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Breakdown of stored glycogen & fat; glycolysis

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Breakdown of stored glycogen & fat; glycolysis

Postby summerfish » Tue Apr 01, 2008 1:30 am

I've done my research but I need clarification/confirmation on how stored glycogen and stored fat enter the cellular respiration pathway.

Does both glycogenolysis (breakdown of glycogen into G6P for cellresp.) and lipid catabolism (breakdown of triglycerides for cellresp.) occur inside the cytoplasm of the cell?
ie. Are glycogen and triglycerides physically in the cytoplasm of the cell while they are broken down for cellular respiration? If so, are they transported by the bloodstream into the cell's cytoplasm before being broken down for cellular respiration?

I know that [glycerol]-->[glucose] via gluconeogensis - but what is the actual reaction taking place?
Also, what is the reaction responsible for [glycerol]-->[dihydroxyacetone phosphate] ? is it phosphorylation?

Lastly, during glycolysis, there are two occasions when ADP-->ATP. Can I say that both 'dephosphorylation' (DPGA-->3-PGA) and 'substrate-level phosphorylation' (ADP-->ATP) occur during each occasion?
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Re: Breakdown of stored glycogen & fat; glycolysis

Postby MrMistery » Tue Apr 01, 2008 1:28 pm

summerfish wrote:I've done my research but I need clarification/confirmation on how stored glycogen and stored fat enter the cellular respiration pathway.

Does both glycogenolysis (breakdown of glycogen into G6P for cellresp.) and lipid catabolism (breakdown of triglycerides for cellresp.) occur inside the cytoplasm of the cell?
ie. Are glycogen and triglycerides physically in the cytoplasm of the cell while they are broken down for cellular respiration? If so, are they transported by the bloodstream into the cell's cytoplasm before being broken down for cellular respiration?

Glycogenolysis occurs in the cytoplasm.
The oxidation of triglicerides to fatty acids and glycerol occurs in the cytoplasm. After that, glycerol is phosphorylated and enters glycolysis, while fatty acids are oxidised elsewhere. The oxidation of fatty acids in its common form(beta-oxidation) occurs in mitochondria and in peroxisomes. Other more uncommon types of fatty acid oxidation are alpha-oxidation(which takes place in peroxisomes) and omega-oxidation(which takes place in the endoplasmic reticulum).
Glycogen and fatty acids are stored locally. When needed, they are broken down, with the energy used by the cell or exported.

summerfish wrote:I know that [glycerol]-->[glucose] via gluconeogensis - but what is the actual reaction taking place?
Also, what is the reaction responsible for [glycerol]-->[dihydroxyacetone phosphate] ? is it phosphorylation?

For the exact reaction from glycerol to glucose, i'm afraid it is not one reaction, but a whole pathway. You should have learned the molecular mechanism of glycolysis before taking a crack at lipid metabolism. I'm sorry to say your teacher is not organizing his course very well. Look here for the link between glycerol and glucose
http://www.biochem.arizona.edu/classes/ ... g15-15.jpg

summerfish wrote:Lastly, during glycolysis, there are two occasions when ADP-->ATP. Can I say that both 'dephosphorylation' (DPGA-->3-PGA) and 'substrate-level phosphorylation' (ADP-->ATP) occur during each occasion?

You need to have it clear in your head what substrate level phosphorylation means. It means that a phosphate group is directly transfered from a substrate to an ADP molecule, yielding ATP. This automatically implies that the substrate is "dephosphorylated" as you say, no need to specify.
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter
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