Chp. 19 (Bio) Viruses

Front 1

What two things make up a virus?

Back 1

nucleic acid surrounded by a protein coat.

p. 381

Front 2

TRUE OR FALSE: Viruses are unable to be crystallized.

Back 2

FALSE. Some viruses could be crystallized.

Front 3

TRUE OR FALSE: Some viruses have a membranous envelope.

Back 3

TRUE.

p. 382

Front 4

What are the four different types of genomes possible for viruses?

Back 4

double stranded -DNA, single stranded DNA, single-stranded RNA, and double-stranded RNA, depending on the type of virus.

p. 382.

Front 5

What is a DNA virus?

Back 5

a virus with a single -stranded DNA or double-stranded DNA.

p. 382

Front 6

What is an RNA virus?

Back 6

a virus with a single-stranded or double-stranded RNA.

p. 382

Front 7

Is the genome of a virus organized in a single linear fashion or a circular fashion?

Back 7

Either or. It depends on the virus. Some viruses consist of multiple molecules of nucleic acid.

p. 382

Front 8

What is a capsid?

Back 8

The protein shell enclosing the viral genome.

p. 383

Front 9

What are the 3 possible shapes for a capsid?

Back 9

rod-shaped, polyhedral, or a more complex shape like T4 phages.

p. 383

Front 10

What are capsids made out of?

Back 10

Capsides are bult from a large number or protein subunits called capsomeres.

p. 383

Front 11

What are helical viruses?

Back 11

rod-shaped viruses.

p. 383

Front 12

What gives rod-shaped viruses their shape?

Back 12

a single type of protein arranged in a helix.

p. 383

Front 13

What is a viral envelope?

Back 13

An envelope derived from the membranes of the host cell, which contails host cell phospholipids and membrane proteins. They also contain proteins and glycoproteins of viral origin.

p.383

Front 14

What two things does a host cell contribute to a viral envelope?

Back 14

host cell phospholipids and membrane proteins.

p. 383

Front 15

What two things do a virus contribute to a viral envelope?

Back 15

proteins and glycoproteins of viral origin.

p.383

Front 16

What type of bacteria typically have the most complex capsids found among the viruses?

Back 16

bacteriophages (phages)

p. 383

Front 17

TRUE OR FALSE: A virus may reproduce by itself or within a host cell.

Back 17

FALSE. A virus can only reproduce within a host cell.

p. 384

Front 18

What is a host range?

Back 18

The limited variety of hosts that each type of virus can infect.

p. 384

Front 19

How do viruses identify their host cells?

Back 19

by a "lock and key" fit between viral surface proteins and specific receptor molecules on the outside of cells.

p. 384

Front 20

When does a viral infection officially begin?

Back 20

A viral infection begins when a virus binds to a host cell and the viral genome makes its way inside.

p. 384

Front 21

What does the mechanism of genome entry depend on for a virus to infect a host cell?

Back 21

It depends on the type of virus and the type of host cell.

p 384

Front 22

What does the host provide to help the virus reproduce?

Back 22

nucleotides for making viral nucleic acids, enzymes, ribosomes, tRNAs, amino acids, ATP, and other components to make viral proteins.

p. 384

Front 23

How do RNA viruses replicate their genome?

Back 23

they use virally encoded polymerases that can use RNA as a templace.

p. 384

Front 24

What happens after RNA viruses produce nucleic acid molecules and capsomeres?

Back 24

They spontaneously self-assemble into new viruses.

p. 384

Front 25

What is a lytic cycle?

Back 25

A phage reproductive cycle that culminates in death of the host cell.

p.385

Front 26

What is a virulent phage?

Back 26

A phage that reproduces only by a lytic cycle.

p. 385

Front 27

What is a restriction enzyme?

Back 27

They cut up identified foreign DNA. They restrict the ability of the phage to infect the bacterium.

p. 385

Front 28

What is a lysogenic cycle?

Back 28

A cycle which allows replication of the phage genome without destroying the host.

p.386

Front 29

What are temperate phages?

Back 29

Phages that are capable of using both, lysogenic cycles and lytic cycles.

p. 386

Front 30

What is the physical difference between T4 and phage lambda?

Back 30

Phage lambda has only one short tail fiber on its tail

p. 386

Front 31

What happens during a lysogenic cycle?

Back 31

The lambda DNA molecule is incorporated into a specific site on the E.coli chromosome by viral proteins that break both circular DNA molecules and join them to each other.

p. 386

Front 32

What is a prophage?

Back 32

A viral DNA that has been integrated into the bacterial chromosome in a particular way.

p. 386

Front 33

What usually triggers a switch over from a lysogenic to a lytic mode?

Back 33

An environmental signal, such as a certain chemical or high-energy radiation, usually tiggers the switchover.

p. 386

Front 34

TRUE OR FALSE: Many animal viruses have both an envelope and RNA genome.

Back 34

TRUE. In fact, nearly all animal viruses with RNA genomes hae an envelope, as do some with DNA genomes

p. 387

Front 35

How does an animal virus enter a host cell?

Back 35

An animal virus is equipped with an envelope -- that is, an outer membrane -- and uses it to enter the host cell.

p. 387

Front 36

What makes the protein parts of the envelope of an animal virus?

Back 36

The protein parts of envelope glycoproteins are made by ribosomes bound to the endoplasmic recticulum (ER) of the host cell;

Front 37

What adds the sugars to the envelope of an animal virus?

Back 37

cellular enzymes in the ER and Golgi apparatus add the sugars.

p. 387

Front 38

How is the viral envelope derived from the host cell's plasma membrane?

Back 38

The viral glycoproteins, embedded in host cell-derived membrane, are transported to the cell surface. Similar to exocytosis, new viral capsids are wrapped in membrane as they bud from the cell.

The enveloped viruses are now free to infect other cells. This reproductive cycle does not necessarily kill the host cell, in contrast to the lytic cycle of phages.

p. 387

Front 39

Are most plant viruses DNA or RNA viruses?

Back 39

RNA viruses.

p. 388

Front 40

TRUE OR FALSE: retroviruses can directly serve as mRna and be translated into viral protein immediately after infection.

Back 40

TRUE. The RNA genome serves as a template for mRNA synthesis.

p. 388

Front 41

Describe how a retrovirus works.

Back 41

The RNA genome is transcribed into complementary RNA strands, which function both as mRNA and as templates for the synthesis of additional copies of genomic RNA.

p. 388

Front 42

TRUE OR FALSE: Not all viruses that require RNA --> RNA synthesis to make mRNA use a viral enzyme capable of carrying out this process.

Back 42

FALSE. All viruses that require RNA --> RNA synthesis to make mRNA use a viral enzyme capable of carrying out that process.

The viral enzyme is packaged with the genome inside the viral capsid.

p. 388

Front 43

What is reverse transcriptase?

Back 43

an enzyme which transcribes an RNA template into DNA, providing an RNA- --> DNA information flow, the opposite of the usual direction.

Front 44

What does HIV stand for?

Back 44

human immunodeficiency virus

Front 45

What does AIDS stand for?

Back 45

acquired immonodeficiency syndrome.

Front 46

Describe HIV and other retroviruses.

Back 46

HIV and other retroviruses are enveloped viruses that contain two identical molecules of single-stranded RNA and two molecules of reverse transcriptase.

p.389

Front 47

What is a provirus?

Back 47

an integrated viral DNA. It never leaves the host's genome, and remains a permanent resident of the cell.

p. 389

Front 48

What are plasmids?

Back 48

small, circular DNA molecules found in bacteria and in the unicellular eukaryotes called yeasts.

Front 49

TRUE OR FALSE: Plasmids exist as a piece of the cell's genome and must replicate with the genome.

Back 49

FALSE. Plasmids exist apart from the cell's genome, can replicate independently of the genome, and are occasionally transferred between cells.

Front 50

What are transposons?

Back 50

DNA segments that can move fro one location to another within a cell's genome.

p. 390

Front 51

What is the important feature that plasmids, transposons and viruses all share with each other?

Back 51

They are mobile genetic elements.

p. 390

Front 52

What are some ways in which a virus can kill a cell?

Back 52

Viruses may damage or kill cells by causing the release of hydrolytic enzymes from lysosomes. Some viruses cause infected cells to produce toxins that lead to disease symptoms and some have molecular components that are toxic, such as envelope proteins.

p.390

Front 53

What does the extent of damage a virus causes depend on?

Back 53

Partly on the ability of the infected tissue to regenerate by cell division.

p. 391

Front 54

What is a vaccine?

Back 54

A harmless variant or derivative of a pathogen that stimulates the immune system to mount defenses against the harmful pathogen.

p. 391

Front 55

What are emerging viruses?

Back 55

Viruses that appear suddenly or are new to medical scientists.

p. 391

Front 56

What three processes contribute to the emergence of viral diseases?

Back 56

1) mutation of existing viruses.
RNA viruses tend to have an unusually high rate of mutation because errors in replicating their RNA genomes are not corrected by proofreading.
2) Dissemination of a viral disease from a small, isolated human population.
3) The spread of existing viruses from other animals.
3/4 of new human diseases originate in this way.

p.392

Front 57

What are the three types of influenza virus?

Back 57

type B, C and A

Front 58

Which two influenza viruses infect only humans, and have never caused an epidemic?

Back 58

type B and C

Front 59

Which influenza viruses infects a wide range of animals, including birds, pigs, horses and humans?

Back 59

type A.

Front 60

What is a pandemic?

Back 60

a global epidemic

Front 61

TRUE OR FALSE: Emerging viruses are generally new.

Back 61

FALSE. Emerging viruses are generally not new; rather, they are existing viruses that mutate, disseminate more widely in the current host species, or spread to new host species.

p. 392

Front 62

TRUE OR FALSE: Changes in host behavior or environmental changes can increaes the viral traffic responsible for emerging diseases.

Back 62

TRUE.

p. 392

Front 63

What are the two major routes for viral diseases in plants?

Back 63

horizontal transmission and vertical transmission.

Front 64

What is horizontal transmission?

Back 64

A plant is infected from an external source of the virus. Damaged by wind, injury, or herbivores, insects, pose a double threat because they can also act as carriers of viruses, transmitting disease from plant to plant.

p. 393

Front 65

What is vertical transmission?

Back 65

a plant inherits a viral infection from a parent. Vertical transmission can occur in asexual propagation or in sexual reproduction via infected seeds.

p. 393

Front 66

Viral genomes and associated proteins can spread throughout the plant by means of __________.

Back 66

plasmodesmata. Virally encoded proteins cause enlargement of plasmodesmatas.

p. 393

Front 67

What are viroids?

Back 67

Circular RNA molecules only a few hundred nucleotides long that infect plants.

Front 68

Do viroids encode proteins?

Back 68

Viroids do not encode proteins but can replicate in host plant cells, apparently using host cell enzymes.

p. 393

Front 69

What are typical signs of viroids?

Back 69

abnormal development and stunted growth.

p. 393

Front 70

What are prions?

Back 70

infectious proteins.

p. 393

Front 71

What are signs of prions?

Back 71

they cause a number of degenerative brain diseases in various animal species.

p. 393

Front 72

How are prions transmitted?

Back 72

Prions are most likely transmitted in food, as may occur when people eat prion-laden beef from cattle with mad cow disease.

p. 393

Front 73

What are two alarming characteristics of prions?

Back 73

1) Prions act very slowly, with an incubation period of at least ten years before symptoms develop.
2) Prions are virtually indestructible; they are not destroyed or deactivated by heating to normal cooking temperatures. To date, there is no known cure for prion diseases.

p.393

Front 74

What does a prion look like?

Back 74

a misfolded form of a protein normally present in brain cells. When the prion gets into a cell containing the normal form of the protein, the prion somehow converts normal protein molecules to the misfolded prion versions.

p.394

Front 75

CONCEPT CHECK 19.1
1. Compare the structures of tobacco mosaic virus (TMV) and influenza virus.

Back 75

TMV consists of one molecule of RNA surrounded by a helical array of proteins. The influenza virus has eight molecules of RNA, each surrounded by a helical array of proteins, similar to the arrangement of the single RNA molecule in TMV. Another difference is that the influenza virus has an outer envelope.

Front 76

CONCEPT CHECK 19.2
1. Compare the effect on the host cell of a lytic (virulent) phage and lysogenic (temperate) phage.

Back 76

Lytic phages can only carry out lysis of the host cell, whereas lysogenic phages may either lyse the host cell or integrate into the host chromosome. In the latter case, the viral DNA (prophage) is simply replicated along with the host chromosome. Under certain conditions, a prophage may exit the host chromosome and initiate a lytic cycle.

Front 77

CONCEPT CHECK 19.2
2. How do some viruses reproduce without possessing or ever synthesizing DNA?

Back 77

The genetic material of these viruses is RNA, which is replicated inside the infected cell by enzymes encoded by the virus. The viral genome (or a complementary copy of it) serves as mRNA for the synthesis of viral proteins.

Front 78

CONCEPT CHECK 19.2
3. Why is HIV called a retrovirus?

Back 78

Because it synthesizes DNA from its RNA genome. This is the reverse ("retro") of the usual DNA --> RNA information flow.

Front 79

CONCEPT CHECK 19.3
1. Describe two ways a preexisting virus can become an emerging virus.

Back 79

Mutations can lead to a enw strain of a virus that can no longer be effectively fought by the immune system, even if an animal had been exposed to the original strain; a virus can jump from one species to a new host; and a rare virus can spread if a host population becomes less isolated.

Front 80

CONCEPT CHECK 19.3
2. Contrast horizontal and vertical transmission of viruses in plants.

Back 80

In horizontal transmission, a plant is infected from an external source of virus, which could enter through a break in the plant's epidermis due to damage by herbivores. In vertical transmission, a plant inherits viruses from its parent either via infected seeds (sexual reproduction) or via an infected cutting (asexual reproduction).

Front 81

CONCEPT CHECK 19.3
3. TMV has been isolated from virtually all commerical tobacco products. Why, then, is TMV infection not an additional hazard for smokers?

Back 81

Humans are not within the host range of TMV, so they can't be infected by the virus.

Front 82

SELF QUIZ
1. A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced would have
a. T2 protein and t4 DNA.
b. T2 protein and T2 DNA
c. a mixture of the DNA and proteins of both phages.
d. T4 protein and t4 DNA.
e. T4 protein and T2 DNA

Back 82

d

Front 83

SELF QUIZ
2. RNA viruses require their own supply of certain enzymes because
a. host cells rapidly destroy the viruses.
b. host cells lack enzymes that can replicate the viral genome.
c. these enzymes translate viral mRNA into proteins.
d. these enzymes penetrate host cell membranes.
e. these enzymes cannot be made in host cells.

Back 83

b

Front 84

SELF QUIZ
3. Which of the following characteristics, structures, or processes is common to both bacteria and viruses?
a. metabolism
b. ribosomes
c. genetic material composed of nucleic acid
d. cell division
e. independent existence

Back 84

c

Front 85

SELF QUIZ
4. Emerging viruses arise by
a. mutaion of existing viruses
b. the spread of existing viruses to new host species.
c. the spread of existing viruses more widely within their host species.
d. all of the above
e. none of the above

Back 85

d

Front 86

SELF QUIZ
5. To cause a human pandemic, the H5N1 avian flu virus would have to
a. spread to primates such as chimpanzees
b. develop into a virus with a different host range.
c. become capable of human-to-human transmission
d. arise independently in chickens in NOrth and South america
e. become much more pathogenic.

Back 86

c