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Microbial Genetics
Dr. David Senchina, Drake University, Medical Microbio notes set 5
54
Microbiology
Undergraduate 2
03/06/2010

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Term
Operons
Definition
Gene regulatory units
Term
Inducible operons
Definition
Operons that are normally "off", but are turned "on" by the presence of substrate. They are typically seen in catabolic processes.
Term
Repressible operons
Definition
Operons that are normally "on", but are turned "off" by the presence of a product. Thy are typically seen in anabolic processes. In this case, the product is the corepressor - meaning that the repressor exists, but until the product binds, it doesn't have the right shape to interact with the operon.
Term
What functions do operons serve?
Definition
Toxin production
Efflux pumps and antimicrobials
Biofilm formation and quorum sensing
Sporulation
Term
What are the four main elements of the lac operon?
Definition
Regulator
Control locus
Structural locus
Terminator
Term
Regulator (operon)
Definition
A gene that codes for the repressor, which may be part of the operon or separate from it
Term
Control locus (operon)
Definition
Consists of a promoter (which is a binding site for RNA polymerase) and an operator (which is a binding site for repressor protein).
Term
Structural locus (operon)
Definition
Genes that code for the enzymes of the operon.
Term
Terminator (operon)
Definition
Indicates the end of the operon.
Term
What are the 3 genes coded within the lac operon?
Definition
lacZ: catabolizes lactose into galactose and glucose
lacY: protein pump into cell membrane which imports lactose
lacA: transfers acetyl groups
Term
When lactose is absent, what happens to the lac operon?
Definition
Repressor protein is produced and binds to the operator, so polymerase can't read the operon, and no lactose catabolism takes place.
Term
What happens to the lac operon when lactose is present?
Definition
Lactose binds to the repressor protein, inhibiting it from binding to the operator. Since the repressor protein is no longer on the operon, polymerase can bind to the promoter and read genes, allowing for production of enzymes and catabolism of lactose.
Term
Rifamycins
Definition
Drugs that interfere with transcription by binding to polymerase in Mycobacterium spp.
Most are synthesized chemically.
Term
Erithromycin
Definition
Binds for the 50s subunit of bacterial ribosomes (preventing proteins from detaching)
Term
Streptomycin
Definition
Binds to the 30s subunit of bacterial ribosome (causing misreading of mRNA and binding trouble)
Term
Tetracycline
Definition
Prevents tRNA from docking with ribosomes (meaning that proteins cannot elongate)
Term
Hemagluttinin (H)
Definition
An influenza peplomer that allows the virus to stick to host cells. There are 16 types.
Term
Neuraminidase (N)
Definition
An influenza peplomer that keeps viruses from sticking to one another. There are 9 types.
Term
Antigenic drift
Definition
Frequent, minor changes in H and N properties of influenza that allow for reinfection (since antibodies no longer will recognize the new virus). This is the cause of local epidemics.
Term
Antigenic shift
Definition
Rare, major changes in H and N properties of influenza, in which a new subtype of influenza is created. This is the cause of global pandemics.
Term
Mutation
Definition
A change in the genetic sequence caused by mistakes in transcription. Seen in all life forms, they may be beneficial, but are most often harmful. Mutations may or may not be repaired, and if they persist, will be passed on to the next generation.
Term
Wild type (strain)
Definition
An individual harboring the original, unchanged DNA sequence
Term
Mutant type (strain)
Definition
An individual harboring a modified DNA sequence
Term
Within a codon, which position has the most wobble? The least?
Definition
Position 3, because of redundancy in the genetic code.
Position 2 has the least wobble.
Term
Point mutation
Definition
A single base pair that has been changed in some way.
Term
Frameshift mutation
Definition
Base pairs are lost or gained, throwing off the reading of the entire rest of the strand. This can happen when viruses insert themselves into a host genome.
Term
Substitution mutation
Definition
One base pair is replaced by another
Term
ATG
Definition
Methionine - the "start" codon
Term
TAA
TAG
TGA
Definition
Stop codons
Term
Silent mutation
Definition
A base pair changes, but the codon's product does not
Term
Missense mutation
Definition
A base pair changes, and the corresponding amino acid changes as a result
Term
Nonsense mutation
Definition
A base pair changes, resulting in a "stop" codon
Term
Back mutation
Definition
A base pair that has already been mutated changes back to the original form
Term
Indel
Definition
An insertion or deletion of base pair(s)
Term
What proofreading machinery do organisms have for their DNA?
Definition
Base excision repair, nucleotide excision repair, mismatch repair, glycosylases, polymerases, ligases, DNA photolyase for UV damage
Term
Base excision repair
Definition
Removes one wrong base
Term
Nucleotide excision repair
Definition
Removes a stretch of bases, even if only one is wrong
Term
Mismatch repair
Definition
Resolves bad bonds
Term
DNA photolyase
Definition
Recognizes abnormal bonds due to UV damage and can repair them
Term
How do viruses repair mutations?
Definition
DNA viruses can use host mechanisms to fix their genomes, but RNA viruses can't, and so are very prone to mutation. In fact, viruses in general mutate and evolve so fast, it's sometimes ridiculous to think of them in terms of "species".
Term
Why do viruses mutate and evolve so fast?
Definition
Their genome is short
Many copies are made per host cell
Little effort is required on behalf of the virus itself
Term
Recombination
Definition
Swapping of genetic material that takes place in all pathogens.
Term
Recombinant organisms
Definition
Any entity that contains and expresses genes from a different distinct entity. We can use genetic engineering and gene therapy to create recombinants.
Term
Conjugation
Definition
Two members of the same species exchange genetic material. Bacteria with the F (fertility) factor more often initiate it.
Term
Transformation
Definition
Release of genetic material into the extracellular matrix, which is picked up through receptors on the outside of the cell. The donor and recipient may be very far away, or may even exist at different points in time.
Term
Transduction
Definition
Exchange of genetic material through bacteriophages
Term
Chromosomal fragments
Definition
Products of cell lysis. They have no way to self-replicate, and must be integrated into the host genome to persist.
Term
How does conjugation occur?
Definition
A sex pilus emerges from the F+ or Hfr bacterium and docks with the recipient, then retracts to draw the two together. A conjugation bridge forms, over which material is shared.
Term
Generalized transduction
Definition
During a viral invasion of the bacterial cell, the host DNA dissociates, and when virions are being assembled, the host DNA gets integrated. When the virions infect a new cell, the host DNA is also delivered.
Term
Specialized transduction
Definition
A phage incorporates its DNA into the bacterial genome, and when it activates, it grabs part of the bacterial genome as well. The virions then contain this extra bit of DNA, which is incorporated into the next cell they infect.
Term
Lysogenic conversion
Definition
When a virus changes the properties of its bacterial host through transfer of genetic material; a form of transduction.
Term
Recombination in eukaryotes
Definition
Mostly occurs during meiosis - conjugation, transformation, and transduction are not seen.
Term
Recombination in viruses
Definition
Can recombine with other organisms (transduction) or other viruses (reassortment)
Term
Reassortment (viral)
Definition
Recombination of segments among segmented RNA viruses
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