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