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MicroBio > Lec. 5 Virology > Flashcards

Lec. 5 Virology Flashcards

1
Q

WHERE DO VIRUSES FIT IN THE SCHEME OF LIVING THINGS?

A
  • Viruses have no cellular structure – either prokaryotic or eukaryotic
  • Viruses lack enzymes for metabolismand protein synthesis
  • All viruses are obligate intracellularparasites
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2
Q

Virus size

A

Virion – a single virus particle (entity, “organism”

)Virion size range = .01-.3μ; not visible with regular microscope; must use an electron microscope

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3
Q

VIRUS GENOMES

A

•All viruses have nucleic acid as their genetic material (genome)
–The nucleic acid may be DNA or RNA but not both.
–RNA viruses are the only “organisms” that have RNA as their genetic material

•Viral genomes may:
–Consist of single stranded (ss) or double stranded (ds) nucleic acid
–Be a single nucleic acid molecule or segmented into multiple pieces
–Be linear or circular

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4
Q

VIRUS CAPSIDS

A
  • Capsid is a protein coat surrounding the viral nucleic acid; together they are called nucleocapsid
  • All viruses have a capsid; it is coded for by the viral genome
  • Capsomeres are subunits of the capsid

•Capsid function;
–to protect the nucleic acid
– for some viruses to attach virus to the cell

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5
Q

COMMON VIRUS CAPSID SHAPES

A
  • Helicat - spiral
  • Cubic - they have 20 diff faces
  • Complex - this infects bacteria and not human directly (some kind of feet like things at the body)
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6
Q

VIRUS ENVELOPES

A
  • Some viruses have a lipid membrane surrounding the capsid
  • The envelope is usually derived from the host cell membrane; in a few viruses it’s from nuclear, endoplasmic reticulum, or Golgi membranes; it is not coded for by the viral genome
  • Many viruses code for proteins that are inserted into the envelope; these are called peplomers (they are coded by the virus and manufactured in cytoplasm & then find their way to __) (spikes) (they mark the exterior of the virus as belonging to it)
  • Many viruses have no envelope; called nonenveloped or naked viruses
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7
Q

HUMAN PAPILLOMAVIRUS

A

Slide 9 structure of an envelop virus

-doesn’t have an envelope… it just has the capsid

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8
Q

VIRUS ENZYMES

A

•Viruses lack most of the enzymes they need and use those of the host cell

•Viruses may have their own enzymes when:
–The host cell doesn’t have the ones they need
–Having their own enzymes would speed up their replication

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9
Q

VIRUS POLYMERASES

A

•Catalyze the formation of new nucleic acid molecules (this is the kind of enzymes that they try to produce)

•4 types based on type of viral genome
–RNA-dependent (template) RNA (product being made) polymerase
–RNA-dependent (template) DNA (product) polymerase (reverse transcriptase)
–DNA-dependent (template) DNA (product) polymerase
–DNA-dependent (template) RNA (product) polymerase (like mRNA)

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10
Q

OTHER VIRUS ENZYMES

A

•May aid in attachment and penetration of the virus into the host cell
–Fusion factors
–Neuraminidase in influenza virus

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11
Q

VIRAL REPLICATIVE CYCLE

A
  • Attachment to host cell
  • Penetration of host cell and uncoating (removal of capsid from the viral genome)
  • Replication of the viral genome and synthesis of viral proteins
  • Assembly of the virus particle
  • Release of virus from the cell into the extracellular space
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12
Q

VIRAL ATTACHMENT POINTS

A
  • For nonenveloped viruses: special capsomeres onpoints of the
  • icosohedral capsid
  • For enveloped viruses, the peplomers, which are fixed tightly into envelope
  • For bacteriophages, the feet (tail fibers)

-whatever sticks out the farthest is what is going to attacht to the ccell

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13
Q

VIRAL ATTACHMENT

A

•Attachment to host cell
–involves a specific chemical reaction between receptors on host cell surface and attachment points on virus surface; fixes virus firmly to cell surface
–Why would a cell have receptors for viruses on its surface?
*the reason is because most molecules there for a certain function for a cell and virus came along later using these receptors so it had to adapt

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14
Q

VIRAL ATTACHMENT PT. 2

A

•Attachment to host cell
–involves a specific chemical reaction between receptors on host surface and attachment points on virus surface; fixes virus firmly to cell surface
–Host cell receptors for viruses are usually molecules necessary for the life of the host cell

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15
Q

PENETRATION AND UNCOATING OF VIRUS

A

•Purpose of penetration and uncoating is to get the viral nucleic acid into a naked form, free of its capsid, so it can be accessible to cellular enzymes and begin to replicate

-Phage secretes lysozyme to make a hole in the bacterial cell wall

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16
Q

ATTACHMENT AND PENETRATION BY TRANSLOCATION IN ANIMAL CELLS

A

SLIDE 24

17
Q

ATTACHMENT AND PENETRATION BY FUSION

A

SLIDE 25

  • only works for enveloped virus
  • memembrane has component that fuses the virus
18
Q

ATTACHMENT AND PENETRATION BY ENDOCYTOSIS

A

SLIDE 27

  • endocytosis is natural process by which cells take things in
  • virus go to these cites and get engulfed
  • cell doesn’t distinguish it as being harmful
19
Q

REPLICATION PHASE

A
  • Viral genome is being replicated using polymerase enzymes.
  • Viral proteins are being replicated using the host cell protein synthesizing system (ribosomes, transfer RNA, amino acids etc.)

make sure you know it!

20
Q

BALTIMORE SCHEME FOR REPLICATION OF VIRAL PROTEINS

A

SLIDE 29

  • do not have to memorize particular viruses
  • know the normal process of manufacture of cellular protiens. Starts with DNA depended to mRNA to Proteins

4

21
Q

RELEASE OF VIRIONS FROM THE CELL(so they can go on to infect other cells)

A

•Budding:
–Most budding viruses push through cell plasma membrane or some other cell membrane
–All budding viruses acquire the membrane as their envelope

•Cell lysis (lytic infection)
–Cell bursts because it is too full of virions
–Cell dies as part of natural life cycle of the cell and virus is released
–Most of these viruses are non-enveloped

22
Q

HPV REPLICATION IS SYNCHRONIZEDWITH EPIDERMAL CELL DIFFERENTIATION

A

SLIDE 36

  • skin is most typical example
  • 1: infection of bassal cells
  • 2: integration of viral DNA (E1/E2 and E6/E7)
  • 3: Viral DNA replication in squamous cells (E6/E7)
  • 4: Viral assembly (L1/L2)
  • 5: Shedding of HPV
23
Q

NONREPLICATIVE VIRUS ENCOUNTERS WITH CELLS

A

•Virus cannot enter a cell because the cell doesn’t have the correct receptor. This often determines species specificity of viruses.

•Abortive infection: Virus can enter cell but can’t replicate because:
–cell is non-permissive, ie. doesn’t have correct enzymes
–cell has mechanisms of inhibiting viral replication

•Latency: virus integrates into host DNA and replicates only when host DNA replicates or only when stimulated by an additional factor, e.g. hormones

24
Q

DO ANY HUMAN VIRUSES HAVE LYSOGENIC/LYTIC CYCLES?

A
  • Called“latency/reactivation”
  • Common in Herpesvirus family

•Triggered by:
–Immmunosuppression
–Stress
–Hormonal changes

25
Q

HOST RANGE OF VIRUSES

A
  • Kingdom level - animal, plant, fungi, protozoans, algae, bacterial
  • Species level - e.g. poliovirus
  • Tissue level - e.g. T cells, liver
26
Q

PROKARYOTIC CELLS INFECTED BY VIRUSES

A
  • Algae (cyanobacteria)

- Bacteria (E. coli

27
Q

TRANSMISSIBLE SPONGIFORM ENCEPHALOPATHIES

A
  • Scrapie
  • Mad Cow Disease
  • Kuru - brain material exposure and they become paralyzed
  • Cruezfeldt-Jakob disease - inherted and they die at a young age
28
Q

WHAT IS CAUSE OF SPONGIFORM ENCEPHALOPATHIES (SE)?

A

-has this name cuz it is sponge like

  • Material from the brains of affected individuals could be transmitted to animals and cause the disease.
  • Original theory was that SE was caused by a “slow virus.” However, no viral DNA or RNA could be identified
  • Although others had hypothesized that the cause was a protein, Pruisner was the first to isolate the protein agent and named it “prion.”
29
Q

PROPERTIES OF INFECTIOUS PRIONS

A
  • Are abnormal proteins
  • Can be transmitted from one human/animal to another
  • Interact directly with normal prion proteins and convertthem to the abnormal form; abnormal proteins do not replicate
  • Are resistant to usual disinfection methods for infectious agents;inactivated only by 700 degree F., formaldehyde, and strong base solutions
  • Coded for by mutated normal human or animal gene
  • Human susceptibility to infectious prion damage may vary among humans and has a genetic component
30
Q

Viruses w/ Peplomers

A
  • Coronavirus

- Rabies

31
Q

CQ

Which of the following necessary for virus replication is never provided by the host cell?

A

A. Amino Acids
B. Ribosomes
C. Template
D.tRNA

Ans: C

32
Q

CQ

Which of the following will correctly describe the virus at the arrows when it exits the cell

A 
A. Nonenveloped helical
B. Enveloped Helical
C. Nonenveloped icosahedral
D. Enveloped iscoahedral
E.none of the above

Ans: D

33
Q

Know Lytic Cycle and Lysogenic Cycle

A
  • know
34
Q

BACTERIOPHAGE USED TO HEAL BACTERIAL INFECTION

A

Phages added up to heal the wound

35
Q

PRION PROTEIN FOLDING

A
  • there is normal prion protien
  • a)= normal, alpha sheet Protien plats a role in normal nerve cell function

b) abnormal, beta sheet Protein plays a role in Protein counteracts normal normal nerve cell function. nerve cell function.

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