Cycloheximide inhibits protein synthesis in eukaryotes, specifically by blocking the translocation step in the process.

Here's a breakdown:

* Eukaryotic protein synthesis: The ribosome moves along the mRNA, reading codons and adding amino acids to the growing polypeptide chain. This movement is called translocation.

* Cycloheximide's mechanism: Cycloheximide binds to the 60S ribosomal subunit, a key component of the ribosome. This binding prevents the ribosome from translocating along the mRNA.

* Result: Without translocation, the ribosome gets stuck, and no further amino acids can be added to the polypeptide chain. This effectively halts protein synthesis.

Important Note: Cycloheximide does not affect prokaryotic protein synthesis. Prokaryotes have a different ribosomal structure, and cycloheximide cannot bind to their ribosomes.