Ch. 6 - Acellular pathogens

What did the tobacco mosaic virus establish?

• Established that there were ultra microscopic pathogens

How was the size of the tobacco mosaic virus determined?

1. Ground leaf pulp put through filter with small 0.2 μm holes

2. Pulp still infected leaves; pathogen was smaller than 0.2 μm

What are characteristics of viruses? What are the 4 types of proteins?

• Acellular, made of nucleic acid wrapped in protein; dsDNA, ssDNA, dsRNA, ssRNA

What kind of parasites are viruses?

• Obligate intracellular parasites; not living

What is the size range of viruses?

• 0.1 nm to 1 μm (100s of nm)

What is the capsid on a virus? What are its 3 shape?

• Protein coat of virus

1. Helical,

2. Icosahedral

3. Envelope

What are naked viruses?

• Just nucleic acid wrapped in protein

What are enveloped viruses?

• Nucleic wrapped in protein + extra outermost layer of phospholipids taken from host cell membranes

Are naked or enveloped viruses harder to destroy?

• Naked viruses; harder to destroy (not the hardest)

What are the spikes on a virus? Function?

• Branching out structures; crucial to infect and attach to human cells

What is a bacteriophage?

• A virus parasitizing or eating specifically bacteria

How does the bacteriophage invade the host cell?

• Bacteriophage; attaches to host cell and injects or shoots down the cell

What is the host range?

• What organisms a pathogen is able to infect

What is a biological vector?

• Infectious agent carried within body of vector (pathogens inside animal)

mosquitos, ticks, arthropods

What is a mechanical vector?

• Carries infectious agent on its outer body

What is horizontal gene transfer?

• Transfer genetic traits or information from one bacteria to another

What two methods does horizontal gene transfer?

1. Conjugation pili

2. Transduction

What type of phages enter lytic cycle?

• Virulent phages

What are example of virulent phage?

• T-even phage; type of well studied bacteriophage

What occurs during the lytic cycle?

• Immediate lysis of host cell, destroying host

What is step 1 of the lytic cycle?

1. Attachment: phage (bacteriophage) attaches to host cell

What is step 2 of the lytic cycle?

2. Penetration: phage DNA enters host cell

What is step 3 of the lytic cycle?

3. Biosynthesis: phage DNA replicates and proteins made

What is step 4 of lytic cycle?

4. Maturation: new phage particles assembled

What is step 5 of lytic cell?

5. Lysis: cell lyses releasing phages

What cycles does the temperate phage enter?

• Enters lytic and lysogenic cycles

What occurs to the host cell in the lysogenic cycle?

• Does not immediately lyse

What is the first step of the lysogenic cycle?

1. Phage infects cell

What is the second step of the lysogenic cycle?

2. Integrates viral genome into host

What is the third step of the lysogenic cycle?

3. Cell divides ange phage is passed on to daughter cells

What is the fourth step of the lysogenic cycle?

4. Under stress; prophage enters lytic cycle

What is the fifth step of the lysogenic cycle?

5. Phage begins biosynthesis, maturation, lysis