Is protein function determined by primary or tertiary structure?

[zzomg]

Is protein function determined by primary or tertiary structure?

I feel like there are conflicting answers to this, probably because both play a role...tertiary structure is the actual 3-D structure, which dictates how the protein interacts on a molecular level, but primary structure ultimately determines tertiary...a recent practice question said primary structure, but I've seen tertiary as the answer before...Does anyone have a clear answer/reasoning for that answer??

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[rxlea]

Well, what happens when a protein is denatured? Does it still maintain function?

 

[whiteshadodw]

Is protein function determined by primary or tertiary structure?

I feel like there are conflicting answers to this, probably because both play a role...tertiary structure is the actual 3-D structure, which dictates how the protein interacts on a molecular level, but primary structure ultimately determines tertiary...a recent practice question said primary structure, but I've seen tertiary as the answer before...Does anyone have a clear answer/reasoning for that answer??

interesting question. what happens if you change an important catalytic residue but maintain tertiary structure? no function. what if you denature something and it loses shape? no function. both are right. a question like this on the MCAT would definitely be more explicit, examples:

it is found that a patient has a single amino acid mutation resulting in the change in activity of phosphofructokinase. this mutation most directly affects?
-answer: primary structure, its a single amino acid mutation, the rest of the protein is probably the same.

urea, a denaturing agent and byproduct of amino acid metabolism is found abnormally in other parts of the body. enzymes in this part of the body are unable to function properly most likely due to a change in:
-tertiary structure. overall shape has changed.

 

[Temperature101]

Is protein function determined by primary or tertiary structure?

I feel like there are conflicting answers to this, probably because both play a role...tertiary structure is the actual 3-D structure, which dictates how the protein interacts on a molecular level, but primary structure ultimately determines tertiary...a recent practice question said primary structure, but I've seen tertiary as the answer before...Does anyone have a clear answer/reasoning for that answer??

That's a tricky question...But I would say when proteins are being denatured, their primary structures are disrupted first (of course).And if the primary stucture of a globular protein is disrupted, the protein loose its function. Therefore, more information is needed to answer this type of question.

 

[ppfizenm]

That's a tricky question...But I would say when proteins are being denatured, their primary structures are disrupted first (of course).And if the primary stucture of a globular protein is disrupted, the protein loose its function. Therefore, more information is needed to answer this type of question.

This is a completely wrong answer. When proteins are denatured the first thing that is lost is tertiary structure. The 3D shape of the molecule breaks down. Primary structure (or protein sequence) is only lost when the protein is degraded by proteases.

To answer the OP's question I would have to say function is determined by tertiary structure. An unfolded protein will have no function (though it generally is the primary structure of the protein that defines tertiary). That being said you would never get a question like this on the MCAT because the answer is up for debate.

 

[ThirdEye]

Both. Primary determines tertiary, tertiary gives shape, shape gives function

 

[tendiw]

Answer: tertiary structure
It is side chain interactions that determine tertiary structure (along with pH and all that good stuff)

If you want to get the question right, pick tertiary. Function depends on shaped which is tertiary.

 

[salim271]

Both. Primary determines tertiary, tertiary gives shape, shape gives function

There's enough ambiguity in this question to make it a verbal question lol... I would pick tertiary if I had to choose between two, because when they say structure determines function, its the tertiary structure that is determining the function. The primary structure does determine the tertiary structure though.

 

[To be MD]

Directly out of my biology notes I have the answer as tertiary.

 

[notbobtrustme]

The way the question is phrased, the answer is tertiary. You can have two proteins with the same primary sequence but be non-functional due to the environment, such as hot temperatures or low/high pH. When you change the primary sequence, you change the tertiary sequence as well, even if it's only one residue out of a thousand.

 

[whiteshadodw]

The way the question is phrased, the answer is tertiary. You can have two proteins with the same primary sequence but be non-functional due to the environment, such as hot temperatures or low/high pH. When you change the primary sequence, you change the tertiary sequence as well, even if it's only one residue out of a thousand.

not always, and its not always something significant. glycine to alanine in hydrophobic region? probably not going to effect things much. any one of 3 from the canonical catalytic triad, then you probably lose function, but even then you may not lose shape. any protein function question is likely to have plenty of information to help make a correct decision.

 

[Chrome19]

It's safer to answer tertiary since two proteins with different primary structures (different amino acid sequences) can have the same function. Most likely, the catalytic domain of both proteins have similar folds, hence tertiary is the most inclusive answer and the most directly related to function.

 

[TieuBachHo]

Is protein function determined by primary or tertiary structure?

I feel like there are conflicting answers to this, probably because both play a role...tertiary structure is the actual 3-D structure, which dictates how the protein interacts on a molecular level, but primary structure ultimately determines tertiary...a recent practice question said primary structure, but I've seen tertiary as the answer before...Does anyone have a clear answer/reasoning for that answer??

The concensus here is tertiary structure. The functions of proteins is determined by its tertiary structure. Primary structure is just a joined AAs sequence. It has nothing to do with a protein's function. How the proteins fold matters most. For example, when a question asks you, which of the following is the rate-determine step? Obviously, the slowest step, right? You can't just say that faster steps dictate the slowest step, and therefore they are also rate-determine steps. This is just my illustration point on the logical fallacy.

To put it in perspective, if the primary structure changes, the tertiary protein's function MAY OR MAY NOT change depending on how it affects the outcome.

 

[Morsetlis]

Consider that, in order to achieve a certain tertiary structure, the unfolded protein needs chaperones and heat shock proteins to protect and help it fold as it exits the ribosome.

Denaturation undoes this. Re-naturation is usually impossible without the hsp and chaperones. But the protein still has the same primary structure.

 

[movax]

It's a really vague question. I totally agree with the posters who have been saying it is tertiary, but at first glance I could see how someone would say primary as well. It's the order of the amino acids that dictate what that protein is in the first place, and the order / acids themselves contribute to the tertiary structure, IIRC. (i.e. cysteines bonding to each other, prolines causing kinks)

 

[hematosis]

You guys are thinking too deep.

The function of a protein is determined by its shape. The shape of a protein is determined by the primary structure.

If you are interested in protein structure-function, read about "the protein folding problem"

http://www.dillgroup.ucsf.edu/dl_papers/Solved_2007.pdf

 

[MD Odyssey]

One way to approach this problem is to consider multiple functional copies of a particular protein, perhaps hemoglobin. If you look at the amino acid sequence of the protein across different species, essentially different versions of the protein, you will find that there can be some variation in the amino acid sequence. This is due to the fact that protein structure is conserved more than amino acid sequence.

So, if one were forced to pick one or the other, tertiary structure is probably a better answer since we can make selective modifications to the amino acid sequence (the primary structure) without altering the protein function.

 

[Pisiform]

For MCAT, protein function is determined by Tertiary structure. Primary structure just dictates the amino acid sequence.