Exam jan feb 2021

Question 1

A mutation with the promoter region can alter transcription of a gene. Describe how this can happen?

Answer 1

A mutation in the promoter region can change the binding site for a transcription factor that normally binds to increase transcription. The mutation could either decrease the ability of the transcription factor to bind, thereby decreasing transcription, or it can increase the ability of the transcription factor to bind, thus increasing transcription.

Question 2

List and explain 3 types regulatory molecules

Answer 2

Repressors: transcription factor that suppresses transcription of a gene in response to an external stimulus by binding to a DNA sequence within the regulatory region called the operator, which is located between the RNA polymerase binding site of the promoter and the transcriptional start site of the first structural gene
Activators transcription factor that increases the transcription of a gene in response to an external stimulus by facilitating RNA polymerase binding to the promote
Inducers regulatory molecule, is a small molecule that either activates or represses transcription by interacting with a repressor or an activator.

Question 3

Explain how an operon operates by a negative repressible mechanism

Answer 3

Trp operon works in negative repressible mechanisms. High amount of tryptophan operon is off
low trp operon is on
When tryptophan is not present in the cell, the repressor by itself does not bind to the operator; therefore, the operon is active and tryptophan is synthesized. However, when tryptophan accumulates in the cell, two tryptophan molecules bind to the trp repressor molecule, which changes its shape, allowing it to bind to the trp operator. This binding of the active form of the trp repressor to the operator blocks RNA polymerase from transcribing the structural genes, stopping expression of the operon. Thus, the actual product of the biosynthetic pathway controlled by the operon regulates the expression of the operon.