I'm new to this community, so hopefully this is the right place to ask this question.

I know my question is really general, but in all of my biology courses we are merely taught the chemical pathways of common reactions in cellular metabolism, but we're rarely told how these reactions were determined or discovered. What approaches do molecular biologists take to determine what molecules are involved in what reactions, what order the reactions take place, where they take place, etc.? Some of these pathways involve tons of steps, huge molecules, and a bunch of enzymes and proteins, and I just don't see how anyone could have pieced it all together. For that matter, how is the molecular structure of anything in the cell determined? For example, what was the setup of the experiment that determined that TNF-R1 even existed on the surface of the cell membrane, and that it triggers the apoptosis pathway? Another example is photosynthesis -- I could see how maybe we could find PS1/2, cytochrome complexes, etc. in a soup of blended up cells, but how in the world did we figure out what each one does and in what order?

The average cell is just so tiny and complex that it doesn't seem like there's any feasible experimental design that could lead to the discovery of these things. Please enlighten me!

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    $\begingroup$ You might find the answers you seek in the autobiography of Arthur Kornberg: “For the Love of Enzymes: The Odyssey of a Biochemist” $\endgroup$ – mdperry Sep 30 '18 at 11:56
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    $\begingroup$ Welcome to SE Biology. What research have you done on this topic? First, molecular biologists had nothing to do with determining biochemical pathways, it was chemists — first called physiogical chemists, then later (in English-speaking countries) biochemists. This should give you a clue how they went about it. How does a chemist study a reaction? How would a chemist determine that yeast converts glucose to carbon dioxide? What's the next step from studying live yeast? And after showing A goes to Z, how would you look to see if there are B, C and D in between? With this in mind, search. $\endgroup$ – David Sep 30 '18 at 15:14
  • $\begingroup$ Have fun. Remember, Rome wasn't built in a day, and that the initial slow and limited progress was built upon by others as technological advances allowed new methods to be used. And, though cells may be small, you can get enough compounds (and enzymes out) with lots of them (e.g. yeast cultures, rat livers and kidneys). Enzyme preparations didn't have to be pure to yield information. And at the time the pathways of central metabolism were worked out (before and immediately after WWII) they didn't know anything about DNA (and probably didn't even think about it). $\endgroup$ – David Sep 30 '18 at 21:55
  • $\begingroup$ @David It's really quite fascinating how recent (late 20th century) the majority of this information came to light. I've always taken it for granted and assumed it was discovered hundreds of years ago, like many of the things we learn in the classroom. $\endgroup$ – Sully Chen Oct 1 '18 at 4:31

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