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What occurs during the stationary phase of bacterial growth?
What occurs during the stationary phase of bacterial growth?
What happens to a bacterial culture when it runs out of nutrients and oxygen?
What happens to a bacterial culture when it runs out of nutrients and oxygen?
Which medium allows bacteria to begin the growth process sooner?
Which medium allows bacteria to begin the growth process sooner?
How can one distinguish whether cells are alive or dead in a sample?
How can one distinguish whether cells are alive or dead in a sample?
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What characterizes the deceleration phase in bacterial growth?
What characterizes the deceleration phase in bacterial growth?
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Which of the following is NOT a disadvantage of using microscopic counts to determine viable cell counts?
Which of the following is NOT a disadvantage of using microscopic counts to determine viable cell counts?
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What is a potential consequence of introducing a new medium into a bacterial culture that is in stationary phase?
What is a potential consequence of introducing a new medium into a bacterial culture that is in stationary phase?
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What does a fluorescence stain indicate when cells are stained red?
What does a fluorescence stain indicate when cells are stained red?
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What is the primary characteristic of AT-rich DNA regions?
What is the primary characteristic of AT-rich DNA regions?
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Which component is NOT involved in the unwinding process during DNA replication?
Which component is NOT involved in the unwinding process during DNA replication?
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What role does SeqA play in the regulation of replication initiation?
What role does SeqA play in the regulation of replication initiation?
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What is the function of DnaG during DNA replication?
What is the function of DnaG during DNA replication?
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How do bidirectional replication forks operate during DNA synthesis?
How do bidirectional replication forks operate during DNA synthesis?
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What happens once the helicase DnaB is active on the lagging strand?
What happens once the helicase DnaB is active on the lagging strand?
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What is the two-state DnaA assembly model required for?
What is the two-state DnaA assembly model required for?
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Which of the following structures prevents single-stranded DNA from reannealing?
Which of the following structures prevents single-stranded DNA from reannealing?
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What happens to transcription of operons for other sugars when glucose is present?
What happens to transcription of operons for other sugars when glucose is present?
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What occurs to cAMP levels when glucose levels are low?
What occurs to cAMP levels when glucose levels are low?
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What is indicated by the lag phase observed during diauxic growth?
What is indicated by the lag phase observed during diauxic growth?
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What is the role of tryptophan in the trp operon?
What is the role of tryptophan in the trp operon?
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What mechanism is primarily used by the trp operon to control gene expression?
What mechanism is primarily used by the trp operon to control gene expression?
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How does the presence of glucose impact the growth rate of cells using a non-preferred carbon source?
How does the presence of glucose impact the growth rate of cells using a non-preferred carbon source?
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What occurs to the transcription levels of metabolizing operons when glucose is abundant?
What occurs to the transcription levels of metabolizing operons when glucose is abundant?
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Which of the following is correct about the effect of cAMP when glucose levels are low?
Which of the following is correct about the effect of cAMP when glucose levels are low?
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Which of the following is NOT one of the five steps involved in bacterial growth?
Which of the following is NOT one of the five steps involved in bacterial growth?
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What does the variable 'n' represent in the equation $b = 1x2^n$?
What does the variable 'n' represent in the equation $b = 1x2^n$?
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Which nutrient is essential for all organisms but typically not a direct carbon source?
Which nutrient is essential for all organisms but typically not a direct carbon source?
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What distinguishes heterotrophs from autotrophs?
What distinguishes heterotrophs from autotrophs?
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What effect does a richer medium have on bacterial growth?
What effect does a richer medium have on bacterial growth?
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Which of the following is a consequence of low temperatures on bacterial cells?
Which of the following is a consequence of low temperatures on bacterial cells?
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At high temperatures, which of the following occurs in bacterial cells?
At high temperatures, which of the following occurs in bacterial cells?
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What is the effect of increasing temperature on the rate of reactions in bacterial cells?
What is the effect of increasing temperature on the rate of reactions in bacterial cells?
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What mechanism does the operon rely on to regulate transcription in the presence of excess tryptophan?
What mechanism does the operon rely on to regulate transcription in the presence of excess tryptophan?
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What occurs in the mRNA leader sequence during histidine starvation?
What occurs in the mRNA leader sequence during histidine starvation?
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How does feedback inhibition primarily function in a linear metabolic pathway?
How does feedback inhibition primarily function in a linear metabolic pathway?
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What is the role of allosteric enzymes in branched metabolic pathways?
What is the role of allosteric enzymes in branched metabolic pathways?
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What are the general properties of allosteric control?
What are the general properties of allosteric control?
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What does covalent modification do to regulate enzyme activity?
What does covalent modification do to regulate enzyme activity?
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What type of enzyme is typically the first in a linear metabolic pathway?
What type of enzyme is typically the first in a linear metabolic pathway?
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Which of the following accurately describes feedback inhibition?
Which of the following accurately describes feedback inhibition?
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Study Notes
Bacterial Growth
-
Five Steps of Bacterial Growth:
- Entrance of nutrients
- Conversion into energy and cell components
- Chromosome replication
- Increase in size and mass
- Division
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Bacterial Growth Equation: b = 1x2^n
- Where n represents the number of doublings or generations
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Factors Influencing Bacterial Growth Curve:
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Nutrients:
- All organisms require: carbon, energy, nitrogen, phosphorus, oxygen, etc.
- Autotrophs (lithotrophs): Get carbon from CO2 and inorganic compounds.
- Heterotrophs (organotrophs): Get carbon from glucose or organic compounds.
- Chemo energy source: Inorganic/organic compounds.
- Photo energy source: Light.
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Temperature:
- Low Temperatures: Membrane gelling (rigid cell membrane) affecting transport processes.
- High Temperatures: Protein denaturation, thermal lysis (cell destruction).
- Increased Temperature: Increased reaction rates, but also increased chromosome replication time.
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Oxygen:
- Cells with oxygen typically grow faster.
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Nutrients:
-
Growth Phases:
- Lag Phase: Cells adjust to the new environment, preparing for growth.
- Exponential (Log) Phase: Rapid growth with constant doubling time.
- Deceleration Phase: Growth rate decreases as resources become limited.
- Stationary Phase: Growth rate is near zero, cells are metabolically active, some grow and some die.
- Death (Not Necessary) Phase: Cells die off, lysis occurs. Some media may have a plateau due to GASP (growth advantage in stationary phase phenotype).
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Rich vs. Minimal Medium:
- Rich Medium: Contains pre-existing nutrients (proteins, peptides, yeast extract), allowing for faster growth.
- Minimal Medium: Requires nitrogen sources (NH4, proteins, minerals). Cells must turn on metabolic pathways to utilize these nutrients, which takes time.
Cell Counting
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Viable Cell Counts:
- Microscopic Counts: Advantages - quick, Disadvantages - difficult to determine if cells are alive or dead.
- Fluorescent Viability Stain: Red - dead, Green - alive. Disadvantages - can be affected by AT-rich regions in DNA.
Initiation of Replication
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Origin of Replication (oriC): Contains AT-rich DNA unwinding elements (DUEs), DnaA binding sites, and two replication forks.
- DUEs create single-stranded regions known as "open complexes".
- The replication forks have bidirectional replication.
- oriC serves as the initiation site for open complex formation.
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Two-State DnaA Assembly Model:
- Involved in initiation of replication.
- Requires ATP presence for assembly.
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Regulation of Replication Initiation:
- DnaA: Positive factor (+ factor) responsible for initiating replication.
- SeqA: Negative factor (- factor) inhibits replication.
Replication Process
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Steps of Replication Initiation:
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Strand Separation: DnaC (loading factor) brings DnaB (helicase) to the region. Once DnaB is bound, DnaC falls off.
- DnaB unwinds DNA.
- SSB (single-stranded binding proteins) maintains single-stranded DNA, preventing re-annealing and inhibiting DNases.
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Unwinding: Continued unwinding by DnaB, recruiting DnaG (primase) to the fork.
- DnaG creates short RNA primers on single-stranded DNA.
- DnaB + DnaG = primosome (ready to go).
- Priming: RNA primers are necessary to provide a 3' Hydroxyl group for DNA polymerase to start replication.
- Elongation: DNA polymerase III extends the DNA strands in the 5' to 3' direction.
- Proofreading: DNA polymerase III corrects errors during replication.
- Termination: Replication process is terminated when the replication forks meet.
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Strand Separation: DnaC (loading factor) brings DnaB (helicase) to the region. Once DnaB is bound, DnaC falls off.
Regulation of Gene Expression
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Attenuation:
- Controls gene expression by influencing the secondary structures of mRNA leader sequences.
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Tryptophan Operon (trp):
- Tryptophan acts as a corepressor, binding to the TrpR repressor protein to block transcription when tryptophan is abundant.
- Uses attenuation in which a 3:4 stem-loop structure formed in the mRNA leader sequence terminates transcription early when tryptophan is in excess.
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Histidine Operon (his):
- Lacks repressors.
- Relies entirely on attenuation.
- Ribosome stalling occurs in the leader sequence under histidine starvation.
- This forms a 2:3 stem loop which prevents the formation of the terminator structure (3:4 loop), enabling continued transcription.
Feedback Inhibition and Allosteric Control
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Feedback Inhibition: The end product of a metabolic pathway inhibits the activity of the first enzyme in the pathway.
- Prevents overproduction of the product.
- Typically targets the allosteric first enzyme in linear pathways.
- Allosteric Control: Effector molecules bind to a site other than the active site (allosteric site) and cause conformational changes, either enhancing or inhibiting enzyme activity.
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Branched Pathways:
- Feedback inhibition is more complex, each branch has its own control mechanisms.
- Key points in branched pathways are controlled by allosteric enzymes.
Covalent Modification
- Covalent Modification: Adding or removing chemical groups to regulate enzyme activity altering its activity.
-
Types of Covalent Modification:
- Phosphorylation: Adding a phosphate group, often using kinases.
- Glycosylation: Adding a carbohydrate group.
- Acetylation: Adding an acetyl group.
- Importance: Covalent modification allows for rapid and reversible regulation of enzyme activity.
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Description
Explore the fundamental concepts of bacterial growth through five key steps, the growth equation, and various influencing factors. This quiz will help you understand nutrient requirements, energy sources, and temperature effects on bacteria. Test your knowledge on the dynamics of bacterial reproduction and growth because it is essential in microbiology.
