Lac Operon

Olivia Hocking
Flashcards by Olivia Hocking, updated more than 1 year ago
Olivia Hocking
Created by Olivia Hocking over 5 years ago


ICFES/Saber 11 Biochemistry (Lac Operon) Flashcards on Lac Operon, created by Olivia Hocking on 06/17/2015.

Resource summary

Question Answer
What is the main function of the Lac Operon? It produces the enzymes needed to convert Lactose into Glucose when Glucose is absent
What is the role of B-Galactosidase? It hydrolyses lactose to galactose and glucose
In the presence of Glucose, what happens to B-Galactosidase? The level of the enzyme is low as it is not needed
What happens to B-Galactosiade when Glucose levels are low? The level of B-Galactosidase increases
What happens to B-Galactosidase when lactose levels are high? The level of B-Galactosidase increases
Why is B-Galactosidase referred to as an inducible enzyme? It's function can be decreased or increased depending on levels of glucose and lactose
How is lactose converted into galactose and glucose? Lactose is hydrolysed by B-galactosidase into galactose and glucose
Apart from B-Galactosidase, what other 2 enzymes are synthesized? Galactosidase ermease and thiogalactosidase transacetylase
What is the role of galactosidase permease? It is required for the transport of lactose across the cell membrane
What is the role of thiogalactoside transacetylase? It's function is unknown - it is not essential for lactose metabolism
What are the 3 structural genes involved in lactose metabolism? B-Galactosidase, thiogalactoside transacetylase, galactosidase permease
What are the genetic elements of the lac operon? Regulatory gene (i), operator site, structural genes
What is the promoter site on the lac operon? It's where the RNA polymerase binds
What is a repressor protein and what does it do? It's something that blocks the transcription of genes - it binds tightly to the operator in the absence of lactose
In the presence of lactose, what happens to the repressor? Lactose (an inducer) binds to the repressor protein causing a conformational shape change and the repressor dissociates from the operator - allowing RNA polymerase to copy the genes and produce an mRNA transcript
Where does the repressor bind when glucose is high? To the operator
Where does RNA polymerase bind to? The promoter
In the presence of glucose, what happens on the repressor? Repressor protein produced by a regulatory gene binds to the operator which prevents RNA polymerase to transcribe the lac operon
Describe how cAMP is made? PPi (pyrosphosphate) is phosphorylated from ATP by adenylate cyclase which gives cAMP
What is adenylate cyclase? The enzyme that phosphorylates ATP to cAMP
When the level of glucose drops, the level of cAMP rises through the action of what enzyme? adenylate cyclase
What is the role of CAP? It binds to the promoter region, stimulating initiation of lac mRNA synthesis
How does CAP bind to the promoter region? When cAMP is produced, it binds to CAP and then the affinity of CAP for DNA increases and therefore it binds to the promoter region
Summarise what happens to the levels of everything involved in the lac operon if lactose is high? Lactose is high Glucose is low cAMP is high CAP is high 3 genes are high - B-galactosidase, transacetylase and permease
Summarise what happens to the levels of everything involved in the lac operon if glucose is high? Glucose is high Lactose is low cAMP is low CAP is low 3 genes are low: B-galactosidase, transacetylase, permease
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