How are chemical reactions organized in prokaryotic and eukaryotic cells?

Question

I realized I only have a vague understanding based on what remember from high school and I don't know if they ever really broke it down for us but:

In general how do both prokaryotic and eukaryotic cells organize their chemical reactions? In prokaryotic cells I thought there were no organelles so does that mean that every reaction depends on the diffusion of the reactants throughout the cell and that any reaction could happen anywhere in the cell? And in eukaryotic cells, are organelles always used to compartmentalize stages in chemical synthesis?

What I'm getting at is that if everything is just floating around freely within a cell, wouldn't a lot of reactions interfere with each other? I'm wondering how these two types of cells approach this problem.

Answer 1

Okay, this is my first post on this site so please bear with me when it comes to the format of my response!

To begin with I'm going to try and answer your question by clarifying some things.

In prokaryotic cells I thought there were no organelles so does that mean that every reaction depends on the diffusion of the reactants throughout the cell and that any reaction could happen anywhere in the cell?

Yes and no, the fact that there are no membrane bound organelles in prokaryotic cells means a majority of the reactions occur in the cell's cytoplasm via diffusion but something to keep in mind is the selectiveness of the cell's membrane will regulate the substances entering the cell in turn controlling that reactions that occur within it.

What I'm getting at is that if everything is just floating around freely within a cell, wouldn't a lot of reactions interfere with each other?

When it comes to eukaryotic cells structures do not float around freely like soup, there is cytoskeleton composed tubules and filaments that is used for intracellular transport, this skeleton acts like a road system to move substances between static organelles. Prokaryotic cells do not require this since they do not have membrane bound organelles and the diffusion of substances into the cell is controlled by the cellular membrane.

in eukaryotic cells, are organelles always used to compartmentalize stages in chemical synthesis?

Not always, you can look at things like cellular respiration to see glycolysis occurring in the cytoplasm.

I hope this helped out some!

Answer 2

Organization of reactions occurs in both prokaryotic and eukaryotic cells. A very basic example of this would be that of multiprotein complexes such as fatty acid synthases and polyketide synthases. Organization of such complexes allows the substrate to be passed from one module to the other; in other words free diffusion of substrate is prevented. This kind of organization can also be seen in case of cell signalling receptors; there are scaffolding proteins that bind different components of signalling cascade together (for example the Grb2 protein).

Regarding organelles:

Prokaryotes do have organelles (in a way); they don't have the membrane bound organelles like ER, mitochondria etc. However, if you consider organelle to be a subcellular structural complex that is dedicated towards a certain function, then prokaryotes do have ribosomes, thylakoids, vacuoles (in some species) etc. All these structures have an organized structure that allows reactions to happen at a faster rate compared to a free-diffusion situation.

In eukaryotic cells, the organelles perform different kinds of function. Organization is one of the molecular aspects; they also can have different chemical (such as redox and ionic) environments which facilitate certain reaction. So their role they play in different metabolic reactions is a composite of all those molecular properties.

Answer 3

One more point to make that wasn't covered in the other answers - in some cases, free diffusion of reactants is desired in order to regulate cellular processes. For example, take amino acid synthesis. At least one of the enzymes in the synthesis pathways of the various amino acids is reversibly inhibited by the presence of the AA itself. Therefore, if AA levels in the cell are high (above a certain threshold concentration) then the pathway is inhibited, and no more of that particular AA is made. However, later on the cell could be in a starved state, AA levels would drop, and the enzyme machinery would start up again to make up the shortfall.

This is a very general example, of course, but there are specific instances of it all over the place - generation of ATP, glucose metabolism, fatty acid synthesis, etc.