bio 205 chapter 13 powerpoint
TRANSCRIPT
![Page 1: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/1.jpg)
BIO 205
Chapter 13
![Page 2: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/2.jpg)
Viruses
![Page 3: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/3.jpg)
• Some capsid proteins are spikes that help the virus attach to and penetrate the host cell
• The nucleocapsid is the capsid with its enclosed genome
• The capsid is the protein coat, made up of capsomeres
• The viral genome contains either DNA or RNA, but not both
• They need a host eukaryote or prokaryote to replicate
• They lack the machinery for generating energy and large molecules
• Viruses are small, obligate intracellular parasites
Viruses Are Tiny Infectious Agents
What are Viruses?
![Page 4: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/4.jpg)
– A virion is a completely assembled, infectious virus outside its host cell
– Viruses surrounded by an envelope are enveloped viruses
– Naked viruses are composed only of a nucleocapsid
![Page 5: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/5.jpg)
Viruses Are Very SmallSize Relationships Among Microorganisms and Viruses
![Page 6: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/6.jpg)
• Viruses that have both helical and isocahedral symmetry have complex symmetry
• Isocahedral viruses have isocahedral symmetry
• Helical viruses have helical symmetry
Viruses Are Grouped by Their Shape
![Page 7: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/7.jpg)
Rabies
Helical Virus Herpes, Icosahedral Virus
Smallpox
Complex Virus
![Page 8: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/8.jpg)
• Many viruses infect certain cell or tissue types within the host (tissue tropism)
• Host range depends on capsid structure
• A host range refers to what organisms the virus can infect
Viruses Have a Host Range and Tissue Specificity
![Page 9: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/9.jpg)
• DNA viruses contain single- or double-stranded DNA genomes
• The International Committee on Taxonomy of Viruses (ICTV) is developing a classification system
• Viruses can be named according to a number of different conventions
Nomenclature and Classification Do Not Use Conventional Taxonomic Groups
The Classification of Viruses
![Page 10: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/10.jpg)
Retroviruses are replicated indirectly through a DNA intermediate
– strand RNA viruses have RNA strands that would be complementary to mRNA
+ strand RNA viruses have mRNA genomes
RNA viruses contain single- or double-stranded RNA genomes
![Page 11: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/11.jpg)
The phage nucleic acid contains only a few of the genes needed for viral synthesis and replication
T-even group bacteriophages are virulent viruses that carry out a lytic cycle of infection
The Replication of Bacteriophages Is a Five-Step Process
Viral Replication and its Control
![Page 12: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/12.jpg)
Bacteriophage
![Page 13: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/13.jpg)
Phase 5: Release is the exit of virions from the bacterium. It is also called the lysis stage when the cell is ruptured
Phase 4: Maturation is the assembly of viral parts into complete virus particles
Phase 3: Biosynthesis is the production of new phage genomes and capsid parts
Phase 2: Penetration occurs when the phage tail releases lysozyme to dissolve a portion of the cell wall. Phage DNA is injected into the bacterial cytoplasm
Phase 1: Attachment occurs when a phage’s tail fibers match with a receptor site on the bacterium’s cell wall
![Page 14: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/14.jpg)
They insert their DNA into the bacterial chromosome as a prophage (lysogenic cycle)
Temperate phages do not lyse the host
![Page 15: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/15.jpg)
Animal viruses attach to host plasma membrane via spikes on the capsid or envelope
Animal Virus Replication Has Similarities to Phage Replication
![Page 16: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/16.jpg)
• This occurs as some animal viruses enter the cell
• Uncoating is the separation of the capsid from the genome
• Animal viruses are usually taken into the cytoplasm as intact nucleocapsids
• Since receptor sites vary from person to person, some people are more susceptible to a certain virus than others
![Page 17: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/17.jpg)
The virus buds, taking the membrane part with it as an envelope
After the new viruses are assembled, envelope proteins are incorporated into a cellular membrane
![Page 18: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/18.jpg)
HIV
It can then be inserted into the host chromosome
Retroviruses use reverse transcriptase to transcribe their RNA to DNA
Some DNA viruses and retroviruses insert their genome into the host chromosome as a provirus
Some Animal Viruses Can Exist as Proviruses
Proviruses
![Page 19: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/19.jpg)
Eventually the provirus will be activated and replicate
They are propagated each time the cell’s chromosome is reproduced
Latent proviruses are immune to the host body’s defenses
It is in a state of latency
The provirus encodes a repressor protein that prevents activation of the viral genes necessary for replication
![Page 20: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/20.jpg)
• maturation/release
• genome replication
• viral penetration/uncoatingSome antivirals exist to affect:
Viruses lack the elements with which antibiotics interfere
Antibiotics do not work against viruses
Antiviral Drugs Can Be Used to Treat a Limited Number of Human Viral Diseases
![Page 21: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/21.jpg)
This prevents the release of new virions into the body
Neuraminidase inhibitors block an enzyme in the spike of influenzaviruses
Protease inhibitors impede the HIV protease that trims viral proteins in capsid construction
Reverse transcriptase inhibitors prevent the synthesis of DNA in retroviruses
• blocking replication of the viral genome
• inserting base analogs in the replicating DNA strand
Most antivirals target the replication enzymes of the virus by:
![Page 22: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/22.jpg)
• Cells in an antiviral state can inhibit viral replication by preventing protein synthesis
• Some IFNs have anti-cancer properties
• Interferon (IFN) is a group of naturally-produced proteins that alert cells to a viral infection
Interferon Puts Cells in an Antiviral State
Interferon
![Page 23: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/23.jpg)
IFNs bind to receptors on cells, triggering them to produce antiviral proteins
![Page 24: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/24.jpg)
Viruses and Virus-Like Agents
![Page 25: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/25.jpg)
• A malignant tumor
Tumor cells can break free from the capsule and spread to other tissues of the body (metastasis)
• A benign tumor
Normally, the body surrounds a tumor with a capsule of connective tissue
A tumor is a clone of abnormal cells
Cancer Is an Uncontrolled Growth and Spread of Cells
Cancer and Viruses
![Page 26: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/26.jpg)
• 60-90% of human cancers are associated with carcinogens.
• Viruses Are Responsible for up to 20 Percent of human Tumors.
![Page 27: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/27.jpg)
• There is now a vaccine against the 2 most common strains of HPV
• Human papilloma virus (HPV) is associated with cervical cancer
• Epstein-Barr virus is linked to Burkitt Lymphoma, a tumor of the jaw
Oncogenic viruses include:
![Page 28: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/28.jpg)
• viruses
• DNA damage
• chemical carcinogens
• radiation
They can be transformed to oncogenes by:
The oncogene theory suggests that protooncogenes normally reside in the chromosomal DNA of a cell
Oncogenic Viruses Transform Infected Cells
![Page 29: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/29.jpg)
The Oncogene Theory
![Page 30: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/30.jpg)
•The v-oncogene can then code of growth factors stimulating uncontrolled cell proliferation
•When the oncogenic viruses infect another cell, the v-oncogene is under the virus’ control not the cell’s control
•V-oncogenes are protooncogenes captured in the viral genome
•When virus replication is triggered, the provirus replicates its only DNA as well as a few adjacent host genes
•Sometimes a virus inserts its DNA (as a provirus) into a cell’s chromosome next to a protooncogene
![Page 31: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/31.jpg)
Oncogenic Virus
![Page 32: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/32.jpg)
• Mutation can occasionally be advantageous and create a new or new strain of virus
• Genetic recombination can lead to “new” viruses
• Emerging viruses may spread to new populations, or may expand host range
• Emerging Viruses Usually Arise Through Natural Phenomena
Emerging Viruses and Viral Evolution
![Page 33: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/33.jpg)
• One hypothesis suggests they originated as introns
• The replication cycle and disease causation process of viroids are not understood
• Viroids are tiny fragments of RNA that cause diseases in crop plants
Viroids Are Infectious RNA particles
Virus-Like Agents
![Page 34: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/34.jpg)
Stanley Prusiner discovered the proteinaceous infectious particle (prion)
Originally, scientists believed TSEs were caused by a virus
TSEs are neurologic degenerative diseases that can be transmitted within or between species
• For example, mad cow disease
Transmissible spongiform ecephalopathies (TSEs) can occur in humans and other animals
Prions Are Infectious Proteins
Prions
![Page 35: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/35.jpg)
Brain tissue showing effects of a prion disease
![Page 36: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/36.jpg)
• Abnormal prions do not trigger an immune response
• This causes normal prions to change shape and become abnormal
• TSEs may spread when infectious prions bind to normal prions.
• Normal cellular prions have a different shape than abnormal prions, the latter of which cause TSEs
• The protein-only hypothesis predicts that prions are composed only of protein and contain no nucleic acids
![Page 37: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/37.jpg)
This results from insoluble aggregates of abnormal prions in the brain
• loss of balance
• weakened muscles
• dementia
Symptoms include:
Death of the host occurs from nerve cell death leading to sponge-like holes in brain tissue
![Page 38: BIO 205 Chapter 13 Powerpoint](https://reader033.vdocuments.site/reader033/viewer/2022051108/546525e6af795988338b4c23/html5/thumbnails/38.jpg)
End of Chapter 13