3 upvotes, 3 direct replies (showing 3)
View submission: Does The Endoplasmic Reticulum Transport ATP?
Hi. The ER is used for the transport of proteins and other complex molecules as you mentioned, but that does not really include ATP. ATP, whether it's made by oxidative reactions (glycolysis --> electron transport chain) or anaerobic respiration, is utilized instantly. Thus, a cell makes ATP *as required*; it isn't transported nor saved for later usage.
ATP doesn't *really* need to travel around cells, since it's used instantly to power reactions that the cell needs. And it's not just made in one location; glycolysis occurs throughout the cytoplasm, which then later shifts to the mitochondria for the Krebs cycle and ETC.
Comment by bioentropy at 17/12/2015 at 02:55 UTC
3 upvotes, 0 direct replies
this isn't entirely accurate. So firstly, ATP isn't just made as needed. This is generally a property of substances that experience a "product sink" or are rate-limiting which is generally correlated with an unfavorable free energy for the reaction. ATP does not fall into this category.
Generally, ATP floats around at, what is thought to be, a typically homogeneous concentration throughout the cell. If ATP was made as needed then its synthesis would be the rate-limiting step in processes like muscular contraction. Its not.
ATP increases within the lumen of the endoplasmic reticulum upon intracellular Ca2+ release
That's the title of the article. They use a flourescent ATP sensor that its genetically engineered to locate in the ER. They show that ATP can be pumped into the ER and this can be triggered by Ca2+ signaling activity. Which makes sense, as its known to cost ATP in order to sequester calcium in the ER. So more signaling needs more energy and the cell regulates transport into the ER accordingly.
Generally ATP is thought to travel by diffusion, facillitated across membranes and simple Brownian motion in the cyto/nucleoplasm. However, I encourage anyone to post a study that shows any exceptions, because that would be really interesting.
P.s. in case you were wondering and don't want to read the paper. They showed that the increase in ER ATP concentration was independent of calcium triggering increased ATP synthesis.
Comment by CharlesOSmith at 17/12/2015 at 14:20 UTC
2 upvotes, 0 direct replies
/u/bioentropy makes some very good points, but I'd like to clear up a little misunderstanding on ATP namely:
Thus, a cell makes ATP as required; it isn't transported nor saved for later usage.
This is wrong.
The cell makes ATP constantly. The reason for this is because ATP is *not* some magic molecule that *stores* energy and gives it away. ATP is the energy molecule of choice for the cell only because the cell maintains the chemical reaction: ADP +Pi --> ATP extremely far away from its chemical equilibrium. The driving force for ATP to break down to ADP + Pi is extremely high in the cell. That is where the energy in ATP is *stored.*
When you think about it that way you can see that the cell can't make ATP only when it needs it. It has to constantly make ATP to maintain the concentration of ATP far from equilibrium.
A cell can drastically increase the rate that it makes ATP in response to an increase in ATP demand.
Comment by Dudeguy21 at 16/12/2015 at 20:54 UTC
1 upvotes, 0 direct replies
Thanks!
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