3.6 - Regulating Gene Expression: Bacterial mal and lac operons Flashcards
How lactose activates lac operon?
When lactose is available, some molecules will be converted to allolactose inside the cell. Allolactose binds to the lac repressor and makes it change shape so it can no longer bind DNA. (Allolactose is an example of an inducer, a small molecule that triggers expression of a gene or operon.)
How does glucose affect the lac operon?
Glucose stops activation of the lac operon, which prevents lactose use and leads to preferential use of glucose.
Why does the lactose operon can’t be activated when both lactose and glucose are present? (for interest only)
Glucose present, lactose absent: No transcription of the lac operon occurs. That’s because the lac repressor remains bound to the operator and prevents transcription by RNA polymerase. Also, cAMP levels are low because glucose levels are high, so CAP is inactive and cannot bind DNA.
Why is lactose also called as inducer?
Lactose acts as an inducer of lac operon when it binds to the repressor protein and prevents it from binding to the operator. In absence of an inducer, the repressor binds to the operator and inhibits RNA polymerase to bind promoter and start transcription.
Where can the transcriptional activator binding site be relative to the promoter?
A. upstream
B. downstream
C. overlapping the promoter
D. all of the above
D
How is the maltose operon regulated?
MalT binds to maltose and undergoes a conformational change that allows it to bind DNA at sequences near the promoters of genes required for uptake and catabolism of these sugars. malT is regulated by catabolite repression via the catabolite activator protein.
MCQ fill in the blank:
Inducers bind to _____ and _____ transcription
A. polymerase; promote
B. promoter; inhibit
C. repressors; promote
D. activators; inhibit
C
T or F:
In prokaryotes, the translation of mRNA can start before transcription is even completed
T
What are the 3 proteins that the Lactose (Lac) operon codes for?
A. LacA B. LacY C. LacZ D. Lacl E. LacL
A B C
Fill in the blank:
If there is no regulatory
protein present, the promoter is most likely
_______(weak/strong) for a negative regulated
gene, and _______(weak/strong) for a
positive regulated gene.
strong, weak
What is the difference between constitutive transcription and regulated transcription?
Constitutive genes are always being expressed (usually at a basal/regular level) but regulated genes are only expressed under certain necessary conditions in order to save cellular energy.
What are the structural components of a bacterial operon?
A regulatory gene: The regulatory gene codes for a regulatory protein.
An operator: The operator is the region of DNA of the operon that is the binding site for the regulatory protein.
A promoter.
Structural genes.
What is gene expression?
The process of transcribing the nucleotide sequence of one strand of a gene (DNA) int oa nucleotide sequence of mRNA and the ntranslating the info in the nucleotide of mRNA to the sequence of amino acids.
What is wild type cell?
Typical form of the cell, organism, gene, protein, or characteristic as it occurs in nature.
How is mutation related to cellular inheritance?
If the mutaton is lethal to the cell, it will not be inherited.