Gluconeogenesis and pentose phosphate pathway

13 important questions on Gluconeogenesis and pentose phosphate pathway

What percentage of NADPH is needed for fatty acid synthesis?

50% (and the only source in red blood cells)

Neutral energetics - mass driven equilibrium

energy invested in forward reaction is released in backward reaction

To which extent is the nature of protein relevant for the outcome of gluconeogenesis?

About 10% is only ketogenic, so cannot be converted into glucose. This means if you can get 66 gram, 10% of this, will result in 60 gram of glucose which can be formed.
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How much gram glucose can be formed out of 100 gram protein?

- Mean MW of amino acids = 137 g/mol
- 100 gram protein = 100/137= 0.73 mol
- Max 1 PEP per amino acid can be formed
- 0.73 mol of PEP --> 0.73/2(because 2 molecules) = 0.36 mol glucose  
- 0.36 mol glucose = 0.36x180 = 66 gram glucose

Energetics in glucose substrate cycling:

- Hexokinase: -1 from glycolysis
-  PF kinase: -1 from glycolysis
- Pyr. kinase: +2 from glycolysis and -4 from gluconeogenesis = -2
- Mito membrane: -2 from gluconeogenesis
--> Total: -6 in glucose substrate cycling

Costs glucose substrate cycling, related to level:

- Glucose: 0
- G-6-P: -1
- F-1,6-P: -2
- PEP: -2
- Pyruvate: -6 (2 pyruvate, so 2x -3)

A high formation of acetyl-coa change to

oxaloacetate

High level of AMP and low ATP stimulates

TCA cycle, condensation of OAA and acetyl-coa

Low level of AMP and high ATP stimulates

gluconeogenesis, OAA is converted to PEP, inhibition of glycolysis

The lactic pathway is used by which organs/cells when ratio of oxygen supply to oxygen need falls below critical level?

skeletal muscles (normal daily happening, does not harm muscle)
heart (myocardial ischemia can occur under (long time) anaerobic conditions)

What about the first law of thermodynamics (conservation of energy)?

- Glucose --> lactate provides 2 ATP
- Lactate --> glucose requires 8 ATP
- But there is always conservation of energy, relating to heat production

What is the ratio in ATP yield of aerobic and anaerobic breakdown of glucose?

- 30/2 = 15
- EE aerobic = 35%
- EE anaerobic = 75%

NADH released during glycolysis is re-used in:

generation of lactate

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