PHM 320 FINAL EXAM
How do negative (-) ssRNA viruses avoid the problem of translating multiple reading frames on
single incoming virus RNA molecule?
- they use their (+) strands as template for more (-) strands and (-) as template for more (+)
strands
Retrovirus structure
- viral particles containing 2 strands of (+) RNA inside 2 protein shells surrounded by an outer
envelope layer
Retrovirus MOA upon entering cell
-convert RNA to dsDNA using reverse transcriptase
-dsDNA can be inserted into the host genome through integration
(T/F) retroviruses do not use their (+) ssRNA as mRNA
- true -- they use it as a template for reverse transcriptase
Describe 2 step process of reverse transcription in retroviruses
- Step 1. a complementary strand of DNA is made forming an RNA-DNA hybrid molecule
Step 2: the original RNA is degraded and a second DNA strand is made
What acts as the primer for reverse transcriptase in retroviruses and how?
- 2 tRNA molecules from the host cell base pair to the retrovirus' 2 (+) ssRA molecules that are
also held together by base pairing
-the tRNA acts as a primer for RT
How does integration occur in retroviruses?
,- the dsDNA is flanked by two long terminal repeats (LTR) that facilitate the insertion
-retrovirus DNA can then be transcribed and expressed like any other host cell gene
How is retrovirus RNA processed?
- addition of a 7-methyl-G-cap and a poly(A) tail
Describe HIV's genome
-regulatory tat and rev genes are each encoded as 2 segments that must be spliced together
at the RNA level during gene expression
-gag, pol, and env are polyproteins that give rise to 2-3 proteins after cleavage
What is the most widespread form of HIV?
- HIV-1
HIV entry/fusion inhibitors MOA
-target gp120/41 or CCR5
-gp120/41 are proteins on HIV surface that bind to host cell receptors to fuse & enter cell
-CCR5 is a co-receptor on host immune cell to allow entry of HIV
HIV nucleoside reverse transcriptase inhibitors (NRTI) MOA
-target reverse transcriptase
-includes AZT, d4T, FTC, ABC
-mimics DNA nucleosides & binds to active site of RT
-causes chain termination (don't have 3' OH)
-prevent incorporation of nucleotide to primer-template
HIV non-nucleoside reverse transcriptase inhibitor (NNRTI) MOA
-rigid or flexible
-bind to allosteric pocket of RT near catalytic site
-causes conformational change that affects RT activity
,What two proteins besides reverse transcriptase do HIV therapies target?
- HIV integrase and HIV protease
Genome of coronavirus
- positive (+) ssRNA
How do coronaviruses replicate?
- use RNA-dependent RNA synthesis to generate mRNAs to be transcribed by host genome
What receptor does the coronavirus spike protein bind to on the host cell and how does it enter
the cell?
- CEACAM-1 receptor; receptor-mediated endocytosis
Translation of coronavirus (+) ssRNA results in _____ via ________
- 2 polyproteins; frameshifting (pp1a & pp1ab)
When coronavirus polyproteins undergo proteolysis, a _________ complex is formed
- replicase-transcriptase
How is RNA(+) used by coronaviruses?
- 1. to make RNA (-) strand
2. to make polyproteins
How is RNA(-) used by coronaviruses?
- 1. to make more RNA(+) to be repackaged into virion progeny
2. to be transcribed in discontinuous transcription to make many different mRNAs
How do coronaviruses make progeny?
, - structural proteins and (+) RNA are sent to golgi apparatus, forming vesicles which become
progeny
How are coronavirus progeny released from the cell?
- exocytosis
In discontinuous transcription, one full length mRNA contains:
- 1. leader transcription regulatory sequence (encodes replicase polyprotein sequence, 2
ORFs)
2. multiple body TRS's that encode structural proteins
Describe discontinuous transcription
- the transcription process stops after it gets to a certain body TRS that codes for a certain
protein and jumps ahead to the leader TRS, skipping the bother body TRS's in between
Transposons are:
- small, mobile pieces of DNA
Insertion of transposon into the middle of a gene _______
- disrupts the coding sequence
DNA inversion:
- a segment of DNA is inverted but remains at the same overall location
Location of second copy when DNA is duplicated:
- the second copy remains near the same location as the original
Some mutagens are carcinogens, meaning they can induce ______
How do negative (-) ssRNA viruses avoid the problem of translating multiple reading frames on
single incoming virus RNA molecule?
- they use their (+) strands as template for more (-) strands and (-) as template for more (+)
strands
Retrovirus structure
- viral particles containing 2 strands of (+) RNA inside 2 protein shells surrounded by an outer
envelope layer
Retrovirus MOA upon entering cell
-convert RNA to dsDNA using reverse transcriptase
-dsDNA can be inserted into the host genome through integration
(T/F) retroviruses do not use their (+) ssRNA as mRNA
- true -- they use it as a template for reverse transcriptase
Describe 2 step process of reverse transcription in retroviruses
- Step 1. a complementary strand of DNA is made forming an RNA-DNA hybrid molecule
Step 2: the original RNA is degraded and a second DNA strand is made
What acts as the primer for reverse transcriptase in retroviruses and how?
- 2 tRNA molecules from the host cell base pair to the retrovirus' 2 (+) ssRA molecules that are
also held together by base pairing
-the tRNA acts as a primer for RT
How does integration occur in retroviruses?
,- the dsDNA is flanked by two long terminal repeats (LTR) that facilitate the insertion
-retrovirus DNA can then be transcribed and expressed like any other host cell gene
How is retrovirus RNA processed?
- addition of a 7-methyl-G-cap and a poly(A) tail
Describe HIV's genome
-regulatory tat and rev genes are each encoded as 2 segments that must be spliced together
at the RNA level during gene expression
-gag, pol, and env are polyproteins that give rise to 2-3 proteins after cleavage
What is the most widespread form of HIV?
- HIV-1
HIV entry/fusion inhibitors MOA
-target gp120/41 or CCR5
-gp120/41 are proteins on HIV surface that bind to host cell receptors to fuse & enter cell
-CCR5 is a co-receptor on host immune cell to allow entry of HIV
HIV nucleoside reverse transcriptase inhibitors (NRTI) MOA
-target reverse transcriptase
-includes AZT, d4T, FTC, ABC
-mimics DNA nucleosides & binds to active site of RT
-causes chain termination (don't have 3' OH)
-prevent incorporation of nucleotide to primer-template
HIV non-nucleoside reverse transcriptase inhibitor (NNRTI) MOA
-rigid or flexible
-bind to allosteric pocket of RT near catalytic site
-causes conformational change that affects RT activity
,What two proteins besides reverse transcriptase do HIV therapies target?
- HIV integrase and HIV protease
Genome of coronavirus
- positive (+) ssRNA
How do coronaviruses replicate?
- use RNA-dependent RNA synthesis to generate mRNAs to be transcribed by host genome
What receptor does the coronavirus spike protein bind to on the host cell and how does it enter
the cell?
- CEACAM-1 receptor; receptor-mediated endocytosis
Translation of coronavirus (+) ssRNA results in _____ via ________
- 2 polyproteins; frameshifting (pp1a & pp1ab)
When coronavirus polyproteins undergo proteolysis, a _________ complex is formed
- replicase-transcriptase
How is RNA(+) used by coronaviruses?
- 1. to make RNA (-) strand
2. to make polyproteins
How is RNA(-) used by coronaviruses?
- 1. to make more RNA(+) to be repackaged into virion progeny
2. to be transcribed in discontinuous transcription to make many different mRNAs
How do coronaviruses make progeny?
, - structural proteins and (+) RNA are sent to golgi apparatus, forming vesicles which become
progeny
How are coronavirus progeny released from the cell?
- exocytosis
In discontinuous transcription, one full length mRNA contains:
- 1. leader transcription regulatory sequence (encodes replicase polyprotein sequence, 2
ORFs)
2. multiple body TRS's that encode structural proteins
Describe discontinuous transcription
- the transcription process stops after it gets to a certain body TRS that codes for a certain
protein and jumps ahead to the leader TRS, skipping the bother body TRS's in between
Transposons are:
- small, mobile pieces of DNA
Insertion of transposon into the middle of a gene _______
- disrupts the coding sequence
DNA inversion:
- a segment of DNA is inverted but remains at the same overall location
Location of second copy when DNA is duplicated:
- the second copy remains near the same location as the original
Some mutagens are carcinogens, meaning they can induce ______
