Bio chap 18

Differential gene expression

The expression of different genes, allowing cells to carry out their specific function

How can two cells within the same set of genes function differently

Each gene requires particular transcription factors. Different cells have different transcription factors

Regulation of enzyme activity

Regulation of enzyme production

A cluster of functionally related genes can be coordinately controlled by a _____

single “on-off switch”

The “switch” is a segment of DNA called an ________ usually positioned within the promoter.

Operator

Operon

The entire stretch of DNA that includes the operator, the promoter, and the genes that they control

The operon can be switched off by a protein _____

regulatory gene

What does the repressor prevent?

Gene transcription by binding to the operator and blocking RNA polymerase

The repressor is the product of a separate?

regulatory gene

What is depicted?

Tryptophan absent, repressor inactive, operon on

The repressor can be in an active or inactive form, depending on the presence of other molecules

True

Corepressor

A molecule that cooperates with a repressor protein to switch an operon off

What is depicted

Tryptophan present, repressor active, operon off

Repressible operon

One that is usually on; binding of a repressor to the operon shuts off transcription

Inducible operon

The one that is usually off; a molecule called in inducer inactivates the repressor and turns on transcription

The trp operon is a repressible operon

True

What is depicted?

Lactose absent, repressor active, operon off

What is depicted?

Lactose present, repressor inactive, operon on

Usually function in catabolic pathways; their synthesis is induced by a chemical signal

Inducible enzymes

Usually function in anabolic pathways, their synthesis is repressed by high levels of the end production

Repressible enzymes

What does the regulation of trp and lac operon involve?

Negative control of genes

What are operon switched off by?

The active form of the repressor

Some operons are also subject to positive control through a stimulatory protein, such as catabolite activator protein (CAP), an _________ of transcription

Activator

When glucose (a preferred food source of E. coli) is scarce, CAP is activated by binding with ______

cyclic AMP

Lactose present, glucose scarce

Lactose present, glucose present

All organisms must regulate which genes are expressed at any given time

True

In multicellular organisms regulation of gene expression is essential for _____ specialization

cell

Differences between cell types result from

differential gene expression

Differential gene expression

The expression of different genes by cells with the same genome

Abnormalities in gene expression can lead to diseases including cancer

True

Gene expression can be controlled by

• DNA packing

• Transcription initiation

• RNA processing

• mRNA transport

• mRNA translation

• Degradation of mRNA

• Protein processing

• Degradation of protein

What are the two main types of gene expression?

Transcription and translation

Which of the following stages of gene expression regulation involves modifications to mRNA after transcription?

Post-translational control

What is the primary function of the operator in an operon?

To serve as the binding site for regulatory proteins

Identify the regulatory protein that promotes RNA polymerase binding and stimulates the transcription process.

Activator

The lac operon is involved in lactose metabolism in bacteria. It is activated under which condition?

In the presence of lactose and the absence of glucose.

In the availability of lactose and the absence of glucose, bacteria express lac operon genes which encode enzymes for lactose uptake and metabolism. Lac operon is an example of:

inducible operons

Why is the trp operon classified as a repressible operon?

Because it is always active unless tryptophan is present.

How does the feedback mechanism of the trp operon ensure the balance of tryptophan synthesis in the cell?

By adjusting the activity of the TRP repressor based on tryptophan levels.

How do the lac operon and trp operon illustrate opposing gene regulation mechanisms?

The lac operon is activated by an inducer, whereas the trp operon is repressed by a corepressor.

Which scenario correctly describes the lac and trp operon regulation when regulatory molecules are absent?

In the absence of allolactose, the lac operon is repressed, and in the absence of tryptophan, the trp operon is active.