AP Bio Viruses

What are two elements that nearly all animal viruses have?

1. can be composed of single stranded DNA/RNA, or double stranded DNA/RNA. 2. Many animal viruses have both an envelope and RNA genome

Steps of the Lytic cycle

1. phage attaches to host cell and injects its viral DNA 2. phage DNA circularizes 3. new phage DNA and proteins are synthesized and assembled into phages 4. cell lyses, releasing hundreds of phages

Steps of the lysogenic cycle

1. phage attaches to host cell and injects its viral DNA 2. phage DNA circularizes 3. phage DNA is integrated into the bacterial chromosome as a prophage 3. The bacterium reproduces normally, copying the prophage and transmitting it to daughter cells

What are three ways bacteria may win the battle against the phages?

1. restriction enzymes 2. natural selection favors bacterial mutants with receptors no longer recognized by a particular type of phage. 3. Instead of using up and killing host cells, some phages coexist with them in the lysogenic state.

What are two alarming characteristics of prions?

1. they act very slowly with an incubation period of at least 10 years before symptoms develop. This prevents sources of infection from being identified. 2. Virtually indestructible: not destroyed or deactivated by heat. No known cure.

9 steps of HIV infection

1. virus binds to certain WBC's 2. the viral envelope fuses with the cell's plasma membrane. Capsid proteins are removed, releasing viral proteins and RNA. 3. Reverse Transcriptase catalyzes the synthesis of a DNA strand complementary to the viral RNA 4. Reverse transcriptase catalyzes the synthesis of a second DNA strand complementary to the first 5. Double stranded DNA is incorporated as a provirus into cellular DNA 6. Proviral genes are transcribed into RNA molecules by host RNA pol. These serve as genomes for the next viral generation and as mRNAs for translation into viral protein. viral proteins include capsid proteins, reverse transcriptase, and envelope glycoproteins. 7. vesicles transport glycoproteins to the cells' plasma membrane 8. capsids are assembled around the viral genomes and reverse transcriptase molecules. 9. New viruses bud off from the host cell.

What are three ways that viruses make us ill?

1. viruses can damage or kill cells by causing the release of hydrolytic enzymes from lysosomes 2. can cause infected cells to produce toxins that lead to disease symptoms 3. Some have molecular components that are toxic.

What portion of a phage enters the host cell and how does it do this?

After phage uses tail fibers to bind to host sites, the sheath of the tail contracts, and DNA only is injected into the cell.

what is the host of a bacteriophage?

Bacteria

What are Transposons?

DNA segments that can move from one location to another within the cell's genome.

what is the role of an envelope in animal viruses?

Helps infect host.

what is meant by host range distinguish between a virus was abroad host range and one with an extremely limited host range and give an example for each

Host range is the variety of hosts of virus can infect. Those with a broad host range such as West Nile virus can infect many species while measles with a limited host range in only effective single species

What is a viroid?

Infectious nucleic acids that cause disease in plants. They are circular RNA molecules only a few hundred nucleotides long. Smaller than viruses: they don't encode proteins but can replicate in host plant cells using host cell enzymes. They cause errors in the regulatory systems that control plant growth.

What does H1N1 mean?

Influenza A version, made up of hemagglutinin (H) (helps virus attach to host cells) and neuraminidase (N) (enzyme that helps release new virus particles). H and N are both viral surface proteins, and there are many variations on them.

which components of a viral envelope are derived from the host cell?

Phospholipids, membrane protein

Compare and contrast a prophage and a provirus. Which one are you likely to carry?

Prophages are integrated viral DNA in host cell genome. Infects bacteria. Proviruses are integrated viral DNA into host cell's genome, in animals. I would carry this one

Capsid

Protein shell enclosing the viral genome, may be rod shaped, polyhedral, or more complex in shape, are composed of protein subunits called capsomeres

which components of a viral envelope are from viral origins?

Proteins, glycoproteins

Who made the model of how prions work?

Stanley pruisner

What was some early evidence of the existence of viruses? Why were they difficult to study?

Tobacco plants would fall ill from a virus before scientists knew they existed. They only had the technology to observe bacteria.

Distinguish between virtulent and temperate phages.

Virulent= phage that reproduces only by lytic cycle. Temperate= phage that can reproduce both ways.

What are restriction enzymes? What is their role in bacteria?r

When foreign phage DNA enters a bacterium, it is recognized as foreign and these cellular enzymes cut it up, restricting the ability of the phage to infect the bacterium.

What might trigger the switchover from lysogenic to lytic mode?

an environmental trigger (chemically or radiation) induced the prophage to exit bacterial chromosome & initiate a lytic cycle

what are the four forms of viral genome?

double-stranded DNA single-stranded DNA double-stranded RNA single-stranded RNA

What are emerging viruses?

existing viruses that mutate, spread more wildly in the current host species, or spread to a new host species.

what was Wendell Stanley's contribution to our knowledge of viruses?

he crystallized the tobacco mosaic virus

What components of the host cell does a virus use to reproduce itself?

host cell provides ATP, ribosomes, tRNA, and amino acids. Needs host enzymes to transcribe the viral genome into mRNA, which host ribosomes use to make more capsid proteins. Host enzymes also replicate the viral genome.

what property of a virus determines its attachment to a host cell?

if it has glycoproteins to match the ones on the host cell membrane

What are prions?

infectious proteins that cause degenerative brain diseases in animals. Prions are midfolded forms of a protein normally present in brain cells. when a prion encounters a normally folded version of the same protein, it induces it into the prions's abnormal shape. The resulting chain reaction: high levels of prion aggregation= cellular malfunction= eventual brain degeneration

how do most RNA viruses replicate their genomes?

it uses host virally encoded polymerases that use host RNA as a template

how does a DNA virus reproduce its genome?

it uses the host's DNA polymerase to make new DNA, using host's DNA as a template

Why don't restriction enzymes destroy the DNA of the bacterial cells that produce them?

phage DNA contains a modified form of cytosine that isn't recognized by restriction enzymes.

Horizontal Transmission in plants

plant is infected by external source. virus must get past outer layer, so plant is more susceptible if damaged by ind, injury, or herbivores. Herbivores can also carry & transmit the virus to the plant.

what are capsomeres?

protein subunits that make up the capsid

compare the host range for the rabies virus to that of the human cold virus

rabies is broad, while the cold only infects cells lining the upper respiratory tract of human

What is a retrovirus? How do they replicate their genome?

reverse transcriptase transcribes an RNA template into DNA. This is an RNA -> DNA info flow, the opposite of the normal direction.

How do viruses spread throughout plant bodies?

spreads through plasmodesmata, cytoplasmic connections that penetrate the walls between adjacent plant cells. Virally encoded proteins cause enlarging of plasmodesmata.

Why do we recover completely from a cold but not from polio?

the infection site of colds, the epilthelium of the respiratory tract, can efficiently repair itself and reproduce. Polio damages mature nerve cells, which can't repair themselves or reproduce so the damage is permanent.

What is a prophage?

the viral DNA integrated into the host cell's DNA. mostly silent within bacterium: one prophage gene silences others.

viruses are obligate intracellular parasites. what does this mean?

they can reproduce only within a host cell

What are vaccines and how do they work?

vaccines are harmless variants or derivatives of the pathogen. They stimulate the immune system to mount defenses against the harmful pathogen.