chapter 18

A(n) ---- is a regulatory sequence of noncoding DNA located near the promoter of a gene.

proximal control element

inducible operon

is turned on when a small molecule binds to a regulatory protein, preventing the regulatory protein from binding to the operator.

Which of the following regulatory elements is not composed of DNA sequences?

activators -are proteins that are involved in transcription initiation.

methylation

addition of methyl group

True or False? Pattern formation refers to events that organize embryonic cells in space

true Pattern formation is the process by which the location of an embryo's body segments is determined.

Which of the following statements about the Bicoid protein is true?

- regulatory transcription factor The Bicoid protein regulates expression of the embryo's early developmental genes.

Operon vocabularyPart complete Can you match terms related to operons to their definitions?

An operon is made up of a promoter and the genes of the operon. The promoter, which includes an operator, is the stretch of DNA where RNA polymerase binds. Regulatory proteins bind to the operator. The genes of the operon code for a related set of proteins. A regulatory gene located away from the operon codes for a protein that controls the operon.

Part complete If deletion of a control element causes a reduction in gene expression, what must be the normal role of that control element? If deletion of a control element causes a reduction in gene expression, what must be the normal role of that control element?

To activate gene expression; without the control element, activators are not able to bind to the enhancer, and the level of gene expression decreases.

acetylation of histones

Unwinds DNA, adds actyl group- changes shape = genes turned ON neutralizes a positive charge on lysine

The ----is/are arranged sequentially after the promoter.

genes of an operon

operon is transcribed quickly through positive control

lac operon: lactose present, glucose absent

operon is transcribed, but not sped up through positive control

lac operon: lactose present, glucose presenttrp operon: tryptophan absent

A(n) ----- is a regulatory protein that is required for the transcription of all protein-coding genes.

general transcription factor

How is the lac operon regulated?

-The lac operon undergoes positive control. -When lactose (and, therefore, allolactose) is absent, the regulatory protein is active. -The lac operon undergoes negative control. -When glucose is absent, cAMP binds to catabolite activator protein (CAP), activating CAP to increase transcription of the operon. The lac operon undergoes both negative control and positive control. Negative control: When lactose is absent, the repressor protein is active, and transcription is turned off. When lactose is present, the repressor protein is inactivated, and transcription is turned on. Positive control: When glucose is absent, another regulatory protein (CAP) binds to the promoter of the lac operon, increasing the rate of transcription if lactose is present.

repressible operon

A(n) repressible operon is turned off when a small molecule binds to a regulatory protein, which then binds to the operator.

Can you describe the process of alternative RNA splicing? opened hint Which choice(s) accurately describe(s) the process of alternative RNA splicing? Select all that apply.

All introns of the primary RNA transcript are removed. Some exons of the primary RNA transcript may be removed. Alternative RNA processing is a process in which all introns are removed and some exons may be removed from the primary RNA transcript.

Overview of operon control

An operon consists of a group of related genes that are transcribed into a single messenger RNA molecule from a single promoter. The switch that controls the transcription of an operon is a segment of DNA called an operator, which is usually part of the promoter. An operon is regulated by a regulatory protein that is transcribed from a regulatory gene outside of the operon DNA. The regulatory protein can be an activator, which in its active form stimulates gene transcription, or a repressor, which switches off the operon. However, a repressor can be inactivated when a small molecule called an inducer binds to the repressor, altering its conformation.

How is the trp operon regulated?

By transcription attenuation .

negative control

Control group where conditions produce a negative outcome. Negative control groups help identify outside influences which may be present that were not accounted for when the procedure was created.

Modification of chromatin structure Part complete Which statements about the modification of chromatin structure in eukaryotes are true? Select all that apply.

DNA is not transcribed when chromatin is packaged tightly in a condensed form. Methylation of histone tails in chromatin can promote condensation of the chromatin. Some forms of chromatin modification can be passed on to future generations of cells. Acetylation of histone tails is a reversible process. Acetylation of histone tails in chromatin allows access to DNA for transcription.

Which of the following regulatory DNA sequences might be located thousands of nucleotides away from the transcription start site of a gene?

Enhancers can function thousands of nucleotides away from the promoter and transcription start site.

True or false? Regulatory and basal transcription factors regulate transcription by binding to the promoter.

FALSE Basal transcription factors do indeed bind to the promoter, but regulatory transcription factors bind to promoter-proximal elements and enhancers.

positive control

Group expected to have a positive result, allowing the researcher to show that the experimental set up was capable of producing results.

You are studying a bacterium that utilizes a sugar called athelose. This sugar can be used as an energy source when necessary. Metabolism of athelose is controlled by the ath operon. The genes of the ath operon code for the enzymes necessary to use athelose as an energy source. You have found the following: The genes of the ath operon are expressed only when the concentration of athelose in the bacterium is high. When glucose is absent, the bacterium needs to metabolize athelose as an energy source as much as possible. The same catabolite activator protein (CAP) involved with the lac operon interacts with the ath operon. Based on this information, how is the ath operon most likely controlled?

Metabolism of the sugar athelose in this hypothetical system is controlled by an operon that exhibits both positive control and negative control. Transcription of the ath operon is turned on when athelose is present (negative control), and sped up when the bacterium runs out of glucose and must rely on athelose for energy (positive control).

Which of the following statements about a gene that shows maternal effect inheritance is true?

Offspring will show a mutant phenotype if the mother has a mutant genotype. This statement is true; the gene is transcribed in the mother, and the mRNA is delivered to the zygote.

^^^

One of the mechanisms by which eukaryotes regulate gene expression is through modifications to chromatin structure. When chromatin is condensed, DNA is not accessible for transcription. Acetylation of histone tails reduces the attraction between neighboring nucleosomes, causing chromatin to assume a looser structure and allowing access to the DNA for transcription. If the histone tails undergo deacetylation, chromatin can recondense, once again making DNA inaccessible for transcription. Recent evidence suggests that methylation of histone tails can promote either the condensation or the decondensation of chromatin, depending on where the methyl groups are located on the histones. Thus, methylation can either inactivate or activate transcription, and demethylation can reverse the effect of methylation. Changes in chromatin structure may be passed on to future generations of cells in a type of inheritance called epigenetic inheritance.

All your cells contain proto-oncogenes, which can change into cancer-causing genes. Why do cells possess such potential time bombs? See Concept 18.5 (Page)

Proto-oncogenes are necessary for the normal control of cell growth and division. Proto-oncogenes can become oncogenes when a mutation or other genetic change increases the activity of the encoded protein.

Which of the following events in transcription initiation likely occurs last?

RNA polymerase binds to the promoter of the gene. RNA polymerase is recruited only when other transcription factors, including TBP, are assembled at the promoter.

If bicoid mRNA is injected at the anterior end of an egg from a bicoid mutant mother, what would the phenotype of the resulting larva be?

The larva would be normal with one head at the anterior pole.

True or false? One possible way to alter chromatin structure such that genes could be transcribed would be to make histone proteins more positively charged.

The positive charge on histone proteins allows them to interact tightly with negatively charged DNA, thus inhibiting transcription. To disrupt this interaction, the histone proteins would have to be made more negatively charged.

Which body part develops in regions with a low concentration of Bicoid protein?

The regions with low concentrations of Bicoid protein develop into posterior structures such as the abdomen.

The trp and lac operons are regulated in various ways. How do bacteria regulate transcription of these operons?

The trp operon is regulated through negative control only. When tryptophan is present, the operon genes are not transcribed. The lac operon is regulated through both negative control and positive control. Negative control: When lactose is absent, the repressor protein is active, and transcription is turned off. When lactose is present, the repressor protein is inactivated, and transcription is turned on. Positive control: When glucose is absent, another regulatory protein (CAP) binds to the promoter of the lac operon, increasing the rate of transcription if lactose is present.

If deletion of a control element causes an increase in gene expression, what must be the normal role of that control element?

To repress gene expression; without the control element, repressors are not able to bind to the enhancer, and the level of gene expression increases.

How is the trp operon regulated? opened hint How is the trp operon regulated? Select the three statements that apply.

When tryptophan is absent, the regulatory protein is inactive. When tryptophan is present, it binds to the regulatory protein, activating it. The trp operon undergoes negative control. When the concentration of tryptophan in the bacterium is low, the repressor protein is inactive, and transcription occurs. When the concentration of tryptophan is high, tryptophan binds to and activates the repressor protein. The repressor protein binds to the operator of the operon, turning off transcription.

Part complete Where is bicoid mRNA translated?

bicoid mRNA is translated at the anterior pole of the fertilized egg.

miRNAs can control gene expression by what action?

binding to mRNAs and degrading them or blocking their translation miRNAs can effectively "silence" genes by binding to mRNA transcripts. The mRNAs are either broken down by enzymes or are unable to physically interact with the ribosomes to complete translation.

A(n) ----- is a regulatory sequence of noncoding DNA located far from the promoter of a gene.

distal control element

A grouping of several regulatory DNA sequences located far from the promoter of a gene is called a(n) ----

enhancer

A(n) ---- is a specific small molecule that binds to a bacterial regulatory protein and changes its shape so that it cannot bind to an operator, thus switching an operon on.

inducer

Regulatory proteins bind to the ------to control expression of the operon.

operator

A(n) ---- is a stretch of DNA consisting of an operator, a promoter, and genes for a related set of proteins, usually making up an entire metabolic pathway.

operon

A(n) ----- is a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.

promoter

A(n) ------ codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes.

regulatory gene

A(n) ------ is a protein that inhibits gene transcription. In prokaryotes, this protein binds to the DNA in or near the promoter.

repressor

both

reversible catalyzed by enzymes alter chromatin structure

A regulatory protein that interacts with control elements of particular genes is called a(n)

specific transcription factor

operon is not transcribed

trp operon: tryptophan presentlac operon: lactose absent