BRS Physiology diagram error?

[pmartinez527]

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Hey all, I had a question about a pair of diagrams in BRS Physiology, 5th edition.

In Figures 7-1 and 7-2 (pp225-226), the G protein is shown with GDP--->GTP beneath it. However, my understanding is that GDP is already bound to the G protein, and then GTP comes in and replaces it.
Page 224 seems to confirm this, saying "GDP is released from the G protein and replaced by GTP". If this is the case, then shouldn't the diagram show GTP--->GDP? Is this an error in both figures or am I just looking at it the wrong way?


Also, does anybody know of any errata (official or unofficial) for BRS Phys 5th edition?

 

[iheartmints]

Hey all, I had a question about a pair of diagrams in BRS Physiology, 5th edition.

In Figures 7-1 and 7-2 (pp225-226), the G protein is shown with GDP--->GTP beneath it. However, my understanding is that GDP is already bound to the G protein, and then GTP comes in and replaces it.
Page 224 seems to confirm this, saying "GDP is released from the G protein and replaced by GTP". If this is the case, then shouldn't the diagram show GTP--->GDP? Is this an error in both figures or am I just looking at it the wrong way?


Also, does anybody know of any errata (official or unofficial) for BRS Phys 5th edition?

The figures are fine and your explanation is fine but you're interpreting the diagram wrong. It's showing exactly what you're saying: GDP was bound to the G protein but it gets replaced by GTP.


("If this is the case, then shouldn't the diagram show GTP--->GDP?" That would mean GTP was bound but is now replaced by GDP which is not right as you explained earlier)

 

[pmartinez527]

The figures are fine and your explanation is fine but you're interpreting the diagram wrong. It's showing exactly what you're saying: GDP was bound to the G protein but it gets replaced by GTP.


("If this is the case, then shouldn't the diagram show GTP--->GDP?" That would mean GTP was bound but is now replaced by GDP which is not right as you explained earlier)

I guess I should have also mentioned that it is a curved arrow, which looks like it is indicating GDP goes in, GTP comes out (as is the case in most biochem drawings).

Right next to it in 7-1 there is adenylate cyclase, beneath which is shown ATP--->cAMP (also a curved arrow). In this case ATP goes in and cAMP comes out... as it should. The text corroborates this exactly. The other arrows in the diagram are all straight lines (i.e. cAMP--->5'-AMP).

It seems rather illogical to illustrate two different concepts using the same symbol 😕

 

[iheartmints]

I guess I should have also mentioned that it is a curved arrow, which looks like it is indicating GDP goes in, GTP comes out (as is the case in most biochem drawings).

Right next to it in 7-1 there is adenylate cyclase, beneath which is shown ATP--->cAMP (also a curved arrow). In this case ATP goes in and cAMP comes out... as it should. The text corroborates this exactly. The other arrows in the diagram are all straight lines (i.e. cAMP--->5'-AMP).

It seems rather illogical to illustrate two different concepts using the same symbol 😕

You're reading way too much into this. The end of the arrow points at what used to be there and the arrowhead points to what is now there. Just move on