Um, what? (ATP-dependent mechanisms)

[chreesteene]

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Um, so have I been secretly sniffing some strong glue or is Kaplan ****ting me when they claim that:

1. Exocytosis of synaptic vesicles at a nerve terminal is ATP-dependent.
I've never heard of this before, not even in my Principles of the Nervous System course. Did I just miss this? I thought that the action potential arriving at the nerve terminal opened voltage-gated calcium channels allowed an influx of calcium, which is somehow correlated to SNARE proteins binding to vesicle receptors, which eventually leads to vesicle fusion with the nerve terminal's membrane --> release of vesicle contents. When does ATP factor into this whole mess?

2. Movement of calcium into a muscle cell is also ATP-dependent.
Again, WUT? Isn't the extracellular calcium concentration like 1000 times higher than intracell. concentrations? Plus: Action potential travels down T-tubules --> opens DHP receptor --> opens ryanodine receptor --> calcium efflux from SR. Only pumping calcium back INTO the SR requires ATP. Right?

Please help if you can! I am majorly freaked out because Kaplan has just shattered my faith in life.

 

[HawkeyePostOp]

1) Vescicular transport proteins such as SNARE require a proton gradient. This gradient is created by a vacuolar type H+ ATPase.

2)Way cool. I had no idea.

http://www.ebi.ac.uk/interpro/potm/2004_3/Page2.htm

"The SERCA2a (ATPase) isoform is expressed in the SR of cardiac muscle, where it plays a key role in the contraction and relaxation of cardiac muscle through its control of cytosolic calcium levels. "

SERCA2 is also found in other tissues, but I still thought Ca didn't really need a pump for movement into a muscle cell.

 

[mytoechondriac]

My EK Bio book also says thtat exocytosis(AND endocytosis) require ATP.

This also came as a surprise to me, since it wasn't mentioned in my cell bio class.

 

[minhaj]

exocytosis and endocytosis require ATP because the microfilaments/microtubules involved in the movement of vesicles require ATP.

 

[tco]

1. I'm not so sure that it's the process itself that requires ATP, but to release clathrin coated pits from the vesicles requires dephosphorylation of GTP, so exocytosis and endocytosis of any kind require energy, but not necessarily ATP. It seems like these review books think that GTP and ATP are the same thing.

SNAREs definitely do not require any energy to function. They operate via hydrophobic interactions...

2. I don't know about movement of calcium into muscle cells, but release of calcium from the sarcoplasmic reticulum is cyclic AMP dependent.

 

[chreesteene]

thank you! thank you! y'all are a smart bunch!

 

[kevindurant]

Um, so have I been secretly sniffing some strong glue or is Kaplan ****ting me when they claim that:

2. Movement of calcium into a muscle cell is also ATP-dependent.
Again, WUT? Isn't the extracellular calcium concentration like 1000 times higher than intracell. concentrations? Plus: Action potential travels down T-tubules --> opens DHP receptor --> opens ryanodine receptor --> calcium efflux from SR. Only pumping calcium back INTO the SR requires ATP. Right?

Please help if you can! I am majorly freaked out because Kaplan has just shattered my faith in life.

Yea, it is ATP dependent. it's not talking about moving calcium from the sarcoplasm into the sarcoplasmic reticulum. that IS passive transport. it's talking about moving calcium from OUTSIDE the entire muscle cell, across the sarcolemma, and into the sarcoplasm. that is active transport because completely OUTSIDE the muscle cell is low Ca2+ with high Ca2+ inside the sarcoplasm. just assume ATP's involved with active transport (unless it was secondary active transport I know there's not ATP, but in this case it's primary).

I learned this lesson through Kaplan, too, haha.