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BI157 > Chapter 19 > Flashcards

Chapter 19 Flashcards

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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?

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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)

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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
How do double-stranded DNA viruses replicate?
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
What are the classes of a single-stranded RNA virus? (3)
3 classes 4 and 5 have a path of RNA > RNA synthesis Class 6 have a path of RNA > DNA
27
What is class 4 of single-stranded RNA viruses?
Virus genome can serve as mRNA and translate its protein immediately after infection
28
What is class 5 of single-stranded RNA viruses?
RNA genome serves as a template for mRNA synthesis
29
What are retroviruses? (2)
viruses equipped with reverse transcriptase An enzyme that transcribes an RNA template into DNA
30
What is HIV?
Human immunodeficiency virus, a retrovirus that causes acquired immunodeficiency syndrome
31
How does HIV replicate? Part 1 (6)
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
How does HIV replicate? Part 2 (6)
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
When did viruses originate?
After the first cells appeared
34
What are plasmids? (4)
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
What are transposons? (2)
DNA segments that can move from one location to another within a cell’s genome Other candidate for original viral genome
36
What are mobile genetic elements?
a feature of moving from cell to cell
37
What idea supports the evolution of viruses? (2)
Some viruses that are not closely related share similar traits Arise from past viruses that were favored by natural selection
38
What is the mimivirus? (3)
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
What is ds/DNA pandoravirus? (3)
largest virus discovered Cannot be classified with other viruses 90% of its genes are related to cellular genes
40
How does a virus cause symptoms in animals? (3)
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
What does the amount of damage a virus can do depend on?
The infected tissues ability to regenerate
42
What is a vaccine? (2)
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
What is a cocktail? (2)
treatment of two nucleoside mimics and protease inhibitor Interferes with an enzyme that assembles viruses
44
What is an emerging virus?
viruses that suddenly become apparent Example- HIV, AIDS
45
What is a hemorrhagic fever?
often fatal illness causing fever, vomiting, bleeding, a circulatory system collapse
46
what is an epidemic?
widespread outbreak
47
What is a pandemic?
global epidemic
48
How do viral diseases emerge? (6)
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
What is influenza?
Viral diseases in three forms, A, B, and C
50
What is the B and C influenza?
only affect humans and have never caused an epidemic
51
What is type A influenza? (3)
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
How do viruses spread in plants? (3)
horizontal transmission vertical transmission Once the virus enter’s the plant’s system, it can spread through plasmodesmata
53
What is horizontal transmission?
plant is infected from an external source of the virus Ex- herbivores carrying diseases and breaking through the plant’s layers
54
What is vertical transmission?
plant inherits a viral infection from a parent
55
What are viroids? (3)
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
What are prions? (4)
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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