MicroLecE3Ch13

Question 1

Characteristics of Viruses

Answer 1

• Contain DNA or RNA
• Protein coat
• Some have envelope
• Some have spikes
• Most infect only specific types of cells in one host

Question 2

Host Range

Answer 2

Determined by specific host attachment sites and cellular factors

Question 3

Viron Structure

Answer 3

• Genetic info (DNA or RNA)

- Protein coat (capsomere)

Question 4

Viron

Answer 4

Complete infectious particle and all the parts it needs to be so

Question 5

Capsid

Answer 5

Entire coating of capsomeres + nucleic acid

Question 6

Virus Morphology

Answer 6

1) Helical
2) Polyhedral
3) Enveloped
4) Complex

Question 7

Helical virus

Answer 7

Long string and nucleic acids wrapped around it w/the capsomeres on the outside. Forms a helical, tube structure
- Ebola

Question 8

Polyhedral virus

Answer 8

Looks like soccer ball. Capsomeres make a polyhedral soccer ball shape w/nucleic acid stuffed inside
- Mastadenovirus (also has spikes)

Question 9

Enveloped virus

Answer 9

Whether helical or polyhedral, have an envelope. Envelope does not always have spikes. Most common in human viruses
- Influenza virus (helical w/envelope), Herpes virus (polyhedral w/envelope)

Question 10

Complex virus

Answer 10

If not helical or polyhedral, considered complex virus. Most common is the bacteriophage
- Orthopox virus

Question 11

Growing and Culturing viruses

Answer 11

1) On agar plate w/bacteria on it. Bacteriophages form plaques on a lawn of bacteria. Viruses must be grown in living cells
2) Animal viruses grown in living animals or embryonated eggs
3) Animal and plant viruses grown in cell culture like human tissue cells

Question 12

Virus Identification

Answer 12

1) Cytopathic effects (CPE): cells start to look strange after being infected by a virus, CPE is looking at whether cells look normal or abnormal
2) Serological tests. Serum will be tested for antibodies against viruses
3) Nucleic Acids (PCR)

Question 13

Lytic Cycle

Answer 13

1) Attachment: phage attaches by tail fibers to host cell
2) Penetration: phage lysozyme opens cell wall; tail sheath contracts to force tail core and DNA into cell. Virus itself does not enter cell, just injects its genetic info
3) Biosynthesis: production of phage DNA and proteins. Once genetic info enters cell, takes over cell and uses it to replicate virus. Makes all components necessary for the viron
4) Maturation: assembly of phage particles. Putting together all components to make mature virons
5) Release: phage lysozyme breaks cell wall. Massive release of virus that is detectable

Question 14

One-Step/Acute Viral Infection

Answer 14

Happens during Step 5 Release when virus breaks out of human cell killing it and there is a lot of detectable virus

Question 15

Lysogenic Cycle

Answer 15

• Virus can choose to pause before Step 3 Biosynthesis until it is triggered
  1) Immune to reinfection: virus combines its genetic info w/host cell DNA
  2) Phage conversion. Can give host cell different attributes
  3) Specialized Transduction: virus takes specific genes from a host cell w/it each time it infects a new host cell

Question 16

Differences btwn Lytic Cycle and Lysogenic Cycle

Answer 16

• Lytic cycle, phage causes lysis and death of host cell
• Lysogenic cycle, virus cells are latent
• Viruses can go from Lysogenic cycle to Lytic cycle at any time

Question 17

Generalized Transduction

Answer 17

Virus is not taking specific genes from host cell when it leaves to infect a new host cell, it is just by accident

Question 18

Specialized Transduction

Answer 18

Virus, every time it leaves a host cell, is taking specific genes from the host cell with it

Question 19

Animal Virus Multiplication

Answer 19

• Pathogens that infect humans
• Most have an envelope and an extra step called Uncoating
• Virus actually penetrates into the cell, not just inject its genetic info
  1) Attachment: virus attaches to cell membrane
  2) Penetration: by endocytosis or fusion
  3) Uncoating: by viral or host enzymes. Virus loses its envelope so the capsid can undergo biosynthesis
  4) Biosynthesis: production of nucleic acids and proteins
  5) Maturation: assembly of nucleic acid and capsid proteins
  5) Release: by budding (enveloped viruses) or rupture. Virus lost its envelope after Step 3 Uncoating but needs an envelope again to exit host cell. Uses host cell’s plasma membrane – buds off and takes host cell’s plasma membrane as its envelope

Question 20

Types of Penetration

Answer 20

1) Pinocytosis: triggers human cell to allow it entrance where it then invaginates into the human cell
2) Fusion: fuse viral envelope w/human plasma membrane b/c they are both phospholipid bilayers. Becomes absorbed

Question 21

Multiplication of a Retrovirus

Answer 21

• Retroviruses are RNA viruses, but get converted into a DNA version in the cell and inserted into the chromosome
• Human cells do not have an enzyme to go from RNA to DNA (can only go from DNA to RNA), so the virus must carry its own enzyme – Reverse Transcriptase
• Important b/c if Reverse Transcriptase can be removed from a retrovirus, the virus is dead and cannot replicate (Ex: HIV fighting drugs do this)

Question 22

Cancer

Answer 22

Cell loses its ability to do. Can happen by Spontaneous or Induced mutations or Viruses

Question 23

Oncogenes

Answer 23

If activated, transform normal cells into cancerous cells. Control cellular growth. If infected by a virus, can lead to cancer

Question 24

Transformed Cells

Answer 24

Increased growth, loss of contact inhibition, tumor-specific transplant antigens and T antigens

Question 25

Viral Infections

Answer 25

1) Acute: like flu
2) Persistent: disease processes occur over long period, generally fatal. Has initial acute infection and then slowly increases and causes signs & symptoms. Unlike latent, it is detectable (Ex: HIV)
3) Latent: virus remains in asymptomatic host cell for long periods (aka Lysogenic cells). Always an acute phase before becoming undetectable (Exs: cold sores, shingles)

Question 26

Prions Characteristics

Answer 26

• Inherited and transmittable by ingestion, transplant, surgical instruments
• Spongiform encephalopathies
• PrPC: normal cellular prion protein, on cell surface
• PrPSc: scrapie protein, accumulates in brain cells forming plaques

Question 27

Prions Replication

Answer 27

Prions mis-fold other proteins causing them to die and get cleared, leaving a hole called an amyloid plaque

Question 28

Viroids

Answer 28

Specific to plants. Infectious RNA

Question 29

Multiplication Differences btwn DNA and RNA Viruses

Answer 29

1) Sense RNA (sRNA): if viral RNA is already in correct direction to be mRNA (5’ to 3’). RNA virus can already provide replication but it needs to make a copy to provide genetic info for new viral cells
2) Anti-sense RNA (asRNA): if viral RNA is in the wrong orientation (3’ to 5’). RNA first must be copied back to mRNA (going to Sense RNA) before being used to make protein and an Anti-sense RNA copy to go back into the new viruses being made