I was wondering if there is any process in cells (any at all, but specifically I was trying to think about mammals that would perform this). That take glucose and break it down to an amino acid and then use it for protein synthesis? I guess to simplify it would there be a process inverse of Gluconeogenesis? Or similar to Gluconeogenesis just taking glucose instead of proteins and breaking it down to conduct protein synthesis?

I have been searching for hours, but any time glucose and protein are together in my search its hundreds of pages on Glycogenesis, Glycogenolysis and Gluconeogenesis and even De Novo Synthesis, but I can't find anywhere saying no this doesn't happen or if there is even a possibility.

But thinking theoretically wouldn't the fuctions of Gluconeogenesis + De Novo Synthesis, leave a possibility for any protein that would be needed in a cell (present or not) to be created from breaking down other cellular materials or energy?

Thank you very much for you time!

We (humans) can and do produce amino acids, though only half of the varieties we need. One example is tryptophan. We can't make it, so is considered an essential nutrient because it must be part of our diet. More specificaly, we can't make the side chain of tryptophan, called an idole group. Basically all amino acid backbones are manufactured from sugar and amino groups, the latter recovered from consumed protein. The rate limiting step is usually the acquisition of nitrogen; a historically limited resource, an entire niche of microorganisms is defined by the ability to convert virtually inert nitrogen gas into biologically available ammonia.

While in principle all of the necessary materials are present in a active human cell to manufacture amino acid backbones, it is the derivation of the side chains that is problematic. So in answer to your question, a human cell cannot make most of it's proteins by simply breaking down parts of itself, it needs more externally sourced nutrients to complete it's complement of available amino acids.

Some complementing of things you can't make, like some vitamins, is done by your gut flora, though I'm not sure of the details in this case.

In an interesting aside, because some microorganisms make the amino acids that we don't, they possess synthesis pathways and enzymes that we don't. In pathogenic organisms these unshared biochemistries are attractive targets for anti-microbial drugs, as they minimise the risk of negative interactions with any human proteins which might be related or perform similar functions.