region of genes

Question 1

promoter

Answer 1

the first region, RNA polymerase binds to this

Question 2

operator

Answer 2

only in prokaryotes, where a repressor protein binds to alter transcription

Question 3

introns

Answer 3

do not code for proteins, are spliced out

Question 4

exons

Answer 4

regions of dna that code for proteins, not spliced out

Question 5

leader

Answer 5

in prokaryotes regulates gene expression - after operator

Question 6

how does repression work?

Answer 6

when there is a lot of tryptophan in the cell, the tryptophan binds to a repressor protein which causes it to change shape and weakly bind to the operator region of the operon.

Question 7

how does attenuation work?

Answer 7

when there is tryptophan readily available and translation and transcription is occurring at the same time. the RNA polymerase transcribes the dna template strand while a ribosome is translating the mrna strand as it is being made. then, as tryptophan is readily provided to the ribosome wherever it is needed, until a stop codon is reached. this stops the ribosome, between regions one and two on the mrna, which attract each other, stopping them from forming a hairpin loop. However, this makes regions 3 and 4 form a loop, pulling the attenuator region away from the rna polymerase as the bonds between u and a are weak. This makes the rna polymerase fall of and stops the transcription of the trp operon