Acellular Pathogens

Question 1

What characteristics of life do viruses contain?

Answer 1

1) either an RNA or DNA genome that is surrounded by a protein coat (capsid)
2) phospholipid membrane that contains glycoproteins

Question 2

What characteristics of life do viruses lack?

Answer 2

1. cells, they are acellular pathogens that can infect all types of cells.
2. lack genes that are required for reproduction and metabolism

Question 3

What is a virion?

Answer 3

reproductive form of a virus that is made in the host cell

Question 4

What is a virion made of?

Answer 4

1. RNA or DNA genome
2. protein coat (capsid)
3. can be enveloped or non-enveloped (naked)

Question 5

What does host range mean?

Answer 5

the type of host cell that a virus can infect

Question 6

What determines host range?

Answer 6

whether a virus can attach to the surface of the host cell

Question 7

What is a capsid?

Answer 7

protein coat that surrounds the nucleic acid of a virus

Question 8

What are the capsid shapes found in viruses?

Answer 8

helical, polyhedral (icosahedral), or complex

Question 9

What is a helical capsid?

Answer 9

rod-shaped hollow tube, its interior looks like a helix

Question 10

What is a polyhedral (icosahedral) capsid?

Answer 10

it is three-dimensional and has many sides that are similar in shape. It has 20 sides and 12 vertices and looks similar to a soccer ball.

Question 11

What is a complex capsid?

Answer 11

it is not polyhedral or helical. It contains structures at its base that make it complex.

Question 12

What types of nucleic acids make up viral genomes?

Answer 12

1) made up of either DNA or RNA that can be single-stranded or double-stranded.
2) Their genomes can be segmented or nonsegmented.
3) RNA in the viral genome can be further classified into positive and negative strands.

Question 13

How are viral genomes different from Bacteria, Archaea and Eukarya?

Answer 13

They are different from Bacteria, Archaea, and Eukarya since each of them only contain double stranded DNA.

Question 14

What is a viral envelope?

Answer 14

phospholipid bilayer that contains glycoproteins, it surrounds the capsid of the virus

Question 15

What is a viral envelope made of?

Answer 15

phospholipid bilayer and glycoproteins

Question 16

Where does a viral envelope come from?

Answer 16

it is picked up by the virus and taken from the plasma membrane of the host cell when it buds off

Question 17

What are the steps of the bacteriophage lytic cycle?

Answer 17

1) Attachment: A bacteriophage attaches to a specific bacterial surface receptor on the host cell.
2) Penetration: the bacteriophage injects the viral genome into the host cell.
3) Biosynthesis: It replicates, transcribes and translates the viral components it needs to build new viruses
4) Assembly: the maturation phase where new virions are assembled
5) Lysis: the cell lyses to release the mature viruses out of the host cell. These new viruses then infect new cells and the lytic cycle repeats

Question 18

What are the steps of viral replication of animal viruses?

Answer 18

1) Attachment: Animal viruses bind to receptors on a host cell.
2) Penetration: receptor-mediated endocytosis of the virus, engulfing it in the cell. Enveloped viruses can also enter through membrane fusion between the membrane of the host cell and the viral envelope.
3) Uncoating: the envelope and protein coat of the virus get removed to expose the viral genome.
4) Biosynthesis: more parts are made to make new viruses
5) Assembly; Next, assembly occurs as new genomes are packaged into the capsid.
5) Release: the new viruses that are made bud off the cell and pick up the envelope. The viruses can also be released via lysis of the host cell.

Question 19

What is lysogeny?

Answer 19

Lysogeny is the process that occurs when a temperate phage infects a bacterium.
1) It begins with the attachment of the bacteriophage to the host cell and penetration as it injects its viral genome.
2) Later, the bacteriophage DNA is integrated into the bacterial chromosome. After this step, the integrated genome is called prophage.
3) Then, the bacterial cells divide, and the prophage DNA is passed on to the daughter cells.
4) When the cell is under stressful conditions, the prophage DNA pops back out (excised)
5) lytic cycle begins with biosynthesis, then assembly, and finally lysis.

Question 20

How is the replication cycle of HIV, a retrovirus, different than many other viruses?

Answer 20

HIV contains reverse transcriptase, a special enzyme in the capsid. Reverse transcriptase uses the positive single-stranded RNA genome as a template to produce a complementary single-stranded DNA copy. This single-stranded DNA is then made into double-stranded DNA that can become an integrated viral genome (provirus) that becomes a permanent part of the host cell. This allows the virus to stay in the host cell for a long time

Question 21

What is latency?

Answer 21

the process in which a virus can stay hidden or is dormant inside the cell.

Question 22

Why is latency important in certain cancers?

Answer 22

if a latent virus inserts itself in an important gene, it can trigger a path that leads to cancer
- ex: if it inserts itself in a tumor suppressor gene, the gene will not function anymore, and this could lead to cancer

Question 23

What is a viral titer?

Answer 23

the amount of virion particles per unit volume

Question 24

Why are viruses more difficult to study and identify in the lab?

Answer 24

1) they need a living host cell in order to replicate. They cannot be grown in pure culture by themselves.
2) It is also difficult to detect viruses.

Question 25

How have we gotten around the challenges that come with studying viruses?

Answer 25

1) There are many methods that can help get around these challenges. For example, tissue culture flasks, plates of bacterial lawns are grown with different amounts of virus, growing viruses in chicken eggs. All of these methods involve growing viruses and studying them as they culture with living host cells.
2) there are detection tests that allow people to identify viruses in the lab. For instance, nucleic acid amplification tests and enzyme immunoassays.

Question 26

How do NAAT detect viruses?

Answer 26

Nucleic acid amplification tests detect the nucleic acid sequences unique to viruses. An example of a NAAT is a polymerase chain reaction test (PCR). PCR uses primers that bind to specific sequences of viral DNA that enable us to identify a virus.

Question 27

How do EIAs detect viral infections?

Answer 27

Enzyme immunoassay uses antibodies to detect and attach to target antigens. They use these antibodies to test and see if a virus is present. If an antibody attaches to the antigen, the virus is present. However, if it does not attach to the antigen, the virus is not present.

Question 28

What are viroids?

Answer 28

made up of only a short strand of circular RNA that is able to self-replicate
- they do not have a protein coat to protect their RNA genome.

Question 29

What is an example of a viroid?

Answer 29

potato tuber spindle disease

Question 30

What are virusoids?

Answer 30

contain single-stranded RNA, but it is not capable of self-replicating. They need a specific helper virus to infect the host cell in order to replicate their RNA.
- its genome is small and only functions to replicate the RNA of the virusoid.

Question 31

What is an example of a virusoid?

Answer 31

hepatitis delta virus aka hepatitis delta virusoid

Question 32

What is a prion?

Answer 32

rogue misfolded proteins
- they can be infectious and cause other proteins to become misfolded

Question 33

How did the name TSE come about?

Answer 33

The name transmissible spongiform encephalopathy (TSE) came about because this disorder causes the brain to become sponge-like as the accumulation of the rogue proteins kills the brain cells and makes holes in the tissue. TSE can be hereditary, or it can be transmitted by consuming contaminated meat or coming in contact with tissue that is contaminated.

Question 34

What are some diseases caused by prions?

Answer 34

1. kuru
2. fatal familial insomnia
3. Creutzfeldt-Jakob disease.

Question 35

What treatments are available for diseases caused by prions?

Answer 35

Currently, there are no treatments available for them

Question 36

Why are prions extremely difficult to destroy?

Answer 36

they are very resistant to chemicals, radiation, and heat.

Question 37

What is the categorization of viruses based on?

Answer 37

1) Capsid shape
2) whether or not they have an envelope
3) what type of nucleic acid they contain
4) Host range

Question 38

What are glycoprotein spikes?

Answer 38

how they recognize and attach and get into its host cell, it determines whether or not the virus can infect the host cell

Question 39

What do tail fibers do?

Answer 39

it is how bacteriophages attach to the bacterial cell wall

Question 40

What does a sheath do?

Answer 40

it is the structure that bacteriophages use to shoot the viral genome into the bacterial cell

Question 41

What is positive strand RNA?

Answer 41

It can be directly translated into viral proteins

Question 42

What is negative strand RNA?

Answer 42

Needs to be copied to make a complimentary strand; copy into the positive strand so it can be translated