Microbial genetics

What defines the 5ʹ end of a DNA strand?

a. Free hydroxyl group

b. Methyl group
c. Sugar ring
d. Free phosphate group

d

What defines the 3ʹ end of a DNA strand?

a. Free hydroxyl group

b. Methyl group
c. Sugar ring
d. Free phosphate group

a

Which base pair has three hydrogen bonds?

a. A-T

b. T-A

c. G-C

d. C-A

c

What is the role of the sugar-phosphate backbone

a. Encodes genetic information
b. Provides structural stability and solubility

c. Catalyzes transcription
d. Initiates replication

b

Which groove allows proteins to distinguish all four DNA bases?

a. Central groove

b. Major groove

c. Minor groove

d. Outer groove

b

Which base pair has two hydrogen bonds?

a. A-T

b. G-A

c. G-C

d. C-A

a

Which base is most thermally stable due to hydrogen bonding?

a. Adenine

b. Thymine

c. Uracil
d. Guanine

d

Which sugar is found in DNA?

a. Ribose
b. Glucose
c. Deoxyribose

d. Fructose

c

What does shape readout primarily detect?

a. Base sequence
b. DNA curvature and groove width

c. RNA structure
d. DNA methylation

b. DNA curvature and groove width

What is the spacing between helices in the HTH motif?

a. 3.4 nm

b. 2.0 nm

c. 5.0 nm

d. 1.5 nm

a. 3.4 nm

What is the role of Tus protein?

a. Initiation
b. Elongation
c. Termination

d. Proofreading

c. Termination

What links adjacent nucleotides in DNA?

a. Phosphodiester bonds

b. Hydrogen bonds
c. Ionic bonds
d. Peptide bonds

a. Phosphodiester bonds

What is the primary strategy used in base readout?

a. Groove width detection
b. Hydrogen bonding with base edges

c. DNA bending
d. Electrostatic repulsion

b. Hydrogen bonding with base edges

Which DNA-binding motif uses a recognition helix to contact the major groove?

a. Zinc finger
b. Leucine zipper
c. Helix-turn-helix (HTH)

d. Beta barrel

c. Helix-turn-helix (HTH)

Which protein initiates replication?

a. Tus
b. DnaA
c. DNA ligase
d. RNA polymerase

b. DnaA

Which sequence in oriC is AT-rich and prone to melting?

a. DnaA box
b. DNA-unwinding element

c. Ter site
d. Dif site

b. DNA-unwinding element

What is the function of DNA ligase?

a. Synthesizes DNA
b. Seals nicks between Okazaki fragments

c. Unwinds DNA
d. Loads β-clamp

b. Seals nicks between Okazaki fragments

Which phase of the bacterial cell cycle involves chromosome replication?

a. I phase

b. D phase

c. G phase

d. C phase

d. C phase

What is the generation time paradox?

1. Cell division occurs faster than genome replication

2. DNA replication is faster than cell division

3. DNA replication is error-prone

4. Cell division is faulty

1. Cell division occurs faster than genome replication

What system prevents Z-ring formation at the cell poles?

a. SlmA
b. MukBEF

c. DARS
d. MinCDE

d. MinCDE

What is the role of the divisome?

a. DNA replication
b. RNA transcription
c. Cell wall synthesis and membrane

constriction
d. Protein translation

c. Cell wall synthesis and membrane

constriction

What happens during the I phase of the bacterial cell cycle?

a. DNA replication
b. Cell division
c. Chromosome segregation

d. Initiation of replication

d. Initiation of replication

Which base is unique to RNA?

a. Thymine

b. Cytosine

c. Uracil
d. Guanine

c. Uracil

Which enzyme synthesizes RNA primers during replication?

a. DNA polymerase I

b. Ligase
c. DnaA
d. Primase (DnaG)

d. Primase (DnaG)

What does SeqA do after replication initiation?

a. Sequesters hemimethylated oriC

b. Synthesizes primers
c. Loads helicase
d. Activates DnaA

a. Sequesters hemimethylated oriC

What strategy allows E. col to divide faster than it replicates its genome?

a. Bidirectional replication

b. Rolling circle replication

c. Multifork replication
d. Linear replication

c. Multifork replication

What structure initiates cell division in E. coli?

a. FtsZ ring

b. OriC
c. DnaA box

d. β-clamp

a. FtsZ ring

What is the role of SlmA in cell division?

a. Activates FtsZ
b. Prevents Z-ring formation over the nucleoid

c. Synthesizes peptidoglycan
d. Loads DNA polymerase

b. Prevents Z-ring formation over the nucleoid

What does the D phase of the cell cycle involve?

a. Chromosome segregation and division

b. DNA replication
c. RNA synthesis
d. Protein folding

a. Chromosome segregation and division

In fast-growing cells, how do the I, C, and D phases behave?

a. Sequentially
b. They overlap
c. They are skipped
d. They are paused during stress

b. They overlap

What makes RNA more reactive than DNA?

a. Lack of phosphate
b. Presence of 2ʹ hydroxyl group

c. Use of uracil
d. Double-stranded nature

b. Presence of 2ʹ hydroxyl group

What sugar is found in RNA?

a. Ribose
b. Glucose
c. Deoxyribose

d. Fructose

a. Ribose

How does RNA form secondary structures?

a. Ribose methylation
b. Phosphodiester bonds
c. Intramolecular base pairing

d. Double helix

c. Intramolecular base pairing

What forms the backbone of RNA?

a. Phosphate and ribose

b. Peptide bonds
c. Lipids
d. Nitrogenous bases

a. Phosphate and ribose

Which RNA has a cloverleaf structure?

a. mRNA

b. rRNA

c. tRNA

d. sRNA

c. tRNA

What forms the RNA polymerase holoenzyme?

a. Core enzyme + sigma factor

b. Core enzyme only
c. Core enzyme + activator
d. Sigma factor only

a. Core enzyme + sigma factor

What maintains the transcription bubble?

a. Sigma factor
b. RNA polymerase

c. DNA ligase
d. Helicase

b. RNA polymerase

What does rho-dependent termination require?

a. Hairpin loop
b. Sigma factor
c. Ribosome binding
d. Rut site and rho helicase

d. Rut site and rho helicase

What does pseudouridine do?

a. Blocks translation

b. Prevents folding
c. Stabilizes structure

d. Degrades RNA

c. Stabilizes structure

What do repressors do?

a. Modify ribosomes
b. Degrade mRNA
c. Block RNA polymerase

d. Enhance transcription

c. Block RNA polymerase

RNA synthesis proceeds in which direction?

a. 3ʹ to 5ʹ
b. Bidirectional

c. Random
d. 5ʹ to 3ʹ

d. 5ʹ to 3ʹ

Which base pair exists only in RNA?

a. A-T

b. G-C

c. G-U

d. C-G

c. G-U

Which RNA carries genetic information?

a. tRNA

b. rRNA

c. sRNA

d. mRNA

d. mRNA

Which RNA is least structured?

a. tRNA

b. rRNA

c. crRNA

d. mRNA

d. mRNA

What does the sigma factor do?

a. RNA elongation
b. DNA replication
c. Ribosome binding
d. Promoter recognition

d. Promoter recognition

What triggers intrinsic termination?

a. Sigma factor release
b. DNA methylation
c. Rho helicase
d. Hairpin followed by uracils

d. Hairpin followed by uracils

What do antitermination proteins do?

a. Bypass terminators
b. Degrade RNA
c. Modify ribosomes
d. Block RNA polymerase

a. Bypass terminators

What is RNA editing?

a. DNA replication
b. Protein folding
c. RNA degradation
d. Sequence alteration after transcription

d. Sequence alteration after transcription

What is an operon?

a. A ribosome subunit
b. A transcription factor
c. A single gene
d. A group of genes transcribed together

d. A group of genes transcribed together

What are the components of a two-component system?

1. Ribosome and RNA polymerase

2. DNA and RNA

3. Sigma factor and repressor

4. Sensor kinase and response regulator

4. Sensor kinase and response regulator

What does the sensor kinase do?

a. Binds ribosomes
b. Autophosphorylates in response to stimuli

c. Blocks transcription
d. Degrades RNA

b. Autophosphorylates in response to stimuli

What does the response regulator do?

a. Degrades proteins
b. Methylates DNA
c. Synthesizes RNA
d. Binds DNA to regulate transcription

d. Binds DNA to regulate transcription

What does attenuation rely on?

a. Coupling of transcription and translation

b. RNA editing
c. Sigma factor switching
d. DNA methylation

a. Coupling of transcription and translation

What forms during high tryptophan in the trp operon?

1. Riboswitch

2. Terminator hairpin

3. Rut site

4. Antiterminator

2. Terminator hairpin

What type of bond links amino acids in a protein?

a. Peptide bond

b. Hydrogen bond

c. Ionic bond
d. Disulfide bond

a. Peptide bond

Which amino acid breaks α-helices?

a. Glycine

b. Proline

c. Serine

d. Leucine

b. Proline

Which amino acid can form Fe-S clusters?

a. Serine
b. Cysteine

c. Glutamine

d. Alanine

b. Cysteine

What defines the tertiary structure of a protein?

a. Amino acid sequence
b. Local folding motifs
c. 3D conformation of a single polypeptide

d. Assembly of subunits

c. 3D conformation of a single polypeptide

Which amino acid is most flexible in protein structures?

a. Glycine

b. Valine

c. Tyrosine

d. Histidine

a. Glycine

What is the quaternary structure of a protein?

a. Assembly of multiple polypeptides

b. Folding of α-helices

c. RNA-protein interaction

d. Signal peptide recognition

a. Assembly of multiple polypeptides

What is the function of stop codons?

a. Start translation
b. Encode methionine
c. Terminate translation

d. Modify tRNA

c. Terminate translation

Which codon typically initiates translation in bacteria?

a. UAG

b. UAA

c. GGA

d. AUG

d. AUG

How many codons are in the standard genetic code?

a. 20

b. 61

c. 64

d. 3

c. 64

What is the wobble position in a codon?

a. First base
b. Second base

c. Third base

d. Stop codon

c. Third base

Which base allows most wobble pairing in tRNA?

a. Uracil
b. Inosine

c. Cytosine

d. Adenine

b. Inosine

What are the bacterial ribosomal subunits?

a. 30S and 50S

b. 20S and 50S

c. 30S and 60S

d. 40S and 60S

a. 30S and 50S

What does the SD sequence do?

a. Terminate transcription
b. Align ribosome with start codon

c. Modify tRNA
d. Fold mRNA

b. Align ribosome with start codon

What is the initiator tRNA in bacteria?

a. tRNA^Met
b. fMet-tRNA^fMet

c. tRNA^Gly
d. tRNA^Trp

b. fMet-tRNA^fMet

What enzyme charges tRNAs?

a. Peptidyl transferase
b. EF-Tu
c. IF2
d. Aminoacyl-tRNA synthetase

d. Aminoacyl-tRNA synthetase

What is a codon box?

a. Ribosome binding site
b. Group of codons encoding the same amino

acid
c. tRNA anticodon

d. Protein domain

b. Group of codons encoding the same amino

acid

Which initiation factor prevents premature subunit joining?

a. IF1

b. IF2

c. IF3

d. EF-G

c. IF3

What catalyzes peptide bond formation?

a. 23S rRNA
b. EF-G
c. IF2
d. tRNA synthetase

a. 23S rRNA

What promotes ribosome translocation?

a. IF1
b. EF-G

c. RF2

d. GroEL

b. EF-G

What recognizes stop codons?

a. tRNA
b. EF-Tu
c. IF3
d. Release factors

d. Release factors

What do RNA thermosensors respond to?

a. Temperature

b. pH
c. Antibiotics
d. Light

a. Temperature

What is the most common target of translational regulation?

a. Elongation

b. Termination

c. Initiation
d. Folding

c. Initiation

What disassembles the ribosome after termination?

a. IF2
b. RRF and EF-G

c. RF1 and RF2

d. GroES

b. RRF and EF-G

What is unusual about the infC start codon?

a. It is AUU instead of AUG
b. It is a stop codon
c. It is not translated

d. It is a frameshift

a. It is AUU instead of AUG

How does RF2 autoregulate its own synthesis?

a. Programmed +1 frameshift

b. RNA editing
c. Riboswitch
d. mRNA degradation

a. Programmed +1 frameshift

What triggers feedback inhibition in amino acid biosynthesis?

a. High product concentration

b. Low ATP
c. High mRNA
d. Low tRNA

a. High product concentration

What type of enzyme is typically inhibited in feedback loops?

a. Final enzyme
b. First enzyme in pathway

c. Ribosomal protein
d. RNA polymerase

b. First enzyme in pathway

What is the benefit of feedback inhibition?

a. Slower gene expression

b. Enhances translation
c. Increases mutation rate

d. Prevents overproduction

d. Prevents overproduction

What is feedback inhibition?

a. Ribosome blocks mRNA
b. RNA degrades protein
c. End product inhibits early enzyme

d. Protein activates transcription

c. End product inhibits early enzyme

What is a "wild type" strain?

a. A strain with multiple mutations
b. A naturally occurring environmental isolate

c. A reference strain used for comparison
d. A strain resistant to antibiotics

c. A reference strain used for comparison

What is a mutant defined as?

a. A strain with enhanced growth
b. A strain with a plasmid
c. A strain with heritable changes in its DNA

d. A strain with no observable phenotype

c. A strain with heritable changes in its DNA

What is an allele?

a. A type of plasmid
b. A protein product of a gene

c. A phenotype
d. A version of a gene

d. A version of a gene

The genotype of an organism refers to:

a. Its observable traits
b. Its complete genetic makeup

c. Its metabolic capabilities
d. Its resistance profile

b. Its complete genetic makeup

The phenotype of a bacterial strain includes:

1. Observable traits resulting from the genotype

2. DNA sequence

3. Gene expression levels

4. Mutation rate

1. Observable traits resulting from the genotype

Gene names in microbial genetics are written:

a. In capital letters
b. In lowercase italics
c. In bold
d. In uppercase roman type

b. In lowercase italics

In binomial nomenclature, the genus and species

are:

a. Written in roman type
b. Written in italics
c. Capitalized and underlined

d. Abbreviated with numbers

b. Written in italics

Why are mutants useful in microbial genetics?

a. They are easier to grow
b. They help infer gene function
c. They are resistant to all antibiotics

d. They have no regulatory elements

b. They help infer gene function

What is the strain name in Escherichia coli MG1655?

a. Escherichia

b. coli
c. MG1655
d. E. coli

c. MG1655

Gene names in microbial genetics are written:

a. In capital letters
b. In lowercase italics
c. In bold
d. In uppercase roman type

b. In lowercase italics

Which of the following best contrasts genotype and phenotype?

1. Genotype is observable; phenotype is genetic

2. Genotype is temporary; phenotype is permanent

3. Genotype is the DNA sequence; phenotype is the observable trait

4. Genotype is environmental; phenotype is inherited

3. Genotype is the DNA sequence; phenotype is the observable trait

The notation lacZ A351G indicates:

a. A deletion

b. A protein fusion
c. A nucleotide substitution

d. A resistance phenotype

c. A nucleotide substitution

What is the protein product of the gene lacZ?

a. lacZ

b. LacZ

c. LACZ

d. lacZ1

b. LacZ

A strain labeled Lac+:
a. Is sensitive to lactose

b. Can metabolize lactose

c. Has a deletion in lacZ

d. Cannot grow on lactose

b. Can metabolize lactose

The notation lacZ Arg31Ser refers to:

a. A gene deletion
b. A promoter exchange
c. An amino acid substitution

d. A plasmid insertion

c. An amino acid substitution

How are temperature-sensitive mutants labeled?

a. Lac−

b. Rif+

c. His−

d. Lacts

d. Lacts

A strain labeled Rifr is:
a. Resistant to rifampicin
b. Sensitive to rifampicin
c. Unable to metabolize rifampicin

d. A wild-type strain

a. Resistant to rifampicin