|In my AP Bio class we learned that a gene codes
for a specific protein (the central dogma of
biology: transcription, translation, etc...).
I've also read that according to the Human Genome
Project that we humans have 30,000 genes, and on
another website I read humans have 100,000
proteins. How can we have more proteins than
genes? Do some genes contain code for more than
one protein? Do some proteins come from pieces
of DNA that aren't "genes"?
Good thinking! To answer your questions, all
proteins come from genes, however, a single gene
can encode for several forms of a single protein.
These are called splice variants and are a result
of alternate splicing by the splicisome during
transcription resulting in slightly different
proteins that may have vastly different functions.
These proteins are often referred to as iso forms.
Additionally, a single gene can produce a single
protein during translation but that protein can
then be altered in a manner that is referred to as
post-translational modification. There are many
different modifications that can occur
(phosphoryltation, gylcosylation, etc.) however if
the protein is post translationally cleaved it
could become a similar protein as the original
product but have a very different structure or
function. Hope this answers your questions. I
have underlined some words that you can trough
into Google if you want more detail.
As you ask, there are some genes that code for
more than one protein. This can happen in two
ways: initiation sequences at different points in
a DNA strand that are frame shifted from other
initiation sequences, causing the transcription
proteins to getup to three different proteins from
a single section of DNA, and also the alteration
of protein strands subsequent to translation,
including different attachments to other proteins,
sugars, lipids, and even simply in different
geometries of itself. I suspect that the bulk of
the extra proteins are of the second type, but I
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