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unit 8 micro
| Question | Answer |
|---|---|
| When the cell is NOT in the presence of tryptophan, | RNA polymerase can transcribe mRNA |
| When is the repressor protein transcribed? | it is always transcribed |
| Why is the tryptophan operon turned off in the presence of tryptophan? | tryptophan binds to and activates the repressor protiens; the repressor protiens, in turn, bind to the operator, preventing transcription |
| what is the overall function of the trp operon | to ensure that the cell has a supply of tryptophan at all times |
| how do the repressor protiens block the transcription of the structural genes | it binds to the operator when activated |
| what is the inducer molecule in the lac operon | allolactose |
| with which genetic region does the repressor protien interact | the operator region |
| when the cell is not in the presence of lactose | the repressor protiens bind to the operator |
| what is the basic function of the lac operon | to code for enzymes involved in catabolizing lactose |
| what genetic element does the RNA polymerase bind to | the promoter |
| mechanisims for controlling enzyme activity include all of the following except | addition of short sections of new amino acid sequence |
| the major site of protien binding in DNA is the major groove. why is this a good site for binding? | beacuse the major groove is wider, it is more accessible to binding protiens |
| - pathways typically utilize - protiens that stimulate binding of RNA polymerase to DNA | catabolic- activator |
| - pathways typically rely on - protiens to inhibit mRNA synthesis | anabolic- repressor |
| in negative cotrol of transcription by the lac operon, how does the presence of a inducer affect transcription? | the inducer prevents the repressor from binding to the operator |
| what occurs when an inducer is added to an environment containing an organism with a metabolic pathway controlled by a repressor | the inducer combines with the repressor and inactivates the repressor |
| in certian circumstances, a single regulatory protien controls multiple operons. this situation would be called a | regulon |
| the promoters of positively controlled operons require activator protiens because | the promoters bind RNA polymerase weakly and utilize activator protiens to help RNA polymerase recognize the promoter |
| cyclic AMP is synthesized from ATP by an enzyme called - which is involved in - | adenylate cyclase / catabolite repression |
| Bacteria can regulate gene expression due to changes in the environment. How are these changes communicated to the cell? | A sensor kinase on the cell membrane recognizes the change and transfers the information to a response regulator in the cytoplasm. |
| Why are two-component regulatory systems particularly useful for controlling gene expression in response to environmental signals? | Phosphorylation is a permanent change so genes are always turned on after signal. |
| Quorum sensing relies upon a large cell population which then turns on transcription. | true |
| Competent cells are cells that | can take up DNA from their surrounding environment and integrate it into their own chromosomes by recombination. |
| Mice that are injected with only the R strain of Streptococcus pneumoniae | stay healthy, because their immune systems can kill this strain easily. |
| What characteristic of the S strain allows it to evade the immune system of the mice? | The cells have a capsule. |
| What most likely explains the recovery of live S strain cells from a mouse injected with heat-killed S strain mixed with live R strain cells? | The R strain picked up the S strain DNA, enabling it to produce a capsule. |
| Which finding is most surprising from Griffith’s experiments? | S strain cells are isolated from the blood of mice infected with heat-killed S strains and live R strains. |
| How does specialized transduction differ from regular lysogeny? | The prophage in specialized transduction carries with it pieces of the host chromosomal DNA. |
| What happens to the packaged DNA of a specialized transduced phage when it infects a new recipient cell? | The host DNA integrates, with the prophage, into the new recipient chromosome. |
| How can specialized transduction contribute to the transfer of antibiotic resistance genes in a bacterial population? | The prophage takes an antibiotic resistance gene with it and is packaged with the newly synthesized viral DNA. |
| A change in the nucleotide sequence of DNA that is passed on to daughter cells is referred to as __________. | a mutation |
| There are several different types of mutations possible in the base sequence of DNA. If a GGC (glycine) codon were changed to UGC (cysteine), it would be termed a __________. | missense mutation |
| A single base substitution happens to cause a nonsense mutation early in the gene for a protein. What will be the result? | The protein will be truncated so much that it is unlikely to function normally. |
| Frameshift mutations can be very severe. What is one reason why they are often so serious? | When a frameshift mutation occurs, it causes changes in many bases downstream and can affect many of the amino acids in the protein. |
| The SOS system repairs DNA that has gaps, breaks, and other lesions by | using specialized DNA polymerases that will synthesize a new DNA strand even if there is not a normal complementary DNA strand to act as a template. |
| Chemical mutagens, UV radiation, and ionizing radiation all increase mutation rates, but they have different mechanisms. Which type of mutagen would be best suited for creating large deletions and rearrangements within a genome? | ionizing radiation |
| What is unique about transduction compared to normal bacteriophage infection? | Transduction transfers DNA from the chromosome of one cell to another. |
| How is generalized transduction different from specialized transduction? | Generalized transduction is initiated during lytic cycle of a virulent bacteriophage; specialized transduction is initiated during the lysogenic cycle of a temperate bacteriophage. |
| A transducing phage | contains fragments of the host chromosome instead of the viral genome. |
| When a transducing phage interacts with a new host cell, | the DNA from the previous host can recombine with the new host chromosome. |
| The F (fertility) plasmid contains a set of genes that encode for the ________ proteins that are essential in conjugative transfer of DNA. | pili |
| How does an F+ cell differ from an Hfr cell? | Hfr strains have the F plasmid integrated into the chromosome. |
| Why does conjugation between an Hfr strain and an F- strain not result in two Hfr strains? | Conjugation is typically disrupted before the fertility factor can be transferred. |
| Which of the following is a characteristic of an F+ cell? | Ability to synthesize sex pili, presence of a fertility factor, and ability to mate with an F- cell. |
| What benefit does the F- strain receive from mating with an Hfr strain? | It acquires new, potentially beneficial genes from the Hfr strain. |
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