fluorescence wavelength exponentials logarithm help

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sushi19921992

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hey guys,

I'm trying to understand at the moment a graph that displays the ratio of wavelengths/fluorescence intensity and concentration. At the moment, I understand the graph that has fluorescence on the y and wavelength on the x, but I don't understand this other curve.

A good example is seen below.


Anyone with any knowledge or mathematically understanding of logarithms / exponentials explain this one to me? I'm confused by it at the moment...

Thanks
 
I see nothing there about fluorescence and wavelength! Is this the right picture?

The first looks like a logistic growth curve, and the second is its derivative.
 
So from the above picture, the graph on the left, say those 2 lines, one of them has a concentration of 6 and the other of 0 (chemical denaturant concentration). Then the picture on the right is what I don't understand. It says Fluorescence ratio (or what you'll find alot of the time on the Y axis is Ratio 330-350nm). I'm not sure what the "Ratio" actually is in this case and how it's calculated
 
I don't think this is (yet) a math question.

To find out what a quantity means, you have to ask the author, or search sources related to the problem domain. What do they say "fluorescence ratio" means?

Once you have a definition, maybe we will be able to help interpret it. But a graph by itself doesn't define the quantities displayed. The graph does resemble a logistic curve, but lots of things behave like that.
 
Hmmm ok, maybe what I could ask, is what an equation might be for a graph like that? What would be an example logarithmic equation? i.e. y = ALogbX where A, B and X are all variable... Could something like that be defined?
 
sushi19921992 said:
Hmmm ok, maybe what I could ask, is what an equation might be for a graph like that? What would be an example logarithmic equation? i.e. y = ALogbX where A, B and X are all variable... Could something like that be defined?
Click to expand...

So, you haven't taken my hint and looked up "logistic curve", which I've mentioned twice??

Try here: https://en.wikipedia.org/wiki/Logistic_function (Note that it is exponential, not logarithmic.)

Of course, this isn't how a formula is determined in science (just looking at a graph and saying what it looks like). In principle, you should have some model of the phenomenon on which to base both the general form and the particular parameters. So far, we don't even know what the phenomenon is.

Maybe you should tell us the real context of your question?
 
Sorry, it's late and my brain didn't realize you said logistic curve twice...

I'm essentially trying to understand how that logistic curve, if that's what it seems to be, is actually calculated in the first place. The Y appears to be ratio of wavelength against something like denaturant concentration or temperature, but... Ratio of wavelength is calculated how? That's why I'm confused on how the curve is somehow logarithmic.
 
I think you really have to gather information from that field. I found the image you sent here, in what is basically an ad for a machine that produces such graphs. I imagine the graphs are just general representations of the concept, not really representative of actual detailed behavior; but in any case, you would look in the documentation for the machine, or in journal articles about the measurements they are doing. Research, not guessing, is what you need.

Trying to help as a complete outsider, it appears that when a protein unfolds, the frequencies of the fluorescence shift upward, and they are looking for the temperature or concentration at which it reaches the midpoint of this shift. It doesn't say what ratio they are measuring. In fact, in searching for articles using keywords from your question, I found this, which mentions several different ratios that can be used, and includes pictures of which your graph would be a generalization.

So, as I expected, the real graphs the machine gives will not be created using a formula, but from actual measurements that are expected to look generally like the logistic curve, whose midpoint is considered an indication of unfolding. You don't need to know the formula. You need to know the science behind the measurements and what they signify. Only that can tell you why the curve looks like it does.
 
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