Bacterial and Viral Genetics Flashcards Preview

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Flashcards in Bacterial and Viral Genetics Deck (55):
1

  • Central Dogma
  • Transcription
    • RNA Polymerase
    • Reads DNA to make RNA
  • Translation
    • Ribosomes
    • mRNA read to make proteins

Protein Synthesis 

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Regulation of Protein Synthesis 

What are the components for transcriptional regulation?

Transcriptional Regulation

  1. Sigma factors
  2. Promoters
  3. Operon

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Regulation of Protein Synthesis

What is the factor for translational regulation?

Translational Regulation

  1. Ribosome binding site

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  • Protein that directs RNA polymerases to transcribe a particular gene(s)
  • Several different sigma factors in a bacterial cell
  • Each sigma factor recognizes specific sequences called promoters
  • Regulate which genes transcribed 

Regulation of Transcription Via

Sigma Factor

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  • DNA sequence recognized by sigma factor/RNA polymerase to begin transcription
  • Different promoter sequences for difference genes 

Regulation of Transcription Via

Promoters 

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Regulation of Transcription

  1. Sigma Factors
    1. Recognizes promoters and regulates what genes will be transcribed 
  2. Promoter 
    1. Different promoters for different genes 

 

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  • Genes that are expressed at all time
  • About 75% of genes in bacterium 

Constitutive Genes

(Part of transcription regulation)

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  • Genes that are turned on and off as the cell's needs change

Facultative genes

(Part of transcription regulation) 

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Reads DNA to RNA 

Transcription

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Reads RNA to proteins

Translation 

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  • A set of genes controlled by a common promoter

Operon 

  • Part of transcription regulation

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  • A set of genes controlled by a common promoter
  • Genes usually related by a common metabolic pathway
  • Transcribed as a single unit, one mRNA transcript for the entire set of genes
  • Each gene is then translated separately 

Operon 

  • Part of the regulation of transcription 

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Operon

  • Part of the regulation of transcription 
  • A set of genes controled by a commmon promoter
  • Genes usually are related by a common metabolic pathway
  • Transscribed as a single unit, one mRNA transcript for entire set of genes
  • Each gene is then translated separately 

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Types of operation regulation(s)

Operon Regulation

  1. Inducible operons 
  2. Repressible operons 

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  • Operon off by default
  • Must be turned on (induced)
  • Activated by molecules called inducers
    • Ex: Lactose operon 

Inducible Operon

  • Example of operon regulation 

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Lactose operons are an example of what type of regulations?

Inducible operons 

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  • In absense of lactose, operon is off
  • Regulatory gene codes for active repressor proetin that binds to operator region of operon 
  • When operator is blocked, RNA polymerase cannot transcribe DNA

Lactose Operon = Inducible Operon 

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Lactose Operon

  • In absence of lactoose, operon is off
  • Regulartory gene codes for active repressor protein than binds to operator region of operon
  • When operator is blocked, RNA polymerase cannot transcribe the DNA

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Lactose Operon

  • When lactose is present, a small percentage of lactose molecules spontaneously convert to allolactose in solution
  • Allolactose binds to active repressor protein, prevents binding of repressor to operator
  • When operator is not blocked, RNA polymerase can transcribe DNA 

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  • Operon on by default
  • Must be turned off
  • Deactivated by molecules called co-repressors
    • Ex: Tryptophan operon 

Represssible Operon

Part of operon regulation 

 

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  • Repressible operon 
  • When levels of tryptophan in the cell are low, the operon is turned on by default
  • The regulatory protein is inactive under these conditions and cannot bind to operator

Tryptophan Operon 

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Tryptophan Operon

  • Part of repressible operon 
  • On by default, but can be turned off (repressed)
  • When levels of tryptophan in the cell are low, the operon is turned on by default
  • The regulatory protein is inactive under these conditions and cannot bind to operator 

 

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  • If protein synthesis ceases, the amount of tryptophan within the cell increases
  • Excess tryptophan (the co-repressor) binds to inactive repressor, activating it
  • Active repressor now binds to operator, repressing the transcription of the trp operon 

Tryptophan Operon

  • Repressible operon 

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Tryptophan Operon 

  • If protein synthesis ceases, the amount of tryptophan within the cell increases
  • Excess tryptophan (the co-repressor) binds to inactive repressor, activating it
  • Active repressor now binds to operator, repressing the transcription of the trp operon 

25

  • Change in the nucleotide sequence of a gene
  • Types
    • Spontaneous
    • Induced 
  • Effect is dependent upon its type
  • Many bacteria have mechanisms that aid in its repair

Mutations

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The two types of mutations

 

  1. Spontaneous
  2. Induced

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  • Due to unrepaired mistaked by replication enzymes
  • 1 in 250,000 to 1 in 250,000,000 bases replicated

Spontaneous mutations

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  • Chemical or physical agents that increase mutation rate
    • Mutagens 

Induced mutations 

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  • UV light
  • Causes thymine dimers
  • Presence of dimers causes DNA molecule to be misshappen, interferes with DNA function
  • Useful for microbial control 

Physical Mutagens 

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Physical Mutagens

  • UV light
  • Causes thymine dimers
  • Presence of dimers causes the DNA molecule to be misshapen, interferes with DNA function
  • Useful for microbial control 

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  • Bacteria that uses seveal mechanisms/ enzymes to "fix" different types mutations

Mutation Repair

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Type of mutation repair that uses the enzyme photolysase

Light Repair

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Explain Light Repair

  • Type of mutation repair
  • Uses the enzyme photolyase that uses energy from visible light
  • Breaks down the covalent bonds in the thymine dimer

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Thymine Dimer Repair by Photolyase

35

  • Type of bacterial genetics
  • Transfer of DNA between cells
  • Donor contributes part of genome to recipient
  • Consists of three types

Horizontal Gene Transfer

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Name the three types of horizontal gene transfer for bacteria

  1. Transformation
  2. Bacterial conjugation
  3. Transduction 

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  • Type of bacterial horizontal gene transfer
  • The ability of some bacterial cells to take in DNA from the environment

Transformation

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Types of transformation

  1. Competency (competent)
  2. Artificial competency

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Explain Competency (competent)

Type of transformation (horizontal bacterial gene transfer)

Property of cells tht can naturally take in DNA from the environment

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Explain artificial competency

Type of transformation (bacterial horizontal gene transfer)

Bacterial cells can be induced in cells using techniques in the lab 

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Transformation

The ability of some bacterial acells to take in DNA from the environement 

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Artifical competency (type of transformation)

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  • Gene transfer mediated by bacteriophage
    • Infect host cell
    • Newly packaged viruses contain host DNA instead of viral DNA
  • Consists of two types

Transduction

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The type types of transduction are:

  1. Generalized
  2. Specialized 

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  • Type of bacterial horizontal gene transfer that consists of:
    • Lytic phage
    • Random DNA fragment from host bacterial cell is carried by phage to recipient bacterial cell

Generalized Transduction 

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Generalized Transduction

  • Lytic phage
  • Random DNA fragment from host bacterial cell is carried by phage to recipient bacterial cell

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Type of transduction which consists of:

  • Lysogenic phage
  • Specific host DNA sequences are carried by phage from donor to recipient bacterial cell
  • Genes that code for certain bacterial toxins (cholera toxin)

Speciaized Transduction 

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  • "Bacterial sex"
  • Some bacteria contain a specific plasmid called F plasmid (F+ cells)
  • The F plasmid contains genes that allow the F+ cell to make a sex pilus
  • F+ cell contacts F- cell
  • Copy of F plasmid is transferred to the F- cell
  • Recipient cell then becomes a F+ cell

Conjugation 

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Conjugation

  • "Bacterial sex"
    • Some bacteria contain a specific plasmid called F plasmid (F+ cells)
    • The F plasmid contains genes that allow the F+ cell to make a sex pilus
    • F+ cell contacts F- cell
    • Copy of F plasmid is transferred to the F- cell
    • Recipient cell then becomes a F+ cell 

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What does microbial genetics consists of in terms of viral genetics?

Viral Genetics

  1. Mutation rate
  2. Antigenic drift
  3. Antigenic shift

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  • Viruses have a mutation rate much faster than bacterial and cellular organisms
  • Viral enzymes are prone to mistakes
  • In bacteriophage, 2 per genome replicated
  • In influenza, 1 per genome replicated

Virus Mutation Rate

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  • Spontaneous mutations during replication
  • Leads to minor changes in glycoproteins
  • Alters recognition of virus by immune system
  • Leads to slight increase in number of seasonal flu cases

Antigenic Drift

(Viral genetics)

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  • Genomoe of influenza made up of 8 different segments
  • On rare occasions, two or more separate strains will infect a single host cell
  • When this occurs, genome segments from different strains will combine in new ways during assembly 

Antigenic Shift

(Viral Genetics) 

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  • In influenza, leads to major changes in antigenic properties
  • Associated with major outbreaks
  • On average, occurs about every 10 years
  • 2009 H1N1 genes from pig, human, and bird influenza strains

Antigenic Shift of Viral Genetics 

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Antigenic Shift

  • In influenza, leads to major changes in antigenic properties
  • Two or more separate strains will infect a single host cell
  • When this occurs, genome segments from different strains will combine in new ways during assembly