Mirco: Chapter 13: Viruses, Viroids, and Prions

Obligatory intracellular parasites

(Viruses have this feature )They absolutely require living host cells in order to multiply

Viruses are entities that :

- contain a single type of nucleic acid, either DNA or RNA -Contain a protein coat (sometimes itself enclosed by an envelope of lipids, proteins, and carbohydrates ) that surrounds the nucleic acid -Multiply inside living cells by using synthesizing machinery of the cell -Causes the synthesis of specialized structures that can transfer the viral nucleic acid to other cells

temperate phages

Lysogentic phages able to proceed though a lytic cycle, but are also capable of incorporating their DNA into the host's DNA to begin lysogenic cycle

Polyhedral virus

Many animals, plants and bacterial viruses are polyhedral or many sided viruses The capsid of most of these are in the shape of an icosahedron , a regular polyhedral with 20 triangular faces and 12 corners the capsomeres of each face form an equilateral triangle Example: adenovirus or poliovirus

Capsid

Nucleic acid of virus is protected by this protein coat The structure of a capsid is determined by the viral nucleic acid and accounts for most of the mass of a virus, especially the small ones The protein coat of a virus that surrounds the nucleic acid can be helical or icosahedral/polyhedral(many sided)

Lysogenic cycle

Stages in viral development that result in the incorporation of viral DNA into host DNA host cell remain alive

Rabies Virus

Strand, one Strand of RNA 70-180 nm Rhabdovirdae Bullet shaped virus with spiked envelope; cases rabies and numerous animal diseases

Lytic Cycle: Maturation

Viral components are assembled into virions bacteriophage DNA and capsids are assembled into complete visions the viral components essentially assemble into viral particles spontaneously, eliminating the need for many nonstructural genes and gene products.

Non enveloped Viruses

Viruses whose capsids aren't covered by an envelope The capsid of a noneveloped virus protects the nucleic acid from nuclease enzymes in biological fluids and promotes the virus's attachment to susceptible host cells

hemaggulation

When viruses uses spikes to clump blood Such viruses bind to red blood cells and form bridges between them This results in clumping and is there basis for several useful lab test example : influenza does this

Chlamydia

elementary body 300 nm bacteria, unusual from structure

Virion

he complete, infective form of a virus outside a host cell, with a core of RNA or DNA and a capsid.

Ebola

internal hemorrhage, bleeding looks like a curled up worm 970 nm

Viroid

looks like rod 300X 10 nm

Virion

one; single particle/agent of virus Is a complete, fully developed, infectious viral particle composed of nucleic acid and surrounds by a protein coat outside a host cell

Specialized transduction

only certain bacterial genes can be transferred mediated by a lysogenic phage with packages bacterial DNA along with its own DNA i the same capsid When a prophage is excised from its host chromosome, it can take with it a bit of the adjacent DNA from the bacterial chromosome

Bacteriophage

phage=virus that infects bacteria/there are human, plant, animals, body parts, that have specific viruses for them/use as transportor/ transfer genes into viruses in hope that gene will go into human and help in cancer/ some good things with viruses 225 nm

Helical Virus

resembles long rods that may be rigid or flexible the viral nucleic acid is found within a hollow, cylinder capsid that has a helical structure the viruses that cause rabies and Ebola hemorrhage fever are helical viruses

What are the 5 stages of Lytic cycle?

Attachment Penetration Biosynthesis Maturation Release

Spikes on virus

Depending on the virus, envelopes may or may not be covered by these - which are carbohydrates-protein complexes that project from the surface of the envelope - Some viruses attach to host cells with spikes -Used as a means of identification -Example: Influenza uses spikes to clump blood

Adenoviridae

Double stranded DNA Non enveloped 70-90 nm Medium sized viruses that causes various respiratory infections in humans Some cause tumors in animals

Capsomere

Each capsid is composed of protein sub units In some viruses the proteins composing the capsomeres are of a single type; in other viruses several types of preteen may be present Arrangement of these depends on the particular virus A protein subunit of a viral capsid

Lytic cycle

Ends with the lysis and death of a host cell A mechanism of phage multiplication that results in the host cell lysis

An Enveloped helical virus

Example of enveloped helical virus: influenza Enveloped viruses are roughly spherical When helical or polyhedral viruses are enclosed by envelops they known as helical enveloped or enveloped polyhedral viruses examples of enveloped polyhedral: human herpes virus

Vaccinia virus

small pox was common until developed vaccine, say this virus is totally wiped form earth, though reservoir where it could exist but when you remove the reservoir you are eliminating the disease looks like a loaf of bread 300X200X100 nm

Lytic Cycle: Release

Host cell lyses, and new visions are released

Results from the Lysogenic cycle

1. lysogenic cells are immune to reinfection by the same phage 2. phage conversion: that is the host cell may exhibit new properties 3. specialized transduction possible

Specialized transduction steps

1. prophage exists in galactose-using host ( contain the gal gene) 2. Phage genome excises, carrying with it the adjacent gal gene 3. phage matures and cell lyses, releasing phage carrying gal gene 4. phage infects cell that cannot utilize gal 5. Along with the prophage the bacterial gal gene becomes integrated into the new host's DNA 6. Lysogenic cell can now metabolize gal

Human red blood cell ( size)

10,000 nm in diameter

E. Coli ( bacterium )

3000X 1000 nm

Virus

A submicroscopic, parasitic, filterable agent consisting of a nucleic acid surrounded by a protein coat

Viruses: Nucleic Acid

A virus can either have DNA or RNA- but never both -Nucleic acid of Virus can be single stranded or double stranded -Can be linear or circular

What are viruses called that infect bacteria ?

Bacteriophages or phages

Multiplication of Bacteriophages

Can multiply 2 alternative mechanism: the lytic cycle lysogenic cycle

Lytic Cycle: Biosynthesis

Phage DNA directs synthesis of viral components by the host cell Biosynthesis of viral nucleic acid and protein occurs Phage uses the host cell's nucleotides and several enzymes to synthesize many copies of phage DNA Transcription: specific early proteins transcribed and translated. Host cell provides amino acids, nucleotides, proteins needed by phage

Lytic Cycle: Attachment

Phages attach to the host cell Attachment some on viruses attaches to a complementary receptor site on the bacterial cell this attachment is a chemical interaction in which weak bonds are formed between the attachment and the receptor sites T- even bacteriophages use fibers at the ends of the tail as attachment sites the complimentary receptor sites are on the bacterial cell wall

Lytic Cycle: Penetration

Phages penetrates the host cell and injects its DNA After attachment, T-even injects the DNA (nucleic acid) into the bacterium. To do this: bacteriophage's tail releases an enzyme, phage lysozyme, which breaks down a portion of the bacterial cell wall During the process of penetration , the tail sheath of the page contracts, and the tail core is driven through the cell wall When tip of core reaches the plasma membrane the DNA from the bacteriophage's head passes through the rail core, though the plasma membrane , and enter the bacterial cell The phage particles function like a hypodermic syringe to inject the DNA into the bacterial cell

Function of the Capsid/Envelope

Protection from host enzymes and chemicals Binding/attachment & penetration into host cell Stimulates immune response

Bacteriophage (phage)

RNA or DNA but never both, can be double stranded or single stranded(uses either as genetic component/usually think of this as DNA, but in viruses they can use either for this job/can use RNA to directly make proteins, etc-all kinds of things) Nucleic acid surrounded by a protein coat called capsid together it is called a nucleocapsid (essential/basic part of every virus!) Multiply inside living cell and use host cell resources (every virus has very specif target/lock and key mechanism/strutctures on surface of virus will attch very specicially to cell, unless they are there, they cannot attach)

Picornaviridae

Rhinovirus nose, common cold, nasal cavity Single stranded RNA + stranded non enveloped 28-30nm

Complex viruses

Some viruses, particularly bacterial viruses , have complicated structures -Example: Bacteriophage Some Bacteriophage have capsids which additional structures are attached In the picture notice how the capsid head is polyhedral and the tail sheath is helical -head contain nucleic acid -Another example : poxviruses, which don't contain clearly identifiable capsids but don't have several coats around the nucleic acid

host range

The host range of a virus is the spectrum of the host cells the virus can infect Most viruses are able to infect specific types of cells of only one host species

Lysogeny

The phage remains late (inactive) the participating bacterial host cells are known as lysogenic cells