Microbiology- Chapter 6 (Viruses)

Front 1

What is the best way to describe viruses?

Back 1

Infectious particles that can be active or inactive.

Front 2

Are cells alive? If not, what are they?

Back 2

No.
Outside the host cell they cannot replicate, don't have metabolism.

So they are..

Obligate intracellular parasites ( Cannot multiply outside host)

Viruses can infect ( all living things) :animals, plants, algae, fungi, and bacteria

Front 3

True or False.

Viruses have none or only a few enzymes of their own.

Back 3

True

Front 4

With what microscope can one see viruses?

Back 4

× The size of viruses ranges from 20 to 14000 nm (*cannot be seen form light microscope, they can be seen by electron microscope)

Front 5

What is the size range of viruses?

Back 5

 Size range
× Most range in size from 5 to 300 nanometers (nm) although some paramyxoviruses can be up to 12,000 nm long.

Front 6

True or False.

Viruses have protein-synthesizing machinery.

Back 6

FALSE

Front 7

In what two forms can virus be in?

Back 7

Naked Virus

and

Enveloped virus

Front 8

Describe a naked virus.

Back 8

Viral particle is composed of :
× Nucleic acid ( DNA or RNA)

× Protein coat- capsid ( Shell, surrounds the nucleic acid)
o Capsid is composed of protein subunits called capsomeres

Front 9

Describe an enveloped virus.

Back 9

× Enveloped viruses
Some viruses have the capsid covered with an envelope (lipids, proteins, and carbohydrates)

Front 10

What are the three different morphological types of viruses?

HINT: Based of capsid structure

Back 10

-Helical (cylinder shaped) *like double helix –rod*

-Polyhedral (spherical)

-Complex (*looks like polyherdran on a helical with legs)
NOTE : helical + polyhedral = hermaphrodite of the virus world, that’s why it’s so complex

Front 11

Describe the structure of a Helical virus, both naked and enveloped.

Back 11

- Helical viruses

× Naked helical viruses
- Long rods
- The capsid is cylindrical with helical structure (tobacco mosaic virus)

NOTE: Picture

http://student.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/images/u2fig2a.jpg

× Enveloped helical viruses
- Helival nucleocapsid placed within an envelope (influenza)

Note: PICTURE

http://student.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/images/u2fig2c.jpg

Front 12

Describe the structure of a Polyhedral virus.

Back 12

 Polyhedral viruses
× The capsid is a regular polyhedron (icosahedron) with 20 triangular faces (poliovirus)
× Nucleic acid packed in the center



NOTE: Picture

http://student.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/images/u2fig2d.jpg

Front 13

Describe the structure of a Complex virus.

Back 13

 Complex viruses
× Bacterial viruses- bacteriophages
- Head- polyhedral
- Tail- helical
- Tail fibers *feet*


NOTE: Picture

http://www.nsf.gov/od/lpa/news/02/images/bacteriophage.jpg

Front 14

What is at the core of the virus?

Back 14

× Viruses contain either DNA or RNA
- Double/single stranded DNA
- Double/single stranded RNA

Genom is small (4 genes in Hepatitis B virus) *genom is genetic information*

Front 15

Describe the positive and negatives points of having a single stranded RNA.

Back 15

× Single stranded RNA

o Positive-sense (directly translated into proteins)

o Negative sense (need to be converterd into proper form, which it can be made into proteins too)

Front 16

What else can a virus contain at the core besides nucleic acids?

Back 16

 Besides nucleic acides core may contain enzymes required for replication (*normally viruses use resources of host cell like the host cells enzymes but some have their own)

Front 17

What are the phases of multiplication of animal viruses?

Back 17

1- Adsorption
2-Penetration
3-Uncoating
4-Biosynthesis
5-Assemby
6- Release

Front 18

Describe adsorption.

HINT: step 1

Back 18

× Viruses use their attachment sites (glycoproteins) to attach themselves to receptor sites on the plasma membrane of animal

× The attachment sites can be:
- Small fibers or spikes on the virus envelope ( ex. influenza)
- Capsid spike (naked viruses)

× The receptor for a particular virus is specific- host range
- Virus can infect only the specific cells (heptatitis B- liver cells) (*must be within host range)

- Can vary from one person to another
× *must have the receptor site required to get infection

NOTE: Range of hosts limits viruses

Front 19

Describe the two mechanisms for penetration of a virus into host cell.

HINT: step 2

Back 19

1. (a) Endocytosis- it is an active process by which nutrients are brought into a cell
× Cell membrane folds inwards forming a vesicle
× Vesicle is transported inside the cell
( Entire virus is engulfed by the cell and enclosed in a vacuole or vesicle)


 2. (b)Fusion with the cell membrane
× Viral envelope fuses with the host cell membrane

( Envelope merges with cell membrane and liberates nuclecapsid into the cell's interior)


NOTE: video

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::500::500::/sites/dl/free/0072995289/571732/Entry_of_enveloped_animal_viruses_into_host_cells.swf::Entry%20of%20Virus%20into%20Host%20Cell

Front 20

Describe the phase of uncoating.

HINT: Step 3

Back 20

× The vesicle, viral envelope and capsid are destroyed and the nucleic acid is released into the cytoplasm
- Enzymes (of the host cell) degrade the proteins of the capsid

Front 21

Describe Biosynthesis of DNA viruses.

HINT: Step 4

Back 21

× Upon entry, the viral DNA takes over the genetic expression of the host
( and instructs it to synthesize the building blocks for new viruses)

× Viral DNA is synthesized in the host nucleus by viral enzymes

× Capsid is synthesized in the cytoplasm by using host enzymes and amino acids
(In the host's ribosomes, using its amino acids"

× Assembly of coat proteins and DNA takes place in the nucleus
× Newly formed virus particle is transported along the endoplasmic reticulum


DNA Virus: Enter host cell's nucleus and are replicated and assembled there.

Front 22

Describe Biosynthesis of RNA viruses.

HINT: Step 4

Back 22

× Different groups of RNA viruses have different mechanism of mRNA formation
× And example: retroviridae- HIV
× Has the enzyme reverse transcriptase- to produce double stranded dna
× Intergrated into host DNA- provirus
× It remains latent or produces new viruses


RNA viruses: replicated and assembled in the cytoplasm.

Front 23

Describe the release of enveloped viruses.

HINT: Last step

Back 23

× In enveloped viruses

- Process is called budding or exocytosis
- The assembled capsid pushes through the plasma membrane
- A portion of the plasma membrane becomes the viral envelope
- The release of viral particles is gradual-- there is no sudden death of the host cell

Front 24

Describe the release of non enveloped (naked) viruses.

HINT: last step

Back 24

× In nonenveloped viruses
- Host cell plasma membrane raptures
- Causes death of the host cell

Front 25

What are the different ways a virus can damage a cell?

Back 25

× Cytopathic effect- change of cell appearance (size, shape, granulation)
× Persistent infection (few weeks- rest of the host’s life) *virus infects the cell but it doesn’t cause major damage so it takes a long time

× Chronic latent state (herpes zoster virus- chicken pox- shingles)
( Periodically becoming reactivated)

× Oncogenic viruses- integrate into host genom- increased rate of growth- cause cancer (*there is an uncontrollable growth)

Front 26

How do oncogenic viruses cause cancer?

Hint: Human and animal genomes normally contain oncogenes. Activation of these genes causes cancer. They can be activated by mutagenic chemicalls, radiation, and viruses

Back 26

× When the oncogenic virus infects the cell, its genetic material is integrated into the host cell’s DNA
× Such infected cells show different characteristic-- uncontrollable growth
About 10% of cancers are virus induced
× DNA Oncogenic viruses
- Human papilomavirus (HPV) – causes cervical cancer
- Hepatitis B virus (HBV)- causes liver cancer
× RNA Oncogenic viruses
- Human T- cell leukemia virus (HTLV-1) – Leukemia
- Feline leukemia virus (FeLV)- leukemia in cats

Front 27

What is a latent viral infection?

Hint: herpes

Back 27

× Some viruses can remain in host for long period of time without causing any symptoms
× Ex. Herpex simplex virus- infection of skin, lives in nerve cells when not in active state. It is activated by fever or sunburn
× Large portion of human population carries this virus only 10-15% exhibits the disease

Front 28

What are viruses that can infect bacteria called?

Back 28

× They are called bacteriophages—(*means “one that can eat the bacteria”)

Front 29

What is the most widely studied bacteriphage?

Back 29

T4

Front 30

What are the two types of life cycles a T4 virus can have?

Back 30

- Lytic
- Lysogenic

Front 31

What is the structure of a T4 virus?

Back 31

× capsid
× tail
× fibers
× baseplate

Front 32

Describe the lytic phase of T4.

Back 32

× Attachment
- Bacteriophage uses its tail fibers as attachment in sites, the complementary receptor sites are located on the bacterial cell wall
× Penetration
- The tail cheath contracts and the tail penetrates the cell wall
- DNA from the head is injected into bacterial cell
- The head remains outside
× Biosynthesis
- The virus DNA triggers host DNA degradation, stops host protein synthesis
- The virus uses the host nucleotides and enzymes to:
× Synthesize its own DNA
× Synthesize its own proteins
× Maturation
- Viral DNA and capsid is assembled into mature viral particles
× Release
- Lysozyme is synthesized within the cell- this causes bacteria cell to break and release the virus particles

Front 33

Describe the lysogenic cycle ( In bacteriophage lambda)

Back 33

Lysogenic cycle (in bacteriophage lambda)

× After penetration, the viral DNA is intergrated into bacterial DNA (prophage)
× Can remain integrated without harming the host
× Action of UV light or come chemicals initiates the lytic cycle
× The phages that have both of these cycles are called lysogenic phages of temperate phages
× The bacterial cell containing a lysogenic phage is called the lysogenic cell

Front 34

What are the characteristics of a lysogenic cell?

Back 34

Characteristics of Lysogenic cell:
× It is immune to new viral infection
× Can exhibit new properties- lysogenic conversion (toxicity of Clostridium botulinum)
× Can transfer genes from one bacterium to another- transduction

Front 35

What is phage therapy?

Back 35

× Use of lytic bacterophages to treat pathogenic bacterial infections
× Phage therapy is a potential alternative to antibiotics
× Advantage: bacteriophages can be much more specific than more common drugs

Front 36

Describe the cultivation of bacteriophages viruses.

Hint: Plaque method

× Viruses must be cultivated within living cells

Back 36

 Plaque method
× Melted agar+ host bacterial cells+ viruses; poured onto a layer of solid medium in Petri dish (*making another layer on top where___ is formed) (*is bacteria formed or bacteriophages)
× A lawn of bacteria is formed
× A virus infects the bacterial cell and lyses occurs
× New infection will result in formation of a clear zone of lysed bacteria- plaque

Front 37

What are the three ways to grow animal viruses?

Back 37

Using:
-Living animals
-Bird Embryos
-Cell (tissues) cultures

Front 38

Describe growing of animals viruses using bird embryos.

Back 38

× Virus injected in the embryonated chicken egg
× The death or damage of the embro indicates the presence of viruses
× Some virus vaccines are produced by this method

Front 39

Describe the growing of animal viruses using cell cultures.

Back 39

 Cell (tissue) cultures
× Animal cells are grown in culture like bacteria
× They form a monolayer by adhering to glass or plastic container
× The cell deterioration can be followed microscopically

Front 40

What are prions and what do they cause?

Back 40

Prions: agents in spongy brain disease

× Proteinaceous infections particles
× Cause neurological disease- spongiform encephalopthies
× Tiny holes appear in the brain cortex causing it to appear like a sponge
× Deterioration of mental and physical abilities