BIO CH 18
Which of these indicates an enhancer region?
A
The diagram below shows a segment of DNA containing an imaginary gene (Z) and the primary RNA transcript that results from the transcription of gene Z. Exons are represented in green and introns are represented in blue. Which of the following choices represent mRNA molecules that could be produced from the primary RNA transcript by alternative RNA splicing? (In each choice, the yellow part on the left represents the 5' cap, and the yellow part on the right represents the poly-A tail.)
ACEI, ACEGI, and ACGI Alternative RNA splicing produces different mRNA molecules from the same primary RNA transcript. During alternative RNA splicing, all introns are removed, and some exons may also be removed. The removal of different exons produces different mRNA molecules, which are then translated into different proteins. Alternative RNA splicing can greatly expand the number of proteins produced from the same gene.
_____ bind(s) to DNA enhancer regions.
Activators Activators are a type of transcription factor that bind to enhancer regions.
Which of the following regulatory elements is not composed of DNA sequences?
Activators Activators are proteins that are involved in transcription initiation.
The diagram below shows two stretches of DNA in the genome of an imaginary eukaryotic cell. The top stretch of DNA includes the fantasin gene, along with its promoter and one of its enhancers. The bottom stretch of DNA includes the imaginin gene, its promoter, and one of its enhancers. The slash marks (//) indicate that more than 1,000 nucleotides separate the promoter and enhancer of each gene. Which statements about the regulation of transcription initiation in these genes are true?
Both the fantasin gene and the imaginin gene will be transcribed at high levels when activators specific for control elements A, B, C, D, and E are present in the cell. Control elements A, B, and C are proximal control elements for the fantasin gene. Control elements C, D, and E are distal control elements for the imaginin gene. The imaginin gene will be transcribed at a high level when repressors specific for the imaginin gene are present in the cell. The fantasin gene will be transcribed at a high level when activators specific for control elements A, B, and C are present in the cell. The fantasin gene and the imaginin gene have identical enhancers. Both the fantasin gene and the imaginin gene will be transcribed at high levels whenever general transcription factors are present in the cell. A, C, and E In the imaginary eukaryotic cell used as an example here, the enhancers for the fantasin gene and imaginin gene are unique because they contain different sets of control elements (A, B, and C for the fantasin gene; C, D, and E for the imaginin gene). Each gene will be transcribed at a high level when activators specific for all of the control elements in its enhancer are present in the cell.
Which of these directly bind(s) to the promoter?
C and D Both RNA polymerase and transcription factors bind with the promoter.
Chemotherapeutic treatment for breast cancer depends on the absence or overexpression of the __________ gene(s).
ERa, PR, and HER2
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.
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.
False 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 of the following best describes the makeup of the human genome?
Genes for noncoding RNA make up the majority of meaningful genetic information in the human genome.
Which of the following terms describes the DNA-protein complexes that look like beads on a string?
Nucleosome The "beads on a string" appearance of nucleosomes comes from the wrapping of DNA around a core of eight histone proteins.
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.
What is the function of a spliceosome?
RNA processing Spliceosomes are involved in RNA processing.
What gene has been called the "guardian angel of the genome?"
The p53 gene
What is the role of proteasomes?
They are giant protein complexes that recognize ubiquitin and degrade the tagged proteins.
A gene on human chromosome 15 is expressed throughout the body. However, in the brain, only the maternal copy of the gene is expressed, whereas the paternal copy of the gene is silent and not transcribed. What accounts for this pattern of expression this gene displays in the brain?
Through genomic imprinting, methylation regulates expression of the paternal copy of the gene in the brain. Imprinting of the paternal copy of the gene by DNA methylation inactivates it and prevents its expression in brain cells. Read about DNA methylation and genomic imprinting.
Which statement(s) about inducible operons is/are correct? In an inducible operon, an inducer inactivates the repressor. Inducible enzymes generally function in synthetic pathways that produce end products from raw materials. In an inducible operon, the repressor is synthesized in an active form.
a and c An inducible operon is usually off but can be turned on when an inducer interacts with and inactivates the repressor. The enzymes in an inducible operon generally function in catabolic pathways. Read about inducible operons.
How are genes coordinately controlled in eukaryotic cells? Coordinately controlled genes in eukaryotic cells are activated by the same chemical signals. Coordinately controlled genes in eukaryotic cells are located together on the same chromosome. Coordinately controlled genes in eukaryotic cells share a set of control elements.
a and c In eukaryotes, specific transcription factors bind to control elements, promoting transcription of coordinately controlled genes, even if the genes are on separate chromosomes. Read about coordinately controlled genes in eukaryotes.
Which noncoding RNAs are correctly matched with their function? Small interfering RNAs (siRNAs) bind to complementary sequences in mRNA and block its translation. Piwi-associated RNAs (piRNAs) reestablish appropriate methylation patterns in the genome during gamete formation. MicroRNAs (miRNAs) bind to complementary sequences in mRNA and block its translation.
a, b, and c
In the lac operon, the inducer is __________.
allolactose, the isomer of lactose
Although the number of genes in the human genome is surprisingly low compared to less complex organisms, the number of possible products from those genes is greatly amplified by __________.
alternate arrangements of exons from a primary transcript
Post-transcriptional processing of a pre-mRNA allows for differential cell expression by a process called __________.
alternative splicing
In prokaryotic genomes, groups of functionally related genes along with their promoters and operators are found together in __________.
an operon
The trp (tryptophan) operon is an example of a(n) __________ that is controlled by __________.
anabolic pathway; feedback inhibition
Cytoplasmic determinants __________.
are RNAs, proteins, and other substances produced by the mother and deposited in the egg
Which statement(s) about repressible operons is/are correct? In a repressible operon, the repressor is synthesized in an active form. Repressible operons usually contain genes that code for anabolic enzymes. A repressible operon is on unless a corepressor is present.
b and c A repressible operon is usually on but can be turned off when a corepressor interacts with and activates the repressor. The enzymes in an inducible operon generally function in anabolic pathways. Read about repressible operons.
Which of the following statements about pattern formation are true? The process of pattern formation involves segmentation of the body but does not involve the development of segment-specific body parts. Differential gene expression affects the developmental process in animals. Homeotic genes establish major body axes. Cells receive molecular signals that communicate their position in relation to other cells. Pattern formation begins in adult animals. Homeotic genes code for transcription factors that control the development of segment-specific body parts. Positional information controls pattern formation.
b, d, f, and g Pattern formation is the development of a multicellular organism's spatial organization, including the arrangement of tissues and organs. Cells receive molecular signals, collectively called positional information, that inform the cells about their location in relation to other cells and to the body axes. Positional information regulates pattern formation. Homeotic genes are regulatory genes that work after the body axes have been established. Homeotic genes identify particular body segments in an individual, eventually leading to the formation of segment-specific body structures in the correct locations on the body.
Cell type-specific transcription is accomplished __________.
by specific enhancer control elements interacting with cell type-specific transcription factors
Gene expression in bacteria is regulated primarily by __________.
controlling the transcription of genes into mRNA
A cancer cell __________.
does not respond to the chemical signals that control cell division
In Drosophila development, the anterior-posterior axis of the embryo is determined by __________.
egg-polarity genes
In a eukaryote, activating transcription factors may stimulate gene expression by binding to a DNA site called a(n) __________.
enhancer
Which of the following regulatory DNA sequences might be located thousands of nucleotides away from the transcription start site of a gene?
enhancer Enhancers can function thousands of nucleotides away from the promoter and transcription start site.
Two different Drosophila flies (fruit flies), fly A and fly B, are shown below. Classify each phrase or term as applying to fly A only, fly B only, or both fly A and fly B. The term "Hox genes" applies to clusters of homeotic genes found in many different animals, including fruit flies. After segmentation genes have established the body segments, Hox genes trigger the development of segment-specific body structures in the correct locations. For more on Hox genes, see Hints 2 and 3.
fly A only: exhibits normal pattern formation, possesses normal Hox genes, and wild type fly B only: exhibits abnormal pattern formation, homeotic mutant, and possesses a mutant Hox gene both fly A and fly B: produces transcription factors triggering gene expression for segment-specific structures
The ___is/are arranged sequentially after the promoter
genes of an operon
In Drosophila development, pattern development in the late embryo, larva, and adult is controlled by __________.
homeotic genes
The control of gene expression is more complex in multicellular eukaryotes than in prokaryotes because __________.
in a multicellular eukaryote, different cells are specialized for different functions
Small noncoding RNAs (ncRNAs) called piwi-interacting RNAs, or piRNAs, __________.
induce the formation of heterochromatin and block the expression of movable DNA elements called transposons
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
The lac operon is an example of a(n) __________ operon.
inducible
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.
look at diagram ch 18 hw
Specific cells that appear undifferentiated under the microscope but are already fated to become muscle cells are called __________.
myoblasts
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
The trp and lac operons are regulated in various ways. How do bacteria regulate transcription of these operons?
operon is not transcribed: trp operon: tryptophan present, and lac operon: lactose absent operon is transcribed, but not sped up through positive control: lac operon: lactose present, glucose present, trp operon: tryptophan absent operon is transcribed quickly through positive control: lac operon: lactose present, glucose absent 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.
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?
positive control: a) inactive activator(blue one with no square), b) cAMP, c) active activator (blue with yellow square and glowing) negative control: d) active repressor (red and glowing, no square), e) athelose, f) inactive repressor (red with yellow square) 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).
A(n) ___ is a specific nucleotide sequences in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place
promoter
In eukaryotes, histone acetylation __________.
promotes transcription
Enzyme complexes that break down protein are called _____.
proteasomes Proteasomes are enzyme complexes that break down proteins.
Protein-phosphorylating enzymes' role in the regulation of gene expression involves _____.
protein activation Proteins are often activated by phosphorylation.
In addition to a promoter, eukaryotic genes have control elements called __________.
proximal control elements and distal enhancers
What two genes are often mutated in colon cancer?
ras and p53
The nuclear membrane's role in the regulation of gene expression involves _____.
regulating the transport of mRNA to the cytoplasm This is the role of the nuclear membrane in the regulation of gene expression.
A(n) ___ codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes
regulatory gene
The trp (tryptophan) operon is an example of a(n) __________ operon.
repressible
In general, operons that encode the enzymes of a biosynthetic (anabolic) pathway (such as the trp operon) are __________, and those encoding the enzymes of a catabolic pathway (such as the lac operon) are __________.
repressible; inducible
A(n) ___ is a protein that inhibits gene transcription. In prokaryotes, this protein binds to the DNA in or near the promoter
repressor
In the trp (tryptophan) operon, the __________ binds to the product of the trp operon synthesis pathway, called __________, forming the __________.
repressor protein; tryptophan; active repressor
MicroRNAs binding to complementary sequences on an mRNA __________.
results in either blocking translation or degrading the targeted mRNA
Which statements about the modification of chromatin structure in eukaryotes are true? Some forms of chromatin modification can be passed on to future generations of cells. Methylation of histone tails in chromatin can promote condensation of the chromatin. Acetylation of histone tails in chromatin allows access to DNA for transcription. Acetylation of histone tails is a reversible process. DNA is not transcribed when chromatin is packaged tightly in a condensed form. Deacetylation of histone tails in chromatin loosens the association between nucleosomes and DNA.
some forms of chromatin modificiation can be passed on to future generations of cells, methylation of histone tails in chromatin can promote condensation of the chromatin, acetylation of histone tails in chromatin allows access to DNA for transcription, Acetylation of histone tails is a reversible process, and DNA is not transcribed when chromatin is packaged tightly in a condensed form 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.
In an inducible operon, the inducer is often the __________ in the pathway being regulated; the inducer binds to the __________, thus rendering it __________.
substrate; repressor; inactive
Both repressible and inducible operons control gene expression at the level of __________.
transcription
MyoD promotes muscle cell development by __________.
turning on the expression of multiple muscle-related genes
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