Viruses seen with an _________ only.
Viruses are _________ with no___________.
acellular with no membrane
Viruses are made of _______ and ___________.
nucleic acids and proteins-protected by a protein coat
Viruses have enzymes of the own and used for ____ and ______ the cell.
Entering and exiting the host cell- viral in origin
Known as ______ parasites
obligate parasites they have to gain entry into the cell and use the cell's machinery- outside the cell they are inert and can't do anything
The first virus discovered was _____________.
tobacco mosaic virus (TMV)
tobacco leaves exhibited a diseased state
- leaves showed mosaic or mottled coloration of leaves
Virus are measured in?
Adolf Mayer attributed the disease to?
unusually small bacteria- could not be seen with a microscope
Dmitri Ivanowsky filtered sap of diseased plants- he assumed he could isolate and remove bacteria causing disease but plants came down with symptoms again and he assumed that the disease was caused by _____ or _______.
very small bacteria or
toxins produced by bacteria through metabolism
Martinus Beijerinck showed through experiments that _________ did not cause the disease.
toxins infectious particles must be reproducing.
True or false. Beijerinck thought that the disease would diminish but it did not. There was no dilution.
What are the viroids?
small segments of RNA- cicular
True or false. All viruses are infectious acellular entities
Do viroids cause human disease?
No- disease in plants only
True or false.Prions are even smaller than viroids and cause disease in humans and plants.
tiny fragments of proteins
Prions are in out nervous system but they are mis-folded proteins and they cause _________.
normal proteins to become misfolded and causes disease and there is no cure for a prion disease
Who was the first to isolate TMV?
What is this virus?
bacteriophage-it only infects bacteria in human cells only
How do you classify viruses since they are always mutating and changing?
You classify by the type of nucleic acid- have RNA or DNA
The structure of nucleic acid- double or single stranded RNA or DNA not typical of a normal cell
Method of replication- lytic and lysogenic
-bacterial viruses (bacteriophage)
-most research done
-animal virses (most studied)
Chemical characteristics- protein can be all the same or all different
Physical characteristics- symmetry, size etc
What are viruses?
infectious agents too small to be seen with a light microscope- electron only
obligate intracellular parasites
contain only one type of nucleic acid
A view of the different sizes of viruses
Naked virus is the _________.
simplest virus- also known as nucleo capsid- the nucleic portion and the protein coat
Components of a viral particle
Nucleic acid and core
-either DNA or RNA not both
-have specific enzymes
Capsid- protein coat protects the virus from digestive enzymes or other things that can damage the virus
-determines the shape of the virus
-protects the nucleic acid
-makes up 50-80% of the biomass
-composed of protein
-arranged in a specific pattern
-form shape and size of virus
-Envelopes means that the coated with another coat and that coat comes from the plasma membrane from the host cell membrane. It is acquired as it exits the cell and it goes undetected because it registers as self
-made of glycoprotein
-helps viral particles attach to receptors on host cell surfaces or to be released from a host cell
- key and lock- HIV virus
Envelope is derived from and ________________.
the host cell and is acquired as it exits the host cell
immune system recognizes the envelope as self
contributes to overall viral shape- spherical
Spikes are ( see above image for picture of spikes)
spikes protrude from envelope
made of glycoprotein
allows viruses to attach to receptors on host cell
give host specificity
The capsid gives the virus its shape
What are the two types of viral morphologies?
image above of helical virus
helical-corresponds to rod shaped viruses/ the TMV has this shape
Polyhedral- corresponds to spherically shaped viruses/ HPV has this shape- picture above is HPV
What is this virus?
Viral replication: two types are-
the lysogenic cycle and lytic cycle
The lysogenic cycle:
host cell is not destroyed replicates normally but every time it replicates it also makes a copy of the viral chromosome and self- all the daughter cells have copy of own DNA or RNA and the viral copy
The lytic cycle
The host cell is destroyed
many copies made
releases 1000s of particles
The lysogenic cycle
The host cell is not destroyed
Viral infections in animals
Two mechanisms of viral internalization
-pinocytosis-cellular drinking /bring fluids into the cells from environment that can bring in bacteria
-fusion-enveloped viruses spikes and envelopes attach to a very specific type of cell
attachment and plasma membrane invaginates and discards envelope and is recoated if necessary
Can only find prions after __________.
a person's death when biopsy done and they can cause serious neurological disease
Prion diseases that affect humans
Creutzfeldt-Jakob syndrome (CJD)
Variant CJD (vCJD)
Fatal familial insomnia
Blue structures are protein and the pipsc is the mishapened protein that causes all normal proteins to misshape.