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Chapter 19: Viruses

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What are the four forms of viral genomes?
double stranded DNA, single stranded RNA, single stranded DNA, double stranded RNA
What is a capsid?
protein shell enclosing viral genome
capsids shape may be rod-shaped, polyhedral or more complex
What is a capsomere?
protein subunits that build capsids.
What are the components of the viral envelope?
1.Host cell phospholipids and membrane proteins derived from membranes of the host cell.

2. proteins and glycoprotiens derived from viral origin.
what is the role of the envelope in animal viruses?
glycoproteins which the cells of animals receive and allow entrance in membrane
What property of viruses determines its attachment to a host cell membrane?
glycoproteins. between viral surface proteins and specific receptor molecules on the outside of the cell
viruses are obligate intracellular parasites. what does this mean?
viruses have to function by invading and living in cells
what is meant by host range?
extra particular virus can infect cells of only a limited number of species.

ex: west nile has a broad host range... can infect insects, humans

ex: measles have limited host range.. can only affect humans
What components of the host cell does a virus use to reproduce itself?
nucleotides, enzymes, ribosomes, RNA, amino acids, and ATP
How does a DNA virus reproduce its genome?
DNA polymerase
How do most RNA viruses replicate their genome?
Virally encoded RNA polymerase
What are bacteriophages?
A virus that infects a BACTERIA
Distinguish between a virulent and temperate phages
V- replicates only by lytic cycle

T-uses lysogenic and lytic cycle to reproduce
What portion of a phage enters the host cell? how does it do this?
Binds glycoprotein to receptor of host cell DNA
What are restriction enzymes? How do they prevent viral infections of bacteria?
metholate DNA in a resistant/restrictive way
Why don't restriction enzymes destroy the DNA of the bacterial cells that produce them?
evolution. instead of lysing their host cells, many phages coesixt with them in a state called lysogeny
what are three ways bacteria may win the battle against the phages?
1. evolution
2. lysogeny
3. restriction enzymes
What is a prophage?
when integrated into the bacterial chromosome, the viral DNA is known as a prophage. one prophage gene codes for a protein that prevents transcriptions of most of the other prophage genes
Describe the lytic mode of bacteriophage reproduction
lytic cycle- phage replicative cycle that cumulates in death of the host cell. Each can infect healthy cell. LASt stage of infection
Describe the lysogenic mode of bacteriophage reproduction
lysogenic cycle- allows replication of the phage genome without destroying the host
what are 2 elements that nearly all animal viruses have?
1. RNA genome have an envelope
2. Replicate in host cells
What is a retrovirus?
equipped with an enzyme called reverse transcriptase which transcribes an RNA template into DNA, providing an RNA---> DNA information flow, opposite of the usual direction.
How does HIV replicate their genome?
After HIV enters the host cell, its reverse transcriptase molecules are released into the cytoplasm, where they catalyze synthesis of viral DNA. Newly made viral DNA then enters the cell nucleus and interprets into the DNA of a chromosome. Provirus never leaves cell.
Compare and contrast provirus and prophage
prophage leaves the cell. provirus never leaves the cell
Plasmids
small circular DNA molecules found in bacteria and yeast. Exist apart from cells genome replicate independently from genome transferred between cells
Transposons
DNA segments that move from one location to another within cells genome
What are 3 ways that viruses make us ill?
1. Damage/kill cells causing release of hydrolytic enzymes from lysosomes
2. cause infected cells to produce toxins
3. molecular components that are toxic, such as envelope proteins

provirus affects mature cells. cells don't divide and can't be replaced
What contribute to the sudden emergence of genes?
1. mutation of existing viruses
2. Solution is isolated in human population
3. Spread of existing viruses from other animals
Horizontal transmission
Plants infected from external source
vertical transmission
plants inherits viral infection from a parent
How do viruses spread throughout plant bodies?
plasmodestata-cytoplasm and connections that penetrate the walls between adjacent plant cells
What is a viroid?
plant pathogen consisting of a molecule of naked, circular RNA a few hundred nucleotides long. A single molecule can be an infectious agent that spreads a disease.

Ex: Mad cow
Prions
infectious proteins that cause brain disease in animal species transmitted through food


incubation period of at least ten years before symptoms develop virtually.