Three daily Biochem questions for you all (6/4)

1. Glucose-6-phosphate dehydrogenase (G6PD) is a cytosolic enzyme that converts Glucose-6-phosphate from Glycolosis into 6-Phosphogluconolactone in the Pentose Phosphate Pathway, generating one NADPH in this reaction. Research interest has growin in a molecule called Compound X, which has been shown to irreversibly inhibit G6PD. Compound X most likely ultimately affects which cellular process?

A) Glycogenisis

B) Cystein oxidation at the ER

C) DNA Replication

D) Glycolosis

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2. Phosphofructokinase-2 (PFK-2) is a unique enzyme in that it contains both a phosphatase domain and a kinase domain. Phosphorylation of PFK-2 by the PKA/cAMP secondary messenger system results in activation of the phosphatase domain and inhibition of the kinase domain on PFK-2. The kinase domain phosphorylates Fructose-6-phosphate into Fructose-2-,6-bisphophate which allosterically activates Phosphofructokinase-1. How would Glucagon binding affect PFK-2 activity in the liver?

A) Glucagon signalling causes dephosphorylation of PFK-2 and thus promotes Glycolosis.

B) Glucagon signalling causes phosphorylation of PFK-2 and thus inhibits Glycolosis.

C) Glucagon signalling causes phosphorylation of PFK-2 and thus promotes Glycolosis.

D) Glucagon has no effect on PFK-2 activity in the liver.

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3. If one NADH is oxidized by Complex I of the Electron Transport Chain, ultimately how many ATP will be generated as a result of this process?

A) 1.5

B) 2.5

C) 3

D) 5

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Answers posted at midnight EST.

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Whoops sorry for the late answers guys I completely forgot. Anyway, here they are!

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1. C. The inhibition of G6PD of the Pentose Phosphate Pathway would result in loss of a cell's ability to produce Ribose-5-phosphate and NADPH. None of the processes mentioned use NADPH, but DNA Replication requires ribose for purine and pyrimidine synthesis. So inhibition of G6PD would result in a cell unable to make Ribose-5-Phosphate and thus a cell could not make nucleotides for DNA Replication, Transcription, etc.

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2. B. B is the correct answer because Glucagon is released by alpha-cells of the pancreas during times of low blood-glucose levels to trigger the liver to export more glucose into the blood via Gluconeogenisis. Gluconeogenisis can only be active if Glycolosis is not running concurrently. Therefor, A and C are automatically wrong. It is stated that PFK-2's phosphatase domain is active when it is phosphorylated and that PFK-2 phosphatase activity lowers F-2,6-BP levels which would lower PFK-1 activity. Seeing as how Glucagon is responsible for activating Gluconeogenisis (which means Glycolosis is shut off and thus PFK-2's phosphatase domain is active) then PFK-2 must be phosphorylated in response to Glucagon binding.

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3. B. When NADH is oxidized by Complex I, 4 protons are pumped by Complex I into the intermembrane space. As the electrons from NADH oxidation are passed along to Complexes III and IV pump 6 more protons (4 from Complex III and 2 from Complex 4) into the intermembrane space. In total, 10 protons are pumped into the intermembrane space as a result of NADH oxidation. It takes 4 protons for every phosphorylation of ADP to ATP. So 10/4 = 2.5 and thus B is correct.