Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of...

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Chapter 13-Viruses of Bacteria

Transcript of Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of...

Page 1: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Chapter 13-Viruses of Bacteria

Page 2: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

General Characteristics of all viruses

• Contain a single type of nucleic acid

• Contain a protein coat

• Obligate intracellular parasites

• Are viruses the only obligate intracellular parasites?

Page 3: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

History began with the Tobacco Mosaic Virus (TMV)

• 1886 Aldolf Mayer showed that a virus was transmissable between plants

• 1892 Iwanowski tried to isolate it by filtering with porcelain filter

Page 4: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Sizes of viruses

Page 5: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Polyhedral virus

• Capsid coat made of capsomeres

• Nucleic acid inside

Page 6: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Parts of a virus

Page 7: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Relationship of virus with host cell

Page 8: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Shapes of a virus

Page 9: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Bacterial viruses

• Known as bacteriophages or phages

• Two different life cycles1. Lytic cycle (virulent)-results in lysis of the

cell

2. Lysogenic cycle (temperate)-may result in lysis of the cell or the virus becomes a permanent part of the chromosome by integrating

Page 10: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

T4 phage replication

Page 11: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Lambda Phage

Page 12: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.
Page 13: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Lambda integrates into the chromosome

Page 14: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Properties conferred by prophage

Page 15: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Some phage are filamentous

Page 16: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Replication of filamentous phage

Page 17: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

M13 is ssDNA…how does it replicate the ssDNA?

Page 18: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Chapter 14: Animal Viruses

Page 19: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

How do animal viruses differ from bacterial viruses?

• Attachment

• Replication of nucleic acid

• Uncoating

• Exit by budding

Page 20: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Entry by membrane fusion

Page 21: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Entry by endocytosis

Page 22: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Replication of nucleic acid

Page 23: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Release by budding

Page 24: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Persistant infections

• Virus is continually present in the body, released by budding

• Three categories– Latent infections– Chronic infections– Slow infections

Page 25: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Latent Infections

• Persistant infection with symptomless period followed by reactivation of virus and symptoms

• Herpesviridae – Herpes simplex virus -1– Herpes simplex virus -2

Page 26: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Latent Viral infections

Page 27: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

DNA Animal Viruses

• Herpesviridae (dsDNA, enveloped virus)

-simplex 1(cold sores)

-simplex 2 (genital herpes)

-chicken pox, shingles

-epstein barr

Page 28: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Herpes Simplex virus-1

Page 29: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

HSV-1 reactivation

Page 30: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Herpes simplex-1

• HHV-1 causes fever blisters, HHV-2 genital herpes

• Symptoms: fluid filled skin lesions

• Treatment: Acyclovir

Page 31: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Varicella (chickenpox) and Herpes Zoster (Shingles)

• HHV-3 causes chicken pox and latent activation known as shingles

• Acquired by respiratory route, 2 weeks later see vesicles on skin

• Vaccine established in 1995 for chickenpox

Page 32: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Epstein Barr

• Causes infectious mononucleosis

• Acquire by saliva, incubation period is 4-7 weeks

• Identify by

-lobed lymphocytes

-heterophile antibodies

-fluorescent antibody tests

Page 33: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Chronic infections

• Infectious virus present at all times

• Disease may be present or absent

• Best example is Hepatitis Type B virus– Carriers produce virus detected in blood, saliva,

and semen– Unique replication of dsDNA

Page 34: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Chronic Viral infections

Page 35: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Hepadnaviridae

• dsDNA, enveloped• Hepatitis B

-passes through intermediate stage (RNA)-three particles in blood Danefilamentoussphericle-exposure through blood/body fluids

Page 36: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Hepatitis B

• Incubation period is ~12 weeks

• 10% of cases become chronic, mortality rate is less than 1%

• About 40% of the chronic cases die of liver cirrhosis

Page 37: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Slow Infections

• Infectious agent increases in amount over a long time during which there are no symptoms

• Examples are HIV found in the Retroviridae family

• Retroviruses use reverse transcriptase to replicate ssRNA

Page 38: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Retrovirus

Page 39: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Viruses and tumors

• dsDNA viruses are most common to cause viral-induced tumors

• Cancer is result of integration of viral genes into the host chromosome

• Transforming genes are called oncogenes

• Examples: papillomavirus, herpesvirus

Page 40: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Viruses associated with cancers

Page 41: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Viruses can alter their genome by reassortment

Page 42: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Orthomyxoviridae-multiple strands of (-)RNA

• Influenza virus– Consists of 8 segments of RNA– Envelope has H spikes (hemagglutinin) and N

spikes (neuraminidase)– Incubation is 1-3 days– Symptoms include: chills, fever, headache,

muscle aches, may lead to cold-like symptoms

Page 43: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Influenza virus

Page 44: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Ways to study viruses

• Since viruses grow in living cells….need a live cell to culture them– Cell culture/tissue culture– Embryonated chicken eggs

Page 45: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Cell Culture

Page 46: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Quantitation of viruses

Page 47: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Proteinaceous infectious particles: PRIONS

• 1982 Stanley Prusiner proposed that there were infectious proteins

• Caused the disease “scrapie” in sheep

• Caused the “mad-cow”disease in 1987

• Human forms suggest a genetic component

Page 48: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Prions

• Contain no nucleic acid

• Abnormal protein promotes conformational change to normal protein

• Results in damage to neurons…transmissable spongiform encephalopahthies

Page 49: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Brain with spongiform encephalopathy

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Infections caused by prions

Page 51: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Mechanism of prion replication

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Picornaviridae (+) ssRNA

• Hepatitis A

-obtain through fecal-oral route, enters GI tract and multiplies

-incubation period is ~4 weeks

-symptoms include: anorexia, malaise, nausea, diarrhea, abdominal discomfort, fever, and chills lasting 2-21 days

Page 53: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Rhabdoviridae (-)ssRNA, enveloped

• Rabies virus

-enters the skin and multiplies in skeletal muscle and connective tissue

-virus travels along nerves to the CNS causing encephalitis

Page 54: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Flaviviridae (+) ssRNA, enveloped

• Hepatitis C virus– Obtain from blood/body fluids– Incubation period averages 6 weeks– Hard to screen blood for the virus– 85% of all cases become chronic

Page 55: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Pathology of rabies

Page 56: Chapter 13-Viruses of Bacteria. General Characteristics of all viruses Contain a single type of nucleic acid Contain a protein coat Obligate intracellular.

Retroviridae-multiple strands of (-)RNA

• HIV

-infects Helper T cells

-requires the enzyme reverse transcriptase

-integrates as a provirus

-is released by budding, or lyses the cell