A viral infection can produce symptoms by a number of dif routes. Viruses may damage or kill cells by causing teh release of hydrolytic enzymes from __.
lysosomes
Some viruses cause infected cells to produce toxins that lead to disese symptoms and some have molecular components that are toxic like __. How much damage a virus causes depends partly on the ability of the infected tissue to regenerate by cell division.
envelope proteins
The ___ is a complex and critical part of the body's natural defenses. It is also teh basis for the major medical tool for preventing viral infections- __, which is a harmless varient or derivative of a pathogen that stimulates the immune system to mount defenses against the harmful pathogen.
immune system
vaccine
Although vaccines can prevent certain viral illnesses, med tech can do little to cure most viral infections once they occur. Few enzymes that are encoded by viruses have provided targets for other drugs. Most antiviral drugs resemble __ and as a result interfere with viral nucleic acid synthesis.
nucleosides
Viruses that appear suddenly or are new to med scientists are often referred to as __.
emerging viruses
How do such viruses burst on the human scene, giving rise to harmful diseases that were previously rare or even unknown?
1- mutation of existing viruses
2- dissemination of a viral disease from a small, isolated human population
3- spread of existing viruses from other animals
general outbreaks of a disease
epidemic
a global epidemic
pandemic
The names H1N1 identifies which forms of two viral surface proteins are present: __ and __. There are 16 types of __ and 9 types of __, an enzyme that helps release new virus particles from infected cells.
hemagglutinin
neuraminidase
hemagglutinin
neuraminidase
True or False
Emerging viruses are generally not new; rather they are existing viruses that mutate, dissemintate more widely in the current host species, or spread to new host species. Changes in host behavior or environmental changes cn increase the viral traffic responsible for emerging diseases.
true
Viral diseases of plants spread by two major routes:
__- a plant that is infected from an external surce of the virus; because the invading virus must get past the plant's outer protecvtive layer of cells (epidermis) and becomes more susceptible to viral infections if it has been damaged by wind injury or herbs.
horizontal transmission
The second way plant viral disease spread are by:
__: a plant inherits a viral infection from a parent; asexual propagation or sexual reproduction via infected seeds
vertical transmission
Once a virus enters a plant cell and begins reproducing, vira genomes and associated proteins can spread throughout the plant by means of __, the cytoplasmic connections that penetratee the walls between adjacent plant cells.
plasmodesmata
As small and simple as viruses are, they dwarf another class of pathogens: __. these are circular RNA molecules, only a few hundred nucleotides long that infect plants; they dont encode proteins but can replicate in host plant cells, apprently by usuing host cell enzymes; they seem to cause errors in the regulatory systems that control plant growth and the typical signs of viroid disease are abnormal development and stunted growth.
viroid
An important lesson from __ is that a single molecule can be an infectius agent that spreads a disease; but they are nucleic acid.
viroids
There are infectious proteins, called __, which appear to cause a number of degenerative brain diseases in various animal species
prions
Two charcteristics of prions are alarming:
__ and __.
act very slowly with an incubation period of at least ten years before symptoms develop
virtuaaaally indestructable
how can a protein, which cannot replicate itself, be a transmissible pathogen?
they are misfolded forms of proteins normally present in brain cells; when they get into cells containing the normal form of the protein they somehow convery normal protein molecules into the misfolded prion versions
