Cell Molec 230 Comp Quiz 3 Mastering Questions

Choose all of the following that correctly describe a characteristic of mismatch repair.

A.DNA polymerase and ligase fill in the gap. B. Helicase unwinds the DNA in the mismatched area. C. Regions of improper base-pairing between parent and daughter strand are detected and repaired. D. Exonuclease removes the newly synthesized DNA in the mismatched area.

Identify which statement(s) is/are true regarding telomere characteristics.

- Telomeres cap the ends of linear chromosomes and prevent them from being recognized by the cell as broken DNA in need of repair. - Telomeres contain repeated nucleotide sequences that are required to replicate the ends of linear chromosomes.

Based on the figure, which of these statements is/are correct?

-For different genes, opposite strands of DNA can serve as a template. -RNA is always polymerized in the 5'-to-3' direction.

The maltose operon contains genes that code for proteins that catabolize the disaccharide maltose. Similar to the Lac operon, which is only efficiently transcribed in the presence of lactose, the maltose operon is only efficiently transcribed in the presence of maltose. How might induction of the maltose operon in response to maltose be achieved?

-Maltose causes an activator to bind an operon with an inefficient promoter. -Maltose removes a repressor from an operon with an efficient promoter.

Translation proceeds in a series of steps in the active site of the ribosome. Which of the following are important steps in polypeptide formation?

-The hydrogen bonds formed between ribosomal RNA and tRNAs position the aminoacyl-tRNAs to catalyze peptide bond formation. -The RNA in the P site makes hydrogen bonds with the 3' end of the aminoacyl-tRNA.

Which of the following statements is/are true of long noncoding RNAs?

-They can regulate the translation and stability of mRNAs. -They are involved in X chromosome inactivation.

The Encyclopedia of DNA Elements (ENCODE) project aims to discover functional elements in DNA. One technique employed is DNase-seq. This technique employs a DNase enzyme that digests accessible regions of chromatin, while inaccessible regions remain undigested. The undigested DNA is then sequenced. Which of the following is likely true of the DNase-seq results?

-Unsequenced DNA is likely part of euchromatin. -Centromeric DNA is likely to be sequenced in all samples.

You have joined a lab studying DNA replication in E. coli. The graduate student you are working with has identified a mutation in primase that makes primase very inefficient. Your project is to characterize the cells with this mutation. Predict the defects you would most likely see in the mutant E. coli cells.

-a longer total time to replicate DNA -a delay in DNA polymerase beginning synthesis

Researchers have created plasmids that only allow expression of inserted genes in response to a metabolite. Researchers can add these plasmids to E. coli cells and increase the expression of the inserted gene by adding the appropriate metabolite to the culture media. Plasmids containing which combination of operator and promoter allow activation of gene expression in response to an added metabolite?

-operator recognized by Lac repressor protein -strong promoter

The DNA helicase animation shows the bacteriophage T7 helicase unwinding DNA. Which of the following are critical components of the helicase mechanism of action necessary to unwind DNA?

-oscillating loops pulling the single-stranded DNA through a central hole -conformational changes of subunits -ATP binding and hydrolysis

Place the following steps of RNA splicing in the correct order from first step to last.

1. BBP and U2AF bind to the A in the branch-point site in the intron, while the U1 snRNP binds to the 5' splice site. 2. The U2 snRNP binds the branch-point site and the U4/U6 and U5 snRNP's bind to the 5' splice site. 3. A conserved adenine in the branch-point site attacks the 5' splice site, cutting the RNA at the 5' splice site. 4. The 5' end of the intron binds the branch-point adenine, forming a lariat. 5. The 3' end of the first exon interacts with the 3' splice site, forming a new bond in the sugar-phosphate backbone. 6. The lariat is released and degraded.

A primary transcript (immature, non-processed) single-stranded RNA molecule has the following nucleotide composition: 30% A, 20% G, 24% C, and 26% U. What is the nucleotide composition of the double-stranded DNA molecule from which it was transcribed?

28% A, 22% G, 22% C, and 28% T

The sequence of the template strand of a DNA molecule is 5'-ACTGGCAATG-3'. What is the sequence of the RNA transcribed from this DNA?

5'-CAUUGCCAGU-3'

The sequence of the coding strand of a DNA molecule (that is, the DNA strand that contains the codons specifying the protein sequence) is 5'-CGGATGCTTA-3'. What is the sequence of the RNA made from this DNA?

5'-CGGAUGCUUA-3'

To determine if DNA replication is semiconservative, dispersive, or conservative (see image below), Matt Meselson and Frank Stahl performed a classic experiment in which they grew E. coli for many generations in a heavy isotope of nitrogen (15N) and then transferred the bacteria to media containing 14N for a single round of DNA replication. Density of the DNA was determined via centrifugation and the result of intermediate density DNA (50% 14N, 50% 15N within a double helix) was consistent with both semiconservative and dispersive DNA replication. Another round of replication can discriminate between semiconservative and dispersive DNA replication. What kind of DNA is expected if these E. coli are grown for a second generation in14N-containing media?

50% intermediate density, 50% light density

Once heterochromatin has been established, it will often spread until it encounters which of the following?

A barrier DNA sequence

Which of the following statements is not true?

A cell will temporarily decondense its chromatin to silence genes during differentiation.

Synthetic biologists are trying to create cells from raw material. One step in the process is encapsulating genetic material into a compartment. Researchers of the origin of life think that the earliest cells on Earth may have used RNA as their genetic material instead of DNA. As biologists consider which genetic material to use in creating their synthetic cells, which of the following characteristics of a single-stranded RNA genome should they keep in mind?

A newly synthesized RNA strand is not identical to the template strand.

What evidence suggests that the large amount of excess "junk" DNA in a genome may serve an important function?

A portion of "junk" DNA is highly conserved in its DNA sequence among many different eukaryotic species.

One of the first steps in obtaining a karyotype (such as that shown below of a cancer cell) is treating cells with a drug that stalls cells in mitosis. Why must cells arrest in mitosis for karyotype analysis?

Only mitotic chromosomes are highly condensed and visible with a light microscope.

Which of the following describes the Lac operon in E. coli when lactose, but not glucose, is present in the culture medium?

CAP, but not the Lac repressor, is bound to the Lac operon's regulatory DNA, and the Lac operon is expressed.

In their 1953 paper on the double-helical structure of DNA, Watson and Crick famously wrote: "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material." What did they mean?

Each strand in a DNA double helix contains all the information needed to produce a complementary partner strand.

Using powerful new sequencing technologies, investigators can now catalog every RNA molecule made by a cell and determine at what quantities these RNAs are present. In an experiment, researchers measured the relative quantities of two different mRNAs—one transcribed from gene A, the other from gene B—in two different cell types. Gene B is expressed in both the liver and the brain whereas gene A is expressed in the brain but not in the liver. Which most likely encodes a housekeeping protein?

Gene B only

If DNA replication were conservative (although we know it is not), what would Meselson and Stahl have seen following the first round of replication in E. coli that had been switched from a heavy (15N-containing) nutrient medium to a light (14N-containing) nutrient medium?

Half the DNA would be heavy, and the other half would be light.

Which statement is true about the association of histone proteins and DNA?

Histone proteins have a high proportion of positively charged amino acids, which bind tightly to the negatively charged DNA backbone.

Which of the following statements concerning leucine zipper protein dimerization and DNA binding is correct?

Leucine zipper proteins function as a dimer with both subunits making contact with the sequence-specific DNA site.

c-Met is an oncogene that contributes to the development of certain cancers by triggering cell division and tumor growth. In a 2009 article, Yan and colleagues found regions in the 3' untranslated region of c-Met mRNA complementary to microRNA-1/206. In addition, higher levels of microRNA-1/206 were associated with slower cell proliferation. What is a likely explanation for the inverse correlation between microRNA-1/206 and cell proliferation?

MicroRNA-1/206 targets c-Met mRNA for destruction via RISC.

Which of the following describes the Lac operon in E. coli when both lactose and glucose are present in the culture medium?

Neither CAP nor the Lac repressor is bound to the Lac operon's regulatory DNA, and the Lac operon is not expressed.

Which of the following statements about nucleosomes is false?

Nucleosomes are found only in mitotic chromosomes.

The genetic code was originally deciphered, in part, by experiments in which synthetic polynucleotides with repeating sequences were used as mRNAs to direct protein synthesis in cell-free extracts. Under these conditions, ribosomes could be made to start translation anywhere within the RNA molecules, with no start codon necessary. What peptide would be made by translation from a synthetic mRNA made of the repeating dinucleotide CGCG...?

a peptide containing alternating arginines and alanines

The genetic code was originally deciphered, in part, by experiments in which synthetic polynucleotides with repeating sequences were used as mRNAs to direct protein synthesis in cell-free extracts. Under these conditions, ribosomes could be made to start translation anywhere within the RNA molecules, with no start codon necessary. What peptide would be made by translation from a synthetic mRNA made of the repeating trinucleotide UCGUCG...?

a polymer of serine (Ser-Ser-Ser...), a polymer of arginine (Arg-Arg-Arg...), and a polymer of valine (Val-Val-Val...)

The loss of purine bases from a strand of DNA is typically caused by which of the following?

a spontaneous chemical reaction

Where is heterochromatin not commonly located?

chromosomal regions carrying genes that encode ribosomal proteins

Researchers often want to isolate a certain type of RNA. For some RNA species, this can be accomplished via affinity chromatography, using beads coated with chains of poly-deoxythymidine (poly-dT). The desired RNA will stick to the beads while unwanted RNAs will flow through the column. The retained RNA can then be eluted. What RNA species can be purified using this method?

eukaryotic mRNA

Homologous recombination occurs only between DNA molecules that are identical in nucleotide sequence without any variation.

false, because only similar sequence is needed

Suppose the 3' splice site is mutated from AGG to ACG. Predict the consequence of this mutation.

Splicing would begin but not be properly completed if the 3' splice site is altered.

The Drosophila regulatory segment that defines the location of Eve stripe 2 contains binding sites for four different transcription regulators: two repressors (Giant and Krüppel) and two activators (Bicoid and Hunchback). For Eve to be efficiently expressed in stripe 2, both repressors must be absent and both activators present. What would you expect to see in flies that lack the gene that encodes Bicoid? (Assume that Bicoid does not influence the expression of Hunchback, Giant, or Krüppel.)

Stripe 2 would become fainter.

Predict what might happen to telomeres in Tetrahymena cells if the Tetrahymena template RNA were mutated from 3'-ACCCCAAC-5' to 3'-AGCCCAAC-5'.

Telomeres would become shorter in every generation compared to normal cells.

Which of the following occurs when a cell repairs a double-strand DNA break by the process of nonhomologous end joining?

The DNA sequence at the site of repair is altered by a short deletion.

Some applications in biology, such as polymerase chain reaction (PCR), require melting the DNA double helix into single strands of DNA. This can be accomplished by heating the DNA. As DNA is heated, why does the double helix structure denature into single strands of DNA but not into individual nucleotides? In other words, why do the single strands remain intact even though the double helix does not?

The double helix is held together with hydrogen bonds, while the single strands are linked by phosphodiester bonds.

Which of the following statements is supported by the information in this image and is consistent with your knowledge regarding genomic architecture in prokaryotes and eukaryotes?

The eukaryotic cell must have a nuclear spliceosome to remove introns from RNA.

Which of the following statements most accurately describes the expression of the repressor protein of the tryptophan operon?

The gene for the tryptophan repressor is expressed constitutively.

In the 1920s, bacteriologist Fred Griffith demonstrated that a heat-killed, infectious pneumococcus produced a substance that could convert a harmless form of the bacterium into a lethal one. Fifteen years later, researchers prepared an extract from the disease-causing S strain of pneumococci and showed that this material could transform the harmless R-strain pneumococci cells into the infectious S-strain form. This change to the bacteria was both permanent and heritable, suggesting that this "transforming principle" represents the elusive genetic material of the cells. The researchers subjected their extract to a variety of tests to determine the chemical identity of the "transforming principle." In one experiment, they treated the material with enzymes that destroy all proteins. This treatment did not affect the ability of the extract to transform harmless bacteria into an infectious form.

The genetic material is not protein.

What would happen to the helix-3 interaction with DNA if a mutation occurred that altered this adenine (as shown) to guanine?

The integrity of the interaction would decrease because one of the two hydrogen bonds would not be able to form.

What problem with replication of linear chromosomes does telomerase address?

The lagging strand stops short of the 3' end during replication, so chromosomes would shorten in each replication cycle without telomerase.

To crack the genetic code, researchers introduced synthetic messenger RNAs into in vitro translation systems and determined which proteins were produced from these synthetic mRNAs. mRNAs consisting of poly-UUC led to production of three different proteins: poly-Phe, poly-Ser, and poly-Leu. What best explains this result?

The synthetic mRNA was read in all three reading frames.

Which of the following statements is not true about the differences between liver cells and kidney cells in the same organism?

They contain different genes.

How do chromatin-remodeling complexes work?

They use the energy from ATP hydrolysis to alter the arrangement of nucleosomes, rendering certain regions of the DNA more accessible to other proteins.

Investigators treat cells with a chemical that introduces random mutations into the DNA, including single-nucleotide changes that turn one base into another. They then isolate two mutants: one produces a protein that carries an alanine at a site that normally contains a valine; the other produces a protein that carries a methionine instead of the valine. When these mutant cells are subjected to the same mutagenic treatment, they both produce proteins that contain a threonine at the site of the original valine. Assuming that the mutations causing these alterations are single-nucleotide changes, what were the codons that specified each of the amino acids discussed?

Val, GUG; Ala, GCG; Met, AUG; Thr, ACG

Which macromolecule(s) is/are critical in the active site of the ribosome for catalysis of peptide bond formation?

ribosomal RNA

It has been proposed that the first cells used RNA for both information storage and catalysis and that DNA and proteins evolved later. Which modern macromolecules may be relics of the hypothesized RNA world?

spliceosome and ribosome

Several organisms have a homologous protein (inherited from a common ancestor) that is highly similar at the amino acid level. You are comparing the genes that code for these proteins in the different organisms when you note that one of the codon nucleotide positions shows more nucleotide variation than the other nucleotide positions. In which codon nucleotide position do you expect to see the most variability among species?

third nucleotide position

The mismatch repair system recognizes mismatched base pairs, removes a portion of the DNA strand containing the error, and then resynthesizes the missing DNA using the correct sequence as a template. But what if the mismatch repair system instead removed a piece of the DNA strand that contained the correct sequence? What would replication of this improperly repaired sequence produce?

two DNA molecules bearing the same mutation

In bacterial cells, the tryptophan operon encodes the genes needed to synthesize tryptophan. What happens when the concentration of tryptophan inside a cell is high?

It activates the tryptophan repressor, which shuts down expression of the tryptophan operon.

Many antibiotics work by inhibiting bacterial protein synthesis. Investigators have isolated a promising new compound and wish to determine its mechanism of action. Using a cell-free translation system similar to the ones originally used to deduce the genetic code, the researchers incubate their drug with the synthetic polynucleotide 5'-AUGUUUUUUUUU. In the absence of the drug, this polynucleotide directs the synthesis of the peptide Met-Phe-Phe-Phe. When the drug is added, only the peptide Met-Phe is produced. Based on this observation, which is most likely the mechanism of action of this potential new antibiotic?

It blocks translocation of the large ribosomal subunit, preventing the movement of peptidyl-tRNA from the A site to the P site of the ribosome.

When does homologous recombination most likely occur in order to flawlessly repair double-stranded DNA breaks?

after the cell's DNA has been replicated

In the absence of repair, what would the replication of a double helix containing a mismatch yield?

one DNA molecule with the normal sequence and one DNA molecule with a mutated sequence