Brock Biology Of Microorganisms Chapter 9

Front 1

Viruses (four facts)

Back 1

1) genetic elements that replicate independently of a cell's chromosome but not independently of cells themselves

2) have both extracellular and intracellular form

3) able to exploit metabolic machinery of cells

4) can infect both bacteria and archae

Front 2

Extracellular form

Back 2

also known as virion form

allows viruses to exist outside the host for long periods

metabolically inert.. no biosynthetic functions

Front 3

What are the extracellular forms of viruses made of?

Back 3

contain a nucleic acid (RNA or DNA) surrounded by a protein coat (capsid) and occassionally other macromolecules

Front 4

Bad and good things about viruses (2)

Back 4

1) can introduce beneficial genes or properties encoded in nucleic acids

2) can also cause cell destruction and cell death

Front 5

Intracellular form

Back 5

occurs when a virus has invaded host cell

viral replication cocurs

components that make up the virus are synthesized by host cell's machinery

Front 6

Three characteristics of Viral Genomes

Back 6

1) may contain RNA or DNA or both and thus may be single or double stranded

2) classified according to their characteristics of their genome

3) also can be classified according to the host they infect

Front 7

size of viruses usually (in microns) and how many bases are they made up of?

Back 7

1) average size is .02-.03 microns

2) viral genomes are 1000-5000 kb

Front 8

why is the small size of the viral genome important?

Back 8

because it restricts the number of different viral proteins that can be made

Front 9

What are two words to define viral structure?

Back 9

1) Capsomere

2) Nucleocapsid

Front 10

Capsomere

Back 10

more complex assembly of the protein coat

Front 11

Nucleocapsid

Back 11

a combination of the virion nucleic acid and protein coat

Front 12

Envelope (in virions)

Back 12

a membrane that surrounds the nucleocapsid

Front 13

Naked (pertaining to virions)

Back 13

extracellular virus that does not have an envelope

Front 14

the two types of virus symmetry

Back 14

1) Helical symmetry

2) icosahedral symmetry

Front 15

Helical symmetry

Back 15

seen in rod-shaped viruses

Front 16

Icosahedral symmetry

Back 16

seen in spherical viruses

Front 17

What is the structure of the Envelope of viruses?

Back 17

1) consists of a lipid bilayer embedded with proteins and glycoproteins

Front 18

where is the lipid portion of the envelope of a virus derived from?

Back 18

from the membrane of the host cell

Front 19

how is the protein portion encoded in an enveloped virus?

Back 19

encoded by virus nucleic acid

Front 20

What types of organisms do enveloped viruses usually infect?

Back 20

they infect animals

Front 21

enzymes in virions

Back 21

1) may play role in infection process

2) bacteriophages produce lysozymes that make small holes in bacterial cell wall

3) some viruses contain their own nucleic acid polymerases

Front 22

Reverse Transcriptase

Back 22

enzyme found in RNA viruses called retroviruses

Front 23

Neuramidases

Back 23

enzymes that help viruses to release from the host

Front 24

Growth of viruses in cultured cells

Back 24

1) many animal and plant viruses can also be grown in cultured cells

2) some cell cultures can be grown indefinitely as permanent cell lines for experimental purposes

Front 25

Plaque assay

Back 25

used to quantify the number of virions in a suspension

accurate way to measure virus infectivity

Front 26

The steps to produce a plaque assay (3)

Back 26

1) Bacterial culture infected with a virus and produces "lawn" growth in culture

2) virus will cause lysis of the bacteria it infects

3) lysed cells produce "clear areas" called plaques

Front 27

Five stages of the life cycle of a virus

Back 27

1) Attachment

2) Penetration

3) Synthesis

4) Assembly

5) Release

Front 28

Four stages of viral nucleic acid synthesis

Back 28

1) Eclipse

2) Latent period

3) Maturation

4) Burst size

Front 29

Eclipse

Back 29

infectivity of the virus dissappears after adsorption of virus by host cell

Front 30

Latent Period

Back 30

replication of viral nucleic acid and protein occurs during this period

Front 31

Maturation

Back 31

newly synthesized nucleic acid molecules are packaged inside protein coats

Front 32

Burst Size

Back 32

nubmer of new virion particles that are released

Front 33

Three facts about viral attachment to the host cell

Back 33

1) attachment of a virion is a highly specific process

2) involves complementary receptors on the surface of a susceptible host cell and the infecting virus

3) if host cell receptor altered by mutation, the virus cannont adsorb and infect

Front 34

penetration of viruses

Back 34

not the same in all virus-host cell interactions

may become uncoated prior to entering the host cell

entire virion may enter host cell and must become uncoated after entering the host cell

Front 35

Restriction endonucleases

Back 35

An example of prokaryotic DNA destruction systems (because they lack immune systems)

protect their own DNA with protective methyl groups at the restriction sites in their genomes

Front 36

Genomes of T-even bacteriophages

Back 36

T2, T4, T6 are closely related viruses

T4 genome is most widely studied

Front 37

3 parts of T4 genome

Back 37

Early Proteins

Middle Proteins

Late Proteins

Front 38

Early and Middle Proteins

Back 38

primarily enzymes involved in DNA replication and transcription

Front 39

Late Proteins

Back 39

head and tail proteins and the enzymes involved in liberating the mature phage particles from the cell

Front 40

T4 virus infectivity

Back 40

it is a virulent virus (can kill cells through a lytic life cycle)

Front 41

How does T4 appropriate the host cells RNA polymerase?

Back 41

1) may insert anti-sigma factor that causes the host cell RNA polymerase to not recognize host promoters-shuts down host transcription

2) may use its own proteins to covalently modify the sub-units of the host RNA polymerase

3) these modification cause the host RNA polymerase to recognize only phage promoters

Front 42

Temperate Bacteriophages

Back 42

Viruses that do not neter a lytic life cycle

Front 43

lysogeny

Back 43

a stage entered into by temperate viruses

most virus genes are not expressed

virus genome (prophage) is replicated in synchrony with the host chromosome

Front 44

Bacteriophage Lamda

Back 44

a double stranded DNA temperate phage

lytic and lysogenic events in lambda controlled by several promoters and regulatory proteins

often infect E. coli

Front 45

Genetic Switch

Back 45

controls whether a lytic or lysogenic pathway will ensue in bacteriophage lambda

Front 46

For lysogenic pathway to ensue it is necessary that (2)

Back 46

1) production of all late proteins must be prevented

2) copy of the lambda genome must be integrated into the host chromosome

Front 47

Three things animal viruses can cause

Back 47

1) persisten infections

2) Transformation

3) Latent Infections

Front 48

Persistent infections

Back 48

produce virus indefinitely

cause lysis of host cell

immediate lytic effect

Front 49

Trasformation

Back 49

coversion of a normal cell into a tumor cell

Front 50

Latent infections

Back 50

delay between infection by the virus and lytic events

symptoms reappear sporadically

Front 51

Retrovirus

Back 51

transfer information from RNA to DNA

contain a genome that is replicated through a DNA intermediate

usea an enzyme caled reverse transcriptase to perform retro-transcription

Front 52

Viroids

Back 52

1) smallest known pathogens

2) do not encode any proteins-completely dependent upon host cell enzymes

3) cause some plant diseases (no viroid diseases in animals)

Front 53

Structure of viroid (3)

Back 53

1) small, circular single stranded RNA molecules

2) contain no protein coat

3) genomes between 246-399 nucleotides

Front 54

Prions

Back 54

1) cause a variety of disease in animals (scrapie in sheep, mad cow in cattle)

2) no known prion diseases in plants

Front 55

Structure of prion (2)

Back 55

1) have a distinct extracellular form that is entirely protein

2) do not contain any nucleic acid