BIO 210 EXAM 4 PT 2

constitutive

Genes that are unregulated (Always on), have essentially constant levels of expression, and frequently encode proteins that are continuously necessary for the survival of the organism.

Repressor

Protein that binds to a cis acting regulatory DNA element and prevents transcription

The somewhat imprecise term that describes how transcriptional regulation is influenced by glucose is _____________ ___________.

catabolite repression

A group of two or more genes under the transcriptional control of a single promoter is termed a(n) _________________ .

operon

In an E. coli cell, when tryptophan levels are low ______.

trpE, trpD, trpC, trpB, and trp A genes will be transcribed trp repressor cannot bind to the operator site

nutritional opportunists

1) must be able to recognize environmental conditions in which they should activate or repress the transcription of the relevant genes 2) must be able to toggle on or off the transcription of each specific gene or group of genes 3) Genes that are unregulated are termed constitutive

Exposure of bacterial cells to lactose increases levels of lactose-utilizing enzymes ______.

1,000- to 10,000-fold

How do a corepressor and an inhibitor differ?

A corepressor binds to a repressor protein, while an inhibitor binds to an activator protein.

The operon is flanked by a(n) ___________ that signals the beginning of transcription and a(n) _____________ that signals the end of transcription.

Promoter: terminator

Activator

Protein when bound to a cis acting regulatory DNA element, such as a promoter or an enhancer, activates transcription of an adjacent promoter

Allosteric transition

a change from one conformation of a protein to another

Allosteric effector

a small molecule that binds to an allosteric site

The intracellular concentration of the inducer ____________ remains high as long as lactose is available in the environment.

allolactose

A conformational change that prevents the lac repressor from binding to the lac operator occurs when __________ binds to the lac repressor.

allolactose (inducer) or lactose

Allolactose molecules bind to regulatory sites on the lac repressor protein called _____________ sites that differ from the region of the repressor that binds the operator.

allosteric

When tryptophan levels are high, tryptophan binds to trp repressor protein causing a conformational change that in turn causes the trp repressor to:

bind to the operator site.

When the lac repressor is bound to the operator, RNA polymerase ______ the lacZ, lacY, or lacA genes.

cannot transCribe

Unregulated genes have ______.

constant levels of expression

Unregulated genes are also called __________ genes.

constitutive (always on)

Many bacterial species use sugars sequentially. This is called ______.

diauxic growth

The research of Monod and Jacob that led to the initial understanding of gene regulation stemmed from an interest in ______.

enzyme adaptation

In catabolite repression, transcription is influenced by the presence of ______.

glucose

The enzyme beta-galactosidase cleaves the sugar lactose into ___________and _________________.

glucose and galactose

When both lactose and glucose are absent, concentrations of cAMP are ______

high

When tryptophan levels are low, the transcription of the trp operon will occur at a ______ rate because ______.

high ; the trp repressor cannot bind to the operator site

The small effector molecule that prevents the lac repressor from binding to the operator site is ______________.

inducer

When both lactose and glucose are absent ______.

lac operon transcription rate is very low lac repressor is bound to the operator CAP is bound to the DNA

The ______ gene encodes a repressor protein.

lacI

Which of the following are protein-coding genes in the lac operon?

lacY lacZ lacA

Monod and Jacob studied _______________ metabolism in E. coli.

lactose

When the tryptophan level in the cell is ______, the ribosome pauses in region one of the trpL mRNA, causing region 2 to to bind to region 3 and transcription to continue.

low

Control of gene expression leads to the production of specific proteins to assist bacterial cells in responses to environmental stressors, preparation for cell division, and ______.

metabolism

A polycistronic mRNA contains the sequence(s) ______.

of two or more genes

Bacteria must ____________ to survive

regulate genes

Induction

relief or repression of a gene or set of genes under negative control

A regulatory protein that binds to DNA and inhibits transcription is known as a(n) _______________ .

repressor

The CAP site and the operator site are ______ that function in gene regulation.

short DNA segments

What type of regulatory element does not need to be adjacent to the gene(s) it is regulating?

trans-acting factor

When glucose is brought into a bacterial cell, the intracellular level of cyclic-AMP falls because the enzyme ____________ ___________ is inhibited.

adenylyl cyclase

Why does transcription of the trp operon continue when tryptophan levels are low?

The ribosome pauses in region 1, preventing the 3-4 stem-loop from forming.

True or False: The lac repressor does not completely inhibit transcription of the lacZ, lacY, and lacA genes.

True Bc of the reversible nature of its binding to the operator, the lac repressor allows low levels of transcription of the lac operon.

When bound to operator, the lac repressor ______.

allows very small amounts of the lac enzymes to be made... bc in reality the repressor does not completely inhibit transcription, so very small amounts of the operon products are made.

When can regulation occur?

1) as the gene is copied into mRNA during transCription 2) as the mRNA is translated into protein during transLation 3) as the protein undergoes posttranslational changes to make it a functional protein

What happens when levels of allolactose rise inside an E. coli cell?

Allolactose binds to the lac repressor and prevents it from binding to the operator.

Operators

DNA element at one end of an operon that is the binding site for the repressor

True or False: Gene Expression is always the same.

False

allosteric site

Site on a protein that binds a small molecule causing a change in the conformation of the protein that modifies the activity of its active site

A regulatory protein that increases the rate of transcription is a(n) ____________.

activator

Cyclic-AMP is a small effector molecule produced by the enzyme ___________ ____________.

adenylyl cyclase

Examples of a(n) ________________ stress that might require a bacterium to produce a specific protein include osmotic shock or heat shock.

environmental

Inducers

environmental agent that triggers transcription from an operon

An operon encodes a(n) _______________ mRNA, an RNA that contains the sequences of two or more genes.

polycistronic

Transcription regulation by an activator protein is considered to be ______ control.

positive

A benefit of gene regulation is that encoded proteins are not made when they are not needed. This ______.

prevents the cell from wasting energy

In bacteria, the most common way to regulate gene expression is by influencing ______.

the rate of transCription initiation

When four molecules of allolactose are bound to the lac repressor, the lac operon is induced, and RNA polymerase ______.

transcribes the operon

True or False: Gene regulation is constant.

False bc gene expression can vary under different conditions.