Initiation of Translation: How Protein Synthesis Begins
- Imagine you’re assembling a complex machine.
- Before you start, you need the right tools, instructions, and a clear starting point.
- In cells, this process begins with translation initiation, the first step in building proteins from mRNA.
The Key Players in Translation
- Before diving into initiation, let’s review the essential components:
- mRNA: Carries the genetic instructions from DNA.
- Ribosome: The molecular machine that reads mRNA and assembles amino acids.
- tRNA: Transfers the correct amino acids to the ribosome.
Step-by-Step Process of Translation Initiation
1. Attachment of the Small Ribosomal Subunit
- The process begins with the small subunit of the ribosome binding to the 5′ end of the mRNA.
- This end is marked by a 5′ cap in eukaryotes, which helps the ribosome recognize and attach to the mRNA.
In prokaryotes, the small subunit binds to a specific sequence called the Shine-Dalgarno sequence.
2. Scanning for the Start Codon
- Once attached, the small subunit moves along the mRNA in the 5′ to 3′ direction, scanning for the start codon (AUG).
- This codon signals where translation should begin.
3. Binding of the Initiator tRNA
- The start codon AUG codes for the amino acid methionine.
