SAT Subject Test in Biology › Transcription
The lac operon is an inducible operon. Which of the following best describes this type of operon?
The operon is usually off and has an active repressor
The operon is usually off and has an inactive repressor
The operon is usually on and has an active repressor
The operon is usually on and has an inactive repressor
None of these
With an inducible system, the operon is off, meaning its repressor is active, or actively repressing the system from turning on. Inducible operons are opposite to a repressible operon, which is always on until it is repressed.
The trp operon is a repressible operon. Which of the following best describes this type of operon?
The operon is usually on and has an inactive repressor
The operon is usually off and has an active repressor
The operon is usually off and has an inactive repressor
The operon is usually on and has an active repressor
None are correct
With a repressible system, the operon is on, meaning the repressor is inactive. Repressible operons are the opposite of inducible operons, which are always off until their repressor is inactivated.
What is the dividing structure that separates transcription from translation in a eukaryotic cell?
Nuclear envelope
Mitochondrial matrix
Rough endoplasmic reticulum membrane
Smooth endoplasmic reticulum membrane
Cell membrane
The nuclear envelope separates transcription from translation in a eukaryotic cell. Translation cannot occur until transcription is finished, which is the opposite of what occurs in a prokaryotic cell. In eukaryotic cells, transcription occurs in the nucleus where mRNA will be produced. Once mRNA is produced, it will exit the nucleus through pores and then proceed to be translated into protein in the cytoplasm.
At what point does transcription occur in relation to gene expression?
It is the first step
It is the last step in this process
It is the step following translation
Transcription is unrelated to gene expression
Transcription is a process that only occurs in eukaryotes
Transcription is the first process of gene expression and happens before translation.