BIO100

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exam 3

Of the three modes of gene regulation shown in the figure, which is the fastest in response time?

post-translational control

Of the three modes of gene regulation shown in the figure, which is the most efficient in resource use?

transcriptional control

At which of the following stages does transcriptional control occur?
DNA -a->mRNA -b-> protein -c-> activated protein

a

Which of the following is true?
Gene expression only needs to be controlled in bacteria.
Gene expression only needs to be controlled for a small set of genes.
The control of gene expression is most like the control of a light using a dimmer switch.
The control of gene expression is most like the control of a light using an on-off switch.

The control of gene expression is most like the control of a light using a dimmer switch.

An operon is _____.

a set of bacterial genes that are regulated together and transcribed into a single RNA

Allosteric regulation occurs whenever _____.

a regulatory molecule binds to a protein to change its shape and activity

The lac repressor protein binds to the operator when it is _____.

not bound to lactose

Which of the following works in the positive regulation of the lac operon?

the CAP protein

What is adenylyl cyclase involved in?

the cell's ability to respond to glucose

Although the expression of most genes is tightly regulated, some genes are expressed at roughly constant rates (i.e., constitutively). Which of the following genes would you predict to be constitutively expressed?

genes that code for ribosomal RNAs

Imagine that you discover a bacterial operon involved in the synthesis of vitamin B12. This operon is regulated by a repressor protein that binds to an operator sequence. Vitamin B12 is the allosteric effector of the repressorthe molecule that binds to the repressor to affect its activity. Predict how vitamin B12 will influence repressor activity.

When vitamin B12 binds to the repressor, the repressor binds to the operator.

What is the pattern of expression of β-galactosidase in lacI- cells and why?

constitutive expression, because there is norepressor

Full induction of the lac operon occurs when _____.

lactose levels are high and glucose levels are low

In the first step of their experiments, Jacob and Monod treated E. coli cells with UV light or X-rays in order to _____.

increase the frequency of mutations in all genes

Imagine that you've added the same indicator used by Monod to E. coli colonies growing on a plate with glucose and no lactose. One colony is yellow and the remainders are white. This result suggests that cells of the yellow colony _____.

have constitutively active lacZ and lacY genes

A compound known as X-Gal is widely used in molecular genetic research. When wild-type (normal) E. coli is grown on medium containing X-Gal, the bacterial colonies turn blue. In contrast, when lacZ mutants are grown on medium containing X-Gal, the bacterial colonies remain their normal white color. What is X-Gal likely to be?

a compound chemically similar to lactose

An E. coli cell without a functional lacI gene is expected to _____.

always produce β-galactosidase

An ____ 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 ___ are arranged sequentially after the promoter

genes of an operon

a _____ is a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place

promoter

a _____ codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes

regulatory gene

regulatory proteins bind to the _____ to control expression of the operon

operator

a ____ is a protein that inhibits gene transcription. in prokaryotes, this protein binds to the dna in or near the promoter

repressor

an _____ 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

operon is not transcribed

trp operon: tryptophan present
lac operon: lactose absent

operon is transcribed, but not sped up through positive control

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

operon is transcribed quickly through positive control

lac operon: lactose present, glucose absent

The operon model of the regulation of gene expression in bacteria was proposed by _____.

jacob and monod

Which of these is NOT a component of the lac operon?

regulatory gene only

Regulatory proteins bind to _____.

the operator

In the presence of a regulatory protein the lac operon is _____.

not transcribed

lactose...

Lactose inactivates the repressor protein so that the lactose-utilization genes can be transcribed.

RNA polymerase.....

RNA polymerase transcribes the genes of the lac operon.

The regulatory gene ...

The regulatory gene is not a part of the operon.

What is the role of lactose in regulating lac operon expression?

It induces transcription by binding to the repressor and removing it from the operator.

The lac repressor protein binds to the operator when it is _____.

not bound to lactose

In negative control of transcription, a gene is activated when _____.

regulatory protein is removed from DNA

The product of the lacI gene is _____.

the repressor

According to the lac operon model proposed by Jacob and Monod, what is predicted to occur if the operator is removed from the operon?

The lac operon would be transcribed constitutively.

Which of the following statements best defines the term operon?

An operon is a region of DNA that codes for a series of functionally related genes under the control of the same promoter.

What molecule binds to promoters in bacteria and transcribes the coding regions of the genes?

RNA polymeras

What is allosteric regulation?

In allosteric regulation, a small molecule binds to a large protein and causes it to change its shape and activity.

Under which conditions are the lac structural genes expressed most efficiently?

No glucose, high lactose

What happens to the expression of the lacI gene if lactose is not available in the cell?

There is no change—the lacI gene is constitutively expressed.

What is the function of the lacZ gene?

This gene encodes an enzyme, b-galactosidase, which cleaves lactose into glucose and galactose.

Which of the following enzymes converts ATP to cAMP?

Adenylyl cyclase

True or false? The mechanism by which glucose inhibits expression of the lac structural genes is known as catabolite stimulation, whereas the mechanism by which lactose stimulates expression of the lac structural genes is known as allosteric regulation.

false

Which of the following leads to the highest rate of lac operon transcription?

high lactose levels and low glucose levels

Which of the following works in the positive regulation of the lac operon?

the CAP protein

What is adenylyl cyclase involved in?

the cell's ability to respond to glucose

Catabolite activator protein (CAP) activity is controlled by cAMP at the _____ level.

post-translational

Extracellular glucose inhibits transcription of the lac operon by _____.

reducing the levels of intracellular cAMP

CAP is said to be responsible for positive regulation of the lac operon because _____.

CAP bound to the CAP binding site increases the frequency of transcription initiation

E. coli adenylyl cyclase is most active when _____.

extracellular glucose levels are low

Which of the following is associated with negative control of the lac operon?

repressor

How would gene expression in your gut-dwelling bacteria change after you drink a glass of milk?

lac operon gene expression would be induced.

Which method is utilized by eukaryotes to control their gene expression that is not used in bacteria?

control of both RNA splicing and chromatin remodeling

Are histone deacetylases (HDACs) associated with negative or positive control of gene expression? Why?

negative control, because they make DNA less accessible for transcription

Which answer best explains why certain patterns of histone chemical modifications could influence whether a cell became a muscle cell or a brain cell?

They could affect which sets of genes are transcribed in different cell types.

The addition of acetyl groups to histones is associated with _____.

chromatin decondensation and high levels of gene expression

A mechanism of inheritance that does not depend on differences in DNA sequence is _____.

epigenetic inheritance

Which of the following is most critical for the association between histones and DNA?

Histones are positively charged.

Imagine you've isolated a yeast mutant that contains a constitutively (constantly) active histone deacetylase. What phenotype do you predict for this mutant?

The mutant will show low levels of gene expression.

_____ bind(s) to DNA enhancer regions.

activators

Which of the following terms describes the DNA-protein complexes that look like beads on a string?

nucleosome

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

activators

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

false

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

enhancer

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

RNA polymerase binds to the promoter of the gene.

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

Differential gene expression is the result of different cells having different _____.

regulatory proteins

The primary difference between an enhancer and a promoter-proximal element is that _____.

enhancers are at considerable distances from the promoter and can be moved or inverted and still function; promoter-proximal elements are close to the promoter and their position and orientation must be maintained

The reason for differences in the sets of proteins expressed in a nerve and a pancreatic cell of the same individual is that nerve and pancreatic cells contain different _____.

sets of regulatory proteins

If cells of an individual contain the same set of genes, how do these cells become different from each other during development?

Different cell type-specific regulatory elements in DNA are created during development.
ORRRR (FIND RIGHT ANSWER)
Differences in extracellular signals received by each cell lead to differences in the types of regulatory proteins present in each cell.

Which answer best explains why the discovery of alternative splicing forced biologists to change their definition of a gene?

It showed that a gene can direct the production of more than one polypeptide or RNA.

Alternative RNA splicing allows for the number of different _____.

proteins to exceed the number of different genes
ORRR (FIND RIGHT ANSWER)
genes to exceed the number of different proteins

MicroRNAs work to _____.

destroy mRNA or block its translation

An example of a basal transcription factor is _____.

the TATA-binding protein

Gene expression is often assayed by measuring the level of mRNA produced from a gene. If one is interested in knowing the amount of a final active gene product, a potential problem of this method is that it ignores the possibility of _____.

translational control

Not long ago, it was believed that a count of the number of protein-coding genes would provide a count of the number of proteins produced in any given eukaryotic species. This is incorrect, largely due to the discovery of widespread _____.

alternative splicing

If a pharmaceutical company wishes to make a protein-based drug from yeast with a particular carbohydrate tag to ensure correct tissue delivery, which stage of gene expression would be altered to change the tag on the protein?

transcription
ORRRR
alternative splicing

During _____ both the contents of the nucleus and the cytoplasm are divided.

the mitotic phase

During _____ the cell grows and replicates both its organelles and its chromosomes.

interphase

Mitosis is responsible for what key process in multicellular eukaryotes?

growth, wound repair, reproduction

During what phase of the cell cycle does the DNA become replicated?

s

What is the difference between a chromatid and a chromosome?

A chromatid is one half of a replicated chromosome, whereas a chromosome consists of DNA wrapped around proteins in a highly organized manner.

A parent cell divides to form two genetically identical daughter cells in the process of mitosis. For mitosis to take place _____.

the parent cell must first replicate its entire genome

Researchers pulsed rapidly dividing cultured cells for 30 minutes with radioactive thymidine. The cells were then exposed to a solution containing non-radiolabeled thymidine. Cells were analyzed at 2-hour intervals. At the 2-hour time point, no cells appeared to be dividing. Only after 4 hours did some labeled cells appear to be in M phase. This result can be explained in the following way:

There seems to be a gap or a lag in the cell cycle, between the synthesis of DNA and cell division.

Scientists isolate cells in various phases of the cell cycle. They find a group of cells that have 1½ times more DNA than do G1 phase cells. The cells of this group are _____.

in the S phase of the cell cycle

The first gap in the cell cycle (G1) corresponds to _____.

normal growth and cell function

prophase

the microtubules of the spindle apparatus begin to assemble from individual tubulin subunits. As the identical chromatids of each pair of sister chromatids condense during this stage, they are held together by cohesin proteins.

prometaphase

marked by fragmentation of the nuclear envelope, expansion of the spindle into the nuclear region, and attachment of some spindle fibers to the chromosomes via the kinetochores.

metaphase

marked by the alignment of chromsomes along the metaphase plate, is brought about by kinetochores aligning and then remaining motionless relative to the poles of the cell.

anaphase

cohesin proteins are cleaved, and the kinetochores move toward the poles of the cell, separating the sister chromatids

telophase

kinetochore microtubules of the spindle disassemble. As the chromosomes reach the poles of the cell, the nuclear envelopes of the two new daughter nuclei form.

during prophase, the microtubules of mitotic spindle ______

lengthen

during anaphase, the nonkinetochore microtubules _____ and move past each other, and the kinetochore microtubules ______

lengthen, shorten

during telophase, the nonkinetochore microtubules_____

disassemble

Which statement is correct concerning the relationship between chromosomes and genes, chromatin, or sister chromatids?

Each replicated chromosome consists of two sister chromatids.

In which mitotic phase are the sister chromatids separated and pulled to opposite poles?

anaphase

The microtubule-organizing center found in animal cells is an identifiable structure present during all phases of the cell cycle. Specifically, it is known as which of the following?

centrosome

The mitotic spindle is a microtubular structure that is involved in _____.

separation of sister chromatids

Some cells have several nuclei per cell. How could such multinucleated cells be explained?

The cell underwent repeated mitosis, but cytokinesis did not occur.

FtsZ is a bacterial cytoskeletal protein that forms a contractile ring involved in bacterial cytokinesis. Its function is analogous to _____.

the cleavage furrow of eukaryotic animal cells

Which of the following is a function of the S phase in the cell cycle?

The synthesis of sister chromatids

The copying of chromosomes occurs during which of the following phases of the cell cycle?

s phase

For the first several divisions of early frog embryos, cells proceed directly from the M phase to the S phase and back to M without gaps. Which of the following is likely to be true about dividing cells in early frog embryos?

The cells get smaller with each generation.

True or false? The M phase is characterized by the replication and division of a cell's chromosomes.

false

If an organism normally has 34 chromosomes, how many molecules of DNA should there be in the G1 phase of the cell cycle?

34

Which of the following events would cause the cell cycle to arrest?

Poor nutrient conditions

Which answer correctly identifies a cell-cycle checkpoint with a criterion for passing it?

G2 checkpoint: Chromosomes have replicated successfully.

Proteins that degrade cyclin are activated by events that MPF initiates. Why is this important for cell-cycle regulation?

It sets up an oscillation in cyclin concentration.

MPF, or mitosis-promoting factor, consists of two important cell cycle regulatory proteins called _____.

cyclin and cyclin-dependent kinase (CDK)

Nerve cells lose their ability to undergo mitosis. Instead, they are permanently stuck in _____.

G0

What happens when MPF (mitosis-promoting factor) is introduced into immature frog oocytes that are arrested in G2?

The cells enter mitosis.

Once a cell completes mitosis, molecular division triggers must be turned off. What happens to MPF during mitosis?

Cyclin is degraded; the concentration of cyclin-dependent kinase remains unchanged, but without cyclin, MPF is not formed.

Which of the following is not an effect of mitosis-promoting factor (MPF) involved in moving a cell into M phase?

degradation of cyclin-dependent kinase

The M-phase checkpoint is designed to make sure all chromosomes are attached to the mitotic spindle. If this fails to happen, in which stage of mitosis would the cells be most likely to arrest?

metaphase

What is the ploidy of organisms that have two sets of chromosomes?

2n

What information can not be obtained from an individual's karyotype?

The sequence of bases of a particular gene

True or false? A haploid organism has one pair of homologous chromosomes.

false

If a cell has 24 chromosomes, how many chromosomes would each of its four daughter cells have after meiosis?

12

Which of the following statements about meiosis and mitosis is true?

Meiosis II is similar to mitosis in that sister chromatids of each chromosome separate.

Which structure is directly correlated with the production of genetic variability in the daughter cells produced during meiosis?

chiasma

What is the composition of a tetrad at the beginning of prophase I?

One pair of homologous chromosomes

Meiosis I produces _____ cells, each of which is _____.

two ... haploid

Meiosis II typically produces _____ cells, each of which is _____.

four ... haploid

prophase II

The events of prophase II are essentially the same as those of mitotic prophase except that prophase II cells are haploid.

anaphase II

During anaphase II sister chromatids separate and migrate to opposite poles.

telophase II and cytokinesis

Four haploid cells are present at the end of telophase II and cytokinesis.

anaphase II

Anaphase II is essentially the same as mitotic anaphase except that the cell is haploid.

telophase I and cytokinesis

At the end of telophase I and cytokinesis there are two haploid cells.

At the end of _____ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.

telophase I

prophase I

Homologous chromosomes pair during prophase I..

metaphase II

Metaphase II is essentially the same as mitotic metaphase except that the cells are haploid.

metaphase I

During metaphase I tetrads align along the metaphase plate.

Synapsis occurs during _____.

prophase I

Homologous chromosomes migrate to opposite poles during _____.

anaphase I

During _____ chromosomes align single file along the equator of a haploid cell.

metaphase II

anaphase I

During anaphase I homologous chromosomes, consisting of sister chromatids, migrate to opposite poles.

At the end of _____ and cytokinesis there are four haploid cells.

telophase II

During _____ a spindle forms in a haploid cell.

prophase II

interphase

During interphase the centrosome duplicates and the chromosomes are not condensed.

Which statement is correct concerning the relationship between chromosomes and chromatids?

A replicated chromosome contains two sister chromatids.

Which event makes meiosis a reduction division and why?

separation of homologs in meiosis I because it produces 2 haploid (n) daughter cells from a single diploid (2n) parent cell

Homologous chromosomes _____.

carry the same genes

In an organism in which 2n = 6, how many chromosomes will be in each gamete?

3

During which phase of meiosis would the cell first become haploid because homologous chromosomes
separate?

anaphase I

Meiosis involves the creation of haploid cells from diploid cells. The haploid chromosome number is created when _____.

homologous chromosomes separate

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