Functional organization of the Human Genome
The human genome comprises an estimated 20,500 "genes",
which can be assigned to functional categories as above.
Only about 20% of the transcripts are
responsible for classical biochemical functions,
loosely catalytic enzymes. Approximately a
quarter of the genome is responsbile for maintenance
of the genome itself, including polymerases,
ligases, helicases, etc. as
discussed under DNA replication, transcription
and control of transcription, and translation
Another
21% are responsible for signal transduction,
for example relaying information about the extracellular
environment across the cell membrane to the cell
nucleus, so as to produce the appropriate response by
change in gene expression.The function of more than
a third of the genome is at present unknown.
Inference of the function of this portion of the genome
proceeds by identification of sequence motifs and comparison with
homologous genes in other creatures.