Ch 13 Viruses
Briefly describe the multiplication phase of the life cycle of viruses.
1) synthesis of viral molecules - virus induces degradation of host cell DNA 2) Replication of viral DNA using host DNA polymerase 3) Transcription of viral genes using host RNA polymerase 4) Translation of viral mRNA using host ribosomes
Structures of viruses
1)Nucleic acid - DNA or RNA organized into genes 2)Capsid - protein coat of virus Capsomeres - protein subunits that make up the capsid 3)Envelope - lipid bilayer surrounding capsid Present in some viruses 4)Spikes (or spike proteins) - proteins embedded in envelope
General Characteristics of Viruses
1)Obligatory intracellular parasites 2)Require living host cells to multiply 3)Contain DNA or RNA - Never both 4)Contain a protein coat 5)No ribosomes 6)No ATP-generating mechanism 7) Size - ultramicroscopic - most viruses are smaller than 0.2 microns (200 nm) 8) Cannot reproduce outside of cells
capsid shapes
1. polyhedral- many-sided 2. helical - hollow, cylindrical capsid 3. complex - complicated structures
lysogenic phage
A change in bacterial phenotype due to expression of genes transferred to bacteria by _______________phage
A) all are derived from the host cell
Bacteriophages derive all of the following from the host cell EXCEPT A) All of the following are derived from the host cell B) tRNA. C) Amino acids. D) Nucleotides. E) A.T.P.
1) bacterium stops synthesizing its own molecules and switches to synthesis of viral molecules - virus induces degradation of host cell DNA 2) Replication of viral DNA using host DNA polymerase 3) Transcription of viral genes using host RNA polymerase 4) Translation of viral mRNA using host ribosomes, tRNA
Briefly describe the multiplication (replication) phase of the life cycle of viruses.
1. Attachment - same as in lytic cycle 2. Penetration - same as in lytic cycle 3. During lysogenic cycle, new virus is not replicated. Instead, the viral DNA becomes part of host cell chromosome The inserted viral DNA is referred to as prophage Prophage is copied along with rest of the chromosomal DNA during the normal cell cycle No new virus are replicated Virus lies dormant and sometimes is referred to as silent infection
Describe lysogenic viral life cycle of bacteriophage.
Viruses absolutely require living host cells in which to multiply They multiply inside host cells using the machinery of the cell
Explain what is meant by obligate intracellular parasite.
a means by which genes for antibiotic resistance and toxins can be spread between bacteria.
Explain what occurs during transduction (as a means of genetic transfer between bacteria).
viruses are not composed of cells
How do viruses differ from bacteria?
lysogeny
Phage DNA is incorporated into host cell DNA.
envelope
Some viruses are also enclosed by an _____________
non lysogenized strain does not alter the phenotype of the host streptococcal cel
Streptococcus pyogenes, that has been infected by a lysogenic phage, can produce the erythrogenic toxin that causes scarlet fever. Non-lysogenized S. pyogenes cannot produce the toxin. Why can the lysogenized strain of S. pyogenes produce the toxin while the non-lysogenized strain cannot?
Budding
The mechanism whereby an enveloped virus leaves a host cell is called
host range
The spectrum (or range) of host cells a virus can infect
specialized transduction
Transduction by lysogenic virus
Transduction
Transfer of bacterial DNA between cells by a virus
True
True or False Viruses cannot reproduce outside of cells.
false
True or False: Viruses use their own catabolic enzymes.
replication of viral DNA
Viral DNA is copied using host cell DNA polymerase, host nucleotides, host ATP
E) It causes lysis of host cells.
Which of the following statements is NOT true of lysogeny? A) It can give infected pathogens the genetic information for toxin production. B) Prophage is inserted into the host genome. C) Lytic cycle may follow lysogeny. D) It is a "silent" infection; the virus does not replicate. E) It causes lysis of host cells.
1) Attachment: phage attaches by tail fibers to host cell 2) Penetration: phage lysozyme opens cell wall; tail sheath contracts to force tail core and DNA into cell 3)Biosynthesis: production of phage DNA and proteins 4) Assembly/Maturation: assembly of phage particles 5)Release: phage lysozyme breaks cell wall. Release of mature virus results in death of host cell
*what are the steps of the lytic cycle*?
Lysogenic cycle
-also called temperate phage -No new virus replicated -Viral DNA incorporated in host DNA (now called prophage) -Does not result in death of host cell (it's dormant)
characteristics of helminths
-heterotrophic -multicellular animals -composed of eukaryotic cells -some have female an male reproductive organs
Platyhelminths
another name for (flatworms)
Tremotoda (flukes)
another name for flukes
Nematodes
another name for roundworms
Cestoda
another name for tapeworms
In prokaryotes, the processes of transcription and translation occur simultaneously in the________________
cytoplasm
helical - appears rod shaped when viewed under EM polyhedral - many sided (icosahedral (20-sided) most common) complex - complicated structures ex. bacteriophages (bacterial viruses) enveloped - appear roughly spherical - envelope surrounds either helical or polyhedral viruses Enveloped viruses are mostly animal viruses
morphology of viruses
transformation
naked DNA from dead or lysed bacteria is transferred to recipient cell
cytoplasmic bridge that connects 2 cells
role of pilus in conjugation
lytic and lysogenic
the 2 cycles for bacteriophage in viruses
phage conversion
the host cell exhibits new properties
generalized transduction
transduction by lytic virus
Transcription of viral DNA
uses host RNA polymerase, host nucleotides, host ATP and produces viral mRNA
Translation of viral mRNA
uses host ribosomes, host tRNA, host amino acids, host ATP and produces viral proteins
Bacteriophages (or phage)
viruses that infect bacteria
gram -
what type of bacteria uses a pilus during conjugation?
lysogenic conversion
when the phage genes carried in the bacterial chromosome cause production of viral toxins or enzymes by the bacterial cells. These toxins and enzymes can cause pathology in humans infected by these bacteria. These bacteria have new traits due to the presence of prophage
prophage
•Inserted phage DNA is known as a ___________
function of capsid/envelope
•Protects nucleic acid when virus is outside host cell •Serves important roles in binding to and penetration of host cell •Proteins in capsid and envelope stimulate production of antibodies •Determines shape of virus particle
lytic cycle
•also called virulent phage •Replicates new virus •Results in lysis and death of host cell
