Microbio Chapter 13

You and a classmate are discussing early experiments in genetics, and you state that Avery, MacLeod, and McCarty provided the first evidence that DNA carries genetic information. Your classmate argues that Griffith was the first to demonstrate this. Which statement best defends your argument?

Multiple Choice

• Although Griffith first demonstrated transformation, Avery, MacLeod, and McCarty provided evidence that DNA rather than protein or RNA was the transforming agent.

• Avery, MacLeod, and McCarty worked with purified DNA extracts while Griffith worked with bacterial strains.

• Enzymes were used in the experiments carried out by Avery, MacLeod, and McCarty while Griffith transformed cells chemically or by using heat.

• Because Avery, MacLeod, and McCarty did their experiments after those done by Griffith, they had much more information regarding the structure and function of DNA.

• DNA used by Avery, MacLeod and McCarty was extracted solely from transformed strains of pneumococci, while Griffith used native pneumococcal strains.

• Although Griffith first demonstrated transformation, Avery, MacLeod, and McCarty provided evidence that DNA rather than protein or RNA was the transforming agent.

Who first demonstrated transformation using mice and two strains of Streptococcus pneumoniae?

Multiple Choice

Griffith

Hershey and Chase

Watson and Crick

Avery, McCarty, and MacLeod

Griffith

Griffith's experiment demonstrated transformation because a mouse injected with live R and heat-killed S strains of Streptococcus pneumoniae resulted in death of the mouse and the isolation of live R as well as live S cells. Hypothesize as to the type of cells that Griffith would have observed if transformation had NOT occurred.

Multiple Choice

Griffith would have isolated only live R cells from the mouse host.

Griffith would have isolated both live R and heat-killed S cells from the mouse host.

Griffith would have isolated only live S cells from the mouse host.

Griffith would have isolated no cells from the mouse host.

Griffith would have isolated only live R cells from the mouse host.

How could the Hershey and Chase experimental procedure be redesigned to support a hypothesis that RNA carries genetic information?

Multiple Choice

Replace T2 bacteriophage with an RNA virus.

Use 35S to label an RNA virus and 32P to label a DNA virus.

Use 35S and 32P to label the same components of an RNA virus and T2 bacteriophage, then add both viruses to Escherichia cells.

Replace Escherichia with an RNA virus.

Extract RNA from Escherichia and mix it with the T2 bacteriophage.

Replace T2 bacteriophage with an RNA virus.

Which was common to experiments done by Avery and colleagues as well as Hershey and Chase?

Multiple Choice

• Radioactive DNA

• Virulent bacteriophage

• Bacterial cells

• Radioactive protein

• Escherichia coli

Bacterial cells

In the Hershey and Chase experiment, how did labeling DNA and protein with different radioactive isotopes demonstrate that DNA, rather than protein, carried the genetic information in the T2 virus?

Multiple Choice

• Researchers could use radio labeling to inactivate DNA and protein in the bacteria.

• Researchers could track which part of the virus entered a bacterial cell.

• Researchers could monitor how DNA interacted with protein in the virus.

• Researchers could distinguish bacterial DNA from viral protein.

Researchers could track which part of the virus entered a bacterial cell.

Which of the following is not a complementary base pair found in DNA molecules?

Multiple Choice

• Adenine-thymine

• Guanine-cytosine

• Adenine-uracil

• All of the choices are correct.

Adenine-uracil

If 20% of nucleotides in a DNA sample contain thymine, estimate the percentage of cytosine that is present in the DNA.

Multiple Choice

• 15%

• 20%

• 30%

• 80%

30%

Which of the following nitrogenous bases is usually found in RNA but not in DNA?

Multiple Choice

• Adenine

• Thymine

• Uracil

• Guanine

Uracil

Which of the following is not present in DNA?

Multiple Choice

• Alpha carbon

• 5'-carbon

• Minor groove

• 3'-hydroxyl

• Double helix

Alpha carbon

A scientist wishes to develop an antimicrobial agent that specifically targets replication elongation in Escherichia coli without interfering with proteins that catalyze other replication processes. Which of the following experimental designs is most appropriate for the scientist to explore?

Multiple Choice

• Develop a molecule that interferes with the DNA-binding ability of DNA polymerase III core enzyme.

• Modify an existing antibiotic to act as a competitive inhibitor of DNA polymerase I.

• Design a drug that modifies the structural configuration of DNA at the oriC locus.

• Create a novel protein that acts as a competitive inhibitor of the DNA ligase binding site.

• Develop a molecule that interferes with the DNA-binding ability of DNA polymerase III core enzyme.

Targeting Elongation: DNA polymerase III is the primary enzyme responsible for the actual process of DNA replication elongation in Escherichia coli. Targeting its core enzyme directly halts the elongation phase.

Specificity: Unlike DNA polymerase I (which is primarily involved in primer removal and DNA repair) or DNA ligase (which seals nicks in the lagging strand during joining), DNA polymerase III is dedicated specifically to the bulk synthesis and elongation process

In terms of relatedness to a specific cellular process, which protein does not belong with the others?

Multiple Choice

• RNA polymerase holoenzyme

• DNA polymerase holoenzyme

• Ribonuclease

• DNA ligase

RNA polymerase holoenzyme

The answer RNA polymerase holoenzyme is correct because it belongs to a completely different primary cellular process than the other three options:

Transcription: RNA polymerase holoenzyme is the primary enzyme responsible for synthesizing RNA from a DNA template (transcription).

DNA Replication: DNA polymerase holoenzyme, DNA ligase, and ribonuclease are all key proteins and enzymes that work together to synthesize, repair, or process DNA strands during DNA replication.

Because RNA polymerase is dedicated to gene expression rather than copying the genome itself, it is the odd one out.

Over twisting or under twisting of helical DNA generates _________blank.

Multiple Choice

• hypertwists

• hypotwists

• hypercoils

• supercoils

supercoils

When a DNA molecule is replicated, the daughter molecules contain one strand of parental DNA and one strand of newly synthesized DNA; this is called _________blank replication.

Multiple Choice

• conservative

• semiconservative

• regulated

• complementary

semiconservative

While examining the sequence of nucleotides in the replicon region of bacterial DNA, you note an abundance of adenine and thymine base pairs. This leads you to conclude that this particular section of the DNA must be the _________blank.

Multiple Choice

• ter site

• replication fork

• oriC site

• Shine-Dalgarno sequence

oriC site

During replication, which enzyme unwinds the two strands of the DNA molecule?

Multiple Choice

• Primase

• Ligase

• Helicase

• DNA polymerase

Helicase

DNA polymerases require which of the following elements to replicate DNA?

Multiple Choice

• A template, a primer, a source of energy

• A ribosome, a template, an RNA polymerase

• A source of energy, a template, an RNA polymerase

• A source of energy, an RNA strand, a ribosome

A template, a primer, a source of energy

The Y-shaped part of the DNA molecule where the actual replication process occurs is called the replication _________.

splice

enzyme

fork

junction

fork

Bacterial DNA replication occurs at a rate of _________blank.

Multiple Choice

• 1,000 base pairs per second

• 1,000 base pairs per minute

• 100 base pairs per second

• 100 base pairs per minute

• 1,000 base pairs per second

The transcribed, but not translated, sequence that is immediately upstream of the region that encodes the functional product is called the _________blank region.

Multiple Choice

• leader

• promoter

• coding

• trailer

leader

The strand of DNA that is copied when RNA polymerase synthesizes mRNA is called the _________blank strand.

Multiple Choice

• transcription

• sense

• template

• leading

• template

If the ultimate product of a functional gene is not a protein, what other product(s) might be encoded by the gene?

Multiple Choice

• tRNA and rRNA

• tRNA and mRNA

• mRNA and rRNA

• mRNA, tRNA, and RNA

tRNA and rRNA

Which of the following is in the coding region of a gene?

Multiple Choice

• Promoter

• Leader

• Trailer

• None of the choices are correct.

• None of the choices are correct.

The transcribed and translated region of a gene is the _________blank region.

Multiple Choice

• leader

• promoter

• coding

• trailer

coding

The process by which the base sequence of all or a portion of a DNA molecule is used to direct the synthesis of an RNA molecule is called _________blank.

Multiple Choice

• transcription

• translocation

• translation

• replication

transcription

The genetic information in DNA is divided into units called _________blank.

Multiple Choice

• proteins

• genes

• genotype

• phenotype

genes

Key sequences exist within promoters, which vary somewhat among promoters but are sufficiently constant that they can be represented by a sequence of bases most often found at each position. These representations are called _________blank sequences.

Multiple Choice

• Shine-Dalgarno

• consensus

• template

• operator

consensus

Which statement defends the concept that the term "gene" is better defined as a nucleotide sequence that encodes for one or more functional products rather than encoding for one or more functional proteins?

Multiple Choice

• Intron sequences in RNA do not encode proteins.

• Products of genes include tRNAs and rRNAs as well as proteins.

• Genes in bacteria are organized as operons that can lead to several protein products.

• The genetic code is redundant, therefore the same codon may be encoded by different DNA triplets.

Products of genes include tRNAs and rRNAs as well as proteins.

Which of the following is common to both factor-dependent and factor-independent transcription termination?

Multiple Choice

• Both types of termination occur following a pause by the polymerase.

• Both types of termination are associated with rho termination factor.

• Both types of termination involve NusA protein.

• None of the choices are correct.

Both types of termination occur following a pause by the polymerase.

The region at which the RNA polymerase binds is the _________blank region.

Multiple Choice

• leader

• promoter

• coding

• trailer

promoter

When RNA polymerase adds a nucleotide to a growing mRNA chain, another product of the reaction is _________blank.

Multiple Choice

• phosphate

• supercoiling

• water

• pyrophosphate

• pyrophosphate

During transcription elongation, how many pyrophosphate molecules are produced from the incorporation of 20 ribonucleoside monophosphates?

Multiple Choice

• 20

• 40

• 60

• 5

20

Which of the following is a correct comparison between RNA polymerase holoenzyme that functions in transcription and the primase enzyme that functions in DNA replication?

Multiple Choice

• Both enzymes synthesize RNA.

• Both enzymes are bound by sigma factor.

• Both enzymes synthesize DNA.

• Both enzymes are composed of RNA.

• Both enzymes synthesize RNA.

Which modification of the terminator region of a gene would specifically prevent rho-independent termination?

Multiple Choice

• Change in the sequence that encodes the mRNA leader

• Change in the adenine-thymine sequence of the promoter

• Change in the rut binding site

• Change in the adenine-rich sequence of nucleotides of the terminator region

• Change in the adenine-rich sequence of nucleotides of the terminator region

The Mechanism: In rho-independent (intrinsic) termination, the mRNA transcript forms a hairpin loop followed immediately by a run of uracil residues. This corresponds to an adenine-rich region on the DNA template strand.

Weak Bonds: The RNA-DNA hybrid in this region consists of weak adenine-uracil (A-U) base pairs. This weakness causes the transcript to dissociate from the DNA template, releasing the RNA polymerase and ending transcription.

How many RNA codons encode 60 amino acids?

Multiple Choice

• 180

• 30

• 20

• 60

  
  

60

Which of the following is not a termination codon?

Multiple Choice

• AUG

• UAA

• UAG

• UGA

AUG

Which of the following is the initiator codon?

Multiple Choice

• AUG

• UAA

• UAG

• UGA

AUG

The genetic code is said to be _________blank because more than one codon will specify a particular amino acid.

Multiple Choice

• ambiguous

• degenerate

• multiplicative

• repetitious

degenerate

Which set of codons terminate transcription in most organisms?

Multiple Choice

• UGA, UAG, UAA

• AGU, UAG, UAA

• ACT, TAC, ATT

• TGA, TAG, TAA

UGA, UAG, UAA

How many different termination codons are used in translation?

Multiple Choice

• One

• Two

• Three

• Four

Three

What would be the most likely outcome if the genetic code was not degenerate?

Multiple Choice

• The effect of some mutations would increase.

• The effect of some mutations would decrease.

• The mutation rate would remain the same.

• The number of stop codons would increase.

• The effect of some mutations would increase.

The process by which the base sequence of an RNA molecule is used to direct the synthesis of a protein is called _________blank.

Multiple Choice

• translocation

• translation

• transcription

• replication

translation

The energy needed for protein synthesis is provided by the hydrolysis of _________blank.

Multiple Choice

• ATP

• GTP

• UTP

• ATP and GTP

• ATP and UTP

• ATP and GTP

The portion of the tRNA molecule that binds to the codon on the mRNA is called the _________blank.

Multiple Choice

• D arm

• anticodon

• Shine-Dalgarno sequence

• acceptor arm

anticodon

Two amino acids that are found in some proteins due to exceptions in the universal genetic code are _________blank.

Multiple Choice

• pyrrolysine and selenocysteine

• lysine and selenocysteine

• pyrrolysine and cysteine

• lysine and cysteine

pyrrolysine and selenocysteine

Amino acids are delivered to ribosomes during translation by _______Blank.

Multiple Choice

• ribosomal RNA (rRNA)

• transfer RNA (tRNA)

• messenger RNA (mRNA)

• transfer RNA (tRNA)

Adjacent amino acids are sequentially linked into a growing polypeptide chain by a / an _______Blank reaction.

Multiple Choice

• translocation

• wobble

• transpeptidation

• activation

transpeptidation

What is the minimum number of aminoacyl-tRNA synthetase enzymes needed to attach amino acids to all the various tRNA molecules?

Multiple Choice

• 20

• 61

• 64

• As many as there are different tRNAs

• 20

The answer is 20 because there are 20 standard amino acids used to build proteins in living cells.

One enzyme per amino acid: Each aminoacyl-tRNA synthetase is specific to a single amino acid (and all the different tRNA molecules that carry that specific amino acid).

The "Wobble" Effect: Even though there are 61 codons that code for amino acids (meaning multiple different tRNAs can carry the same amino acid), a single synthetase enzyme is able to recognize and charge all the different tRNA variants associated with its specific amino acid.

What might be a reason for the accumulation of improperly folded proteins in the bacterial cytoplasm following translation?

Multiple Choice

• A problem exists with the functioning of molecular chaperones.

• The cell is synthesizing proteins too rapidly.

• Polysomes are forming on the mRNA.

• The proteins are being transcribed but not translated.

• A problem exists with the functioning of molecular chaperones.

Proteins are moved from the cytoplasm to the plasma membrane or periplasmic space in _______Blank, while proteins are moved from the cytoplasm to the external environment in _________Blank.

Multiple Choice

• secretion; translation

• translocation; secretion

• secretion; translocation

• translocation; translation

• translocation; secretion

How were experiments done by Griffith similar to those done by Avery, MacLeod, and McCarty?

Multiple Choice

• Both used pneumococcal bacteria.

• Both used purified DNA.

• Both used a mouse host.

• Both were done in the 1940s.

• Both used enzymes that destroyed DNA.

Both used pneumococcal bacteria.

Who first demonstrated transformation using mice and two strains of Streptococcus pneumoniae?

Multiple Choice

• Hershey and Chase

• Avery, McCarty, and MacLeod

• Griffith

• Watson and Crick

Griffith

Choose the correct order of proteins that function in the initiation, elongation, and termination stages of DNA replication.

Multiple Choice

• DnaA, DNA polymerase III, DNA polymerase I, DNA ligase

• DnaA, DNA polymerase I, DNA polymerase III, DNA ligase

• DNA polymerase III, DNA polymerase I, DNA ligase, DnaA

• DNA polymerase I, DnaA, DNA polymerase III, DNA ligase

• DnaA, DNA polymerase III, DNA polymerase I, DNA ligase

Here is the succinct breakdown of the role each protein plays in DNA replication:

DnaA: Binds to the origin of replication to initiate the process by melting/opening the DNA double helix.

DNA Polymerase III: The primary enzyme responsible for the elongation phase, synthesizing the new DNA strands by adding nucleotides.

DNA Polymerase I: Removes RNA primers used during elongation and replaces them with DNA nucleotides.

DNA Ligase: Seals the remaining nicks in the sugar-phosphate backbone, finalizing the process during termination.

Which enzyme is a topoisomerase?

Multiple Choice

• DNA gyrase

• DNA ligase

• DNA polymerase I

• DNA polymerase III

DNA gyrase

Which statement defends the concept that the term "gene" is better defined as a nucleotide sequence that encodes for one or more functional products rather than encoding for one or more functional proteins?

Multiple Choice

• Products of genes include tRNAs and rRNAs as well as proteins.

• Genes in bacteria are organized as operons that can lead to several protein products.

• The genetic code is redundant, therefore the same codon may be encoded by different DNA triplets.

• Intron sequences in RNA do not encode proteins.

Products of genes include tRNAs and rRNAs as well as proteins.

A bacterial _________blank is the nontranscribed region of the DNA to which RNA polymerase binds in order to initiate transcription.

Multiple Choice

• operon

• operator

• promoter

• initiator

promoter

The region at which the RNA polymerase binds is the _________blank region.

Multiple Choice

• leader

• promoter

• coding

• trailer

promoter

The genetic code is translated in groups of _________blank bases.

Multiple Choice

• two

• three

• four

• five

three

Bacterial ribosomes _________blank.

Multiple Choice

• comprise multiple tRNA binding sites, three proteins, and two rRNA subunits

• comprise two tRNA binding sites, three rRNA subunits, and multiple proteins

• comprise two rRNA subunits, multiple proteins, and three tRNA binding sites

• comprise two proteins, three tRNA binding sites, and multiple rRNA subunits

comprise two rRNA subunits, multiple proteins, and three tRNA binding sites

Ribosomes can attach to the mRNA and begin translation even though transcription has not been completed in _______Blank.

Multiple Choice

• bacteria

• eukaryotes

• fungi

• protozoa and some plants

bacteria

Ribosomes consist of _________blank separate subunits that come together as part of the initiation process and dissociate immediately after termination.

Multiple Choice

• two

• three

• four

• five

two

One benefit of transporting molecules via outer membrane vesicles and extracellular vesicles versus a typical secretion system is that _________blank.

Multiple Choice

• the vesicle contents are protected by the lipid bilayer that surrounds them, extending their viability outside of the cell

• it requires much less energy to transport the molecules in vesicles

• transport from one cell to another occurs at a much more rapid rate

• vesicles form regardless of the environmental conditions that surround the bacterial cells

• the vesicle contents are protected by the lipid bilayer that surrounds them, extending their viability outside of the cell

The Sec system is used by _________blank.

Multiple Choice

• both monoderm and diderm bacteria

• neither monoderm nor diderm bacteria

• monoderm bacteria only

• diderm bacteria only

both monoderm and diderm bacteria

Griffith's experiment demonstrated transformation because a mouse injected with live R and heat-killed S strains of Streptococcus pneumoniae resulted in death of the mouse and the isolation of live R as well as live S cells. Hypothesize as to the type of cells that Griffith would have observed if transformation had NOT occurred.

Multiple Choice

• Griffith would have isolated only live R cells from the mouse host.

• Griffith would have isolated both live R and heat-killed S cells from the mouse host.

• Griffith would have isolated only live S cells from the mouse host.

• Griffith would have isolated no cells from the mouse host.

• Griffith would have isolated only live R cells from the mouse host.

Which of the following is NOT a pyrimidine?

Multiple Choice

• Adenine

• Cytosine

• Thymine

• Uracil

Adenine

A scientist wishes to develop an antimicrobial agent that specifically targets replication elongation in Escherichia coli without interfering with proteins that catalyze other replication processes. Which of the following experimental designs is most appropriate for the scientist to explore?

Multiple Choice

• Develop a molecule that interferes with the DNA-binding ability of DNA polymerase III core enzyme.

• Modify an existing antibiotic to act as a competitive inhibitor of DNA polymerase I.

• Design a drug that modifies the structural configuration of DNA at the oriC locus.

• Create a novel protein that acts as a competitive inhibitor of the DNA ligase binding site.

Develop a molecule that interferes with the DNA-binding ability of DNA polymerase III core enzyme.

Each chromosome has one or more _________blank site(s) where replication begins.

Multiple Choice

• promoter

• replicon

• operator

• origin

origin

Which is true regarding translation in bacteria?

Multiple Choice

• Translation begins with formation of the 30S initiation complex.

• Translation ends when the Shine-Dalgarno sequence is reached.

• The 70S ribosome is composed of a 20S and 50S subunit.

• All of the choices are correct.

• Translation begins with formation of the 30S initiation complex.

If you wished to design an antimicrobial agent that prevented the formation of the 70S initiation complex in bacterial translation, which molecule should specifically be targeted?

Multiple Choice

• IF-3

• mRNA

• Peptidyl transferase

• EF-1

• IF-3