The Genetics of Viruses and Bacteria. Chapter 18. Virus. Bacterium. Animal cell. 0.25 m. Animal cell nucleus. Figure 18.2. Microbial Model Systems. Recall that bacteria are prokaryotes With cells much smaller and more simply organized than those of eukaryotes Viruses
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Is a phage reproductive cycle that culminates in the death (lysis) of the host
Replicates the phage genome without destroying the host
DOCKING with the host receptor protein
PENETRATION of the viral nucleic acid into the host cytoplasm (Restriction Endonucleases, A.K.A. restriction enzymes break up host DNA)
BIOSYNTHESIS of the viral components
Assembly (MATURATION) of the viral components into complete viral units
RELEASE of the completed virus from the host cell
Are capable of using both the lytic & lysogenic cycles of reproduction
When viral DNA is integrated into the bacterial chromosome (Plasmid)
Viral genome (RNA)
2 of each
(b) The SARS-causing agent is a coronavirus like this one (colorized TEM), so named for the “corona” of glycoprotein spikes protruding from the envelope.
(a) Young ballet students in Hong Kong wear face masks to protect themselves from the virus causing SARS.
Figure 18.11 A, BSARS – Severe Acute Respiratory Syndrome
Is the alteration of a bacterial cell’s genotype and phenotype by the uptake of naked, foreign DNA from the surrounding environment
Phages carry bacterial genes from one host cell to another
A cell carrying an F plasmid(an F+ cell) can form amating bridge with an F– celland transfer its F plasmid.
DNA replication occurs inboth donor and recipientcells, using the single parental strands of the F plasmid as templates to synthesize complementary strands.
The plasmid in the recipient cell circularizes. Transfer and replication result in a compete F plasmid in each cell. Thus, both cells are now F+.
A single strand of the F plasmid breaks at a specific point (tip of blue arrowhead) and begins tomove into the recipient cell. As transfer continues, the donor plasmid rotates(red arrow).
Confer resistance to various antibiotics
A T C C G G T…
A C C G G A T…
T A G G C C A …
T G G C C T A …
(a) Insertion sequences, the simplest transposable elements in bacteria, contain a single gene that encodes transposase, which catalyzes movement within the genome. The inverted repeats are backward, upside-down versions of each other; only a portion is shown. The inverted repeat sequence varies from one type of insertion sequence to another.
(b) Transposons contain one or more genes in addition to the transposase gene. In the transposon shown here, a gene for resistance to an antibiotic is located between twin insertion sequences. The gene for antibiotic resistance is carried along as part of the transposon when the transposon is inserted at a new site in the genome.
(b) Regulation of enzyme production
Figure 18.20a, b
Genes of operon
Start codon Stop codon
Polypeptides that make up
enzymes for tryptophan synthesis
(a) Tryptophan absent, repressor inactive, operon on. RNA polymerase attaches to the DNA at the promoter and transcribes the operon’s genes.
Figure 18.21aThe trp operon: regulated synthesis of repressible enzymes
No RNA made
Tryptophan present, repressor active, operon off. As tryptophan
accumulates, it inhibits its own production by activating the repressor protein.
The lac operon: regulated synthesis of inducible enzymes
Lactose absent, repressor active, operon off. The lac repressor is innately active, and inthe absence of lactose it switches off the operon by binding to the operator.
Lactose present, repressor inactive, operon on. Allolactose, an isomer of lactose, derepresses the operon by inactivating the repressor. In this way, the enzymes for lactose utilization are induced.