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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"?
Answer 1:

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.

Answer 2:

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 don't know.


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