Microbiology Test 3
Chapter 9: DNA and RNA Structure and Replication
Q: What did Griffith's experiments on transformation demonstrate?
A: Griffith demonstrated that genetic material could be transferred between organisms, as heat-killed virulent bacteria transformed non-virulent bacteria into a virulent form.
Q: What are the major structural differences between DNA and RNA?
A: DNA is double-stranded, contains deoxyribose, and uses thymine. RNA is single-stranded, contains ribose, and uses uracil.
Q: What bonds link nucleotides together in nucleic acids?
A: Phosphodiester bonds.
Q: Define bacterial origin of replication, replisome, and replicon.
A:
Origin of replication: Site where replication begins.
Replisome: Protein complex for replication.
Replicon: Unit of DNA replicated from one origin.
Q: What occurs during the three phases of DNA replication?
A:
Initiation: Origin of replication is recognized, and helicase unwinds DNA.
Elongation: DNA polymerase synthesizes new strands.
Termination: Replication ends when forks meet or at terminator sequences.
Q: Compare leading and lagging strands in DNA synthesis.
A: Leading strand is synthesized continuously; lagging strand is synthesized in Okazaki fragments.
Q: What is an Okazaki fragment?
A: A short DNA segment synthesized on the lagging strand.
Q: What is meant by semi-conservative replication?
A: Each new DNA molecule consists of one parental strand and one newly synthesized strand.
Chapter 10: Gene Expression
Q: What are the key parts of a bacterial protein-coding gene?
A: Promoter, coding region, and terminator.
Q: What is the structure of bacterial RNA polymerase?
A: Core enzyme with α, β, and β' subunits, and a sigma factor for promoter recognition.
Q: Describe the three phases of transcription.
A:
Initiation: RNA polymerase binds the promoter.
Elongation: RNA strand is synthesized.
Termination: RNA polymerase releases RNA at terminator sequence.
Q: What is the role of bacterial promoters and sigma factors?
A: Promoters initiate transcription; sigma factors guide RNA polymerase to promoters.
Q: Define factor-independent and rho-dependent transcription termination.
A: Factor-independent relies on RNA secondary structure. Rho-dependent uses the rho protein to stop transcription.
Q: What is the wobble hypothesis?
A: It explains how the third base of a codon can vary without affecting the encoded amino acid, reducing the number of required tRNAs.
Q: What happens at the A, P, and E sites during translation?
A:
A site: tRNA brings in new amino acid.
P site: Peptide bond forms.
E site: Empty tRNA exits.
Q: What is the role of molecular chaperones?
A: Assist in protein folding, e.g., DnaK and GroEL.
Chapter 11: Regulation of Gene Expression
Q: What are housekeeping, constitutive, inducible, and repressible genes?
A:
Housekeeping: Always expressed.
Constitutive: Constantly expressed.
Inducible: Expressed in response to stimuli.
Repressible: Turned off by specific signals.
Q: How is the lac operon regulated?
A: By lactose (inducer) and glucose levels; lactose removes the repressor, and low glucose increases cAMP for CAP activation.
Q: How is the trp operon regulated?
A: By tryptophan levels; high tryptophan activates a repressor.
Chapter 12: Mutations and Gene Transfer
Q: Differentiate spontaneous and induced mutations.
A: Spontaneous arise naturally; induced are caused by mutagens.
Q: What are the types of DNA repair mechanisms?
A: Proofreading, mismatch repair, excision repair, direct repair, recombinational repair.
Q: What are F+, Hfr, and F' cells?
A:
F+: Donor with F plasmid.
Hfr: F plasmid integrated into chromosome.
F': F plasmid with chromosomal DNA.
Q: Compare generalized and specialized transduction.
A:
Generalized: Random DNA transferred by phage.
Specialized: Specific DNA near phage integration site transferred.
Chapter 18: Virology and Prions
Q: What are the five steps of a virus life cycle?
A: Attachment, penetration, replication, assembly, release.
Q: Compare antigenic drift and antigenic shift.
A: Drift: Minor mutations; shift: Major genome reassortments.
Q: What are prions, and how do they replicate?
A: Misfolded proteins that induce normal proteins to misfold, violating the central dogma.
Q: Name two human prion diseases.
A: Creutzfeldt-Jakob Disease (CJD) and kuru.