chapter 8 - mastering microbiology

diphtheria toxin kills eukaryotic cells by affecting translation. more specifically, the toxin prevents movement of tRNAs from the A site to the P site of the ribosome. predict what the result(s) of this inhibition would be

-new tRNAs will not be able to enter the ribosome -protein synthesis will be interrupted bc the peptide chain is inhibited from growing in order for protein synthesis to occur, the polypeptide chain must elongate. elongation is dependent on the movement of tRNAs from the A to P to the E site. during infection, the toxin that is produced by C. diphtheriae will block the A site. this effectively shuts down the ability of the ribosome to function. if the cell is unable to synthesize proteins, it will not survive

lagging strand synthesis

1. DNA polymerase beings synthesizing the lagging strand by adding nucleotides to a short segment of RNA 2. after each piece of the lagging strand is complete, it is released from DNA polymerase 3. a different DNA polymerase replaces the RNA segments w DNA 4. DNA ligase seals the gaps between the pieces, and eventually forms a continuous strand

the ability of C. diphtheriae to produce toxin is acquired via the process of specialized transduction. this is just one of the mechanisms that bacteria use to transfer genetic material to other bacteria, a process known as horizontal gene transfer. there are different mechanisms for horizontal gene transfer in bacteria, each with its own unique features 1. transformation 2. conjugation 3. generalized transduction 4. specialized transduction

1. transformation - naked DNA is transferred from donor to recipient and requires the recipient cell to be competent 2. conjugation - requires direct contact bw bacterial cells, which is typically mediated by a sex pilus and donor/recipient cells must be of an opposite mating type 3. generalized transduction - a phage infects the bacterial cell, thereby transferring bacterial, plasmid, and/or viral DNA to the recipient 4. specialized transduction - during phage infection, particular bacterial genes are transferred to the recipient

if the sequence of amino acids encoded by a strand of DNA is serine-alanine-lysine-leucine, what is the order of bases in the sense strand of DNA? UUA - leucine UAA - nonsense GCA - alanine AAU - asparagine AAG - lysine UGC - cysteine GUU - valine UCG,UCU - serine

3' AGACGTTTCAAT

if the sequence of amino acids encoded by a strand of DNA is serine-alanine-lysine-leucine, the coding for the antisense strand of DNA is

5' TCTGCAAAGTTA

during elongation, how is the RNA synthesized?

5' to 3'

the anticodon for valine is valine - GUU

CAA

during infection, C. diphtheriae expresses a variety of genes that are used to establish infection and cause disease. one of these genes encodes for diphtheria toxin. expression of the toxin requires the genetic information contained in DNA be converted into protein. the 1st step in this process is transcription, in which DNA is converted into mRNA. the following is a short piece of the DNA sequence for diphtheria toxin (written 5' to 3'): TAA GCG TAG AAC TTG. which of the following sequences represents the mRNA (written 5' to 3') that will be generated from this template DNA sequence

CAA GUU CUA CGC UUA

what characteristic of DNA allows two connected DNA polymerases to synthesize both the leading and lagging strands?

DNA is flexible

the molecule that seals the gaps between the pieces of DNA in the lagging strand is

DNA ligase

what builds new strands of DNA?

DNA polymerase, by adding DNA nucleotides one at a time

which of the following is a DNA strand complementary to CGA ATC AGC ?

GCT TAG TCG

an enzyme that copies DNA to make a molecule of RNA is

RNA polymerase

which finding is most surprising from Griffith's experiments?

S strain cells are isolated from blood of mice infected with heat-killed S strains and live R strains

during DNA replication, which nucleotide will bind to an A nucleotide in the parental DNA?

T

which of the following amino acids is coded by only one codon?

Trp

what is transferred during bacterial conjugation?

a bacterial plasmid

what kind of bond is formed when two amino acids join together?

a peptide bond

insertion sequences target which areas on a target DNA sequence?

a sequence of nucleotides identical to the inverted repeat sequence found on the insertion sequence itself

a gene is best defined as

a sequence of nucleotides in DNA that codes for a functional product

what would happen if the mRNA codon that coded for Cys was mutated in the third position from a U to an A

a stop codon would be introduced prematurely

which of the following might result in a frameshift mutation? a. benzopyrene b. nitrous acid c. 5-bromouracil

a. Benzopyrene

bacteria are growing in an open protein shake you placed in the refrigerator three weeks ago. the shake's ingredients include glycine and leucine - amino acids the bacteria are capable of synthesizing. the shake also contains sucrose and fructose - sugars the bacteria are capable of catabolizing. assuming the gene expression necessary for all four of these functions is controlled by operons, which of the following statements is true? a. sucrose will bind to the repressor, and the structural genes for catabolizing sucrose will be expressed b. glycine will bind to the repressor, and the structural genes for synthesizing glycine will be expressed c. leucine will NOT bind to the repressor, and the structural genes for synthesizing leucine will NOT be expressed d. fructose will bind to the repressor, and the structural genes for catabolizing fructose will NOT be expressed

a. sucrose will bind to the repressor, and the structural genes for catabolizing sucrose will be expressed

which statement about DNA replication is CORRECT? a. the leading strand is built continuously, and the lagging strand is built in pieces b. the lagging strand is built continuously c. the leading strand is one of the strands of parental DNA d. the lagging strand is one of the strands of parental DNA e. DNA ligase helps assemble the leading strand

a. the leading strand is built continuously, and the lagging strand is built in pieces

if you knew the sequence of nucleotides within a gene, which one of the following could you determine with the most accuracy? a. the primary structure of the protein b. the quaternary structure of the protein c. the tertiary structure of the protein d. the secondary structure of the protein e. the answer cannot be determined based on the information provided

a. the primary structure of the protein

if base 4 is thymine, what is base 4'?

adenine

what is the inducer molecule in the lac operon?

allolactose

assume the two E. coli strains shown below are allowed to conjugate Hfr: pro+, arg+, his+, lys+, met+, ampicillin-sensitive F-: pro-, arg-, his-, lys-, met-, ampicillin-resistant What supplements would you add to glucose minimal salts agar to select for a recombinant cell that is lys+, arg+, amp-resistant?

ampicillin, proline, histidine, methionine

transformation is the transfer of DNA from a donor to a recipient cell

as naked DNA in solution

GAU codes for

aspartic acid

which of the following statements is false? a. the leading strand of DNA is made continuously b. DNA replication proceeds in only one direction around the bacterial chromosome c. DNA polymerase joins nucleotides in one direction (5' to 3') only d. the lagging strand of DNA is started by an RNA primer e. multiple replication forks are possible on a bacterial chromosome

b. DNA replication proceeds in only one direction around the bacterial chromosome

which of the following is NOT a product of transcription? a. tRNA b. a new strand of DNA c. mRNA d. rRNA e. none of the answers are correct; all of these are products of transcription

b. a new strand of DNA

which of the following does NOT accurately apply to the Ames test? a. the test can be used to qualitatively test potential mutagens b. the ames test is based on the observation that reversions CANNOT occur in mutant bacteria c. the Ames test measures the reversion of histidine auxotrophs of Salmonella d. the test uses bacteria as mutagen carcinogen indicators

b. the Ames test is based on the observation that reversions CANNOT occur in mutant bacteria this statement is false. the whole premise of the test is to look for chemicals that cause reversions to a previous phenotype. these reversions are due to changes in the DNA sequence

which type of transposon would contain a gene for transposase?

both simple and complex transposons

which statement about DNA replication is FALSE? a. DNA polymerase builds a new strand by adding DNA nucleotides one at a time b. the two strands of parental DNA are separated during DNA replication c. DNA ligase adds nucleotides to the lagging strand d. the lagging strand is made of a series of pieces that must be joined together to make a continuous strand e. because the two strands of parental DNA run in opposite directions, the new strands must be made in different ways

c. DNA ligase adds nucleotides to the lagging strand

which of the following statements concerning transcription is true? a. transcription is the process whereby identical copies of DNA are made in preparation for cell division b. during transcription, entire chromosomes are copied bc the starting position of genes is unknown c. all types of RNA in the cell are synthesize by transcription, which uses a portion of DNA as a template for copying d. promoter sequences signal the end of a gene and mark the place where transcription stops

c. all types of RNA in the cell are synthesized by transcription, which uses a portion of DNA as a template for copying

a nucleotide-altering chemical

can alter nitrogenous bases of DNA, resulting in incorrect base pairing

competent cells are cells that

can take up DNA from their surrounding environment and integrate it into their own chromosomes by recombination

how do complex transposons differ from simple transposons?

complex transposons code for additional genetic elements, such as antibiotic resistance genes; simple transposons only code for the transposase gene essential for the transposon itself

bacterial conjugation is often referred to as bacterial sex. why is this term inaccurate?

conjugation does not result in the formation of new offspring

which statement about conjugation is false?

conjugation is a process of bacterial reproduction

a transducing phage

contains fragments of the host chromosome instead of the viral genome

the _______ contains a promoter and an operator

control region

the damage cause by ultraviolet radiation is

cut out and replaced

Frederick Griffith did experiments on genetic transformation. Which of the following statements about his experiments is accurate? a. Griffith used bacteria in which the non-pathogenic strain was encapsulated but the pathogenic strain was not b. Griffith used on pathogenic bacteria in his experiments c. the combination of living non-encapsulated bacteria and heat-killed encapsulated bacteria did not cause disease d. Griffith found that hereditary material release from dead (virulent) bacteria entered like (avirulent) bacteria and changed them genetically, causing them to become virulent

d. Griffith found that hereditary material released from dead (virulent) bacteria entered live (avirulent) bacteria and changed them genetically, causing them to become virulent - this result indicated that live bacteria obtained genetic information (DNA) from the dead bacteria. in this case, the new genes provided directions for synthesis of the capsule, which allowed the live bacteria to become virulent

what of the following pairs is mismatched? a. DNA polymerase makes a molecule of DNA from a DNA template b. DNA gyrase relaxes supercoiling ahead of the replication fork c. DNA ligase joins segments of DNA d. RNA polymerase makes a molecule of RNA from an RNA template e. transposase insertion of DNA segments into DNA

d. RNA polymerase makes a molecule of RNA from an RNA template

which of the following enzymes unwinds the two strands of DNA so that they can be copied during replication? a. DNA polymerase b. DNA gyrase c. transposase d. helicase

d. helicase

which of the following best describes the flow of information in cells? a. DNA is converted to RNA, which is then converted to protein b. ribosomes make proteins by randomly linking amino acids together c. DNA acts as a messenger. it binds to a ribosome and provides instructions for making protein d. mRNA is made by coping specific regions of DNA called genes. Ribosomes use mRNA as instructions, which provide a code specifying the order of amino acids in a protein

d. mRNa is made by coping specific regions of DNA called genes. Ribosomes use mRNA as instructions, which provide a code specifying the order of amino acids in a protein

true/false: cell-to-cell contact is required for transduction to occur

false

true/false: transposition (insertion of a transposon into a DNA sequence) results in the formation of base substitution mutations in a cell's DNA

false

order the correct sequence of events for the tryptophan repressible operon. the starting point is that tryptophan levels are low

first - RNA polymerase binds to the promoter second - structural genes are transcribed third - translation of mRNAs occurs; proteins are produced fourth - tryptophan levels increase fifth - tryptophan binds to the repressor sixth - repressor binds to the operator

during infection, C. diphtheriae grows and multiplies within the upper respiratory tract. as each bacterial cell prepares for division the chromosome must be replicated so that each daughter cell receives a copy of the genetic information. the following statements summarize the major steps in replicating the bacterial chromosome. arrange the statements in the correct order to describe the process of replication of the leading strand

first - double stranded DNA is unwound by helicase second - proteins bind to the DNA in order to stabilize the single strands third - primase synthesizes an RNA primer fourth - dna polymerase catalyzes formation of a sugar phosphate bond bw neighboring nucleotides fifth - hydrogen bonds form bw the complementary bases

a base insertion or deletion in the translated region of the gene may lead to

frameshift mutation

deleting or inserting one nucleotide pair in the middle of a gene is an example of ...

frameshift mutation

how is generalized transduction different from specialized transduction?

generalized transduction is initiated during lytic cycle of a virulent bacteriophage; specialized transduction is initiated during the lysogenic cycle of a temperate bacteriophage

Imagine the operator has been damaged such that the active repressor no longer binds to it. how would this damage affect the growth of Pseudomonas?

growth on soap would not change much, but the damage would decrease the species' growth elsewhere - damage of the operator would most likely prevent activated repressors from binding to it. normally, a bound repressor blocks transcription, so if the repressor cannot bind, then transcription will happen continuously. in other words, damage of the operator would cause the soap-metabolizing enzymes to be expressed all the time. the pseudomonas species would still be able to grow on soap, so its growth on soap would not be affected. but growing elsewhere, the bacteria would waste resources by expressing these genes unnecessarily. this would lead to decreased growth in other (non-soap) environments

the necessary ingredients for DNA synthesis can be mixed together in a test tube. the DNA polymerase is from Thermus aquaticus, and the template is from a human cell. The DNA synthesized would be most similar to

human DNA

where would one find an uncharged tRNA molecule in a ribosome?

in the P site and E sites

how would one increase the concentration of particular polypeptide in a cell?

increase the level of transcription

mutagens

increase the likelihood of mutations in DNA

which operons are never transcribed unless activated?

inducible operons

which of the following relies on a molecule binding to the repressor to prevent the repressor from binding to the operator?

induction - is the expression of an operon's structural genes in response to the presence of an inducer. for example, lactose is the inducer of the (inducible) lac operon. the presence of the allolactose causes the expression of lactose-metabolizing enzymes. allolactose does this by binding to the repressor protein and preventing it from binding to the operator sequence of the lac operon

________ increase expression of the structural genes. this typically occurs in response to the ________ of a substrate

induction, presence

a recombinant cell

is a cell that receives DNA from an outside source and incorporates it into its own

which of the following describes how 5-bromouracil might create a mutation?

it can replace the base thymine, and can base pair with guanine rather than adenine

which of the following are terms associated with Okazaki fragments?

lagging strand, DNA ligase, and discontinuous

which DNA strand is synthesized continuously?

leading strand

the start codon also codes for which amino acid?

methionine

thymine dimers result from

non-ionizing radiation

prostate cancer is probably the result of which kind of mutation?

nonsense ( stop codon )

a base substitution that changes a codon coding for an amino acid to a stop codon is called a..

nonsense mutation

what is considered to be the average natural mutation rate that occurs during DNA replication?

one in every billion nucleotides replicated

how frequently do silent mutations occur?

one out of every three mutations

the _____ controls whether RNA polymerase can advance along the DNA strand or not

operator

an ______ controls the expression of functionally related genes and consists of a control region and structural genes

operon

the ________ is the region of DNA where RNA polymerase initially binds

promoter

how does replicative transposition differ from cut-and-paste transposition?

replicative transposition results in the transposon being copied to a new location; in cut-and-paste transposition, the entire transposon moves to the new location

what operons are always transcribed unless deactivated?

repressible operons

________ decrease expression of the structural genes. This typically occurs in response to an _________ of a substance

repression, overabundance

the _______ operates differently depending on whether the operon is inducible or repressible

repressor

a mutation that affects the genotype of the organism but not the phenotype is called a...?

silent mutation

how many codons code for the amino acid arginine?

six

the cancer gene ras produces mRNA containing an extra exon that includes a number of UAA codons. cancer cells produce ras mRNA missing this exon. this mistake most likely is due to a mistake by

snRNPs

mice that are injected with only the R strain of Streptococcus pneumoniae

stay healthy, because their immune systems can kill this strain easily

RNA that has hydrogen bonded to itself forms a ...?

stem loop

according to the operon model, for the synthesis of an inducible enzyme to occur, the...

substrate must bind to the repressor

RNA polymerase is guided by the...?

template strand of DNA

when a transducing phage interacts with a new host cell,

the DNA from the previous host can recombine with the new host chromosome

what most likely explains the recovery of live S strain cells from a mouse injected w heat-killed S strain mixed w live R strain cells

the R strain picked up the S strain DNA, enabling it to produce a capsule

if an indeterminate frameshift mutation occurred in the sequence of bases shown below, what would be the sequence of amino acids coded for? 3' ATTACGCTTTGC UUA - leucine UAA - nonsense GCA - alanine AAU - asparagine AAG - lysine UGC - cysteine GUU - valine UCG,UCU - serine

the answer cannot be determined based on the information provided

how does the ribosome know if the entering charged tRNA is correct?

the anticodon on the tRNA base pairs to the codon on the mRNA

what characteristic of the S strain allows it to evade the immune system of the mice?

the cells have a capsule

what must occur for bacterial conjugation to take place?

the cells must come into contact with each other

the initial effect of ionizing radiation on a cell is that is causes

the formation of highly reactive ions

if the gene that codes for transposase is mutated so that it no longer produces the fully functional enzyme, how will the insertion sequence be affected?

the insertion sequence would lose its ability to effect its own movement

the major virulence factor produced by C. diphtheria is diphtheria toxin. the production of diphtheria toxin during infection is controlled by a repressor, DtxR. the activity of DtxR is regulated by iron, which acts as a corepressor. during an infection, the levels of iron available in the tissues for use by C. diphtheria are low. what effect will the decreased iron availability have on the production of diphtheria toxin

the lack of corepressor binding to DtxR will lead to a loss of repression and an increase in the production of toxin

where on the DNA strand does the repressor bind?

the operator

with which genetic region does the repressor protein interact?

the operator region

according to the animation, to what genetic element does the RNA polymerase bind?

the promoter

what is the initial target of RNA polymerase?

the promoter

when the cell is not in the presence of lactose,

the repressor proteins bind to the operator

which of the following genetic elements is transcribed into a single mRNA?

the structural genes

why is the DNA synthesis of the lagging strand considered discontinuous?

the synthesis is moving in the opposite direction from the replication fork

what makes an insertion sequence different from other DNA sequences found in a cell?

they are capable of effecting their own movement from one location to another on DNA

what is the function of the connector proteins?

they link the leading strand DNA polymerase and the lagging strand DNA polymerase together

if base 4 is thymine, what is base 11' (remember the complimentary configuration of bases in DNA)?

thymine

what is the basic function of the lac operon?

to code for enzymes involved in catabolizing lactose

what is unique about transduction compared to normal bacteriophage infection?

transduction transfers DNA from the chromosome of one cell to another

which of the following is an example of horizontal gene transfer in bacteria?

transduction, conjugation, and transformation

what is the hallmark of all horizontal gene transfers?

transfer of DNA between organisms of the same generation

conjugation differs from reproduction because conjugation

transfers DNA horizontally, to nearby cells without those cells undergoing replication

genetic change in bacteria can be brought about by

transformation mutation transduction conjugation

what is the sequence of amino acids encoded by the following sequence of bases in a strand of DNA (pay attention to the polarity of the DNA here)? 3' ATTACGCTTTGC

translation would stop at the first codon

true/false: both base substitution and frameshift mutations can result in the formation of premature stop codons

true

true/false: in the Ames test, any colonies that form on the control should be the result of spontaneous mutations

true

true/false: open-reading frames are segments of DNA in which both start and stop codons are found

true

DNA is constructed of

two strands of nucleotides running in an antiparallel configuration

protein synthesis in eukaryotes is similar to the process in prokaryotes in that both eukaryotes and prokaryotes

use codons to determine polypeptide sequences

how is translation terminated?

when a protein called a release factor enters and binds to the A site

if the repressor is not bound to the operator, then RNA polymerase _____ transcribe the structural genes

will

if the repressor is bound to the operator, then RNA polymerase ______ transcribe the structural genes

will not

during the initiation step of translation, the fMet charged tRNA assembles in which site of the ribosome?

P site