Eukaryotic cells express different genes at the same time
Eukaryotic cells express different genes at the same time because the gene contain same response elements in their regulatory promoters, all of which bind the same transcription activator.
The genes expressed at same time must have same regulatory element sequence in promoters and transcription factors or activators bind to the regulatory elements so that genes can be transcribed.
This is called as coordinate gene expression. It means genes having same regulatory element in the promoter will transcribed or expressed at the same time.
The response elements are known as binding sites for transcriptional activators to elevate transcription.
The response element can be same for different genes and therefore it allows multiple genes to be activated by the same stimulus.
In eukaryotic cells, gene expression can be controlled so that all proteins in a pathway are expressed at the same time. This can be controlled as genes on different parts of chromosomes contain same DNA response element in their promoter.