Microbio Exam 2

Which of the following is the most resistant to
destruction by chemicals and heat?
a) Bacterial endospores
b) Fungal spores
c) Mycobacterium tuberculosis
d) E. coli

a) Bacterial endospores

A common environmental organism that may even
grow in certain chemical disinfectants is
A. Escherichia coli.
B. Streptococcus pneumoniae.
C. Pseudomonas aeruginosa.
D. Influenza virus

C. Pseudomonas aeruginosa.

Ultraviolet light kills bacteria by
a) generating heat.
b) damaging DNA.
c) inhibiting protein synthesis.
d) damaging cell walls.

b) damaging DNA.

How does microwaving a food product kill
bacteria?

Kills by heat not by radiation

Which concentration of alcohol is the most
effective germicide?
a) 100%
b) 75%
c) 50%
d) 25%

b) 75%

Highly Resistant Microbes

Bacterial Endospore, Protozoan Cysts, Mycobacterium, Pseudomonas

Pseudomonas

can even grow in some disinfectants

Moist Heat

Irreversibly denatures proteins

High Temp Short Time (HTST)

72ºC for 15 mins, most common

Ultra High Temp (UHT)

140ºC and few seconds (shelf stable)

Pasteurization

treatment used to reduce the number of spoilage organisms and eliminate pathogens without changing the characteristics (flavor/texture) of the product

Autoclave = Pressurized Steam

Typical conditions: 121ºC, 15 psi, 15 mins

Types of Autoclave Indications

Tape and biological

Ionizing Radiation

Targets DNA and cytoplasmic membranes

Gamma Rays

DNA and RNA strands break

UV (220-300nm)

Damages DNA

Microwaves

Kills by heat not radiation

Alcohols

Denatures proteins and damages liquid membranes

Most effective for Alcohol

60-80% ethyl or iospropyl

Why is Aqueous solutions more effective than pure alcohol

Slower evaporation, better penetration, requires water to denature proteins (most effective)

Aldehydes

Forms chemical bonds that inactivate proteins and nucleic acids (ex: Gluteraldehyde)

Chlorine (Halogen)

Likely targets proteins, can kill bacteria

Phenolics

Targets cytoplasmic membranes and proteins (ex: Triclosan)

1. Unlike a disinfectant, an antiseptic

• a) sanitizes objects rather than sterilizes them.

• b) destroys all microorganisms.

• c) is non-toxic enough to be used on human skin.

• d) requires heat to be effective.

• e) can be used in food products.

• c) is non-toxic enough to be used on human skin.

All of the following could be used to sterilize an item except

• a) boiling.

• b) incineration.

• c) irradiation.

• d) sporocides.

• e) filtration.

• a) boiling.

All of the following are routinely used to preserve foods except

• a) high concentrations of sugar.

• b) high concentrations of salt.

• c) benzoic acid.

• d) freezing.

• e) ethylene oxide.

• e) ethylene oxide.

Aseptically boxed juices and cream containers are processed using which of the following heating methods?

• a) Commercial canning

• b) High-temperature-short-time (HTST) method

• c) Autoclaving

• d) Ultra-high-temperature (UHT) method

• e) Boiling

• d) Ultra-high-temperature (UHT) method

Which of the following is false?

• a) A high-level disinfectant cannot be used as a sterilant.

• b) Critical items must be sterilized before use.

• c) Low numbers of endospores may remain on semicritical items.

• d) Standard sterilization procedures do not destroy prions.

• e) Quaternary ammonium compounds can be used to disinfect food preparation surfaces.

• a) A high-level disinfectant cannot be used as a sterilant.

Without changing the sequence or the orientation of
the sequence(s), which is/are complementary to the
sequence 5' AGGCUAAC 3'?
rev: 09_30_2015_QC_CS-26785
A. 5' TCCGATTG 3’
B. 3' TCCGATTG 5’
C. 5' CTTAGCCT 3’
D. 3' TAAGCTTA 5'

B. 3' TCCGATTG 5’

A ribosome binds to the following mRNA at the site
indicated by the dark box. At which codon will
translation likely begin?
5′ ■
GCCGGAAUGCUGCUGGC
a) GCC
b) GGC
c) AUG
d) AAU

c) AUG

1. All of the following are involved in transcription except

a) polymerase.

b) a primer.

c) a promoter.

d) a sigma factor.

e) uracil.

b) a primer.

All of the following are involved in DNA replication except

a) a polysome.

b) gyrase.

c) polymerase.

d) primase.

e) a primer

a) a polysome.

3. All of the following are directly involved in translation except

a) a promoter.

b) ribosomes.

c) a start codon.

d) a stop codon.

e) tRNAs.

a) a promoter.

Using the portion of DNA shown here as a template, what will be the sequence of the RNA transcript? (Diagram shows a promoter arrow pointing from left to right above two DNA strands)

• 5' GCGTTAACGTAGGC 3'

• 3' CGCAATTGCATCCG 5'

• a) 5' GCGUUAACGUAGGC 3'

• b) 5' CGGAUGCAAUUGCG 3'

• c) 5' CGCAAUUGCAUCCG 3'

• d) 5' GCCUACGUUAACGC 3'

• a) 5' GCGUUAACGUAGGC 3'

Which of the following statements about gene expression is false?

• a) More than one RNA polymerase can be transcribing a specific gene at a given time.

• b) More than one ribosome can be translating a specific transcript at a given time.

• c) Translation begins at a site called a promoter.

• d) Transcription stops at a site called a terminator.

• e) Some amino acids are coded for by more than one codon.

• c) Translation begins at a site called a promoter.

DNA polymerase

Synthesizes DNA polymers.

Primase

Synthesizes a short RNA primer that is complementary to the template DNA strand.

DNA ligase

Seals gaps between adjacent Okazaki fragments on the lagging strand.

DNA gyrase

An enzyme that relieves the tension caused by the unwinding of two strands of the DNA helix.

Which of the following characteristics are shared by DNA and RNA polymerase? 

1. Direction of polymerization of nucleotides.

   Correct answer

2. The type of nucleotides used.

3. The requirement for a primer to initiate synthesis.

4. Initiation at a specific sequence.

1. Direction of polymerization of nucleotides.

   Correct answer

Which of the following is found at the 5' end of a DNA strand?

• a phosphate group

• a hydrogen bond

• a hydroxyl group

• histones

• a methyl group

• a phosphate group

The DNA strand that serves as the template for transcription is called the

• (+) strand

• (-) strand

• polycistronic message

• promoter

• (-) strand

Which of the following is not involved in translation?

• rRNA

• tRNA

• mRNA

• sigma factor

• ribosome-binding site

• sigma factor

DNA helicases

• unwind the DNA helix at the replication fork.

• synthesize short DNA molecules important for the function of DNA polymerase.

• seal gaps between DNA fragments.

• proofread DNA molecules.

• assist in recognition of promoters during transcription.

• unwind the DNA helix at the replication fork.

What is attached at the 3’ of DNA

OH group

What is semiconservative

After DNA replication is complete one old strand and one new strand make up new DNA strand

Origin of replication

A specific sequence of nucleotides where DNA replication begins.

Primer requirement (Replication vs. Transcription)

DNA polymerase can only add nucleotides to an existing strand (needs a primer), while RNA polymerase can start a new chain from scratch.

Polycistronic mRNA

A single mRNA molecule that carries information for more than one gene; common in bacteria.

Sigma factor

A protein that associates with RNA polymerase to help it recognize and bind to a specific promoter to start transcription

DNA Replication Steps

1) Gyrase and Helices breaks and unzips DNA

2) RNA primers added to DNA

3) DNA pol starts synthesis

4) RNA primers replaced with DNA
5) DNA ligase seals gaps

Transcription Steps

1) Sigma Factor recognizes promoter region

2) RNA starts synthesis

3) Terminator = sequence where RNA pol disengages

Capping

Add Guanine to 5' end (Stability/Recognition).

Polyadenylation

Add Poly A tail to 3' end (Stability/Export).

Splicing

Cut out Introns (non-coding), keep Exons (coding).

Constitutive

These genes are always ON (Glycolysis)

Inducible

Usually OFF, but can be turned ON when needed. (B-galactosidase)

Repressible

Usually ON, but can be turned OFF (Amino Acids)

Alternative Sigma Factors

• Sigma factors = subunits of RNA polymerase = form holoenzyme

• Recognize different promoters

• Housekeeping = σ70

Regulatory Proteins (DNA-Binding Proteins)

These sit directly on the DNA to block or help transcription.

Repressor

Blocks transcription

Activator

Facilitates or "starts" transcription

Induction

The repressor starts out bound to the operator, blocking RNA polymerase

inducer

molecule must bind to the repressor to change its shape so it falls off the DNA, turning transcription ON

Repression

The repressor alone cannot bind to the operato

corepressor

must bind to the repressor to help it attach to the operator and block RNA polymerase, turning transcription OFF

operon

a group of genes that are transcribed together

lac operon contains genes to break down lactose

lacZ, lacY, lacA

No Lactose present

The repressor binds to the operator. Transcription is OFF.

Lactose present

Some lactose is converted to allolactose (the inducer). Transcription is ON.

Under which of the following conditions will
transcription of the lac operon occur?
a) Lactose present/glucose present
b) Lactose present/glucose absent
c) Lactose absent/glucose present
d) Lactose absent/glucose absent

b) Lactose present/glucose absent

When glucose is not available, Escherichia coli synthesizes __________, which leads to the activation of the lac operon.

• ATP

• lactose

• cyclic AMP

• pyruvate

• the catabolic activator protein

• cyclic AMP

Inducible operons

• are active in the presence of a repressor.

• are generally catabolic pathways.

• are always transcribed but only translated when they are induced.

• usually require a repressor for transcription.

• are also constitutive.

• are generally catabolic pathways.

__________ uses short RNA strands to identify specific RNA transcripts for destruction in Eukaryotic cells.

• Interference RNA (RNAi)

• Riboswitch RNA (riRNA)

• Restriction RNA (rRNA)

• Antisense RNA (aRNA)

• Capped RNA (cRNA)

• Interference RNA (RNAi)

A functioning unit of prokaryotic DNA containing a cluster of genes that are under the control of a single promoter is called a(n):

• transcriptome

• co-regulator

• operon

• operator

• operon

Which of the following must be removed from a eukaryotic mRNA molecule before it can be translated?

• promoter

• exon

• intron

• anticodon

• 5'-formyl-methionine group

• intron

All of the following are characteristics of eukaryotic gene expression except

• a) a 5' cap is on the mRNA.

• b) a poly A tail is on the 3' end of mRNA.

• c) introns must be removed to create the mRNA that is translated.

• d) the mRNA is often polycistronic.

• e) translation begins at the first AUG.

• d) the mRNA is often polycistronic.

Which best describes a bacterial strain designated
His-, Kan R
A. Prototroph that requires histidine in the growth
medium and is resistant to kanamycin
B. Auxotroph that requires histidine in the growth
medium and is resistant to kanamycin
C. Auxotroph that makes histidine and is sensitive
to kanamycin
D. Prototroph that makes histidine and is sensitive
to kanamycin

B. Auxotroph that requires histidine in the growth
medium and is resistant to kanamycin

Vertical Gene Transfer

passed on to daughter cells from parent

Horizontal Gene Transfer

Genetic information passed in same generation

Auxotroph (-)

Nutritional Mutant, only grows if supplement in media

Phototroph (+)

Wild Type, can grow in minimal media (sugar and salt)

Amp r

Resistant to Ampicillin

Amp s

Sensitive to Ampicillin

UV light exposure forms
A. covalent bonds between the two strands of DNA.
B. hydrogen bonds between the two strands of DNA.
C. covalent bonds between adjacent thymine
nucleobases on the same strand of DNA.
D. covalent bonds between adjacent guanine and
cytosine nucleobases on the same strand of DNA.

C. covalent bonds between adjacent thymine
nucleobases on the same strand of DNA.

On which of the following DNA strands would UV radiation
have the most effect?
A. AATTAGTTC
B. AACCGGG
C. TATATACG
D. AUAUCGAU

A. AATTAGTTC

Base Analogs

Mimics naturally occurring bases, DNA pol uses them by mistake

Intercalating Agents

Causes a frameshift (Ethidium Bromide)

Ultraviolet Light (thymine dimers)

Causes a covalent bond to form between two adjacent thymines, RNA pol gets confused and stops

Mismatch Repair

Repair Enzyme that corrects errors missed by DNA pol

Methylation of template strand

enzyme knows which one to fix

Repairing Thymine Dimers

Photo reactivation = breaks covalent bonds, Excision repair = cut and repair

SOS Repair

DNA pol has no proofreading

Direct Selection

Use a medium that kills the parent but allows mutant to grow

Indirect Selection

Used to find mutants (axotrophs) that can’t grow on minimal media,

• More difficult

• Needs replica plating to find mutants

Genetic changes that are due to errors in DNA replication (i.e. during normal cell processes) and result in alterations of a cell's genotype are called __________ mutations.

• relaxed

• spontaneous

• cumulative

• recombinant

• spontaneous

The __________ of an organism is the actual set of genes in its genome, whereas its __________ refers to the physical and functional traits expressed by those genes.

• phenotype; genotype

• paradigm; genotype

• genotype; phenotype

• phenotype; heredity

• genotype; phenotype

Which of the following are NOT responsible for the creation of mutations?

• Transposition

• Radiation

• Transcription

• Intercalating agents

• Alkylating agents

• Transcription

A(n) __________ has lost the ability to synthesize certain substances required for growth as the result of mutational changes.

• auxotroph

• prototroph

• autotroph

• phototroph

• chemotroph

• auxotroph

Which of the following statements about R plasmids is false?

• Many are conjugative and are capable of being transferred to many different hosts.

• They are able to replicate outside of their host.

• They often encode genes conferring resistance to several antimicrobial compounds.

• They are circular DNA molecules that possess their own origin of replication and, as a consequence, are replicated independently of the chromosome.

• They are able to replicate outside of their host.