CHARACTERIZATION and CLASSIFICATION OF VIRUSES, VIROIDS AND PRIONS

1. Acellular

2. With nucleic acid- either DNA or RNA, but never both

3. With extracellular and intracellular state

4. Obligate intracellular parasite

Characteristics of Viruses

Virion

extracellular state

Capsid

a protein coat, surrounding a nucleic acid core

Nucleocapsid

nucleic acid and capsid

Envelope

a phospholipid membrane surrounding the nucleocapsid; provides both protection and recognition sites

VIRION

extracellular state

Nucleic acid

viral genome

Envelope

- phospholipid membrane

- for protection and recognition sites

Viruses

Are inert macromolecules outside of a cell , but become active inside a cell

Viruses

Do not divide to grow

Viruses

acellular

Viruses

Obligate intracelular parasites

Viruses

Contain either DNA or RNA, never both

Viruses

Genome can dsDNA, ssDNA, dsRNA, or ssRNA

Viruses

Ultramicroscopic in size, ranging from 10nm 30nm

Viruses

Have proteinaceous capsid around genome; some have na envelope around the capsid

Viruses

Replicate in an assembly-line manner using the enzymes and organelles of a host cell

Cells

Metabolize on their own

Cells

Divide and grow

Cells

Cellular

Cells

Most free-Iving

Cells

Contain both DNA and RNA

Cells

Genome is dsDNA

Cells

300 nm to 12cm in diameter

Cells

Surrounded by a phospholipid membrane and often a cell wall

Cells

Self-replicating by asexual and/or sexual means

Genetic material of viruses

Host of viruses

Sizes of Viruses

Capsid Morphology

Viral shapes

Viral envelope

Viruses differ in the following:

Genetic material of viruses

either DNA or RNA (the primary way in which scientist categorized and classify viruses)

e.g. dsDNA, ssRNA, ssDNA, dsRNA

Host of viruses

ALL types of organisms are susceptible

Specific- e.g. HIV virus specifically attacks helper T lymphocytes Generalists- e.g. Rabies virus, infects mammals from humans to bats

HIV virus

Specific- e.g ____specifically attacks helper T lymphocytes

Rabies virus

Generalists- e.g. ____, infects mammals from humans to bats

10 to 300 nm in diameter (400nm largest measurement)

Sizes of Viruses

1892, Dmitri Ivanowsky

(first account of plant viruses-TMV or Tobacco Mosaic Virus); Family: Solanaceae

1935, Wendell Stanley

isolated and characterized the TMV using microscope

Family: Solanaceae

What family does (TMV), Tobacco Mosaic virus belong?

10,000 nm in diameter

0-2500 nm

Red blood cell size

1000 nm x 3000 nm

0-375-750 nm

E. coli ( a bacterium) size

30 nm

Poliovirus size

24 nm

Bacteriophage MS2 size

25 nm

Bacterial ribosomes size

50 nm x 225 nm

Bacteriophage T4

200 nm x 300 nm

Small pox virus

15 nm x 300 nm

Tobacco mosaic virus

Capsid Morphology

- proteinaceous subunits called capsomeres (some capsomeres are composed only of a single type of protein)

- for protection and means of attachments

capsomeres

proteinaceous subunits called (some - are composed only of a single type of protein)

virions

The shapes of _ are also used to classify viruses

helical virus

capsomeres in spiral fashion forming a tube around the nucleic acid)

Polyhedral virus

roughly spherical; icosahedron (most common-with 20 sides)

Complex virus

with capsids of different shapes

small pox virus , rabies virus

examples of complex virus

Viral envelope

ALL viruses lack cell membrane. But some, particularly animal viruses, have a similar in composition to a cytoplasmic membrane surrounding their capsids.

animal viruses

have a similar in composition to a cytoplasmic membrane surrounding their capsids

enveloped viruses

a phospholipid bilayer &proteins (glycoproteins); which appear as spikes for recognition of host cells; acquires it from their host cell

International Committee on Taxonomy of Viruses (ICTV) 1966

was established to provide a single taxonomic scheme for viral classification and identification

Classification of Viruses

based on the type of nucleic acid, presence of envelope, shape and size

1) The Lytic Replication

2) The Lysogenic Repkication Cycle orLysogeny

Viral Replication

1) Attachment

2) Entry

3) Bacterial chromosome degraded

4) Synthesis

5) Assembly

6) Release

The Lytic Replication Cycle

The Lytic Replication Cycle Assembly

Replication of Animal Viruses

Shared by both RNA and DNA viruses

a) Direct penetration

b) Membrane fusion

c) Phagocytosis

The Three Mechanisms of Entry and Uncoating of Animal Viruse

Poliovirus and dengue virus

Example of direct penetration

measles and mumps virus

Example of membrane fusion

Adenoviruses and herpesviruses

Example of Phagocytosis or endocytosis

dsDNA

by RNA polymerase in (nucleus or cytoplasm of cel)

dsDNA

Each strand fo DNA serves as template for its complement (except for hepatitis B, which synthesizes RNA to act as thetemplate for new DNA)

ssDNA

By RNA polymerase in (nucleus of cell )

ssDNA

Complementary strand of DNA si synthesized to act as template

+ssRNA

Genome acts as mRNA

+ssRNA

RNA is synthesized to act as template

+ssRNA (Retroviridae)

DNA is synthesized from RNA by reverse transcriptase; mRNA is transcribed from DNA or RNA polymerase

+ssRNA (Retroviridae)

DNA

-ssRNA

By RNA-dependent RNA transcriptase

-ssRNA

-RNA (mRNA)

dsRNA

Positive strand fo genome acts as mRNA

dsRNA

Each stand of genome acts as template for its complement

budding

Because the host cell is not quickly lysed, _ allows an infected cell to remain alive for some time.

Budding

Release of Enveloped Animal Viruses is through

persistent infections

Infections with enveloped viruses in which host cells shed viruses slowly and relatively steadily are called

1. Exocytosis

2. Lysis

3. Death

Naked Animal Viruses are Released via:

latent viruses or proviruses

Chickenpox and herpes viruses, may remain dormant in cells in a process known as latency; the virus involved in latency is called

Latency

may be prolonged for years with no viral activity, signs and symptoms.

lysogeny

lysogenic

Though latency is similar to as seen with bacteriophages, there are differences.

Some latent viruses do not become incorporated in the chromosomes of their host cells, whereas _ phages always do.