A2.3 viruses

Question 1

structural features common to all viruses

Answer 1

-small fixed size
-nucleic acid RNA or DNA
-capsid made of proteins
-no cytoplasm
-few to no enzymes

Question 2

function of capsid

Answer 2

-protection of genetic material
-unique structure
-contain specialized sites on capsid that contain specialized proteins that allow genetic material of virus to penetrate host cell

Question 3

diversity in the structure in viruses

Answer 3

-can have either RNA or DNA double or single stranded
-some have an envelope outside capsid
-10-400nm, exceptions as big as bacteria
-wide variation in shape

Question 4

features of bacteriophage lambda

Answer 4

• capsid head protecting double strand DNA
  -tail fibers that allow attachment to cost cell
  -tail sheath made of proteins that drive tail tube through hosts outer membrane
  -DNA is injected through tail
  host: e-coli

Question 5

features of coronavirus

Answer 5

-spherical shape
-single stranded RNA
-envelope outside capsid
-projections of spike proteins on envelope
host: cells in airway of lungs

Question 6

features of HIV

Answer 6

-has an envelope outside capsid
-two identical strands of RNA in capsid
-is known as a retrovirus because it makes DNA copies of RNA code
-envelope has spikes
-contains viral enzymes
-host cell specificity is white blood cells

Question 7

steps of the lytic cycle

Answer 7

'’lysis’’= rupturing of cell membranes by an enzyme called lysozyme

1. phage attaches to host cell
2. inject genetic material
   3)DNA replication within cell
   4)transcription turns viral DNA into mRNA
   5)translates mRNA into proteins to assemble more viruses
   6)cell busts

Question 8

steps of the lysogenic cycle

Answer 8

1)virus attaches to cell
2)inserts genetic material
3)viral DNA becomes part of hosts DNA (integration)
4)host cell divides with incorporated viral DNA

Question 9

difference of lytic and lysogenic cycle

Answer 9

lytic=
-kills host cell
-reproduces and bursts
-detective
lysogenic=
-DNA integrated
-undetectable
-stimuli can cause virus to switch to lytic
-doesn’t kill host cell

Question 10

reasons why viruses evolve rapidly
+in cases of influenza and HIV

Answer 10

-short generation time
-lots of mutations
-natural selection favors viruses that help evade detection
INFLUENZA=
-rapidly evolving RNA virus
-high mutation rate
-transmittion between species cause new strains
HIV=
-RNA reversed transcribed into DNA with no proof reading
-HIGH mutation rates
-many different strain can infect at the same time
-drug resistant

Question 11

evidence for several origins of viruses

Answer 11

-viruses need host cell to replicate- shows cells evolved before viruses
-use same universal genetic code-viruses evolved from cells
-viruses are diverse= convergent evolution
-could have evolved from cells by series of step by step loss of components