Question

An RNA leader whose secondary structure, and thus its effect on gene expression, is determined by whether or not it's bound to a small molecule effector is called a(n):

a) Riboswitch
b) Regulator
c) Promoter
d) Attenuator

Answer 1

An RNA leader that is affected by the binding of a small molecule effector, altering gene expression, is known as a riboswitch. It is a regulatory element within prokaryotic RNA that can influence the formation of secondary structures, affecting transcription and translation.

Step-by-step explanation:

An RNA leader whose secondary structure, and thus its effect on gene expression, is determined by whether or not it's bound to a small molecule effector is called a riboswitch. This is a small region of noncoding RNA found within the 5' end of some prokaryotic mRNA molecules. When this riboswitch is bound to a small molecule, like a metabolic product, it can stabilize certain secondary structures of the mRNA molecule, impacting the synthesis of the mRNA and the protein production.

Riboswitches play a role in regulatory mechanisms such as attenuation, a process that influences the continuation or termination of transcription based on the formation of RNA stem-loops within the leader sequence of the mRNA. In the context of the trp operon in E. coli, the mRNA can form a terminator stem-loop that leads to the dissociation of RNA polymerase and the end of transcription or it can form an antiterminator stem-loop that allows transcription to continue.