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Definition
completely dependent on host cells and cannot replicate unless they are in the hosts cell
not cells made up of cells, not organisms
cannot manufacture their own ATP, amino acids, nucleic acids, proteins
enter a host cell take over its biosynthetic machinery and use it to make new generation of virus
each type infects a specific unicellular species or cell type |
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| virus that infects bacteria |
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affect T cells and macrophages (part of immune system)
If HIV succeeds in infecting a cell and reproducing, the cell dies and new particles break out to infect more cells
Body cont replaces T cells and macrophages, but it can’t keep up with HIV
T cell count drops, so immune system is susceptible to disease |
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viruses grow in culture or harvest from a host…isolate by passing through a filter
expose uninfected host cells to this filtrate
isolate and infect to confirm that it is causative agent of infection |
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Definition
| enclosed by a shell of protein |
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| enclosed by a shell of protein and membrane-like structure |
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| nonenveloped consist of genetic material and poss one or more enzyme inside a capsid- protein coat |
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| All infect via replicative growth or in dorm form called latency (animal) or lysogeny (baceteriophage) |
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| viral infection cycle in six steps |
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Definition
| (1) entry into a host cell, (2) production of viral proteins, (3) replication of the viral genome, (4) assembly of a new generation of virus particles, (5) exit from the infected cell, and (6) transmission to a new host |
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| In terms of diversity, the key feature of viruses is _______ |
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| the nature of their genetic material. The genomes of viruses may consist of double-stranded DNA, single-stranded DNA, double-stranded RNA, or one of several types of single-stranded RNA |
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| The first step in studying a virus is ________ |
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Definition
| to isolate it. Researchers use Koch's postulates to isolate a virus and confirm that it is the causative agent of infection. |
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| viruses infect their host cells in one of two ways: ________ |
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Definition
| via replicative growth or in a dormant form called latency in animal viruses or lysogeny in bacteriophages |
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| viruses infect their host cells in one of two ways: ________ |
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Definition
| via replicative growth or in a dormant form called latency in animal viruses or lysogeny in bacteriophages |
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| in the lytic replication cycle, _______ |
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Definition
| viral particles are made and released from the cell, usually killing the host cell in the process |
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| In the lysogenic replication cycle, _______ |
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Definition
| viral DNA becomes integrated into the host's chromosome and copies of the viral genome are transmitted to daughter cells of the host. In the lysogenic or latent state, the virus is quiescent and no new particles are being made |
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| The replication cycle of a virus begins when _______ |
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Definition
| a free viral particle enters a target cell |
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| when the genome of a nonenveloped virus enters the host cell, ______ |
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Definition
| a portion of the capsid seals the hole and the remainder of the capsid remains on the cell wall or plasma membrane. |
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| HIV particles can enter cells only if ________ |
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Definition
| the virions bind to a membrane protein called CD4 and a co–receptor |
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| when enveloped viruses bind to a host cell, ________ |
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Definition
| the capsid enters the cell |
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| when the proteins in a virion's envelope bind to both CD4 and a co–receptor, ________ |
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Definition
| the lipid bilayers of the particle's envelope and the plasma membrane of the helper T cell fuse |
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| mRNAs that code for proteins that make up the capsid or inner core of the viral particle are translated by ribosomes in the cytoplasm. The resulting polypeptides are cut into functional proteins by a viral protease |
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Definition
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| Most RNA viruses use a viral enzyme called RNA replicase. RNA replicase is an RNA polymerase that synthesizes RNA from an RNA template. |
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| In other RNA viruses, the genome is transcribed from RNA to DNA by a viral reverse transcriptase. |
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Definition
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| nveloped viruses bud from a cell through the cell membrane. They take part of the cell membrane with them, including envelope proteins that were inserted into the membrane |
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| Nonenveloped viruses burst out of the cell. These viruses can infect host cells that have a cell wall and exit by enzymatically degrading the cell wall |
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Definition
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| In positive–sense viruses, the genome contains the same sequences as the mRNA required to produce viral proteins. |
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Definition
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| In negative–sense viruses, the base sequences in the genome are complementary to those in viral mRNAs. |
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| Ambisense viruses contain both positive– and negative–sense sections. |
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| escaped–genes hypothesis states that viruses descended from clusters of genes that physically escaped from bacterial or eukaryotic chromosomes long ago. |
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| he degeneration hypothesis suggests that organisms gradually degenerated into viruses by slowly losing the genes required to synthesize ATP, nucleic acids, amino acids, and other compounds. |
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ouble–Stranded DNA (dsDNA) Viruses
The dsDNA viruses have a single molecule of double–stranded DNA.
Viral genes must enter the nucleus to be replicated, so they can infect only cells that are actively dividing. |
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RNA Reverse–Transcribing Viruses (Retroviruses)
The genomes of the RNA reverse–transcribing viruses are composed of single–stranded RNA.
Virus particles are diploid, with two copies of their single–stranded RNA genome.
The retroviruses only infect vertebrates – birds, fish, and mammals.
Retroviruses contain reverse transcriptase. The enzyme synthesizes a viral cDNA that is then made double–stranded. Integrase catalyzes the integration of the viral genes into the host chromosome. |
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Double–Stranded RNA (dsRNA) Viruses
These viruses typically have a genome usually consisting of multiple double–stranded RNA molecules.
Once in the host cell, the double–stranded genome is a template for synthesis of single–stranded viral RNAs, which are then translated into viral proteins.
Copies of the genome are created when a viral enzyme makes the single–stranded RNA double stranded. |
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Negative–Sense Single–Stranded RNA ([–]ssRNA) Viruses
The single–stranded genome of these viruses is complementary to the viral mRNA.
Once in a host cell, a viral RNA polymerase uses the negative–sense template to make viral mRNAs. The viral mRNAs are then translated to form viral proteins and new negative–sense single–stranded RNA. |
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Definition
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Positive–Sense Single–Stranded RNA ([+]ssRNA) Viruses
Because the sequence of bases in a positive–sense RNA virus is the same as mRNA, it does not need to be transcribed before proteins are produced. |
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Definition
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| Viruses use cells to produce new generations of viruses. |
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Definition
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| Vaccines contain antigens that stimulate immune system cells and "prime" the immune system for a subsequent infection with a particular virus. |
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| The genome is integrated into the host chromosome during lysogenic growth |
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| iruses must somehow bypass both the cell membrane and cell wall (if present) to enter a cell and replicate. |
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| Which of the following molecules provided by the host cell is required for all viral replication? |
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| Viral mRNAs are translated by ribosomes attached to the rough ER |
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| Reverse transcriptase is not a normal part of a human cell's biosynthetic machinery. |
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