Microbial Genetics Answers – Flashcards
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| Operons |
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| Gene regulatory units |
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| Inducible operons |
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| Operons that are normally "off", but are turned "on" by the presence of substrate. They are typically seen in catabolic processes. |
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| Repressible operons |
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| 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. |
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| What functions do operons serve? |
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| Toxin production Efflux pumps and antimicrobials Biofilm formation and quorum sensing Sporulation |
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| What are the four main elements of the lac operon? |
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| Regulator Control locus Structural locus Terminator |
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| Regulator (operon) |
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| A gene that codes for the repressor, which may be part of the operon or separate from it |
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| Control locus (operon) |
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| Consists of a promoter (which is a binding site for RNA polymerase) and an operator (which is a binding site for repressor protein). |
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| Structural locus (operon) |
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| Genes that code for the enzymes of the operon. |
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| Terminator (operon) |
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| Indicates the end of the operon. |
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| What are the 3 genes coded within the lac operon? |
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| lacZ: catabolizes lactose into galactose and glucose lacY: protein pump into cell membrane which imports lactose lacA: transfers acetyl groups |
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| When lactose is absent, what happens to the lac operon? |
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| Repressor protein is produced and binds to the operator, so polymerase can't read the operon, and no lactose catabolism takes place. |
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| What happens to the lac operon when lactose is present? |
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| 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. |
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| Rifamycins |
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| Drugs that interfere with transcription by binding to polymerase in Mycobacterium spp. Most are synthesized chemically. |
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| Erithromycin |
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| Binds for the 50s subunit of bacterial ribosomes (preventing proteins from detaching) |
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| Streptomycin |
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| Binds to the 30s subunit of bacterial ribosome (causing misreading of mRNA and binding trouble) |
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| Tetracycline |
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| Prevents tRNA from docking with ribosomes (meaning that proteins cannot elongate) |
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| Hemagluttinin (H) |
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| An influenza peplomer that allows the virus to stick to host cells. There are 16 types. |
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| Neuraminidase (N) |
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| An influenza peplomer that keeps viruses from sticking to one another. There are 9 types. |
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| Antigenic drift |
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| 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. |
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| Antigenic shift |
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| 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. |
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| Mutation |
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| 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. |
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| Wild type (strain) |
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| An individual harboring the original, unchanged DNA sequence |
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| Mutant type (strain) |
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| An individual harboring a modified DNA sequence |
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| Within a codon, which position has the most wobble? The least? |
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| Position 3, because of redundancy in the genetic code. Position 2 has the least wobble. |
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| Point mutation |
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| A single base pair that has been changed in some way. |
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| Frameshift mutation |
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| 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. |
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| Substitution mutation |
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| One base pair is replaced by another |
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| ATG |
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| Methionine - the "start" codon |
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| TAA TAG TGA |
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| Stop codons |
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| Silent mutation |
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| A base pair changes, but the codon's product does not |
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| Missense mutation |
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| A base pair changes, and the corresponding amino acid changes as a result |
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| Nonsense mutation |
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| A base pair changes, resulting in a "stop" codon |
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| Back mutation |
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| A base pair that has already been mutated changes back to the original form |
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| Indel |
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| An insertion or deletion of base pair(s) |
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| What proofreading machinery do organisms have for their DNA? |
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| Base excision repair, nucleotide excision repair, mismatch repair, glycosylases, polymerases, ligases, DNA photolyase for UV damage |
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| Base excision repair |
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| Removes one wrong base |
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| Nucleotide excision repair |
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| Removes a stretch of bases, even if only one is wrong |
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| Mismatch repair |
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| Resolves bad bonds |
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| DNA photolyase |
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| Recognizes abnormal bonds due to UV damage and can repair them |
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| How do viruses repair mutations? |
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| 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". |
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| Why do viruses mutate and evolve so fast? |
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| Their genome is short Many copies are made per host cell Little effort is required on behalf of the virus itself |
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| Recombination |
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| Swapping of genetic material that takes place in all pathogens. |
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| Recombinant organisms |
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| Any entity that contains and expresses genes from a different distinct entity. We can use genetic engineering and gene therapy to create recombinants. |
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| Conjugation |
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| Two members of the same species exchange genetic material. Bacteria with the F (fertility) factor more often initiate it. |
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| Transformation |
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| 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. |
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| Transduction |
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| Exchange of genetic material through bacteriophages |
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| Chromosomal fragments |
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| Products of cell lysis. They have no way to self-replicate, and must be integrated into the host genome to persist. |
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| How does conjugation occur? |
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| 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. |
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| Generalized transduction |
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| 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. |
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| Specialized transduction |
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| 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. |
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| Lysogenic conversion |
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| When a virus changes the properties of its bacterial host through transfer of genetic material; a form of transduction. |
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| Recombination in eukaryotes |
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| Mostly occurs during meiosis - conjugation, transformation, and transduction are not seen. |
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| Recombination in viruses |
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| Can recombine with other organisms (transduction) or other viruses (reassortment) |
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| Reassortment (viral) |
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| Recombination of segments among segmented RNA viruses |
