Genetics exam 4

Which of the statements about the transcription factors illustrated in the network diagram are true? Please select all that apply.

- LIN-39 regulates four -EGL-27 does not regulate -MAB-5 regulates LIN-39

AUU, AUC, and AUA all encode isoleucine, but AUA is used only ~10% of the time. Why is this thought to be the case?

-A and G are both purines -A and G are both pyrimindines

A diagram of the mutagenesis and crossing strategy used by Nüsslein-Volhard and Wieschaus to generate and maintain segmentation mutants is shown. Male flies were exposed to EMS (a mutagen) and mated to a non-mutagenized female. How did the researchers ensure that the offspring of Cross B (i.e., the offspring seen in generation C in the diagram) were heterozygotes that carried a mutagenized chromosome? Please select all that apply.

-CyO -the female parent

Which of the following methods have been used to generate libraries of disrupted genes for an organism? Please select all that apply.

-RNAi -Targeted insertion

With a few exceptions, the genetic code is universal. What are the implications of this? Please select all that apply.

-all living organisms -finite genetic differences -a gene from one organism

Position-specific weight matrix tables show relatively few substitutions for cysteine and tryptophan compared with other proteins. Which of the following are possible explanations for this? Please select all that apply.

-cysteine and tryptophan are more likely to have essential roles -cystenine and tryptophan have unusual structures - the codons

Nüsslein-Volhard and Wieschaus used Drosophila melanogaster as a model organism in genetic screens to examine developmental biology. Why was Drosophila a good model organism for this study?

-drosophila has a short generation time - drosophila embryos can be studied easily -balamver chromosomes

Which of the following are characteristics of translation initiation? Please select all that apply.

-first codon is for methionine - tRNA used for initiation

Attenuation is involved in the regulation of tryptophan production in E. coli. Which factors are involved in the tryptophan attenuation mechanism?

-hairpin -transcription termination -translation

Match the protein binding patterns at the lac operon with the appropriate transcriptional outcomes.

-lac operon not transcribed= CAP and lac -lac operon is weakly= Neither CAP nor lac -lac operon is strongly= CAP bound to DNA

During investigation of the lac operon, Jacob and Monod found that mutations in the same gene did not always lead to the same phenotypic outcome. For example, some mutations in the lacI gene led to constitutive lactose breakdown, whereas other mutations led to an inability to ferment lactose under any conditions. Which of the following statements are true about lacIs mutations? Please select all that apply.

-lacl5 mutants cannot be complemented -lacl5 mutants are unable to utilize lactose

which of the following statements about polar mutations are true? select all

-polar mutations usually increase the distance between two genes - mutations in the last gene

Which of the following are advantages of random mutagenesis compared to targeted mutagenesis? Please select all that apply.

-random mutagenesis is unbiased -targeted mutagenesis IS LIMITED

Which of the following statements about the lac and trp operons in E. coli are true? Please select all that apply.

-the lac operon -the lac repressor

what is BLOSUM matrix used for? select all.

-to assess the probability - to show the probability

Which of the following are limitations of ChIP experiments? Please select all that apply.

-transciption factors - ChIP does not provide info

Why is it difficult to accurately identify transcription factor binding sites by scanning the genome sequence? select all.

-transcription factor binding sites are variable -distance between transcription

which of the following statements abot transcription translation are true? select all.

-translation in bacteria -rRNA is involved in translation -mRNA is transported out of nucleus

events of translation in order

1= tRNA is charged 2= tRNA interacts 3= peptide bond forms 4= tRNA leaves

Put the following steps in a ChIP experiment in order, beginning with the first

1=cross-linked 2= fragment 3=precipitate 4= sequence

There are 4 different bases and 64 possible codons in the genome, 20 different amino acids, and a large but variable number of tRNA genes (400-500 in mammals). How many aminoacyl synthetase genes are there?

20

[A] on [B], which is held within a tunnel in the [C], base-pairs with [D] on tRNA. The 5' of the anticodon corresponds to the [E] of the codon and the 3' of the anticodon correspond to the [F] of the codon.

A= a codon B= mRNA C= ribosome D= an anticodon E= 3' F= 5'

match the site in the ribosome to its function

A= charged tRNA enters B= tRNA holds C= uncharged tRNA leaves

In developing Drosophila embryos, [A] mRNA is evenly distributed through the embryo whereas [B] mRNA is confined to the posterior pole. Nanos protein binds to hunchback mRNA and represses its transcription. This produces a gradient of Nanos protein in the embryo, with more at the [C] end, and a corresponding gradient of Hunchback protein, with more at the [D] end.

A= hunchback B= nanos C= posterior D= anterior

Match the points on the bacterial growth curve with their descriptions.

A= no cell division B= cells doubling C=nutrients D= cell death

Tryptophan is an essential amino acid. Wild-type E. coli can synthesize their own tryptophan and are called [A]. Mutants that cannot synthesize an essential nutrient like tryptophan are called [B]. Transcription of the genes for tryptophan synthesis is not [C]: i.e., the genes are transcribed only when needed. Transcription is therefore [D]. When tryptophan is [E], the repressor [F] and transcription of the tryptophan mRNA proceeds. When tryptophan is [G], the repressor [H] and transcription is prevented.

A= prototrophs B=auxotrops C=constitutive D= repressible E= absent F= does not bind G= presnt H= bind to DNA

Different biological processes are governed by different types of regulatory networks that often reflect the type of regulation needed. For example, the stress response in yeast is very [A] and involves a small number of transcription factors activating [B] genes. For very [C] processes such as the cell cycle, many transcription factors are involved in regulating [D] genes. Transcription networks are hierarchical, with [E] controlling large networks; these are in turn coordinated by [F].

A= rapid B=many C=controlled D=a few E= master regulators F= microRNAs

In the Nüsslein-Volhard and Wieschaus experiment, embryos lacking in a contiguous region across segments had mutations in [A] genes. Mutants lacking every other segment had defects in [B] genes. Mutants that had alterations in specific regions of the embryo were defective in [C] genes. Finally, mutants that exchanged the identity of a region for that of another region were defective in [D] genes.

A=gap B=pair-rule C=segment polar D=homeotic

Experiments showed that cell cycle mutants stalled at specific points in the cycle. Mutants could be classified in relation to recognizable steps called [A] events. Cells with a particular mutation stalled at [B] point in the cell cycle, despite the individual cells starting the experiment at [C] point in the cycle. This indicated that the gene product was critical at a specific point in the cycle but was not always needed throughout the cycle. These critical points were termed the [D] point for each gene.

A=landmark B=the same C=a different D=execution

Iron response proteins (IRPs) are involved in regulating iron levels in the cell through translational regulation. Which of the following statements regarding IRP regulation is untrue?

IRP binding prevents transferrin translaion

what is an evolutionarily accepted mutation?

a mutation that does not have adverse impact on the function of a protein

what is a regulon?

a set of genes controlled by an activator

which of the following is not a post-translational modification?

addition of a 5' cap

Fill in the blank. Many transcription factors target their own gene for regulation. This is termed ________________

autoregulation

A growth curve is shown for E. coli cultivated in media containing lactose and glucose. At which points on the growth curve is the lac operon transcribed? Please select all that apply.

b

In the regulatory system that controls the lac operon, which molecule directly reflects the level of glucose in the cell?

cAMP

Fill in the blank. The biochemical process of breaking down a complex molecule into its simpler components is termed _____

catabolism

Tryptophan is involved in transcriptional regulation of the tryptophan-encoding genes. It does this by binding to the tryptophan repressor. Tryptophan is therefore a ________

corepressor

Components and analogs of the lac operon are used by researchers as experimental tools. Match the molecule with its activity.

derepresses lac= allolactose turns blue= X-gal breaks down lactose= B-galactosidas binds to lac= IPTG

Which of the following is an advantage of a genome-wide mutagenesis screen compared to a random mutagenesis screen?

each gene can be targeted in a genome-wide screen

True or false? Biochemically similar amino acids are likely to have similar codons. This reduces the chance that a mutation will cause an amino acid to be substituted with a different amino acid.

false

True or false? Forward genetics involves disruption of a known gene to see what phenotypes will be produced. Reverse genetics involves introducing random mutations and examining the resultant phenotypes to discover the causative gene.

false

True or false? When Nüsslein-Volhard and Wieschaus conducted their genetic screen in Drosophila, they continued to find new genes of interest with increasing numbers of experiments, but the number of new mutations they discovered tailed off after about 2000 chromosomes had been tested.

false

true or false? operons are a key mechanism for co-regulation of genes in bacteria and eukaryotes

false

true or false? the majority of genes in mammals encode proteins

false

True or false? Eukaryotic genes are controlled by more than one transcription factor, but each transcription factor is only involved in the transcription of one gene.

fasle

Fill in the blank. In the lac operon, cAMP-CAP is produced and binds to the CAP binding site when ____ is low

glucose

fill in the blank. Descent from a common ancestor is defined as___

homology

During which stage of translation is translational regulation most likely to occur?

initiation

which of the following is the critical regulatory stage for the majority of genes?

initiation of transcription

Fill in the blank. _____ enzymes carry out post-translational phosphorylation of peptides.

kinase

fill in the blank. Another name for a genetic screen is a ____ screen

mutant

where do repressor proteins bind?

operator sequence

as ____ consists of multiple genes that are transcribed as a single transcript

operon

Fill in the blank. Temperature-sensitive mutations exhibit the mutation when grown at the restrictive temperature. They exhibit a wild-type phenotype when grown at a _____ temperature.

permissive

Fill in the blank. Receptor tyrosine kinases add a _______ to specific tyrosine residues in target proteins

phosphate

Which characteristic of Drosophila melanogaster was exploited in the screen that led to the discovery of the ras pathway?

phototaxis

Match the levels of protein structure to their descriptions.

primary= peptide amino secondary= regional folding tertiary= three-dimensional quaternary= combination

In ChIP, what sort of molecule is used to isolate chromatin attached to the transcription factor of interest

protein

Fill in the blank. In genetic screens, the chance of discovering a novel gene decreases as the screen proceeds. When the chance of finding a new gene is very low and the effort expended to discover a new gene is not justifiable, the screen has been _________.

saturated

the ras gene is a major component of which sort of pathway?

signal transduction

The regulation that determines the anterior and posterior ends of a developing Drosophila embryo is primarily ______

spatial

which is not true of translation termination?

stop codons bind to special tRNA molecules

Tryptophan is an essential amino acid that Neurospora crassa needs in order to be able to grow. The tryptophan biosynthetic pathway has three main steps by which the amino acid tryptophan is produced from chorismate. In an experiment, three N. crassa strains that were suspected of having defects in tryptophan synthesis were cultured on minimal medium (without tryptophan) and on minimum medium (plus tryptophan), with the following results. Which strain is defective in the tryptophan biosynthetic pathway?

strain 1

Arginine is synthesized in a pathway involving several enzymes and biosynthetic intermediates. Five Neurospora crassa strains were cultured on minimal media containing various additives, and the results are shown. Match each N. crassa strain with its description.

strain A= wild-type Strain B= defective in enzyme 2 Strain C= not defective strain D= defective enzyme 3 strain E= defective in enzyme 1

what is the term used for a mutation that overcomes the effect of another mutation?

suppressor mutation

Which of the following features of genetic screens was not key to the success of Beadle and Tatum's early Neurospora crassa experiments with nutritional auxotrophs?

targeted insertional mutagenesis

Which of the following statements about the lac repressor is true?

the lac repressor is encoded by (lacl) which is located OUTSIDE the lac operon

Which of the following is true of dominant loss-of-function mutations?

the mutant phenotype is seen EVEN if an additional gene is present

Hartwell and colleagues used the yeast Saccharomyces cerevisiae to examine the cell cycle. However, most cell cycle mutants are lethal. How did the researchers get around this problem in their experiments?

the researchers used conditional mutants

Many receptor tyrosine kinase genes are essential, making it difficult to assess the function of such genes. How did researchers get around this problem when examining the roles of the sev gene?

the researchers used sub-lethal mutations in the sev gene

True or false? To identify genes in the sev pathway, sev mutants were further mutagenized and the phenotype examined. Mutations that alleviate the sev phenotype are called suppressor mutations and mutations that exacerbate the sev phenotype are called synthetic enhancer mutations.

true

true or false? the majrity of polypeptides are post-translationally modified

true

Which of the following techniques is used to compare the expression profiles of cells under different conditions?

two-channel microarray

Fill in the blank. Position 3 in the codon is the least likely to influence which amino acid is encoded and has the weakest base-pair interaction; i.e., the position can _______

wobble