Concepts

In both prokaryotic and eukaryotic cells, multiple ribosomes may be attached to a single mRNA, generating a structure called a polyribosome.

Connecting Concepts j"

A Comparison of Bacterial and Eukaryotic Translation

We have now considered the process of translation in bacterial cells and noted some distinctive differences that exist in eukaryotic cells. Let's take a few minutes to reflect on some of the important similarities and differences of protein synthesis in bacterial and eukaryotic cells.

First, we should emphasize that the genetic code of bacterial and eukaryotic cells is virtually identical; the only difference is in the amino acid specified by the initiation codon. In bacterial cells, AUG codes for a modified type of methionine, N-formylmethionine, whereas, in eukaryotic

Stop codon

Release factors

The polypeptide is released from the tRNA in the P site.

When the ribosome translocates to a stop codon, there is no tRNA with an anticodon that can pair with the codon in the A site.

Stop codon

Release factors

^ .and RF3 forms a complex with GTP and binds to the ribosome.

The polypeptide is released from the tRNA in the P site.

I GTP associated with RF3 is hydrolyzed to GDP.

I GTP associated with RF3 is hydrolyzed to GDP.

release factors are released from the ribosome.

Conclusion: When a stop codon is encountered, release factors associate with the ribosome and bring about the termination of translation.

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