ID #2345

1. Does DNA replication only occur during Mitosis? 2. Does mRNA in Eukaryotes have Ribosome Binding site? Or does the 40S complex bind with 5'cap of mRNA,and it's done? 3. What are the differences between snRNA and snRNP, structurally and functionally?

1. DNA replication occurs during the interphase (S-phase) and the cell division or sister chromatids get separated during mitosis. 
2. In eukaryotes, the 40S subunit binds to the mRNA and scans for the “initiator codon: AUG” while moving in the 5’to 3’ direction. Initiation in eukaryotes is discussed in detail in your texbook. The 40S subunit in eukaryotes will bind to the 5' methylguanosine cap, and then it will scan for the nearest AUG start codon. mRNA in eukaryotes do not have ribosome binding sites. Also remember that eukaryotic mRNAs are monocistronic, so a given mRNA will only have one 5' cap and will code for only one protein. Initiator AUG recognition is illustrated in one of the slides from the Lecture 19 notes.
3. In eukaryotes, primary RNA has introns and exons and these intron-exon junctions are recognized by snRNPs. snRNPs are composed of snRNA and proteins. You can read more about the snRNPs from the textbook. Also, here is the FAQ link for it: 

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