Viruses

Question 1

shared features of viruses

Answer 1

1. non-cellular (no cytoplasm, metabolism, enzymes)
2. obligate intracellular parasites
3. multiple origins (no shared ancestor)
4. small, fixed size (smaller than the host cell, lack structural features, do not grow)
5. nucleic acid as genetic material (same as host cell - where their proteins are synthesized, same genetic code)
6. capsid made of protein subunits

Question 2

which enzymes do viruses have

Answer 2

• replication of genetic material
• infecting host cells
• lysis (bursting hist cells)

Question 3

what kind of genetic material can viruses have

Answer 3

• double/single-stranded RNA which can be circular/linear
• double/single-stranded DNA which can be positive/negative sense

Question 4

positive vs negative sense

Answer 4

positive sense - can be used immediately as mRNA - negative has to be transcribed before translation

Question 5

diversity of viruses

Answer 5

1. genetic diversity - no genes occur in all viruses
2. structural diversity (can be enveloped or non-enveloped)

Question 6

virus membrane is made out of

Answer 6

phospholipids (from the hosts’ plasma membrane (lysis))
glycoproteins (from the virus)

Question 7

virus membrane function and which viruses have it

Answer 7

helps the virus to make contact and infect the host cell
animal viruses are enveloped
(plant and bacteriophages are mostly non-enveloped)

Question 8

Influenza virus

Answer 8

• infects epithelial cells of respiratory system
• eight single-stranded negative-sense RNA
• enveloped
• RNA-replicase enyzme

Question 9

TMV (Tobacco Mosaic Virus)

Answer 9

• infects plant cells
• one single-stranded positive-sense RNA
• non-enveloped
• 1st discovered virus

Question 10

Bacteriophage

Answer 10

• infects bacteria
• one double-stranded DNA
• non-enveloped

Question 11

COVID-19

Answer 11

• infects epithelial cells of human respiratory system
• single-stranded positive-sense RNA
• enveloped (have spike proteins on the capsid - receptors, initiate fusion of the virus with the host cell)

Question 12

HIV

Answer 12

• infects human T-lymphocyte cells (a type of white blood cell that is a part of the immune system - develop in bone marrow)
• two single-stranded positive-sense RNA
• enveloped
• retrovirus - converts RNA to DNA - reverse transcriptase (has the highest mutation rate)

Question 13

lytic cycle

Answer 13

virus attaches and injects its genetic material which produces viruses inside of the host cell and then bursts it

Question 14

steps of lytic cycle

Answer 14

1|attachment (to a host cell using tail fibers)
2|penetration - genetic material entered via tail and pores in the membrane
3|DNA replication (100 copies)
4|sythesis of viral proteins - using mRNA transcribed from viral genetic material
5|assembly (of new viruses)
6|lysis (host bursting)

Question 15

lysogenic cycle

Answer 15

viral genetic material becomes integrated into the host cell’s genetic material - virus is temperate in this state because it does not kill its host (causes minimal harm) - daughter cells of the host inherit the undetected and inactive viral genes - stimulus for lysis can come from inside or outside of the host
- steps the same as in lytic but with integration

Question 16

how is the viral genetic material while its integrated called

Answer 16

prophage

Question 17

why is lysogenic cycle called that

Answer 17

it could change to the lytic state and then cause lysis

Question 18

evidence for several origins of viruses

Answer 18

1|obligate parasites - cells evolved before
2|use the same genetic code as living organisms - evolved from cells by losing cell components and life functions
3|diverse in structure and genetic constitution (similarities due to convergent evolution)
4|evolved from cell components (some virus-like cell components)

Question 19

main reasons for rapid rates of evolution in viruses

Answer 19

1|short generation times (under an hour) in the lytic cycle
2|high mutation rates (RNA viruses)
3|intense natural selection (host cells defending (antibodies))

Question 20

why do influenza and HIV have high mutation rates

Answer 20

influenza - RNA replicase replicates genetic material and does not proofread or correct errors - transmission of flu between humans and other species triggers evolution
HIV - reverse transcriptase converts single-stranded RNA genome to DNA - does not proofread or correct errors - enzyme cytidine deaminase made by the host that converts C to U - highest mutation rate produces genetically different strains, becomes resistant to drugs, evades the immune system, chronic infection