VIRUS MEANS

“POISON”!

MADE OFPROTEIN ANDNUCLEIC ACID(EITHER DNA or

RNA)

Protein part isthe CAPSID

NA isinsidecapsid

Living or Not?They have

genetic material & structural proteins

BUT:

No RibosomesNo Organelles

No NucleusCan’t Use Energy

AND:

They CannotReproduce

on their own

SO:They are

NON-LIVING!

They arereferred to as

ObligateIntracellular

Parasites

They need aHOST CELLin order toreplicate.

They can beclassified3 Ways:

INTERESTINGSHAPES!

Polyhedron,Helical, Complex

Some are“enveloped”with a membrane-like structure

Their nucleicacid type:

Either DNA orRNA virus

DNA virus:DNA is inserted into

cell, then protein

synthesis using virus mRNA

OR, Virus DNAjoins host cell

DNA and replicates withhost cell DNA

RNA Virus:virus RNA isinserted into

host cell,makesproteins directly

OR, RNA retrovirus:

DNA, made by reverse

transcription, joins host DNA,

followedby protein synthesis

Classifiedby whether or not the virus

isdisease-causing

Virus can be“virulent”--causesdisease right away

(like a cold orflu)

If virulent,they undergo

theLYTIC CYCLE

Lytic Cycle:1)

Adsorption:virus

attachesto host cell

2) Entry:virus NA is

injected intohost cell

3) Replication:Host cell startsmaking virus

parts

4) Assembly:virus parts

getput together

5) Release:host cell gets so

full of new virusesthat it bursts,

releasing viruses

Virus can be“temperate”--waits

to cause diseaselater

(like HIV)

a) If temperate,virus goes intothe LYSOGENIC

CYCLE

b) LYSOGENICCYCLE:

Starts like lyticcycle with

adsorption & entry

c) Then,Attachment:

virus DNA joinswith host DNA

d) Replication:Host cell

undergoesreplication; virusDNA gets copied

e) Activation:something

triggers thevirus to becomevirulent (lytic)

Then,it startsthe LYTIC

CYCLE andcauses

infection (disease).

How are virusesspread?

Bodily fluidsThrough air, waterDirect contact

What is smaller than a virus?

Viroid--NA onlycause plant

diseases

Prion--smallstrand of aminoacids; mammal diseases like CWD or Mad Cow disease

How could youprevent viralinfections?

VaccinationsWash hands!Cover your mouth when sneezing or coughing!Safe sex!