and, simulataneouly, an electron is passed to complex III
What happens in complex IV?
In complex IV (Cytochrome c ocidase) four electrons are removed from 4 molecules of cytochrome c and transferred to molecular oxygen to produce 2 molecules of water
What is the final electron acceptor?
Oxygen
What inhibits complex IV?
Potassium cyanide
How is ATP finally produced?
The proton gradient created from transferring protons across the IMM to the intermembrane space increases membrane potential and drives ATP synthase (therefore ATP production) as the built up H+ rushes back into the matrix
What is the complete equation for cellular resperation?
6C6H12O6 + 6O2 —> 6H2O + 6CO2 + ~38 ATP
Why migth actual ATP be less?
Premature leakage of e-s to O2
