Chapter 14 Gene Expression
What is cyclic AMP (cAMP)?
A small effector molecule involved in the positive control of the lac operon
What is an inducer?
A small effector molecule that increases the rate of transcription
Histone modifications can result in which of the following?
Activation of transcription Loosening of chromatin
Which of the following are proteins involved in regulating the rate of transcription in eukaryotes?
Activators Repressors
How do activator proteins diminish the level of chromatin compaction at the site of the gene that is to be transcribed?
Activators bind to an enhancer site and then recruit other proteins to unravel and loosen the packed chromatin.
What is the inducer molecule for the lac operon?
Allolactose
Which of the following is a form of gene regulation in which a eukaryotic pre-mRNA can be processed to produce more than one mature RNA?
Alternative splicing
What is a repressible operon?
An operon that can be inhibited by the presence of a small effector molecule
In eukaryotes, the core promoter, by itself, results in a low level of transcription that is known as_________ transcription.
Basal
The effector molecule cAMP enhances the transcription of the genes of the lac operon via binding to a protein called
CAP
The lac operon is also under positive control by an activator protein called what?
CAP
When glucose is present in a bacterial cell, it can act to repress the expression of the lac operon because it is preferentially used compared to other sugars. What form of transcriptional regulation is this?
Catabolite repression
Which of the following elements are DNA sequences that regulate gene transcription? Select all that apply.
Enhancers Silencers
What is the function of general transcription factors (GTFs) in the initiation of transcription?
GTFs and RNA polymerase come together at the core promoter for the initiation of transcription.
How does glucose repress the expression of the lac operon?
Glucose inhibits the production of cAMP, thereby preventing the activation of the lac operon.
A small effector molecule that increases the rate of transcription is called a(n)
Inducer
How does allolactose affect the lac repressor protein?
It binds to the repressor
Of the four possible environments E. coli could encounter with regard to lactose and glucose, which has the highest levels of lac operon transcription?
Low glucose and high lactose
Which of the following is a common modification that affects the structure of DNA?
Methylation
How can DNA methylation inhibit transcription?
Methylation can alter chromatin structure. Methylation can prevent an activator from binding to an enhancer.
Bacteria and eukaryotes can regulate genes at the level of transcription. In eukaryotes, gene expression is also commonly regulated at the levels of RNA____________ and translation.
Processing
Which of the following are similarities between eukaryotic and bacterial transcriptional regulation?
Proteins influence the ability of RNA polymerase to bind to the DNA. Small effector molecules are involved in gene regulation.
Why are interactions between RNA polymerase II and GTFs important for transcription in eukaryotes?
RNA polymerase II and GTFs must interact for the polymerase to bind properly at the core promoter site of the DNA.
What are silencers?
Regulatory elements that can prevent or decrease transcription
Which of the following best describes the organization of sequences in a typical eukaryotic promoter?
Regulatory elements — TATA box — Transcriptional start site — Structural gene
In order for transcription of protein coding genes in eukaryotes to begin, the promoter must have several key features. What are they?
TATA box, regulatory elements, transcriptional start site
Which of the following describe the TATA box? Choose all that apply.
The TATA box determines the precise starting point for transcription. The TATA box is a sequence upstream of the transcriptional start site.
What is the role of the TATA box?
The TATA box determines the starting point of transcription.
What is chromatin?
The complex formed by DNA and its associated proteins
Which of the following are key differences between eukaryotic and bacterial transcriptional regulation?
The complexity of eukaryotic development requires that transcription be more coordinated and integrated than in bacteria. The majority of genes are organized individually in eukaryotes, but are organized as operons in bacteria. Combinatorial control of gene expression is more common in eukaryotes.
What is the role of the corepressor in the expression of the trp operon?
The corepressor binds to the repressor protein and causes a conformational change, which allows the repressor to bind to the operator site.
The transcription of the lac operon genes is inhibited when the lac repressor protein binds to
The lac operator
What is basal transcription?
The low level of transcription activated by the core promoter alone
How does the mediator protein interact with RNA polymerase and the GTFs during the initiation of transcription?
The mediator protein controls interactions between the preinitiation complex and other regulatory elements.
Which is a result of alternative splicing?
The proteome size is increased and the genome size is minimized.
The binding of the corepressor to the trp repressor results in what?
The repressor binds to the operator and prevents transcription.
What is the role of the repressor protein in the transcription of the trp operon?
The repressor protein binds to the operator site and prevents the transcription of the trp operon.
What is the function of the genes encoded by the trp operon?
The synthesis of the amino acid tryptophan
Which of the following is a repressible operon?
The trp operon
What is the function of ATP-dependent chromatin-remodeling complexes?
They cause a change in the locations and/or compositions of nucleosomes.
What is the first nucleotide that is transcribed called?
Transcriptional start site
How do CAP and cAMP increase the transcription of the lac operon?
When CAP and cAMP bind to the CAP site, this enhances binding of RNA polymerase to the promoter site.
Why is the lac operon considered inducible?
When allolactose is produced, this causes the transcription of the lac operon.
How does the presence of lactose in the cell influence the transcription of the lac operon?
When lactose is present, transcription of the lac operon is high. When lactose is present, the lac repressor protein does not bind to the operator site and transcription can occur.
Under what conditions does the lac repressor bind to the operator of the lac operon and prevent transcription?
When the concentration of lactose is low in the cell
The lac repressor binds to the lac operon when lactose is ______, and the trp repressor binds to the trp operon when tryptophan is ______.
absent; present
In eukaryotes, the rate of transcription of genes is influenced by regulatory transcription factors that bind to regulatory elements. These proteins are called
activators repressors
The lac operon is an example of an operon involved in Blank______.
breakdown of a substance
Glucose inhibits lactose metabolism by preventing the production of______.
cAMP
How does cAMP play a role in the transcription of the lac operon?
cAMP binds to CAP and together they bind to the DNA, which enhances transcription of the lac operon.
When ______ binds to CAP, the resulting complex binds to the CAP site near the lac ______. This causes a bend in the DNA that enhances the ability of RNA polymerase to bind, and so the transcription rate is increased.
cAMP; promoter
A ______-effect is mediated by a DNA element that binds regulator proteins, whereas a ______-effect is mediated by genes that encode diffusible regulatory proteins.
cis; trans
Iron is a vital ______ for many cellular enzymes, but is ______ at high levels.
cofactor ; toxic
Heterochromatic regions found in the same locations in all cell types are called Blank______ heterochromatin.
constitutive
DNA methylation may prevent transcription by blocking a(n) ______ site or by altering the structure of _____.
enhancer ; chromatin
In eukaryotic DNA, certain regulatory elements function to increase the rate of transcription. These elements are known as
enhancers
Transcription of the lac operon will be highest when ______ is absent and ______ is present.
glucose; lactose
Transcription of the trp operon is ______ when levels of tryptophan are low in the cell.
increased
In mammals, when iron levels are high, iron binds to the iron regulatory protein. This results in ______.
increased translation of ferritin
In E. coli, the lac operon is ______ in the presence of lactose, and the trp operon is ______ in the presence of tryptophan.
induced; repressed
Which of the following genes encodes the lac repressor protein?
lacl
The catabolite activator protein (CAP) is involved in ______ control of the lac operon.
positive
An advantage of alternative splicing is that it increases the size of the ______ while minimizing the size of the ______.
proteome ; genome
The trp operon is regulated by a(n)_______ protein that is encoded by the trpR gene.
repressor
The transcriptional start site contains ______.
the first base that is transcribed
According to the histone code hypothesis, proteins recognize histones based on______.
their covalent modifications
In mammals, iron toxicity is prevented by regulating the Blank______ of ferritin.
translation
Which of the following is an example of an operon that is involved in the biosynthesis of a substance?
trp operon
The genes in the trp operon encode enzymes that make the amino acid
tryptophan
High levels of tryptophan ______ the transcription of the trp operon.
will result in a decrease in
