Chapter 16 Flashcards
1
Q
gene targeting:
A
method for inserting DNA into a genome that relies on homologous recombination; the DNA is targeted for insertion into a specific place in the genome by sequence similarity.
2
Q
Eukaryotes:
A
organisms whose cells have nuclei encased in a membrane
3
Q
Archae:
A
organisms living in extreme conditions such as highly salty, hot, or anaerobic environments.
4
Q
prokaryotes:
A
single-celled organisms, such as bacteria, whose DNA is not contained within a nucleus.
5
Q
All bacteria…
A
lack a defined membrane and membrane bound organelles such as mitochondria
6
Q
nucleoid body:
A
a folded bacterial chromosome.
7
Q
pathogen:
A
an agent, for example a microorganism, that causes disease in its host.
8
Q
toxin:
A
a poison of plant or animal origin that causes disease at low concentrations.
9
Q
Bacteria are prokaryotic cells meaning …
A
they do not have a membrane enclosed nucleus nor membrane bound organelles
10
Q
Bacteria are capable of rapid evolution, and as a result…
A
these organisms vary enormously in size, shape, metabolism ,and the habitats they adapt to.
11
Q
A typical human body carries…
A
30-50trillion bacteria. Most of these are either harmless or helpful bu a few are pathogenic, causing disease.
12
Q
bacterial chromosome:
A
a bacterial genome; usually a single circular molecule of double-helical DNA.
13
Q
True or False: Little repeated DNA exists in bacteria
A
True
14
Q
core genome:
A
genes shared by all bacterial strains of a given species.
15
Q
pangenome:
A
the core genome of a bacterial species plus all genes found in some strains but not others.
16
Q
insertion sequences (ISs):
A
small bacterial transposons that do not contain selectable markers.
17
Q
Tn element:
A
a bacterial transposon carrying transposase and drug resistance genes flanked by ISs.
18
Q
plasmids:
A
small circles of double-stranded DNA that can replicate in bacterial cells independently of the bacterial chromosome; commonly used as cloning vectors.
19
Q
Plasmids can be []
A
transferred from one bacterium to another, sometimes across species.
20
Q
Bacteria normally []
A
live in communities
21
Q
metagenomics:
A
the collective analysis of genomic DNA from natural communities of microbes.
22
Q
Human Microbiome Project:
A
the initiative to identify all species of microorganisms that are symbionts with humans, and to correlate differences in microorganism populations with phenotypic differences and disease states.
23
Q
Genes in bacterial chromosomes are []
A
tightly packed, with no introns and very short intergenic regions.
24
Q
The core genome …
A
consists of genes shared by all members of the bacterial species.
25
The core genome plus all of the strain specific genes is called
the pangenome for the species,
26
Transposons in bacterial genomes...
can carry genes, including those conferring drug resistance.
27
Plasmids are...
circular DNA molecules replicate autonomously and can be transferred between cells.
They often contain genes from drug resistance of pathogenicity, or for specialized metabolic functions.
28
Metagenomics is
the analysis of the collective bacterial genome in a particular environment. Metagenomic studies may clarify the roles of bacteria in human health and may identify bacterial genes with unique properties.
29
Bacteria is used in labs because...
it has the ability to grow a large number of cells quickly.
However, only a few bacterial species can be grown in a lab. Most species can only be maintained in their native environment.
30
colony:
a mound of genetically identical cells that all descend from a single cell.
31
The rapidity of bacterial multiplication makes...
it possible to examine rare genetic events
32
Most bacterial genomes...
carry one copy of each gene and are therefore monoploid.
33
In the absence of a wild type allele for each gene...
all mutations express their phenotype.
34
Classes of bacterial mutants
Colon morphology mutants: Whether a colony is large small, shiny or dull, round or irregular.
Resistance mutations: resistance to bactericidal agents such as antibiotics or bacteriophages.
Auxotrophic mutants: unable to grow and reproduce on a minimal medium. They cannot synthesize crucial complex compounds from simple materials.
Catabolisms mutations: the ability of cells to break down and use complicated chemicals in the environment is affected.
35
Essential gene mutations:
production of proteins required from growth is affected.
36
genetic selection:
a process that establishes conditions in which only the desired mutant will grow.
37
genetic screen:
a process whereby researchers examine a large number of organisms and identify rare individuals with a mutant phenotype of interest.
38
A single bacterial cell divides to ...
form a colony of millions of genetically identical descendants
39
Features of bacteria aiding genetic research are ...
monoploidy, facilitating mutant identification and rapid exponential growth, allowing recovery of rare mutants.
40
Bacterial mutants can be identified in ...
screen or selections. In a screen, individual colonies are tested for a particular phenotype. In a selection, only bacteria with the phenotype in question are recovered as colonies, enabling the identification of extremely rare mutants.
41
vertical gene transfer:
the passage of genes from one generation to the next, particularly during sexual reproduction.
42
horizontal gene transfer:
the introduction and incorporation of DNA from an unrelated individual or from a different species.
43
In bacteria gene transfer...
one gene is the donor and the other the recipient.
44
Donor:
in gene transfer in bacteria, the cell that provides the DNA to the recipient.
45
Recipient:
during gene transfer in bacteria, the cell that receives the DNA.
46
3 different mechanisms of bacterial gene transfer:
transformation: a mechanism by which bacteria transfer genes from one strain to another; occurs when DNA from a donor is added to the bacterial growth medium and is then taken up from the medium by the recipient.
The recipient cell is known as a transforman
conjugation: a mechanism by which bacteria transfer genes from one strain to another; the donor carries a special type of plasmid that allows it to transfer DNA directly when it comes in contact with the recipient.
- The recipient is known as an exconjugant.
transduction: a mechanism by which bacteria transfer genes from one strain to another; donor DNA is packaged within the protein coat of a bacteriophage and transferred to the recipient when the phage particle infects it.
Recipient cells are known as transductants.
47
Transfer is only...
one direction with most recipients only receiving about 3% of donor material.
exconjugants contain more.
48
natural transformation:
a process by which a few species of bacteria transfer genes from one strain to another by spontaneously accepting DNA from their surroundings.
49
artificial transformation:
a process to transfer genes from one bacterial strain to another, using laboratory procedures to weaken cell walls and make membranes permeable to DNA.
50
competent cells:
cells treated so that they are able to take up DNA from the medium.
51
When a recipient takes up DNA by natural transformation...
only one strand of a fragment donor of DNA enters the cell, while the other strnad is degraded. The entering strand recombines with the recipient chromosome producing a transformation when the recipient cell divides.
52
cotransformation:
the simultaneous transformation of two or more genes.
53
origin of transfer:
during bacterial conjugation, the spot on the F plasmid where replicative transfer of DNA from the donor to the recipient cell initiates.
54
episomes:
plasmids, like the F plasmid, that can integrate into the host genome
55
During infection of bacteria...
a virus particle may incorporate a piece of the bacterial chromosome and introduce this piece of bacterial DNA into other host cells during subsequent rounds of infection.
56
When a bacteriophage injects its DNA into a cell...
the phage DNA takes over the cell’s protein synthesis and DNA replication machinery, forcing it to express phade genes, produce phage protein, and replicate the phage DNA.
57
lytic cycle:
the bacterial cycle of phage-infected cells resulting in cell lysis and release of progeny phage.
58
lysate:
a population of phage particles released from the host bacteria at the end of the lytic cycle.
59
Many kinds of bacteriophages...
encode enzymes destroying the chromosomes of the host cells.
Digestion of the bacterial chromosome by these enzymes sometimes generates fragments of bacteria DNA about the same length as the phase genemoe and these phase length bacterial DNA fragments occasionally become incorporated into phage particles in place of the phage DNA.
60
After lysis of the host cell,
the phage particles can attach to, and inject the DNA they carry into, other bacterial cells. In this way phage transfers genes from the first bacterial strain (the donor) to a second strain (the recipient).
61
What completes the transfer?
Recombination between the injected DNA and the chromosome of the new host
62
generalized transduction:
a type of transduction (gene transfer mediated by bacteriophages) that can result in the transfer of any bacterial gene between related strains of bacteria.
63
Two genes close together on the bacterial chromosome...
may be contransduced.
64
cotransduction:
transfer of different bacterial genes together in one phage by transduction.
65
The frequency of contransduction depends
directly on the distance between two genes: the closer they are the more likely they are to appear on the same short DNA fragment and be packaged into the same transducing phase.
66
what genes cannot be contransduced
Two genes further apart than the length of DNA and can be packaged into a single phage particle
67
virulent:
describes bacteriophages that always enter the lytic cycle, multiply rapidly, and kill the host.
68
Temperate:
although they can enter the lytic cycle, they can also enter the lysogenic cycle
69
lysogenic cycle:
the integration of a bacteriophage into the bacterial host genome as a prophage, which does no immediate harm to the cell.
70
prophage:
a phage genome integrated into the bacterial host genome.
71
lysogen:
a bacterial cell that carries a prophage
72
Once integrated into the chromosome, the phage genome is ...
a passive partner replicating along with the chromosome but not producing the proteins leading to the production of more virus particles.
73
The choice of lytic or lysogenic occurs when a...
temperate phage injects its DNA into a bacterial cell and the environmental condition.
74
Horizontal gene transfer has
significant evolutionary and medical implications.
75
genomic islands:
large DNA segments transferred from one bacterial species to another.
Genomic islands carry many different types of genes promoting the fitness of a recipient bacterium in a new environment, such as genes encoding new metabolic enzymes or proteins mediating antibiotic resistance.
76
pathogenicity islands:
segments of DNA in disease-causing bacteria that encode several genes involved in pathogenesis. Pathogenicity islands appear to have been transferred into the bacteria by horizontal gene transfer from a different species.
77
Horizontal gene transfer bacteria occurs through three mechanisms:
transformation, conjugation, and transduction.
78
In transformation, donor DNA
in the growth medium enters a recipient cell.
79
Conjugation depends on...
direct cell-to-cell contact between a donor carrying either a conjugative plasmid or an integrated conjugative element, and a recipient lacking such an element.
80
For genes close together, the frequencies of cotransformation and cotransduction...
are inversely related to the distance between the genes.
81
Bacteria evolve rapidly due to...
horizontal transfer of genes, including packets of genes called pathogenicity islands between bacterial species,
82
To identify mutant genes, a wild type bacterial genomic library in plasmids is used to...
transform the mutant bacterial strain. A transformed bacterium in which the mutant phenotype is reduced to wild type likely harbors a plasmid containing a wild type copy of the corresponding gene.
83
Transposons are useful as mutagens because...
they act as molecular tags for genomic DNA sequences rapidly identifiable by inverse PCR.
84
In gene targeting, homologous recombination between the...
bacterial chromosome and a linear DNA construct synthesized in vitro can generate a null mutation in any gene.
