[scientizscht (OP)]

Hello!

All cells in the human body have the exact same genome, however the cells are so different!
This is probably due to different genes expressed in different cells.

How is this implemented?
I am also particularly interest to know if some genes are 'covered' by proteints or other molecules so that they are 'protected' from gene expression. Is this something real?

[evan_au]

if some genes are 'covered' by proteints or other molecules so that they are 'protected' from gene expression?

Yes, methylation markers on DNA control the extent of expression of particular genes.
- The way the DNA is wrapped around histones also controls its availability for transcription

The study of these controls is called "epigenetics", see:
https://en.wikipedia.org/wiki/Epigenetics

There are even genes that control epigenetic markers...

Modern DNA sequencing machines can report on the DNA sequence, as well as methylation markers.
- However, I have not heard of sequencing machines that report on the histone structure.

The set of genes which are active in a particular cell can be deduced from:
- The frequency of Transfer RNA sequences in the cell: the "transcriptome"
- The frequency of proteins produced in the cell: the "proteome"

[chris]

All cells in the human body have the exact same genome

Not entirely! Apart from the fact that tissues evolve a complement of genetic mutations over a lifetime, cells of the immune system have different DNA because, in order to produce their T and B cell receptors, they "throw away" segments of DNA to produce unique receptor-encoding sequences.