Diversity Of Microorganisms 1- Acellular

PART 1 Acellular Microbes: Virus, Viroids and Prions

Complete

virus

particles

are

called

virions. Size range from 10-300 nm in diameter. Virus could only be seen using an EM. Viruses can infect all organisms! Many human diseases are caused by viruses. Oncogenic viruses or oncoviruses caused specific types of cancer.

They

posses either DNA or RNA They are unable to replicate on their own They do not divide by binary fission, mitosis or meiosis They lack genes and enzymes necessary for energy production They depend on the ribosomes, enzymes, and metabolites

Genetic

Material- DNA or RNA Capsid– composed of capsomeres Envelope- composed of lipids and polysaccharides Some have tail, sheath and tail fibers

Type

of genetic material: DNA or RNA Shape of the capsid Number of capsomeres Size of the capsid Presence or absence of an envelope Type of host that it infects Type of disease it produces Target cells Immunologic or antigenic properties

One

theory states that viruses existed before cells. The other theory states that cells came first and that viruses represent ancient derivatives of degenerate cells or cell fragments

Family

names end in -viridae Genus names end in -virus Viral species: A group of viruses sharing the same genetic information and ecological niche (host). Common names are used for species Subspecies are designated by a number

 Herpesviridae-

Herpes virus, icosahedral, enveloped, DNA • HSV 1- orofacial

herpes • HSV 2- geniteal herpes • VZV- chicken pox and shingles

Retroviridae-

Retrovirus, RNA, helical, enveloped • Lentivirus- HIV

HIV

 Adenoviridae-

Adenovirus, icosahedral, nonenveloped, DNA • Human Adenovirus A- respiratory infections, conjunctivitis, gastroenteritis. • Viral encephaliltis and meningitis

 Picornaviridae-

Picornaviruses, icosahedral, RNA, and non-enveloped. • Poliovirus- causes

poliomyelitis • Coxscakie viruseshand, foot and mouth diseases • Echoviruses- nervous disorder

Coronaviridae-

coronavirus, helical, RNA and enveloped • SARS • Common colds • Gastroenteritis • Upper and lower respiratory tract infections

Three categories: Icosahedron bacteriophages- Almost spherical shape with 20 triangular facets Filamentous bacteriophages- long tubed form by a capsid proteins assembles into a gelical structure Complex bacteriophages- icosahedral heads attached to helicaltails

Complex Bacteriophage

Single

stranded DNA phages Double stranded DNA phages Single stranded RNA phages Double stranded RNA phages

LYTIC CYCLE  Attachment  Penetration

 Biosynthesis  Maturation  Release

Phage attaches by tail fibers to host cell Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell Production of phage DNA and proteins Assembly of phage particles Phage lysozyme breaks cell wall

Bacterial cell wall

Bacterial chromosome

Capsid

DNA Capsid

1 Attachment:

Phage attaches to host cell.

Sheath Tail fiber Base plate Pin Cell wall

Tail

Plasma membrane

2 Penetration:

Phage pnetrates host cell and injects its DNA.

Sheath contracted

Tail core

3

Figure 13.10.1

Tail DNA

4 Maturation:

Viral components are assembled into virions.

Capsid

5 Release:

Host cell lyses and new virions are released.

Tail fibers

The Lysogenic Cycle

Viruses

that infects human and animals. Some are DNA viruses; others RNA. May consist solely of nucleic acid surrounded by a protein coat or they maybe more complex.

Multiplication of Animal viruses  Attachment

Viruses attaches to cell membrane  Penetration By endocytosis or fusion  Uncoating By viral or host enzymes  Biosynthesis Production of nucleic acid and proteins  Maturation Nucleic acid and capsid proteins assemble  Release By budding (enveloped viruses) or rupture

Attachment, Penetration, and Uncoating

Figure 13.14

Release of an enveloped virus by budding

Multiplication of DNA Virus Papovavirus

1 Virion attaches to host cell

7 Virions are released

Host cell DNA Capsid

2

DNA Cytoplasm

6 Virions mature

Capsid proteins

mRNA

5 Late translation; capsid proteins are synthesized

4 Late transcription; DNA is replicated

3 Early transcription and

translation; enzymes are synthesized

Virion penetrates cell and its DNA is uncoated

Viral Infections Latent

Viral Infections • Virus remains in asymptomatic host cell for long periods • Cold sores, shingles Persistent Viral Infections • Disease processes occurs over a long period, generally fatal • Subacute sclerosing panencephalitis (measles virus)

Oncogenic Viruses Activated

oncogens transform normal cells into cancerous cells. Transformed cells have increased growth, loss of contact inhibition, tumor specific transplant and T antigens. The genetic material of oncogenic viruses becomes integrated into the host cell's DNA.

 Epstein-Barr

Viruscause of infectious mononucleosis (not a type of cancer), but also causes 3 types of cancer • Nasopharyngeal cancer • Burkitt’s Lymphoma • B-cell Lymphoma

 HBV

and HCV • Hepatocellular carcinoma  HSV 8 • Kaposi’s Sarcomatype of cancer common in AIDS patients.  HPV • Causes different kinds of cancer, including cervical cancer.

 Usually

transmitted via insects; mites; nematodes; infected seeds, cuttings and tubers; and contaminated tools.  Ex. TMV

Some Plant Viruses

Consists

of short, naked fragments of single stranded RNA. Can interfere with the metabolism of plant cells. Transmitted between plants. Ex: potato spindle tuber, citrus exocortis, diseases of chrysanthemums So far, no animal diseases have been discovered that are caused by viroids.

 Infectious

proteins  Inherited and transmissible by ingestion, transplant, & surgical instruments • PrPC, normal cellular

prion protein, on cell surface • PrPSc, scrapie protein, accumulate in brain cells forming plaques

Awarded:

1997 Nobel Prize for Medicine He coined the term “prion” He studied the role of prions in disease

 Fatal

spongiform encephalopathies:  Sheep scrapie  Creutzfeldt-Jakob Disease  Gerstmann-Sträussler-Scheinker Syndrome  Fatal familial insomnia in humans  Kuru