Lactose Metabolism and Lac Operon in E. coli

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What happens when the ribosome reaches the two UGG codons for tryptophan?

Translation proceeds smoothly because tryptophan is abundant. (correct)

The ribosome completely detaches from the mRNA.

Translation stalls due to lack of tRNAs.

The ribosome binds to an alternative protein.

What is the role of remodeling complexes in relation to nucleosomes?

They cause the degradation of nucleosomes.

They induce nucleosomes to release RNA.

They enable nucleosomes to slide along the DNA. (correct)

They permanently change the DNA sequence.

What is the fate of the structural genes when transcription terminates at the attenuator?

They are not transcribed at all. (correct)

They are partially transcribed.

They are fully transcribed and translated.

They are transcribed but not translated.

How does DNA methylation affect gene transcription?

Heavily methylated DNA is linked to transcription repression. Signup and view all the answers

How does antisense RNA inhibit translation of the ompF mRNA?

By binding to a complementary sequence in the mRNA. Signup and view all the answers

What triggers the production of micF RNA in E.coli?

Increase in osmolarity. Signup and view all the answers

What characterizes the epigenome?

The overall pattern of chromatin modifications. Signup and view all the answers

What role do riboswitches play in gene expression?

They alter mRNA secondary structures to influence translation. Signup and view all the answers

What is necessary for normal levels of transcription to occur?

Transcriptional regulator proteins must be present. Signup and view all the answers

Why is the regulation of the ompF gene in E.coli important?

It prevents excessive movement of substances due to osmolarity changes. Signup and view all the answers

What is a function of transcriptional activators?

They stabilize the basal transcription apparatus. Signup and view all the answers

In what ways can transcriptional regulators influence transcription?

By binding to regulatory promoters and enhancers. Signup and view all the answers

What effect does the ribosome have on region 2 of the mRNA when it is covering region 1?

It inhibits the pairing with region 2. Signup and view all the answers

Which statement about general transcription factors is correct?

They assemble into the basal transcription apparatus. Signup and view all the answers

What defines the primary function of antisense RNA in bacterial gene regulation?

To inhibit translation of specific mRNAs. Signup and view all the answers

How can coactivators assist transcriptional activators?

By interacting with other proteins to enhance transcription. Signup and view all the answers

What is the role of β-galactosidase in the metabolism of lactose by E.coli?

It catalyzes the breakdown of lactose into glucose and galactose. Signup and view all the answers

Which protein is responsible for transporting lactose into the E.coli cell?

Permease Signup and view all the answers

What triggers the induction of the lac operon?

Allolactose Signup and view all the answers

What effect does the presence of lactose have on the lac operon?

It causes a thousand fold increase in protein synthesis of the operon’s genes. Signup and view all the answers

What is the primary function of the protein encoded by the lacI gene?

To act as a repressor that blocks transcription. Signup and view all the answers

How does allolactose influence the lac operon?

It releases the repressor from the DNA. Signup and view all the answers

Which of the following enzymes has an unknown function in lactose metabolism?

Transacetylase Signup and view all the answers

What is coordinate induction in the context of the lac operon?

The simultaneous synthesis of several proteins stimulated by a specific inducer. Signup and view all the answers

What is the role of the 5′ untranslated region (5′ UTR) in the trp operon?

It serves as a regulatory mechanism. Signup and view all the answers

What occurs when cellular levels of tryptophan are high?

The attenuator structure leads to transcription termination. Signup and view all the answers

What is true about the secondary structures formed by the 5′ UTR?

The structure formed is influenced by tryptophan concentration. Signup and view all the answers

What defines the structure labeled as an antiterminator in the trp operon?

The base pairing of regions 2 and 3. Signup and view all the answers

Which statement accurately describes the trp promoter?

It allows RNA polymerase to initiate transcription when tryptophan levels are low. Signup and view all the answers

What is the consequence of the presence of two UGG codons in region 1?

They require tryptophan for the translation of the 5′ UTR sequence. Signup and view all the answers

During the transcription process of the trp operon, what occurs when tryptophan levels are low?

The enzymes that synthesize tryptophan are produced. Signup and view all the answers

What role does the long 5′ UTR serve in the regulation of the trp operon?

It facilitates the formation of secondary structures involved in transcription regulation. Signup and view all the answers

What role do insulators play in gene expression?

They block or insulate the effects of enhancers. Signup and view all the answers

What is the primary consequence of the action of adenosine deaminase on RNA?

It converts cytosine into uracil, resulting in a stop codon. Signup and view all the answers

In the T-antigen gene of the mammalian virus SV40, which factor determines which protein is produced?

The choice of alternative 5′ splice site. Signup and view all the answers

What determines the amount of protein synthesized from a gene?

The amount of corresponding mRNA available for translation. Signup and view all the answers

What happens to an mRNA molecule at the 5′ end during the degradation process?

Its 5′ cap is removed first. Signup and view all the answers

Which of the following statements about poly(A)-binding proteins (PABPs) is true?

They stabilize the poly(A) tail of mRNA. Signup and view all the answers

What is one common pathway for mRNA degradation?

5′→3′ removal of nucleotides. Signup and view all the answers

How does the stability of eukaryotic mRNA vary?

Some mRNAs last for only a few minutes, while others persist much longer. Signup and view all the answers

What happens to the mRNA when the poly(A) tail is shortened below a critical limit?

The 5′ cap is removed, leading to mRNA degradation. Signup and view all the answers

What role do P bodies play in mRNA regulation?

They store mRNA for later release or degradation. Signup and view all the answers

What percentage of human genes is suggested to be regulated by RNA interference?

30% Signup and view all the answers

How do small interfering RNAs (siRNAs) and microRNAs (miRNAs) primarily differ in their interaction with mRNA?

siRNAs tend to pair perfectly, whereas miRNAs often form less-than-perfect pairings. Signup and view all the answers

Which of the following is NOT a mechanism of gene regulation by RNA interference?

Promotion of transcription Signup and view all the answers

In an RNA-induced silencing complex (RISC), what is the role of the RNA component?

To bind with proteins and facilitate mRNA cleavage. Signup and view all the answers

What term describes the phenomenon of gene regulation through RNA interference?

Posttranscriptional gene silencing Signup and view all the answers

What occurs when RISC contains an siRNA?

It cleaves mRNA near the middle of the bound siRNA. Signup and view all the answers

Study Notes

Lactose Metabolism and the Lac Operon of E. coli

Lactose is a major carbohydrate in milk, metabolized by E. coli bacteria in the mammalian gut.
Lactose, to be used as an energy source, must be transported into the E. coli cell by permease.
Permease actively transports lactose into the cell.
Beta-galactosidase breaks lactose into galactose and glucose.
Beta-galactosidase can also convert lactose to allolactose.
Allolactose plays a crucial role in regulating lactose metabolism.
Thiogalactoside transacetylase is another enzyme produced by the lac operon, but its function in lactose metabolism is not yet known.

Regulation of the lac Operon

The lac operon is a negative inducible operon.
The enzymes beta-galactosidase, permease, and transacetylase are encoded by adjacent genes in the lac operon (lacZ, lacY, and lacA).
These enzymes share a common promoter (lacP).
If lactose is present in the medium and glucose is absent, synthesis of the three proteins increases a thousand-fold within 2-3 minutes, coordinated induction.
The lacI gene codes for a repressor
The repressor binds to laco (the operator) which overlaps the 3' end of the promoter and the 5' end of lacZ.
When the repressor binds to the operator, RNA polymerase is blocked, and transcription is prevented.
When lactose is present, some is converted to allolactose, which binds to the repressor.
This binding inactivates the repressor, releasing it from DNA.
RNA polymerase is no longer blocked, transcription of lacZ, lacY, and lacA takes place, and lac proteins are produced.

The trp Operon of E. coli

The trp operon controls the biosynthesis of the amino acid tryptophan.
It is a negative repressible operon.
Transcription is normally "on" and must be repressed.
When tryptophan levels are low, transcription occurs.
When tryptophan levels are high, tryptophan binds to the repressor, making it active.
The trp repressor binds to the operator, stopping RNA polymerase from transcribing the genes.

Regulation of Transcription Through Attenuation

Some operons, like the trp operon, regulate transcription through attenuation, a process that affects the continuation of transcription rather than its initiation.
Transcription begins at the start site, but termination takes place prematurely, before RNA polymerase reaches the structural genes.

RNA Molecules Controlling Gene Expression

Some small RNA molecules, called antisense RNA, are complementary to particular sequences on mRNA.
Antisense RNA controls gene expression by binding and inhibiting translation.
The ompF gene encodes an outer-membrane protein and functions in the passive diffusion of small polar molecules.
When osmolarity increases, the cell depresses OmpF protein production, regulating osmolarity.

Riboswitches

mRNA molecules contain regulatory sequences called riboswitches.
They control gene expression by influencing the formation of secondary structures in the mRNA.
Riboswitches are often found in the 5' UTR of mRNA molecules and fold into compact secondary structures.
Some can cause premature termination of transcription or prevent translation initiation, depending on the presence of a specific small molecule.

Gene Regulation in Eukaryotes

Eukaryotic gene regulation is more complex than bacterial gene regulation.
Genes are not usually organized into operons.
Chromatin structure affects transcription, as DNA must unwind for transcription to occur.
Changes in chromatin structure, such as histone modifications and chromatin remodeling, alter gene expression.
DNA methylation can affect chromatin structure and gene expression.
Transcription factors and transcriptional regulator proteins control gene initiation.
Activators stimulate transcription, while repressors inhibit it.
Enhancers are regulatory sequences that can stimulate transcription from a distance.
Insulators limit the effects of enhancers and prevent unwanted interactions.

mRNA Editing

mRNA editing is a process where sequences of mRNA change after transcription.
A significant example is the production of apolipoprotein B100 and apolipoprotein B48.

Alternative Splicing

An example of this is the T-antigen gene of the SV40 virus, where different proteins (large T and small t antigens,) can be produced from the same gene depending on which splice sites are used.

RNA Degradation

The amount of protein synthesized depends on the amount of mRNA available for translation.
The amount of mRNA depends on the rates of mRNA synthesis and mRNA degradation.
Various mRNA degradation mechanisms exist.

RNA Interference

RNA interference (RNAi) is a process that controls gene expression.
It employs small interfering RNAs (siRNAs) and microRNAs (miRNAs), which pair with target mRNA molecules, leading to mRNA cleavage, translation inhibition, transcriptional silencing, and mRNA degradation.

Post-translational Processing of proteins

Polypeptides emerging from ribosomes are often inactive and need post-translational modifications.
These modifications can include folding, cleavage proteolysis, chemical modifications, and modification of protein intein splicing to activate or alter the protein's function and activity.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the fascinating world of lactose metabolism in E. coli through this quiz. Learn about the lac operon, its components, and how E. coli utilizes lactose as an energy source. Test your knowledge on the regulation and function of enzymes involved in this metabolic process.