Question

Describe the mechanism behind the expression of an eukaryotic, post-translational polypeptide that is repressed when the gene producing it is turned off due to a threshold concentration being reached.

Answer 1

• The mechanism behind the expression of an eukaryotic, post-translational polypeptide is that of an operon.An operon is a group of genes that encode biosynthetic enzymes for a particular amino acid.
• When the amino acid level are high,they gets repressed (turned off).This may be because the aminoacid have reached a threshold concentration.
• The repressor gene does not always bind to DNA. Instead it binds and blocks transcription only when the aminoacid is present.When thew aminoacid is present, it attaches to the repressor molecules and changes their shape so they become active.The molecule which switches the repressor gene into its active state, is called a co-repressor.
• Another mechanism for reducing expression of the operon when levels of aminoacids are high is attenuation.It is based on coupling of transcription and translation.