Microbiology Recall: Viral Genetics, Pathogenesis, & Phylogeny

Front 1

What is a wild-type organism?

Back 1

A standard to which genetic mutants are compared?

Front 2

What is a mutant?

Back 2

An organism that deviates from normal in some recognizable characteristic (phenotype).

Front 3

What is a mutation?

Back 3

A change in the base sequence of DNA.

Front 4

What is an unstable mutation?

Back 4

A mutation that frequently changes back to its original state.

Front 5

How are nucleotides classified?

Back 5

Purines: adenine, guanine have two rings
Pyrimidines: cytosine, thymine have one ring

Pyrimidines contain the letter "y".

Front 6

What is a point mutation?

Back 6

A mutation that only affects 1 base pair

Front 7

Waht are two types of point mutations?

Back 7

1) Transition sustitution
2) Transversion substitution

Front 8

What is a transition substitution?

Back 8

A point mutation where a purine is subtituted for a purine or a pyrimidine is substituted for a purine.

Front 9

What is a transversion substitution?

Back 9

A point mutation where a purine replaces apyrimidine or vice-versa.

Front 10

What is an inversion mutation?

Back 10

A mutation where a string of base pairs are deleted and reinserted in the same position, but in the opposite direction.

Front 11

What is a silent mutation?

Back 11

A mutation that alters base pairs, but not the specific amino acid they encode.

Front 12

What is a missense mutation?

Back 12

A mutation that alters base pairs resulting in the replacement of one amino acid residue for another.

Front 13

What is a nonsense mutation?

Back 13

A mutation resulting in a stop codon, prematurely terminating the elongation of a polypeptide chain.

Front 14

What is a frame-shift mutation?

Back 14

A mutation that changes teh reading frame of the genetic code, resulting in a misreading of all downstream nucleotides adn altering the encoded amino acids of the polypeptide chains, often rsulting in early stop codons.

Front 15

What are conditional-lethal mutations?

Back 15

Mutations that allow gene expression and protein formation under permissive conditions, but fail to replicate or allow gene expression under restrictive conditions.

Front 16

What is the clinical significance of conditional-lethal mutations?

Back 16

These mutations allow for identification of specific genes responsible for viral properties and can be used to create live-attenuated vaccines that take advantage of these mutations.

Front 17

What are defective-interfering particles?

Back 17

Deletion mutations that are incapable of replication unless the deleted function is supplied by a "helper" virus.

Front 18

What is the clinical significance of defective-interfering particles?

Back 18

They interfere with growth of normal viruses and stimulate cellular immune responses, thereby limiting spread of the virus

Front 19

What are four interactions that occur when two different viral strains infect teh same cell?

Back 19

1) Recombination
2) Reassortment
3) Complementation
4) Phenotypic mixing

Front 20

What is recombination?

Back 20

Exchange of genes between two chromosomes by crossing over of regions with base pair homology?

Front 21

What viruses display a higher rate of recombination?

Back 21

dsDNA viruses

Front 22

Which is reassortment?

Back 22

Exchange of gene segments between viruses with segmented genomes.

Reassortment results in a higher frequency of gene exchange than recombination.

Front 23

What is a clinically important example of reassortment?

Back 23

Influenza virus undergoes major antigenic changes (antigenic shift) via reassortment that causes devastating worldwide epidemics.

Front 24

What is complementation?

Back 24

A process by which a virus is able to assist a mutated virus by providing functional proteins for the defetive virus.

Front 25

What is an important example of complementation?

Back 25

Hepatitis B virus provides surface antigen for defective hepatitis delta virus (HDV), allowing HDV to replicate in coinfected cells causing a more sevree form of hepatitis.

Front 26

What is phenotypic mixing?

Back 26

A process by which the genome of a virus type A can be coated with the surface proteins of virus type B, producing a phenotypically mixed virus.

Front 27

What is the significance of phenotypic mixing?

Back 27

Phenotypically mixed viruses infect cells based on the cells' type B protein coat.

Front 28

What is the genetic makeup of the progeny of virions resulting from phenotypic mixing?

Back 28

Progeny virions have the genome and protein coat of the type A virus (virions will contain the protein coating of the virus whose genome is present)

Front 29

What are five effects of viral infection on the cell?

Back 29

1) No morphologic or physiologic change
2) Fusion of cells to form multinucleated giant cells
3) Malignant transformation
4) Death by lysis
5) Death by apoptosis

Front 30

What are multinucleated giant cells?

Back 30

Enlarged cells that are formed by membrane fusion of infected cells.

Multinucleated giant cells are also called syncytial cells.

Front 31

Which two families of viruses typically cause miltinucleated giant cell formation?

Back 31

Herpes viridae
Paramyxoviridae

Front 32

What is malignant transformation?

Back 32

A process causing virus-infected cells to have altered morphology, abnormal growth control, and distinct cellular and biochemical properties, i.e., cells become cancerous.

Front 33

How is morphology altered with malignant transformation?

Back 33

Cells lose there defined shape and appear more rounded.

Front 34

How is their growth control abnormal with malignant transformation?

Back 34

Cells have unrestrained growth, prolonged survival, and lose contact inhibition resulting in a pile of cells.

Front 35

How are cellular properties altered in malignant transformation?

Back 35

Cells have mutated genomes and DNA synthesis is induced

Front 36

How are biochemical properties altered in malignant transformation?

Back 36

Cells produce less cyclic adenosine monophosphate (cAMP), have increased anaerobic metabolism, and produce altered sugar moieties on membrane-bound glycoproteins.

Front 37

What causes cell death?

Back 37

Inhibition of protein and/or nucleic acid syntheisis or stimulation of apoptosis.

Front 38

what is the cytopathic effect (CPE)?

Back 38

A hallmark change in the appearance of virus-infected cells with rounding and arkening of the cell, eventually leading to lysis or giant cell formation and apoptosis.

Front 39

What is the name of the inclusion bodies found in rabies virus-infected neurons?
What are they?

Back 39

Negri bodies

Eosinophilic cytoplasmic inclusion

Front 40

How do the inclusion bodies seen with CMV infection appear microscopically?

Back 40

As owel's-eye nuclear inclusions

Front 41

What are four stages in a typical viral infection?

Back 41

1) Incubation period during which the patient is asymptomatic
2) Prodromal period during which the patient has nonspecific symptoms
3) Viral-specific illness period
4) Recovery period

Front 42

What are two methods of transmission?

Back 42

Vertical
Horizontal

Front 43

What's the difference between vertical and horizontal transmission?

Back 43

Vertical transmission involves the spread of a virus form parent to offspring whether in utero or during the birth process (CMV).

Horizontal transmission involves the spread of a virus between two people other than during the bith process or while the fetus is in utero, e.g., influenza virus.

Front 44

What are two ways a virus can spread from a site of entry resulting in a disseminated infection?

Back 44

Hematogenous spread
Neural spread

Front 45

Which viruses use the respiratory tract as a portal of entry?

Back 45

1) Influenza virus (flu)
2) Rhinovirus (common cold)
3) Respiratory syncytial virus (bronchiolitis)
4) EBV (infectious mono)
5) Varicella-zoster virus
6) Herpes simplex virs type 1
7) CMV (mono)
8) Measles
9) Mumps
10) Rubella
11) Hantavirus (pheumonia)
12) Adenovirus (pneumonia)

Front 46

Which viruses use the GI tract as a portal of entry?

Back 46

Hepatitis A virus (hepatitis A)
Poliovirus (poliomyelitis)
Rotovirus (diarrhea)

Front 47

Which viruses use the Skin as a portal of entry?

Back 47

Rabies virus
Yellow fever
Dengue
HPV

Front 48

Which viruses use the GU tract as a portal of entry?

Back 48

HPV
Hepatitis B
HIV
Herpes simplex virus type 2

Front 49

Which viruses use the blood as a portal of entry?

Back 49

1) Hepatitis B
2) Hepatitis C
3) Hepatitis D
4) Human T-cell leukemia virus
5) HIV
6) CMV

Front 50

Which viruses use the placenta as a portal of entry?

Back 50

Rubella
CMV
Herpes simplex virus
HIV

Front 51

Which bacteria are transmitted transplacentally?

Back 51

Treponema pallidum
Listeria monocytogenes

Front 52

Which protozoa are transmitted transplacentally?

Back 52

Toxoplasma gondii

TORCHES represents the mc infections transmitted transplacentally:
1) Toxoplasmosis
2) Rubella
3) CMV
4) Herpes / HIV
5) Syphilis

Front 53

Whic viruses are transmitted during parturition?

Back 53

Hep B
Hep C
Herpes type 2
HIV
HPV

Front 54

What is an attenuated virus?

Back 54

A mutat virus that has dimished ability to cause disease in imminocompetent individuals

Front 55

What is the clinical significance of attenuated viruses?

Back 55

Attenuated viruses may be used in vacines to induce an appropriate immmune response to the wild-type virus.

Front 56

What are three viruses that cause hepatocellular pathology mainly by inducing an inappropriate immune response?

Back 56

Hep A
Hep B
Hep C

Front 57

What are five factors that predispose one to chronic viral infections?

Back 57

1) Immunosuppression
2) Formation of antigen-antibody complexes that remain infectious
3) Antigenic variation
4) INfection in an area that is isolated from an immune response (CNS, testes)
5) Integration of the viral genome with the host cell genome

Front 58

What are three types of clinically important chronic viral infections?

Back 58

Chronic carrier infections
Latent infections
Slow virus infections

Front 59

What are chronic carrier infections?

Back 59

Infections with viruses that continue to produce significant amounts of viral progeny for extended periods of time.
Hep B &C
Congenital Rubella
HIV
CMV

Front 60

What are latent infections?

Back 60

Infections with viruses where thepatient recovers from the initial infection and production of viral progeny ceases; however, the patient never clears the virus.

A future stumulus can cause the virus to replicate and symptoms to recur

Front 61

What families of viruses have the characteristic of latent infections?

Back 61

Herpesviridae family demonstrate latent infections

Front 62

What are slow virus infections?

Back 62

Infections with a prolonged period between the initial infection and the onset of disease

JC virus