[Hannah LS (OP)]

Laveena asks:

In humans, are all naturally occurring proteins encoded in the DNA?

What do you think?

[Bored chemist]

Arguably, one of the most common proteins- collagen- is not coded for in DNA.

However the precursors are coded for.

[evan_au]

A lot of proteins and enzymes found in the human body are not coded in the human DNA.
...because our microbiome has DNA code for more proteins than does human DNA

To a lesser extent, some proteins are coded in viral RNA (ie not DNA)

[chris]

Two clever, and interesting answers so far! I'd not thought about collagen like that before...

[evan_au]

In the early days of studying the human genome, there were some estimates that suggested the human genome might contain as many as 100,000 protein-coding genes, in order to account for the observed number of proteins in the human body.

However, the Human Genome Project revealed "only" around 25,000 protein-coding genes.

The actual proteins in our body are based on segments of DNA, and these segments can be connected up in different ways to produce different proteins.

See: https://en.wikipedia.org/wiki/Alternative_splicing