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BI157 > Chapter 19 > Flashcards

Chapter 19 Flashcards

1
Q

What is a virus? (3)

A

an infectious particle made of genes in a protein coat

Cannot reproduce or metabolize outside a host cell

Lacks metabolic enzymes for making proteins

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2
Q

What are bacteriophages? (2)

A

viruses that infect bacteria

Phages that infect the same bacteria are often similar in structure

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3
Q

How big are viruses? (3)

A

About 20 nm in diameter

The largest ones can be 100 nm

Smaller than a ribosome

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4
Q

What are viruses made of? (3)

A

Genome

capsid

viral envelope

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5
Q

What is a capsid? (3)

A

protein shell that encloses the genome

Capsomeres- protein subunits making up capsid

Can carry viral enzymes

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6
Q

What are helical viruses?

A

a rod-shaped virus with capsid being arranged around the genome in a helix

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7
Q

What is a viral envelope? (2)

A

-a membranous envelope that surrounds the capsids and helps infect the host

Made from the membranes of the host cell’s phospholipid and membrane protein

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8
Q

What is a virus genome? (3)

A

Different virus possesses different genomes

Ranges from double-stranded DNA, single-stranded DNA, double-stranded RNA, etc.

Named either DNA or RNA virus based on the genome

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9
Q

What are obligate intracellular parasites?

A

parasites that can replicate only within a host cell

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10
Q

What is a host range? (4)

A

the amount of cells a particular virus can effect

A type of virus can only affect hosts the virus can recognize

Similar to a lock and key

Often limited to a particular tissue
Example- AIDS virus only bind to immune system cells

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11
Q

What are the steps for viral replication cycle? (6)

A

The virus enters the cell, uncoats, and releases viral DNA and capsid proteins

The host enzymes then replicate the viral genome

The host provides the virus with nucleotides, enzymes, ribosomes, tRNA, amino acids, ATP, and more

The host enzyme then transcribes the viral genome into viral mRNA

Host ribosomes then use viral mRNA to produce more capsid proteins

Viral genomes and capsid proteins self-assemble into new viruses, and leaves the cell

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12
Q

How does viral replication difer between RNA and DNA viruses?

A

DNA viruses use host DNA polymerase to synthesize new genomes along viral DNA

RNA viruses encode RNA polymerases into the cell and use RNA as a template

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13
Q

How doess a virus enter a cell? (4)

A

Depends on the type of virus and host cell

Some use tails to inject DNA

Others enter through endocytosis

Some fuse with the membrane

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14
Q

How can phages replicate? (2)

A

Lytic cycle

Lysogenic cycle

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15
Q

What is the lytic cycle?

A

A phage replicative cycle that results in the death of the host cell

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16
Q

What are virulent phages?

A

a phage that replicates only by a lytic cycle

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17
Q

What are the steps to the lytic cycle? (5)

A

The virus enters the cell, with the empty casing left outside

Phage DNA directs the production of phage protein and genome using the host cell’s materials

Proteins self-assemble into a virus

The phage then directs the production of enzymes that breaks down cell walls

Fluids enter and burst the cell

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18
Q

How does a bacteria defend against proteins? (3)

A

Natural selection favors mutations of surface proteins viruses cannot recognize

Restriction enzymes- enzymes that identify viral DNA and cut it up

Host DNA is methylated to prevent attacks

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19
Q

Why is the lysogenic cycle?

A

Phage replication that doesn’t kill host cells

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20
Q

What are temperate phages? (2)

A

phages capable of both lytic and lysogenic cycles

Cycle changes are triggered by environmental signals

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21
Q

What are the step to the lysogenic cycle? (5)

A

A virus enters the cell and either enters a lytic or lysogenic cycle

if it enters lytic cycle, it Immediately turns the host into a virus-producing factory and lyses immediately

If it enters a lysogenic cycle

Incorperates viral DNA into host chromosomes
Forms a prophage

Prevents transcription of other prophage genes

As the host cells divides, it replicates the viral DNA along with its own

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22
Q

How are animal viruses classified, and what do they possess? (3)

A

whether the genome is double or single-stranded

Single-stranded RNA are further classified into 3 classes

All animal viruses with RNA genomes have an envelope

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23
Q

What are viral glycoproteins?

A

proteins on viral envelopes that bind to specific receptor molecules on the host cell surface

24
Q

How does an animal virus enter a cell? (9)

A

Capsid and viral genome enter the cell.

Cell enzymes digests the capsid which results in a release in viral genome

Viral genome functions as a template for RNA synthesis by a viral RNA polymerase

New copies of RNA are made

Template strand of viral RNA can function as mRNA

Translates capsid protein (in the cytosol) and glycoproteins (ER and Golgi)

Vesicles transport glycoproteins to plasma membrane

Capsid assembles arround viral genome molecules

Each new virus buds from the cell, envelope studded with synthesized glycoproteins embedded in the membrane

25
Q

How do double-stranded DNA viruses replicate?

A

Replicate within the host cell nucleus to replicate and transcribe its DNA

Can leave behind viral DNA in the nucleus

Outside factors can trigger the viral DNA left behind to begin virus production

26
Q

What are the classes of a single-stranded RNA virus? (3)

A

3 classes

4 and 5 have a path of RNA > RNA synthesis

Class 6 have a path of RNA > DNA

27
Q

What is class 4 of single-stranded RNA viruses?

A

Virus genome can serve as mRNA and translate its protein immediately after infection

28
Q

What is class 5 of single-stranded RNA viruses?

A

RNA genome serves as a template for mRNA synthesis

29
Q

What are retroviruses? (2)

A

viruses equipped with reverse transcriptase

An enzyme that transcribes an RNA template into DNA

30
Q

What is HIV?

A

Human immunodeficiency virus, a retrovirus that causes acquired immunodeficiency syndrome

31
Q

How does HIV replicate? Part 1 (6)

A

Viral Envelope of glycoproteins enables virus to bind to receptors on white blood cells

Virus fuses with host’s membrane and capsid proteins are removed

Releases viral proteins and RNA

Reverse transcriptase catalyzes the synthesis of DNA complementary to viral RNA

Reverse transcriptase catalyzes the synthesis of a second DNA strand complementary to the first

Double stranded DNA is incorporated as a provirus into the cell’s DNA

32
Q

How does HIV replicate? Part 2 (6)

A

Provirus never leaves the host’ genome

Proviral genes are transcribed into RNA molecules, serving as genomes for progeny viruses and as mRNAs for translation into viral proteins

Viral proteins include capsid protein and reverse transcriptase and envelope glycoproteins

Vesicles transport glycoprotein to the host cell’s plasma membrane

Capsids assemble in the host around viral genomes and reverse transcriptase molecules

New viruses with viral envelope glycoprotein bud from the host cell

33
Q

When did viruses originate?

A

After the first cells appeared

34
Q

What are plasmids? (4)

A

small, circular DNA found in bacteria

Candidate for original source of viral genome

Exists apart from and can replicated independently
from the bacterial chromosome

Transferred between cells

35
Q

What are transposons? (2)

A

DNA segments that can move from one location to another within a cell’s genome

Other candidate for original viral genome

36
Q

What are mobile genetic elements?

A

a feature of moving from cell to cell

37
Q

What idea supports the evolution of viruses? (2)

A

Some viruses that are not closely related share similar traits

Arise from past viruses that were favored by natural selection

38
Q

What is the mimivirus? (3)

A

large virus discovered that helps genes found in only cellular genomes

Either evolved before the first cell and formed an exploitative relationship

Or evolved recently and scavenged for genes from hosts

39
Q

What is ds/DNA pandoravirus? (3)

A

largest virus discovered

Cannot be classified with other viruses

90% of its genes are related to cellular genes

40
Q

How does a virus cause symptoms in animals? (3)

A

Viruses killing/ damaging cells causing lysosomes to release hydrolytic enzymes

Viruses causing infected cells to produce toxins that produce disease symptoms

Viruses containing toxic molecular component

41
Q

What does the amount of damage a virus can do depend on?

A

The infected tissues ability to regenerate

42
Q

What is a vaccine? (2)

A

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

Although vaccines can prevent diseases, not much can be done once infected

43
Q

What is a cocktail? (2)

A

treatment of two nucleoside mimics and protease inhibitor

Interferes with an enzyme that assembles viruses

44
Q

What is an emerging virus?

A

viruses that suddenly become apparent

Example- HIV, AIDS

45
Q

What is a hemorrhagic fever?

A

often fatal illness causing fever, vomiting, bleeding, a circulatory system collapse

46
Q

what is an epidemic?

A

widespread outbreak

47
Q

What is a pandemic?

A

global epidemic

48
Q

How do viral diseases emerge? (6)

A

Mutation of existing viruses

RNA viruses mutate easily because viral RNA does not proofread errors

Dissemination of a viral disease from a small, isolated human population

Spread of existing viruses from other animals

Can mutate as it passes from one host species to another

Two different strains of a viral disease can undergo ginetic recombination

49
Q

What is influenza?

A

Viral diseases in three forms, A, B, and C

50
Q

What is the B and C influenza?

A

only affect humans and have never caused an epidemic

51
Q

What is type A influenza? (3)

A

affects a wide range of animals and caused four flue epidemics

Influenza A was named H1N1

Named after the two viral surface protein- hemagglutinin and neuraminidase

52
Q

How do viruses spread in plants? (3)

A

horizontal transmission

vertical transmission

Once the virus enter’s the plant’s system, it can spread through plasmodesmata

53
Q

What is horizontal transmission?

A

plant is infected from an external source of the virus

Ex- herbivores carrying diseases and breaking through the plant’s layers

54
Q

What is vertical transmission?

A

plant inherits a viral infection from a parent

55
Q

What are viroids? (3)

A

Circular RNA molecules that infects plants

Do not encode protein but replicate in plant cells

Cause error in the regulatory system and stunts growth

56
Q

What are prions? (4)

A

Infectious proteins that causes degenerative brain disease

Acts very slowly, and have around 10+ years of incubation periods

Virtually indestructible

Infects by converting a healthy protein into misfolded versions

BI157 (21 decks)

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