Chapter 19 Flashcards
What is a virus? (3)
an infectious particle made of genes in a protein coat
Cannot reproduce or metabolize outside a host cell
Lacks metabolic enzymes for making proteins
What are bacteriophages? (2)
viruses that infect bacteria
Phages that infect the same bacteria are often similar in structure
How big are viruses? (3)
About 20 nm in diameter
The largest ones can be 100 nm
Smaller than a ribosome
What are viruses made of? (3)
Genome
capsid
viral envelope
What is a capsid? (3)
protein shell that encloses the genome
Capsomeres- protein subunits making up capsid
Can carry viral enzymes
What are helical viruses?
a rod-shaped virus with capsid being arranged around the genome in a helix
What is a viral envelope? (2)
-a membranous envelope that surrounds the capsids and helps infect the host
Made from the membranes of the host cell’s phospholipid and membrane protein
What is a virus genome? (3)
Different virus possesses different genomes
Ranges from double-stranded DNA, single-stranded DNA, double-stranded RNA, etc.
Named either DNA or RNA virus based on the genome
What are obligate intracellular parasites?
parasites that can replicate only within a host cell
What is a host range? (4)
the amount of cells a particular virus can effect
A type of virus can only affect hosts the virus can recognize
Similar to a lock and key
Often limited to a particular tissue
Example- AIDS virus only bind to immune system cells
What are the steps for viral replication cycle? (6)
The virus enters the cell, uncoats, and releases viral DNA and capsid proteins
The host enzymes then replicate the viral genome
The host provides the virus with nucleotides, enzymes, ribosomes, tRNA, amino acids, ATP, and more
The host enzyme then transcribes the viral genome into viral mRNA
Host ribosomes then use viral mRNA to produce more capsid proteins
Viral genomes and capsid proteins self-assemble into new viruses, and leaves the cell
How does viral replication difer between RNA and DNA viruses?
DNA viruses use host DNA polymerase to synthesize new genomes along viral DNA
RNA viruses encode RNA polymerases into the cell and use RNA as a template
How doess a virus enter a cell? (4)
Depends on the type of virus and host cell
Some use tails to inject DNA
Others enter through endocytosis
Some fuse with the membrane
How can phages replicate? (2)
Lytic cycle
Lysogenic cycle
What is the lytic cycle?
A phage replicative cycle that results in the death of the host cell
What are virulent phages?
a phage that replicates only by a lytic cycle
What are the steps to the lytic cycle? (5)
The virus enters the cell, with the empty casing left outside
Phage DNA directs the production of phage protein and genome using the host cell’s materials
Proteins self-assemble into a virus
The phage then directs the production of enzymes that breaks down cell walls
Fluids enter and burst the cell
How does a bacteria defend against proteins? (3)
Natural selection favors mutations of surface proteins viruses cannot recognize
Restriction enzymes- enzymes that identify viral DNA and cut it up
Host DNA is methylated to prevent attacks
Why is the lysogenic cycle?
Phage replication that doesn’t kill host cells
What are temperate phages? (2)
phages capable of both lytic and lysogenic cycles
Cycle changes are triggered by environmental signals
What are the step to the lysogenic cycle? (5)
A virus enters the cell and either enters a lytic or lysogenic cycle
if it enters lytic cycle, it Immediately turns the host into a virus-producing factory and lyses immediately
If it enters a lysogenic cycle
Incorperates viral DNA into host chromosomes
Forms a prophage
Prevents transcription of other prophage genes
As the host cells divides, it replicates the viral DNA along with its own
How are animal viruses classified, and what do they possess? (3)
whether the genome is double or single-stranded
Single-stranded RNA are further classified into 3 classes
All animal viruses with RNA genomes have an envelope
What are viral glycoproteins?
proteins on viral envelopes that bind to specific receptor molecules on the host cell surface
How does an animal virus enter a cell? (9)
Capsid and viral genome enter the cell.
Cell enzymes digests the capsid which results in a release in viral genome
Viral genome functions as a template for RNA synthesis by a viral RNA polymerase
New copies of RNA are made
Template strand of viral RNA can function as mRNA
Translates capsid protein (in the cytosol) and glycoproteins (ER and Golgi)
Vesicles transport glycoproteins to plasma membrane
Capsid assembles arround viral genome molecules
Each new virus buds from the cell, envelope studded with synthesized glycoproteins embedded in the membrane
How do double-stranded DNA viruses replicate?
Replicate within the host cell nucleus to replicate and transcribe its DNA
Can leave behind viral DNA in the nucleus
Outside factors can trigger the viral DNA left behind to begin virus production
What are the classes of a single-stranded RNA virus? (3)
3 classes
4 and 5 have a path of RNA > RNA synthesis
Class 6 have a path of RNA > DNA
What is class 4 of single-stranded RNA viruses?
Virus genome can serve as mRNA and translate its protein immediately after infection
What is class 5 of single-stranded RNA viruses?
RNA genome serves as a template for mRNA synthesis
What are retroviruses? (2)
viruses equipped with reverse transcriptase
An enzyme that transcribes an RNA template into DNA
What is HIV?
Human immunodeficiency virus, a retrovirus that causes acquired immunodeficiency syndrome
How does HIV replicate? Part 1 (6)
Viral Envelope of glycoproteins enables virus to bind to receptors on white blood cells
Virus fuses with host’s membrane and capsid proteins are removed
Releases viral proteins and RNA
Reverse transcriptase catalyzes the synthesis of DNA complementary to viral RNA
Reverse transcriptase catalyzes the synthesis of a second DNA strand complementary to the first
Double stranded DNA is incorporated as a provirus into the cell’s DNA
How does HIV replicate? Part 2 (6)
Provirus never leaves the host’ genome
Proviral genes are transcribed into RNA molecules, serving as genomes for progeny viruses and as mRNAs for translation into viral proteins
Viral proteins include capsid protein and reverse transcriptase and envelope glycoproteins
Vesicles transport glycoprotein to the host cell’s plasma membrane
Capsids assemble in the host around viral genomes and reverse transcriptase molecules
New viruses with viral envelope glycoprotein bud from the host cell
When did viruses originate?
After the first cells appeared
What are plasmids? (4)
small, circular DNA found in bacteria
Candidate for original source of viral genome
Exists apart from and can replicated independently
from the bacterial chromosome
Transferred between cells
What are transposons? (2)
DNA segments that can move from one location to another within a cell’s genome
Other candidate for original viral genome
What are mobile genetic elements?
a feature of moving from cell to cell
What idea supports the evolution of viruses? (2)
Some viruses that are not closely related share similar traits
Arise from past viruses that were favored by natural selection
What is the mimivirus? (3)
large virus discovered that helps genes found in only cellular genomes
Either evolved before the first cell and formed an exploitative relationship
Or evolved recently and scavenged for genes from hosts
What is ds/DNA pandoravirus? (3)
largest virus discovered
Cannot be classified with other viruses
90% of its genes are related to cellular genes
How does a virus cause symptoms in animals? (3)
Viruses killing/ damaging cells causing lysosomes to release hydrolytic enzymes
Viruses causing infected cells to produce toxins that produce disease symptoms
Viruses containing toxic molecular component
What does the amount of damage a virus can do depend on?
The infected tissues ability to regenerate
What is a vaccine? (2)
harmless variant or derivative of a pathogen that stimulates the immune system to mount defenses against the harmful pathogen
Although vaccines can prevent diseases, not much can be done once infected
What is a cocktail? (2)
treatment of two nucleoside mimics and protease inhibitor
Interferes with an enzyme that assembles viruses
What is an emerging virus?
viruses that suddenly become apparent
Example- HIV, AIDS
What is a hemorrhagic fever?
often fatal illness causing fever, vomiting, bleeding, a circulatory system collapse
what is an epidemic?
widespread outbreak
What is a pandemic?
global epidemic
How do viral diseases emerge? (6)
Mutation of existing viruses
RNA viruses mutate easily because viral RNA does not proofread errors
Dissemination of a viral disease from a small, isolated human population
Spread of existing viruses from other animals
Can mutate as it passes from one host species to another
Two different strains of a viral disease can undergo ginetic recombination
What is influenza?
Viral diseases in three forms, A, B, and C
What is the B and C influenza?
only affect humans and have never caused an epidemic
What is type A influenza? (3)
affects a wide range of animals and caused four flue epidemics
Influenza A was named H1N1
Named after the two viral surface protein- hemagglutinin and neuraminidase
How do viruses spread in plants? (3)
horizontal transmission
vertical transmission
Once the virus enter’s the plant’s system, it can spread through plasmodesmata
What is horizontal transmission?
plant is infected from an external source of the virus
Ex- herbivores carrying diseases and breaking through the plant’s layers
What is vertical transmission?
plant inherits a viral infection from a parent
What are viroids? (3)
Circular RNA molecules that infects plants
Do not encode protein but replicate in plant cells
Cause error in the regulatory system and stunts growth
What are prions? (4)
Infectious proteins that causes degenerative brain disease
Acts very slowly, and have around 10+ years of incubation periods
Virtually indestructible
Infects by converting a healthy protein into misfolded versions
