Hoatlin: Fundamentals

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  • 1) When you talk about the number of base pairs in a genome, the number 3 x 10^9 was mentioned and I wanted to double check, is this for the haploid genome? And just out of curiosity, why is it reported for the haploid genome?
  • 2) When you were talking about DNA replication a "licensing factor" was mentioned, and I was wondering, is this a protein? And what is it's function?
  • 1. Yes, for haploid. Diploid cells have two homologous copies of each chromosome (in humans, one from the mother and one from the father) to you would be counting twice. YOu could do that, but it is important to say which genome you are talking about. I think the haploid number is reported b/c it is the total number of unique sequences.
  • 2. Yes licensing factor is the old name for a set of proteins that bind to the origins. Licensing factor is now thought to include the proteins Cdc6 and Cdt1. These proteins bind to the origin recognition complex, and are synthesized only in a specific phase of the cell cycle (G1). Once replication origins "fire" (or start) these proteins are degraded or exported and the origin can't be "licensed" for firing again until the proteins are synthesized and enter the nucleus in the next cell cycle. That's how the cell controls replication so that the DNA is replicated once and only once.

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