virus

Question 1

virus

Answer 1

• small infectious particle that has DNA or RNA in a protein capsule
• very small: hundreds of thousands can fit into one human cell

Question 2

virus structure

Answer 2

• DNA or RNA, not both
• capsid-protein coating around the DNA/RNA
• no cytoplasm

Question 3

naked vs. enveloped virus

Answer 3

enveloped viruses have an envelope surrounding the nucleocapsid: nucleic acid + capsid

Question 4

DNA and RNA

Answer 4

carry information that provides instructions for synthesizing protein molecules

Question 5

host cells

Answer 5

the cell that a virus enters

Question 6

host range

Answer 6

viruses infect specific cells or tissues of specific hosts
- HIV: certain immune cells (white blood cells)
- common cold: upper respiratory tract
- rabies virus: all species of mammals+birds

Question 7

what causes symptoms of a virus infection + examples

Answer 7

• when a virus replicates inside our cells, it destroys host cells
• our immune system responds to the infection
• e.g. fever, sore throat, most coughs

Question 8

are viruses living?

Answer 8

no: they can’t reproduce on their own (need host cell) and can only evolve/mutate

Question 9

what criteria are viruses classified based on?

Answer 9

• size
• shape
• type of genetic material (DNA/RNA)

Question 10

viral shapes

Answer 10

• polyhedral
• spherical (e.g. coronavirus)
• helical
• complex

Question 11

bacteriophage

Answer 11

• complex shape (capsid, collar, phage tail)
• infect & destroy bacterial cells

Question 12

surface proteins

Answer 12

• lock and key mechanism
• outside of viral particles have proteins that are involved in attachment to host cells
• binding of viral surface proteins and host cell receptors is very specific

Question 13

infectious cycles

Answer 13

• viruses enter host cells and then replicate
• lytic cycles and lysogenic cycle

Question 14

lytic cycle steps

Answer 14

• binding
• synthesis of viral proteins and nucleic acids
• assembly of the unit
• lysis

Question 15

lytic cycle: binding

Answer 15

binding: proteins on virus surface interact with host cell receptors and virus binds to surface of host cell

Question 16

lytic cycle: synthesis

Answer 16

synthesis of viral proteins and nucleic acids: viral genetic materials are released from the virus and enter nucleus of the host cell to be replicated

Question 17

lytic cycle: assembly

Answer 17

assembly of the units: viral DNA/RNA instructs cell to make and assemble new viral DNA and capsids

Question 18

lytic cycle: lysis

Answer 18

lysis: host cell bursts, new viruses leave to find new infection site (go on to infect other cells)

Question 19

lysogenic cycle

Answer 19

• seen in viruses that do not kill the cell right away (e.g. Cancer-causing viruses HPV, Hepatitis C)
• viral DNA is dormant in cell and carried through many generations without harm to host

Question 20

lysogenic cycle steps

Answer 20

• binding & attachment - virus attaches to host cell
• integration - DNA/RNA integrated into cell’s DNA
• replication - viral DNA/RNA is replicated with host DNA and passed to daughter cells
• cycle continues until a trigger activates the lytic cycle (e.g. UV radiation, stress, chemical or environmental factors)

Question 21

lysogeny and induction

Answer 21

lysogeny: dormant state during lysogenic cycle
induction: activation of lytic cycle

Question 22

dormant infection examples

Answer 22

shingles (reactivation of virus that causes chickenpox) and cold sores (herpes simplex)

Question 23

vaccines

Answer 23

• contain weakened forms or parts of a dangerous virus
• trigger an immune response without actually making us sick
• produces chemicals that will stay in our body for a long time, so if we are exposed to the virus again, our body can quickly respond before we even feel symptoms

Question 24

gene therapy

Answer 24

• when a genetically modified virus (vector) carries genetic information that will enter the cells of a patient who lacks the gene for a protein