Question

How does a eukaryotic ribosome select its start codon? Describe the sequences in eukaryotic mRNA that provide an optimal context for a start codon.

Short answer

The eukaryotic ribosome selects its start codon by scanning from the 5' end of the mRNA to the 3' end until it finds the start codon, usually 'AUG'. Sequences that provide an optimal context for this process are found in the Kozak consensus sequence around the start codon.

Step-by-step solution

Understand the concept of a start codon

The start codon is the first codon of a mRNA transcript (usually AUG) that is translated by a ribosome. In both eukaryotes and prokaryotes, the first step in translation is the binding of the ribosome to the mRNA. The first codon that it encounters which has the correct complimentary anticodon is where translation begins, this codon is the start codon.

Elucidate on selection of start codon in eukaryotes

In eukaryotes, the ribosome scans from the 5' end of the mRNA to the 3' end until it finds the start codon which is usually AUG. The eukaryotic ribosome recognizes the start codon by using initiation factors, they help to assemble the ribosome on the mRNA and locate the first AUG in a good context.

Describe the sequences that provide an optimal context for start codon

The sequences in eukaryotic mRNA that provide an optimal context for a start codon, often referred to as the Kozak consensus sequence. It is a sequence of nucleotides around the start codon AUG that is more likely to initiate translation.