Biol 300 progress test 4

Why is it essential that bacterial cells be able to regulate the expression of their genes?

Expression of some genes is required only under certain conditions.

What are the energetic and evolutionary advantages of regulated gene expression?

-Regulated gene expression prevents synthesis of unnecessary proteins, which might be in competition to the detriment of the organism.

-Regulated gene expression allows bacteria to adapt their metabolism to match changes in the environment.

Is the expression of all bacterial genes subject to regulated expression?

no

Compare and contrast the difference between regulated gene expression and constitutive gene expression.

Constitutive gene expressions applies to the genes whose expression is always required, whereas regulated gene expression applies to the genes whose expression is required only under certain conditions.

Identify what binds at this site to produce positive regulation.

CAP-cAMP complex

Under what circumstances does the binding occur?

When glucose is not available.

How does the binding exert a positive effect?

The CAP-cAMP complex alters the structure of the promoter and allows RNA polymerase to bind to it

Mutation of consensus sequence in the lac promoter.

Transcription is blocked.

Mutation of the repressor binding site on the operator sequence.

Transcription is constitutive.

Mutation of the lac I gene affecting the allosteric site of the protein.

Transcription is blocked.

Mutation of the lac I gene affecting the DNA-binding site of the protein.

Transcription is constitutive.

Mutation of the CAP binding site of the lac promoter.

Transcription will not exceed basal levels.

Four independent lac−lac− mutants (mutants A to D) are isolated in haploid strains of E. coli. The strains have the following phenotypic characteristics: Mutant A is lac−lac− but transcription of operon genes is induced by lactose. Mutant B is lac−lac− and has uninducible transcription of operon genes. Mutant C is lac+lac+ and has constitutive transcription of operon genes. Mutant D is lac+lac+ and has constitutive transcription of operon genes. A microbiologist develops donor and recipient varieties of each mutant strain and crosses them with the results shown below. The table indicates whether inducible, constitutive, or noninducible transcription occurs, along with lac+lac+ and lac−lac− growth habit for each partial diploid. Assume each strain has a single mutation.

MatingTranscription and GrowthA ×× Blac−lac−, inducibleA ×× Clac+lac+, inducibleA ×× Dlac+lac+, constitutiveB ×× Clac+lac+, inducibleB ×× Dlac+lac+, constitutiveC ×× Dlac+lac+, constitutive

Use this information to identify which laclac operon gene is mutated in each strain.

C has a mutation in lacIlac I.

D has a mutation in lacOlacO.

A has a mutation in lacZlacZ.

B has a mutation in lacPlacP.

Growth medium contains lactose and glucose.

Choose the correct explanation for your answer.

Basal

The presence of lactose prevents the repressor from binding to the operator. The presence of glucose reduces the cAMP level, which prevents CAP-cAMP from forming and stimulating transcription at a high level.

Growth medium contains glucose but no lactose.

Choose the correct explanation for your answer.

none

In the absence of lactose, the repressor binds to the operator and represses transcription.

Growth medium contains lactose but no glucose.

Choose the correct explanation for your answer.

activated

The presence of lactose prevents the repressor from binding to the operator. The absence of glucose results in high cAMP levels, which allows CAP-cAMP to form and stimulate transcription at a high level.

A bacterial inducible operon, similar to the laclac operon, contains three genes - RR, TT, and SS - that are involved in coordinated regulation of transcription. One of these genes is an operator region, one is a regulatory protein, and the third produces a structural enzyme. In the table below, "++" indicates that the structural enzyme is synthesized and "−−" indicates that it is not produced. Use the information provided to determine which gene is the operator, which produces the regulatory protein, and which produces the enzyme.

-R is the operator

- S produces the regulatory protein

- T produces the enzyme

A promoter

is a DNADNA sequence where RNARNA polymerase binds and begins the process of transcription.

An enhancer

is a DNADNA sequence that binds regulatory proteins that interact with promoter-bound proteins to activate transcription.

A silencer

is a DNA sequence that binds regulatory proteins that inhibit transcription.

RISC

is the protein complex that is part of the RNARNA interference (RNAiRNAi) mechanism. It denatures short double-stranded RNARNAs to single strands that carry out RNAi.

Dicer

is the enzyme complex that is active in RNARNAi, where it cuts double-stranded regulatory RNARNAs into 21-bpbp to 26-bpbp segments that are subsequently denatured by RISC.

What general role does acetylation of histone protein amino acids play in the transcription of eukaryotic genes?

Histone acetylation events are most often associated with transcription activation.

promoter sequence is likely to be:

-located upstream of the gene it controls

-located within a few dozens nucleotides of the gene it controls

-orientation dependent

enhancer sequence is likely to be:

-located upstream of the gene it controls

-orientation independent

-located whitin a few dozens nucleotides of the gene it controls

Choose the correct definition of epigenetics.

Epigenetic refers to heritable states of chromatin structure.

List examples illustrating the phenomenon.

-Prader-Willi syndrome

-Angelman syndrome

Based on your analysis, what is the most likely molecular abnormality causing the disease allele?

A pre-mRNA spicing mutation causes a deletion of exon 3.

Explain the differential effects of deletions B and F on expression in the two tissues.

-Mutant B only mildly affects UG4UG4 transcription in leaves, but knocks it out almost entirely in stems. This indicates the use of different promoter sequences in the transcription of UG4UG4 in these tissues.

-The deletion in mutant F has no effect on UG4UG4 expression in either tissue, indicating that this region contains no sequences required for promoter action in those cells.

Why does deletion D raise UG4UG4 expression in leaf tissue but not in stem tissue?

Mutations that increase expression typically remove silencers; therefore, mutant D lacks a silencer sequence that regulates the level of transcription of UG4UG4 in leaf tissue but not in stem tissue.

Why does deletion E lower expression of UG4UG4 in leaf tissue but not in stem tissue?

Mutations in regions at a distance from the transcription start site that prevent expression typically affect an enhancer; therefore, mutation E deletes a required enhancer sequence for UG4UG4transcription in leaf tissue but not in stem tissue.

Why are diseases of the blood more likely targets for treatment by gene therapy than are many other genetic diseases?

Because the bone marrow cells that give raise to blood cells can be isolated, cultured and manipulated in vitro.

Could RNAi be used in gene therapy for a defect caused by a recessive allele?

A dominant allele?

no

yes

What might be the major obstacle to using RNAi as a therapeutic agent?

the inability to accurately deliver the double-stranded RNA molecule to all of the correct cells and no other cell type

population

a group of interbreeding individuals

Gene Pool

-the sum fo all of the genes in a population

-the source of genetic information from which the next generation is produced

Neither of the two:

-the sum of the most common genes in a population

-a group of individuals of different species

random mating

involves individuals chosen by chance

inbreeding

refers to mating between related individuals

-is used in selection

both of the two

occurs in nature

natural selection

favors reproduction of individuals with a specific heritable phenotype

genetic drift

alters allele frequency in a random manner

both of them

phenomenon that alters allele frequencies

-evolutionary source

Polymorphic trait

-a phenotype that exists in more than one form

-exists within a population

Polymorphic gene

a gene for which there are two or more alleles

Neither of them

-a gene that is found in two or more individuals

-a trait that is found in two or more individuals

founder effect

is a result of the allele frequency of a small number of ancestors

genetic bottleneck

is a result of the allele frequency of cataclysm survivors

both of these

-causes changes in allele frequency

-is random

In a population, what is the consequence of inbreeding?

Inbreeding increases the frequency of homozygotes and decreases the frequency of heterozygotes.

What is the effect of inbreeding with regard to rare recessive alleles in a population?

Inbreeding increases the number of members of the population expressing the recessive trait.

Identify the evolutionary forces that can cause allele frequencies to change from one generation to the next.

- migration

-natural selection

-mutation

-random genetic drift

Thinking creatively about evolutionary mechanisms, identify at least two schemes that could generate allelic polymorphism in a population except natural selection that favors heterozygotes.

mutations that do not severely affect viability and reproductivity

continuous migration of individuals with new alleles into the population

The ability to taste the bitter compound phenylthiocarbamide (PTC) is an autosomal dominant trait. The inability to taste PTC is a recessive condition. In a sample of 500 people, 349 have the ability to taste PTC and 151 do not. Calculate the frequency of:

the recessive allele

0.55

dominant allele

0.45

homozygous dominant genotype

0.20

the homozygous recessive genotype

0.30

the heterozygous genotype

0.50

If you compared the allele frequencies in the two populations, what would you expect to find?

the allele frequencies of both populations are likely to be similar.

An earthquake destroys the bridge between the island and the mainland, making migration impossible for the deer. What do you expect will happen to allele frequencies in the two populations over the following 10 generations?

Eventually, the allele frequencies in the two populations will be expected to differ.

In which population do you expect to see the greatest allele frequency change?

Inhibiting the forest on an island.

Why?

Because the force driving change is random genetic drift, which has a larger impact on smaller populations.

What is inbreeding depression?

Inbreeding depression refers to the reduced fitness or viability of a species caused by inbreeding, which drives genetic loci to homozygosity

Why is inbreeding depression a serious concern for animal biologists involved in species-conservation breeding programs?

Inbreeding depression is counterproductive for restoring species.

The number of people expected in each blood-type category is:

NOT

333.39,497.37,184.98

342,500,187

Perform a chi-square analysis using the number of people observed and expected in each blood-type category.

NOT

24.75

0.0411

State whether the sample is in H-W equilibrium.

The hypothesis that the population is at Hardy-Weinberg equilibrium cannot be rejected.

What is a genetic bottleneck?

A genetic bottleneck is a reduction in population size that decreases genetic variation and alters allele frequencies.

Explain how a genetic bottleneck and its aftermath could result in a population that carries a lethal allele in high frequency.

The pogroms reduced the Ashkenazi Jewish population randomly with respect to genotype. The Tay−−Sachs allele frequency in the reduced population was greater

The pogroms reduced the Ashkenazi Jewish population randomly with respect to genotype. The Tay−Sachs allele frequency in the reduced population was greaterthan that in the original population and remained greateras that population re-expanded.

than that in the original population and remained high

The pogroms reduced the Ashkenazi Jewish population randomly with respect to genotype. The Tay−Sachs allele frequency in the reduced population was greaterthan that in the original population and remained greateras that population re-expanded.

as that population re-expanded.

In the population described, what is the frequency of the recessive allele that produces Tay−−Sachs disease?

NOT

0.045

Assuming mating occurs at random in this population, what is the probability a couple are both carriers of Tay−−Sachs disease?

0.001

Use this information to determine the frequency of ABOABO blood group alleles in the sample.

Recall that when considering genes with three alleles whose frequencies are represented by the variables p, q, and r, the sum of genotype frequencies resulting from trinomial expansion is:

(p + q + r )2 = p 2 + 2pq + q 2 + 2pr + r 2 + 2qr = 1

0.58,0.29,0.13