chapter 19 - fungi

Question 1

what is a virus?

Answer 1

an infectious particle consisting of genes packaged in a protein coat

Question 2

are viruses alive?

Answer 2

“borrowed life” - shady area bw life-forms and chemicals, they cannot reproduce or carry out metabolism outside host cell

Question 3

tobacco mosaic disease

Answer 3

a disease that stunts tobacco plant growth and gives leaves mosaic coloration, used to think it was small bacteria but realized it’s virus bc it didn’t grow on nutrient media

Question 4

who confirmed TMV pathogen was a virus?

Answer 4

wendell stanley in 1935

Question 5

what does a virus consist of?

Answer 5

nucleic acid enclosed in protein coat and sometimes membranous envelope

Question 6

viruses have between _____ genes in their genome

Answer 6

3-2,000

Question 7

what is a capsid?

Answer 7

protein shell surrounding the viral genome

Question 8

what are capsids built from?

Answer 8

protein subunits called capsomeres

Question 9

what are viral envelopes?

Answer 9

they are derived from membranes of host cells, surround capsids of influenza viruses and many other viruses

Question 10

what are bacteriophages?

Answer 10

viruses that only infect bacteria. aka phages

Question 11

host range

Answer 11

a limited number of host cells that the virus can infect

Question 12

cross-species transmission (CST) or spillover is…

Answer 12

rare

Question 13

how do viruses replicate once they enter host cells?

Answer 13

cell starts manufacturing viral proteins, making use of host enzymes, ribosomes, tRNAs, ATP, etc. viral nucleic acid molecules and capsomeres self-assemble into new viruses

Question 14

what are the two alternative reproductive mechanisms of phages?

Answer 14

lytic and lysogenic cycle

Question 15

what is the lytic cycle?

Answer 15

a phage replicative cycle that occurs in the death of host cells

Question 16

virulent phage

Answer 16

a phage that reproduces only by the lytic cycle

Question 17

what is the lysogenic cycle?

Answer 17

replicates the phage genome without destroying the host; viral DNA molecule incorporated into host cell chromosomes

Question 18

temperate phages

Answer 18

phages that use both the lytic and lysogenic cycles

Question 19

prophage

Answer 19

the integrated viral DNA

Question 20

bacteria’s defense against phages

Answer 20

• natural selection favors bacterial mutants w/ surface proteins that cannot be recognized as receptors by a particular type of phage
• foreign DNA can be identified and cut up by restriction enzymes

Question 21

what are restriction enzymes?

Answer 21

nucleases that cut double-stranded DNA at specific nucleotide sequences “molecular scissors”

Question 22

what do bacteria and archaea use to protect themselves from viral infection?

Answer 22

CRISPR-Cas system (clustered regularly interspaced short palindromic repeats)

Question 23

many viruses that infect humans have a…

Answer 23

membranous envelope

Question 24

what are the two key variables used to classify viruses that infect animals?

Answer 24

1. RNA vs DNA genome, either single or double-stranded
2. the presence or absence of a membranous envelope

Question 25

where does the viral envelope come from?

Answer 25

the host cell's plasma membrane as viral capsids exit

Question 26

what are retroviruses?

Answer 26

use an enzyme called reverse transcriptase to copy their RNA genome into DNA (HIV)

Question 27

human immunodeficiency virus causes...

Answer 27

AIDS (acquired immunodeficiency syndrome)

Question 28

provirus

Answer 28

viral DNA that is integrated into the host genome; remains PERMANENT resident of host cell

Question 29

which enzyme transcribes proviral DNA to RNA?

Answer 29

RNA polymerase

Question 30

dsDNA w/ envelope present...

Answer 30

smallpox virus. (lesions on skin)

Question 31

ssDNA w/ no envelope

Answer 31

B19 parovirus (mild rash, rosy cheeks)

Question 32

dsRNA w/ no envelope

Answer 32

rotavirus (intestinal distress, diarrhea)

Question 33

ssRNA w/ envelope (serves as mRNA)

Answer 33

zika virus (mosquito, gestational distress and abnormalities in fetus development)

Question 34

ssRNA w/ envelope (serves at template for mRNA synthesis)

Answer 34

ebola virus (hemorrhagic fever)

Question 35

what are prions?

Answer 35

smaller, less complex infectious proteins that can cause disease in plants and animals. they cause degenerative brain disease in animals

Question 36

how do vaccines work?

Answer 36

a harmless version of the virus that stimulates an immune system response so body is prepared when actual virus infection occurs

Question 37

how can antiviral drugs help treat viral infections?

Answer 37

they inhibit synthesis of viral DNA and interfere with viral assembly

Question 38

emerging viruses

Answer 38

viruses that suddenly become apparent, Ebola, Zika, chikungunya

Question 39

what is an epidemic?

Answer 39

a widespread occurrence of an infectious disease in a community

Question 40

what is a global epidemic called?

Answer 40

pandemic

Question 41

example of epidemic

Answer 41

flu-like illness caused by influenza virus H1N1 in Mexico and US in 2009

Question 42

pandemic examle

Answer 42

black death, 1918 spanish flue, HIV/AIDS, covid-19

Question 43

endemic disease

Answer 43

exists permanently in a particular region

Question 44

endemic disease example

Answer 44

malaria in Africa and chicken pox in the US

Question 45

sporadic disease

Answer 45

diseases that are only seen occasionally, usually w/o geographic concentration

Question 46

what are the three processes contribute to the emergence of new viral diseases

Answer 46

1. RNA viruses have very high mutation rates 2. disease can be spread from an isolated place to worldwide 3. 3/4 of new human diseases originate by spreading to humans from animals

Question 47

vertical transmission

Answer 47

inheriting the virus from a parent

Question 48

horizontal transmission

Answer 48

viruses entering through damaged cell wall

Question 49

diseases caused by prions

Answer 49

mad cow disease, scrapie in sheep, Creutzfeldt-Jakob disease in humans

Question 50

prions might be involved in human diseases such as...

Answer 50

such as Alzheimer’s and Parkinson’s disease

Question 51

for the flu H1N1, what does “H” and “N” stand for?

Answer 51

H: Hemagglutinin (helps with attachment and entry to host cell) N: Neuraminidase (helps exit) proteins on the surface of influenza virus

Question 52

how does CRISPR-Cas work?

Answer 52

Invasion - A virus (like a phage) injects its DNA into the bacterium. Capture - The bacterium snips out a small piece of the viral DNA and stores it in its own genome in the CRISPR region. → These bits are called “spacers” and act like a memory system. Transcription - If the virus comes back, the bacterium transcribes that stored spacer into RNA. Targeting - The spacer RNA guides a Cas protein (like Cas9) to the matching viral DNA. Destruction - Cas cuts up the viral DNA

Question 53

why is HIV unusual?

Answer 53

- exceptionally high mutation rate - virus can rapidly adapt to challenges like the immune system's response or antiretroviral therapy - evolves too quickly for vaccine

Question 54

HIV and medications

Answer 54

antiretroviral therapy (ART) - targeting different stages of the virus's replication cycle 1. NRTIs and NNRTIs block the enzyme reverse transcriptase, preventing the virus from converting its RNA into DNA. 2. Protease inhibitors (PIs) stop the enzyme protease, which is needed to create new viral particles. 3. Integrase inhibitors block the integrase enzyme, stopping viral DNA from joining the host cell’s DNA. 4. Entry inhibitors prevent HIV from entering host cells. 5. Post-attachment inhibitors block HIV from attaching to host cells.

Question 55

"ghost" bacteriophages

Answer 55

the empty shell or protein coat that remains after the phage infects a bacterium and injects its genetic material

Question 56

what causes a cold sore? how is it treated?

Answer 56

caused by herpes simplex virus, contagious treatments - antiviral medication: topical treatments and oral antivirals like valacyclovir

Question 57

R₀ (R-naught)

Answer 57

represents the average number of people that one infected person will spread the disease to in a completely susceptible population (i.e., where no one has immunity and no preventative measures are in place).

Question 58

R-naught values

Answer 58

R₀ = 1: On average, each infected person will spread the disease to one other person. The disease will neither spread nor die out on its own. R₀ > 1: The disease will spread, and the number of infections will increase. R₀ < 1: The disease will eventually die out because each infected person spreads the disease to fewer than one person on average.

Question 59

disease with high R-naught values

Answer 59

Measles: R₀ = 12-18. Measles is one of the most contagious diseases known. An infected person can spread the virus to many others, especially in settings where people are in close contact. COVID-19: The early estimates of R₀ for COVID-19 ranged from 2.5 to 3.5, meaning each infected person could spread the virus to 2.5 to 3.5 other people on average. Chickenpox: R₀ = 10-12. Chickenpox is highly contagious and can spread easily in households or schools.

Question 60

disease with low R-naught values

Answer 60

Polio: R₀ = 5-7. While still highly contagious, the spread of polio is generally lower than diseases like measles. HIV/AIDS: R₀ = 2-5. HIV is spread through specific modes (sexual contact, blood transfusion, sharing needles), so its R₀ is much lower compared to airborne diseases. Ebola: R₀ = 1.5-2. Ebola spreads through contact with bodily fluids, so its transmission rate is lower compared to more easily spread diseases like measles.