Question

RECALL What is the Shine-Dalgarno sequence? What role does it play in protein synthesis?

Short answer

The Shine-Dalgarno sequence is a ribosomal binding site in prokaryotic mRNA, playing a key role in the initiation of protein synthesis by aligning the ribosome with the start codon.

Step-by-step solution

- Define the Shine-Dalgarno Sequence

The Shine-Dalgarno sequence is a ribosomal binding site in bacterial and archaeal messenger RNA, located upstream of the start codon. Its consensus sequence is AGGAGGU.

- Understand Its Position

Identify that the Shine-Dalgarno sequence is typically found 6-10 nucleotides upstream of the start codon, AUG, in prokaryotic cells.

- Describe Its Role in Protein Synthesis

The Shine-Dalgarno sequence plays a crucial role in the initiation of protein synthesis by aligning the ribosome with the start codon, ensuring that translation begins at the correct location.

Key concepts

Ribosomal Binding Site

The Shine-Dalgarno sequence is a key player in protein synthesis. This sequence acts as a ribosomal binding site in prokaryotic organisms like bacteria and archaea. Located in the messenger RNA (mRNA), it is found just upstream of the start codon. Specifically, its consensus sequence is AGGAGGU.
This critical sequence ensures that the ribosome attaches to the mRNA correctly. Once attached, the ribosome can start translating the mRNA into a protein. Without the Shine-Dalgarno sequence, the ribosome could miss the start codon, leading to errors in protein synthesis.
Understanding this binding site helps us grasp how the genetic code is translated correctly, allowing living organisms to function properly.

• Located upstream of the start codon
• Consensus sequence: AGGAGGU
• Ensures proper ribosome attachment and alignment

Prokaryotic Translation Initiation

In prokaryotic cells, the initiation of translation is a well-coordinated process. It starts when the ribosome binds to the mRNA at the Shine-Dalgarno sequence. This sequence is typically found 6-10 nucleotides upstream of the start codon, AUG.
The small subunit of the ribosome first attaches to the mRNA with the help of initiation factors. Once the small subunit is in place, the large ribosomal subunit joins, completing the ribosomal assembly.
The Shine-Dalgarno sequence guarantees that the ribosome is positioned correctly. This ensures that translation begins precisely at the start codon.
This step is vital because any mistake in the alignment could lead to the production of non-functional proteins.

• Occurs in prokaryotic cells
• Initiation factors help in ribosome assembly
• Correct alignment is crucial for functional protein synthesis

Start Codon Alignment

The start codon, usually AUG, signals the beginning of protein synthesis. Proper alignment of this codon is critical. The Shine-Dalgarno sequence plays an essential role in this alignment.
By binding to the Shine-Dalgarno sequence, the ribosome's small subunit can make sure it is positioned correctly. This alignment allows translation to start at the right point on the mRNA.
Once aligned, the ribosome can accurately translate the mRNA into a protein, codon by codon. Every three nucleotides on the mRNA, called a codon, corresponds to a specific amino acid.
Any misalignment could cause translation to start at the wrong point, leading to incomplete or faulty proteins. With precise alignment, cells can produce the proteins they need to function.

• Start codon is usually AUG
• Shine-Dalgarno sequence ensures correct alignment
• Accurate translation is crucial for functional proteins