6. ATP yield Flashcards
GE of glucose = (kj) ?
2816
Formation of ATP by substrate-level phosphorylation: direct. How is this performed? What enzyme is responsible for this?
For example: Glycolysis
- Phosphate is added to ADP > ATP
- Molecule of conversion now has one phosphate less
- Enzyme able to perform direct substrate phosphorylation = kinase
Indirect formation of ATP: oxidation
Three ways this can happen?
- Reaction with oxygen
- Withdrawal of electrons
- Dehydrogenation (reducing & oxidizing: NAD
-> NADH)
For everything that becomes oxidated, something else becomes reduced.
Oxidation = ?
Reduction = ?
Oxidation = loss of electrons
Reduction = gain of electrons
An oxidizing agent is a substance that causes oxidation by accepting electrons; therefore, it gets reduced. A reducing agent is a substance that causes reduction by losing electrons; therefore it gets oxidized.
Inner vs outer membrane mitochondria in terms of permeability?
Outer membrane mitochondria: partially permeable
Inner membrane: very impermeable
What compartmentalizes mitochondria?
- Cristae and matrix compartmentalize mitochondrion space
How is oxidative phosphorylation performed?
- Nutrients provide high energy electrons in the form of NADH
- NADH = used by membrane protein complexes to pump protons from matrix to intermembrane space
- Proton gradient to matrix
- When they re-enter matrix through ATP synthase, ATP is catabolized.
O2 is the terminal electron aceptor: protons carry through the membrane when they meet oxygen. Water is made.
Oxidative phosphorylation:
Takes place where? What does it regenerate?
Cristae in mitochondria. Proteins located in the inner mitochondrial membrane.
Regenerates NADH and FADH by oxidation and phosphorylation of ADP > ATP
Why is NADHc that has to enter mitochondria worth less ATP?
Takes some ATP to let NADH enter mitochondria. Is now worth 1.5 ATP.
Energy transfer by oxidation: who is the acceptor and who is the donor?
Substrate: electron or H-donor
Oxygen: electron or H-acceptor
What is respirometry?
measuring oxygen consumption and thereby mitochondrial activity.
How is ROS formed during oxidative phosphorylation?
Electrons are very unstable. Sometimes, during oxidative phosphorylation, electrons can escape the respiratory chain/proteins to yield O2. Results in ROS. One radical every 25 molecules O2 reduced
Uncoupling proteins: what do they do?
They make sure there is no ATP synthesized by interfering in the ox. phosph.
E.g. DiNitroPhenol: binds to membrane and takes up H+ meant for the ATP synthase. Releases it back to the mitochondrial matrix. Very toxic, for heat production instead of energy storage (losing weight)
Are uncoupling proteins naturally present in the body? If so, where?
Brown adipose tissue
Muscle and other tissues
Important to keep your temperature stable. Heat production to maintain body temperature: non-shivering thermogenesis. Also important in body weight regulation.
The glycerophophate shuttle: what does it do? How much ATP?
Transport of reducing equivalents (NADH) from cytoplasm into the mitochondrion by the glycerophosphate shuttle
This ‘shuttle’ has a specific transporter on the membrane. When NADH in the cytosol needs to enter the mitochondrial matrix, you will always lose 1 ATP (2.5 – 1 = 1.5 ATP). This happens because it is converted to FADH2.
So, what may the mitochondrial electron transport chain produce?
- ROS
- ATP from ATP
- Heat
- (water)
isolated mitochondria are incubated with 10 mol (cytoplasmic) NADH. How many mol of ATP will be formed?
1.5 x 10 = 15 mol ATP
1 mol NADHc = 1.5 ATP
What If you use a homogenate of mitochondria
homogenate = crushed mito’s, so not intact. Nothing happens.
What main event happens in the case of uncoupling of oxidative phosphorylation?
No ATP formed
Krebs cycle: What is needed? Where is it located? Common pathway of what?
Acetyl-CoA: needed for the cycle. Can come from protein, glucose, fat. Will produce 2 CO2 and a lot of H+ carriers. Krebs cycle is fully in the matrix of the mitochondria.
> is the common pathway to oxidize carbohydrates, fat and protein
> Acetyl-CoA is the ONLY substrate (activated acetic acid)
> Carbohydrates, fat and protein have first to be converted to acetyl-CoA.
At the krebs cycle, one … and four … reactions are happening
Four oxidation reactions
one substrate-level phosphorylation.
Krebs cycle in terms of C-carbons?
4C OAA + 2C acetyl-CoA -> 6 Citrate
4C oxaloacetate
+ 2C Acetyl-CoA
6C Citrate
6C isocitrate
5C ketoglutarate
4C succinyl-CoA
4C succinate
4C fumarate
4C malate
4C oxaloacetate
What is step 1 of the Krebs cycle? (You can use metabolic map). Energy ?
- Condensation of acetyl CoA and oxaloacetate -> citrate (no energy requested/produced)
What is step 2 of the Krebs cycle? (You can use metabolic map). Energy ?
- Citrate converted into cis-aconitate into isocitrate (no energy requested/produced)
What is step 3 of the Krebs cycle? (You can use metabolic map). Energy ?
- First oxidation happening: decarboxylation (-CO2) and oxidation -> ketoglutarate. 2.5 ATP and one carbon released.
What is step 4 of the Krebs cycle? (You can use metabolic map). Energy ?
- Another oxidation: decarboxylation and oxidation -> succinyl CoA. 1 NADH and CO2 formed.
What is step 5 of the Krebs cycle? (You can use metabolic map). Energy ?
- Substrate-level phosphorylation. Production of GTP by succinyl CoA synthetase. (So, +1ATP)
All reactions in krebs cycle are reversible.
What is step 6 of the Krebs cycle? (You can use metabolic map). Energy ?
- Dehydrogenation -> carbon-carbon double bond. FADH formed, 1.5 ATP.
What is step 7 of the Krebs cycle? (You can use metabolic map). Energy ?
- Addition of water across the carbon-carbon double bond. No energy needed or produced. Malate formed.
What is step 8 (final) of the Krebs cycle? (You can use metabolic map). Energy ?
- Oxidation to reform oxaloacetate. Energy produced in the form of NADH.
How much ATP is produced for each Acetyl-CoA entering the krebs cycle?
For every acetyl-CoA entering the cycle, 10 ATP is produced.
What is the rate limiting enzyme of TCA cycle?
Citrate synthase. This enzyme converts OAA -> citrate.
How is citrate synthase regulated?
Inhibited by high ratio’s of
ATP over ADP
Acetly-CoA over CoA
NADH over NAD+
And by high frquency of citrate and succinyl-CoA
For each glucose, you will get … ATP from the krebs cycle, because ..
For each glucose, you will get 20 ATP from the cycle. Gluc = 6C -> 2x pyruvate = 3C, lose one C each. = 2x acetyl-CoA
How can fat burn in the presence of carbohydrate?
> Lot of Acetyl-CoA from fat
Also need lot of oxaloacetate = made from pyruvate, originating from the glycolysis.
Only when a lot of acetyl-CoA is coming and the OAA pool needs to be refuelled
When is the carbon of acetyl-CoA released in tje krebs cycle?
not released in the first cycle, but in the next.
