Where does the small ribosomal subunit bind on the mRNA before scanning for the start codon?

The small ribosomal subunit binds to the mRNA at the 5' end before scanning for the start codon. This process is crucial for translation initiation in eukaryotic cells, as the ribosome must locate the correct start codon (usually AUG). The binding at the 5' end enables the ribosomal subunit to scan along the mRNA in the 5' to 3' direction until it encounters the appropriate start codon in the context of the ribosome's initiation factors and the scanning mechanism.

Understanding this process is important because the initiation of translation is a key step in gene expression, and the proper functioning of the ribosome is essential for synthesizing proteins based on the mRNA's encoded information.