viruses and bacteria ch. 18. viruses parasite that requires a host cell in order to live they take...
DESCRIPTION
Structure Made of either DNA or RNA enclosed in a protein coat called a capsid Many viruses also have a viral envelope which is a membrane that cloaks the capsids A virus can only infect one specific type of cell The reason for this is that the virus binds to specific receptors on the surface of the cellTRANSCRIPT
![Page 1: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/1.jpg)
Viruses and Bacteria
Ch. 18
![Page 2: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/2.jpg)
Viruses
Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to
create the proteins it needs to make new viruses Typically creates thousands of new viruses and
eventually kills the host cell
The range of organisms that a virus can attack is referred to as its host range
A new viral disease that harms humans (ex. Hanta virus) may result from a mutation in the virus that expanded its host range
![Page 3: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/3.jpg)
Structure
Made of either DNA or RNA enclosed in a protein coat called a capsid
Many viruses also have a viral envelope which is a membrane that cloaks the capsids
A virus can only infect one specific type of cell The reason for this is that the virus binds to specific
receptors on the surface of the cell
![Page 4: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/4.jpg)
![Page 5: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/5.jpg)
Bacteriophages Most complex virus; Infects bacteria Also known as the shortened term “phages” Can reproduce by either the lytic cycle or lysogenic
cycle
Lytic Cycle: Phage enters host cell Takes control Replicates itself Causes cell to burst
This releases a new generation of phage viruses to go and do the same thing
![Page 6: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/6.jpg)
![Page 7: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/7.jpg)
Lysogenic Cycle Replicate without killing the host cell Incorporated into the host’s DNA Stays dormant and is called a prophage When host cell divides, prophage is replicated with it Leads to a population of infected cells Environmental trigger causes prophage to switch to the
lytic phase
Viruses capable of both types of reproducing are called temperate viruses
![Page 8: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/8.jpg)
![Page 9: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/9.jpg)
Retroviruses
Viruses that contain RNA instead of DNA and replicate unusually
Virus infects host cell, uses its own RNA to create complementary DNA (cDNA)
Reverse the usual flow of information from DNA to RNA This is why they are called retroviruses
Reverse transcription is made possible by an enzyme called reverse transcriptase
Newly made DNA integrates into a chromosome in the nucleus
The integrated viral DNA is called a provirus
![Page 10: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/10.jpg)
![Page 11: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/11.jpg)
Transduction
Phages carry bacterial genes from one host cell to another
There are two forms of transduction:
Generalized Transduction: moves random pieces of bacterial DNA as a cell is lysed by the phage and infects another (lytic cycle)
Restricted Transduction: moves specific pieces of DNA that were near the prophage site on the bacterial chromosome. Can only be done by a temperate phage.
![Page 12: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/12.jpg)
![Page 13: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/13.jpg)
Prions
Infectious proteins that can cause several brain diseases like “mad cow” disease in cattle
Prion is a misfolded version of a protein normally found in the brain
Causes normal proteins to misfold in same way Prions are not considered cells or viruses
![Page 14: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/14.jpg)
Bacteria
Chromosomes are circular, double-stranded DNA tightly packed into a nucleoid
A nucleoid has no nuclear membrane Bacteria replicate DNA in both directions from a single
origin of replication This is called theta replication
Reproduction: Conjugation: direct transfer of genetic material
between two bacterial cells that are temporarily connected
Binary Fission: asexual reproduction
![Page 15: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/15.jpg)
Plasmid: foreign, small, circular, self-replicating DNA molecule in a bacterium
A bacterium can have several plasmids
The first plasmid discovered is the F plasmid
F stands for fertility Bacteria that contain the plasmid are F+
Bacteria that do NOT contain the plasmid are F-
The F plasmid has the genes that produce pili Pili are cytoplasmic bridges that connect cells and
allow conjugation
![Page 16: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/16.jpg)
Another plasmid worth knowing is the R plasmid
Resistance to antibiotics for the host bacteria R plasmid can also be transferred from one bacteria
to another by conjugation Bacteria that have the R plasmid have a big
advantage because they are resistant to antibiotics Resistant bacteria are more likely to survive and
reproduce quickly This is bad news for doctors!
![Page 17: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/17.jpg)
The Operon Important to gene regulation Operon is a set of genes and “switches” that control the
expression of those genes Discovered in 1940’s by Jacob and Monod
Two types of operons:
Inducible: switched off until it is “induced” to turn on
Repressible: always on until it is not needed and becomes “repressed” (turned off)
![Page 18: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/18.jpg)
Tryptophan Operon
A repressible operon Continuously turned on unless turned off by a corepressor Repressor is encoded by the regulatory gene and is initially
inactive This means RNA polymerase is free to bind to the promoter
and transcribe the structural genes, producing tryptophan When the inactive repressor combines with the corepressor
(tryptophan) it changes its shape and binds to the operator, stopping transcription
If tryptophan levels are high, no more is needed, so the production is turned off
Tryptophan is an allosteric effector
![Page 19: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/19.jpg)
![Page 20: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/20.jpg)
![Page 21: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/21.jpg)
Lac Operon
Inducible Operon Turned off until it is “induced” to turn on
Repressor is initially active; binds to the operator located on the promoter, which blocks RNA polymerase from binding there, stopping production
Allolactose (derivative of lactose) acts as the inducer It binds to the repressor, changing its conformation (shape) Now that the shape has changed the repressor cannot bind
to the operator, which turns the operon on
![Page 22: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/22.jpg)
![Page 23: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/23.jpg)
![Page 24: Viruses and Bacteria Ch. 18. Viruses Parasite that requires a host cell in order to live They take the host cell hostage and use the cell to create the](https://reader036.vdocuments.site/reader036/viewer/2022062311/5a4d1b7a7f8b9ab0599b8976/html5/thumbnails/24.jpg)
Transposons Transposable genetic elements Also called “jumping genes” Discovered by Barbara McClintock
Two types:
Insertion sequences: made of only one gene, which codes for transposase, the enzyme responsible for moving the sequence from one place to another
Complex transposons: longer and include extra genes. One or more genes located between two insertion sequences