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Genetics Chapter 7
Bacterial and Viral Genetic Systems
| Question | Answer |
|---|---|
| techniques for studying bacteria: culture media typically contains what? (4) | carbon source. essential elements (N,P), certain vitamins, and other required ions and nutrients |
| techniques for studying bacteria: minimal medium contains what? | only the nutrients required by prototrophic (wildtype) cells |
| techniques for studying bacteria: complete medium contains what? | all the nutrients required for growth and synthesis, including those normally synthesized by the organism (nutritional mutants can grow on it) |
| as each bacterium grows and divides on the agar plate, it gives rise to a visible clump of genetically identical cells called a _________ | colony |
| techniques for studying bacteria: selective medium | a medium that lacks an essential nutrient |
| bacteria | unicellular organisms that lack a nuclear membrane |
| MOST bacterial genomes consist of a ________ chromosome that contains a singly DNA molecule several million base pairs in length | circular |
| however, some bacterial genomes have 2 circular chromosomes, 3, etc, and some even have _________ chromosomes | linear |
| in addition to having a chromosome, many bacteria possess _________ | plasmids |
| plasmids | small, circular DNA molecules |
| in general, plasmids carry _____ that are not essential to bacterial function but may play an important role in the life cycle and growth | genes |
| some plasmids promote _______ while others produce compounds that ______ | mating, kill |
| plasmids are used extensively in genetic engineering and some play a role in the spread of _________ ________ among bacteria | antibiotic resistance |
| each plasmid possesses what? | an origin of replication (a specific DNA sequence where DNA replication is initiated) |
| _________ are plasmids that are capable of freely replicating and are able to integrate into bacterial chromosomes | episomes |
| plasmid replicates ___________ of its bacterial chromosome | independently |
| what are the 3 general stages of plasmid replication? | begins at origin of replication, strands separate and replication takes place in both directions, eventually producing 2 circular DNA molecules |
| bacteria exchange genes through _________, __________, and ___________ | conjugation, transformation, and transduction |
| these 3 mechanisms entail some type of DNA _______ and ___________ between the transferred DNA and the bacterial chromosome | transfer, recombination |
| conjugation | mechanism by which genetic material may be exchanged between bacterial cells |
| during conjugation, two bacteria lie close together and a _________ bridge forms between them | cytoplasmic |
| a ________ or sometimes part of the _________ ________ passes from one cell (the donor) to the other (the recipient) | plasmid, bacterial chromosome |
| after conjugation, _________ _____ may take place between homologous sequences in the transferred DNA and the chromosome of the recipient cell | crossing over |
| in conjugation, DNA is transferred DNA found in the medium is taken up by the cellwith no __________ exchange | reciprocal (only from donor to recipient) |
| Transformation | mechanism by bacterium takes up DNA is taken up by the cell from the medium it's growing in |
| after transfromation, __________ may take place between the introduced genes and those of the bacterial chromosome | recombination |
| Transduction | takes place when a bacterial virus carries genes from one bacterium to another. |
| after transduction, after the virus is in the new cell, the newly introduced DNA may undergo __________ with the bacterial chromosome | recombination |
| in most bacteria, conjugation depends on a ________ factor | fertility (F) |
| the F factor is present in the ________ cell and absent in the ________ cell | donor, recipient |
| cells that contain F factor are referred to as ___ and cells that lack the F factor are referred to as ___. | F+, F- |
| what does the F factor contain | an origin of replication and a number of genes required for cunjugation |
| conjugation between F+ and F- cells: during conjugation a _________ connection between F+ and F- cells forms | cytoplasmic |
| conjugation between F+ and F- cells: Then one DNA strand of F factor is nicked at an origin | nicked |
| conjugation between F+ and F- cells: When the DNA strand is nicked, it begins to ________ | separate |
| conjugation between F+ and F- cells: __________ takes place on the F factor, replacing the nicked strand | replication |
| conjugation between F+ and F- cells: the __ end of the nicked DNA passes into the recipient cell | 5' |
| conjugation between F+ and F- cells: What happens to this single strand of DNA now in the recipient cell | it replicates |
| conjugation between F+ and F- cells: What is formed after this replication? | a circular, double-stranded copy of the F plasmid |
| conjugation between F+ and F- cells: the F- cells now becomes ___ | F+ |
| in Hfr (high-frequency recombination) cells, what happens to the F factor? | the F factor is integrated into the bacterial chromosome |
| Hfr cells behave like ___ cells, forming sex pili and undergoing conjugation with F- cells | F+ |
| conjugation between Hfr and F- cells: the integrated F factor is _____ | nicked |
| conjugation between Hfr and F- cells: What happens after the F factor is nicked? | the end of the nicked strand moves into the F- cell, and because the F factor has been integrated into the bacterial chromosome, the chromosome follows it into the recipient cell. |
| conjugation between Hfr and F- cells: In mating of Hfr and F-, the F- cell almost never becomes F+ or Hfr because of why? | because the F factor is nicked in the middle in the initiation of strand transfer (placing part of the F factor at the beginning and part at the end of the strand to be transferred) |
| When is an Hfr cell converted into an F' cell? | when the F factor excises from the bacterial chromosome and carries bacterial genes with it. |
| F' cells | cells containing an F plasmid with some bacterial genes |
| conjugation between Hfr and F' cells: During conjugation, the F plasmid is transferred to the F- cell, which means what? | any genes on the F plasmid, including those from the bacterial chromosome, may be transferred to F- recipient cells (called sexduction) |
| conjugation between Hfr and F' cells: What does this conjugation produce? | partial diploid (or merozygotes) |
| conjugation between Hfr and F' cells: partial diploid (or merozygotes) | cells with two copies of some genes, one of the bacterial chromosome and one on the newly introduced F plasmid |
| F factor summary: What is the F factor characteristic of type F+? | present as separate circular DNA |
| F factor summary: What is the F factor characteristic of type F-? | absent |
| F factor summary: What is the F factor characteristic of type Hfr? | present and integrated into bacterial chromosome |
| F factor summary: What is the F factor characteristic of type F'? | present as separate circular DNA, carrying some bacterial genes |
| F factor summary (conjugation): F+ x F- produces what cell types? | two F+ cells (F- cell becomes F+) |
| F factor summary (conjugation): Hfr x F- produces what cell types? | one HFr cell and one F- cell (no change) |
| F factor summary (conjugation): F' x F- produces what cell types? | two F' cells (F- cell becomes F' cell) |
| conjugation can be used to map bacterial genes by mixing ___ and ___ cells that differ in genotype | Hfr and F- |
| conjugation can be used to map bacterial genes by mixing Hfr and F- cells that differ in genotype and do what? | interrupt conjugation at different intervals |
| what indicates the relative positions of the genes on the bacterial chromosome when using conjugation as a method of mapping? | the amount of time required for the individual genes to be transferred from the Hfr to the F- cells |
| another way that DNA can be transerred between bacteria is through t_________ | transformation |
| transformation requires what two things? | the uptake of DNA fro the surrounding medium and it's incorporation into a bacterial chromosome (or a plasmid) |
| transformation: cells that take up DNA through their envelopes are said to be ________ | competent |
| what is competence influence by? (3) | growth stage, concentration of available DNA, and environmental challenges |
| transformation: the DNA taken up by a competent cell does not have to be _______, any type of DNA can be taken up by competent cells under the appropriate conditions | bacterial |
| transformation: as a DNA fragment enters the cell, one of the strands is _________ | hydrolyzed |
| transformation: the other strand does what? | moves across the membrane. pairs with homologous region, and integrates into the bacterial chromosome |
| transformation: the remainder of the single strand of DNA fragment is ________ | degraded |
| transformation: When the cell replicates and divides, one of the resulting cells is ________ and the other is not | transformed |
| gene mapping (transformation): requires two strains of bacteria that differ in several ___________ traits | genetic |
| gene mapping (transformation): the recipient strain is treated to _______ competency, and DNA from the donor strain is added to the medium | increase |
| gene mapping (transformation): fragments of the donor DNA enter the recipient cells and undergo _________ with homologous DNA sequences on the bacterial chromosome | recombination |
| gene mapping (transformation): cells that receive genetic material through transformation are called _________ | transformants |
| gene mapping (transformation): genes can be mapped by observing the ____ at which two or more genes are transferred together in transformation | rate (called cotransformed) |
| gene mapping (transformation): if two genes are more likely to cotransform if they are ______ on the chromosome | close |
| horizontal gene transfer in bacteria | many bacteria have acquired genetic information from other species of bacteria and even from some eukaryotes |
| the bacterium E. coli is an important model genetic organism because of what advantages? (3) | small size, rapid reproduction, and a small genome |
| virus | replicating structures with DNA and RNA genomes that may be double stranded or single stranded, linear, or circular |
| viruses that infect bacteria are called what? | bacteriophages, or phages |
| bacteriophages have 2 alternative life cycles. What are they? | lytic and lysogenic |
| lytic cycle | phage attaches to a receptor on the bacterial cell wall and injects its DNA into the cell. The DNA replicates, transcribes, and translated in the hose producing more phage DNA/proteins |
| lytic cycle: after more phage DNA is produced in the host, the phages do what? | produce an enzyme that breaks open the host cell, releasing the new phages |
| _______ phages reproduce strictly through the lytic cycle and kill their host | virulent phages |
| __________ phages can undergo either the lytic or the lysogenic cycle | temperate phages |
| lysogenic cycle begins like the lytic cycle but, inside the cell, the phage DNA does what? | integrates into bacterial chromosome where it remains as an inactive prophage |
| lysogenic cycle: what then happens to this inactive prophage? | it is replicated along with the bacterial DNA and is passed on when the bacterium divides. |
| lysogenic cycle: certain stimuli can cause the prophage to _________ from the bacterial chromosome and enter into the lytic cycle, producing new phage particles and lysing the cell | dissociate |
| genetic transduction | any gene may be transferred |
| specialized transduction | only a few genes are transferred |
| does genetic exchange between bacteria always require cell-to cell contact? | no |
| Lederberg and Zinder discovered generalized transduction. Through their experiement they discovered that genetic exchange did not take place through conjugation, later discovered was that a ______ was shown to be the agent of transfer | phage |
| For some types of bacteriophage, a piece of the bacterial chromosome instead of phage DNA occasionally gets packaged into a phage coat. These phage particles are called ___________ _______ | transduction phages |
| this transducing phage does what to a new cell? | infects, releasing the bacterial DNA |
| the introduced genes may then become _________ into the bacterial chromosome by a double crossover | integrated |
| Bacterial genes can be moved from one bacterial strain to another in the process, producing recombinant bacteria called ________ | transductants |
| not all phages are capable of transduction. What three things does this rare event require? | (1)the phage degrade the bacterial chromosome (2)the process of packaging DNA into the phage protein not be specific for phage DNA and (3) the bacterial genes transferred by the virus recombine with the chromosome in the recipient cell |
| only genes located close together on the bacterial chromosome will be transferred together, or ___________ | cotransduced |
| how is transduction used to map bacterial genes | by using the rates of cotransduction to indicate the physical distance between genes on a bacterial chromosome |
| transduction gene mapping: to map genes by using transduction, what are use? | two bacterial strains with different alleles at several loci |
| explain how phage genes can be mapped | by infecting bacterial cells with two different phage strains and counting the number of recombinant plaques produced by the progeny phages |
| RNA viruses: RNA viruses capable of integrating into the genomes of their hosts are called ____________ | retroviruses |
| RNA viruses: Because the retroviral genome is RNA and the host is DNA, a retro virus must produce _______ ____________ | reverse transcriptase |
| RNA viruses: reverse transcriptase | an enzyme that synthesizes complementary DNA (cDNA) from either RNA or a DNA template |
| RNA viruses: the reverse transcriptase enzyme is used to make a DNA copy of the viral genome, which then integrates into the host genome as a ________ | provirus |
| RNA viruses: provirus | viral genome incorporated into the host chromosome |
| RNA viruses: the provirus is _________ by host enzymes when the host chromosome is duplicated | replicated |
| RNA viruses: the provirus undergoes__________ to produce numerous copies of the original RNA genome. the viral RNA are assembled and buds from the cell membrane | transcription |
| RNA viruses: ___ is a retrovirus that is the causative agent for AIDS | HIV |
| RNA viruses: what is influenza caused by? | RNA influenza viruses |
| RNA viruses: one of the dangers of influenza virus is that it evolves rapidly, with new new strains appearing frequently. Influenza evolves in _#_ ways | two |
| RNA viruses: each strain continually changes through MUTATIONS arising in the viral RNA. This typ eof continual change is called __________ _____ | antigenic drift |
| RNA viruses: major changes in the viral genome take place through ________ _____, in which genetic material from different strains is combined in a processed called reassortment. | antigenic shift |
Created by:
cmccartney2
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