Effects of insulin on metabolic processes

[HopefulMDclass2020]

If a diabetic patient injects insulin into their bloodstream, which of the following enzymes is most likely to increase in activity as a result?

Glycogen phosphorylase
Carnitine-acylcarnitine translocase
Fatty acid synthases
Glucose-6-phosphatase

"B is correct. This question is asking us to determine the effects of a sudden increase in insulin on the activity of four enzymes. We know that insulin acts to increase the uptake of glucose and fatty acids so that they can be catabolized into energetically useful molecules. Since carnitine acylcarnitine translocase is involved in the catabolism of fatty acids.
A: Glycogen phosphorylase is involved in breaking glycogen down into glucose, which opposes the effects of insulin.
C: Insulin acts to decrease the amount of fatty acids in the body.
D: Glucose-6-phosphatase removes a phosphate from glucose-6-phosphate, which is a step in gluconeogenesis, which opposes the effects of insulin."

Shouldn't C be correct? I thought that insulin stimulated the conversion or fuel to long-term storage (fat). It seems a little odd that insulin would stimulate beta-oxidation. Thoughts?

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[sc4s2cg]

Which book is this from? I didn't think we had to know the enzymes this in depth, although you could probably infer some from the name and background knowledge I suppose.

In any case: insulin actually inhibits fatty acid breakdown. Remember that the initial condition (from cell POV and prior to insulin) was that there wasn't enough glucose, or at least the cells couldn't get their grubby little hands on glucose. So they then switch to alternative fuel sources, especially beta oxidation, and use fats available from your adipose cells. Once insulin is available again, glucose is able to be transported inside the cells for ATP production. And once the preferred mode of energy source is now available and in abundance, beta oxidation is no longer needed. So insulin turns it off, IE: FA are not so much being broken down as they are remade and plugged back into adipose tissue, and that's how "insulin acts to decrease the amount of fatty acids in the body".

Glucagon does the opposite: it hears the starving cries of our cells, assumes there is not enough of the primary energy source (glucose), and stimulates adipose cells to release those FA. Once the FA are out beta oxidation is stimulated, the cells get some limited energy. Then we shoot up insulin, which will cause adipose to suck the FA back up and have the cells switch over to the now-available glucose.

Simplified version, but I hope it helps.

 

[HopefulMDclass2020]

This was a next step full length, and some of the enzymes were talked about in the passage. The issue with this is, carnitine translocase is an enzyme used in beta oxidation. So it seems very odd. You even mentioned yourself that it "inhibits fatty acid breakdown". I just figured with insulin triggers a "fed state" that we would not need to be breaking down fats, but rather synthesizing them. What do you think? I am still do not like this question lol.

 

[amy_k]

The carnitine-acylcarnitine shuttles FA back and forth across the mitochondrial membrane, i am wondering if the question is referring to increased uptake of FA by expelling the FA out of the mitochondria into the cytosol, thus increasing its activity in reverse. Rather than promoting beta oxidation, the carnitine shuttle is releasing any fatty acids in the mitochondrial matrix into circulation where they can then be taken up for long-term storage conversion. Insulin is known to trigger increased fat storage so this must be what they are getting at.

 

[kingtal0n]

wow this was a tough one. I would not have gotten this. For starters "glycogen" looks kind of like "glucose" and in a rush on a test you might mistake one for the other
, also knowing your phosphatases from your phosphorylases. I could rule out the fatty acid synthases, when I think insulin I do naturally consider that those fatty acids are coming into the cells so we would decrease the internal manufacture of them, if that is what a fatty acid synthase does (sounds like it but you never know right!)