Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MICR3320 > 10 - Retrovirus & Hepadnavirus Replication > Flashcards

10 - Retrovirus & Hepadnavirus Replication Flashcards

1
Q

Retroviridae

A
  • Enveloped (+)ssRNA genomes
  • USe RT to synthesise cDNA intermediate
  • Includes HIV and HTLV
  • Exist in human genomes in endogenous or exogenous form
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Endogenous form of retroviral genomes

A
  • Common in the genomes of humans (4-8%)
  • Ancient relics of germ line infection that occurred millions of years ago
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Exogenous

A

Horizontally transmitted, infectious viruses (eg HIV) that integrate dsDNA, complimentary to their genome, into a host
chromosome for gene expression

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Retrovirus endogenisation and human endogenous retrovirus (HERV) formation

A
  • During replication, retroviral RNA is reverse-transcribed into a double stranded DNA (dsDNA) provirus and integrated into the cellular genome
  • All current human retroviruses target somatic cells, showing a horizontal transmission from an infected individual to new hosts
  • The exogenous retroviruses that gave rise to HERVs were
    also able to infect germ line cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Key components of HIV

A
  • gp120-gp41
  • tRNA lys
  • Integrase
  • Capsid (cone shaped)
  • Matrix
  • Reverse Transcriptase
  • Nucleocapsid
  • Diploid genome
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Diploid retroviral genome

A
  • Diploid RNA genome (both copies identical)
  • Coated with nucleoproteins
  • Bound to tRNA, that is bound
    to viral RNA at the primer binding site PBS and serves as primer for reverse transcription
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

High genetic variability of HIV-1

A
  • Due to fast replication cycle and high mutation rate
  • May cause the generation of many viral variants in a single infected patient during a single day
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Major HIV group

A

Group M (main)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

HIV replication cycle

A
  • HIV-1 reverse transcription occurs in the cytoplasm with dsDNA transported to the nucleus.
  • Viral dsDNA integrates into a host chromosome using viral integrase.
  • Viral genes are transcribed by host Pol II which produces typical eukaryotic mRNA.
  • mRNA is transported to the cytoplasm where translation occurs
  • Some proteins enter the nucleus to affect gene expression
  • Genome-length mRNA is synthesized which is then transported to the cytoplasm and packaged
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Receptor binding in HIV entry

A

gp120 binds to CD4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Two major domains of retrovirus RT enzyme

A

p66 and p51

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Two active sites of RT

A
  • The polymerase active site
  • The RNase H active site
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

RNase H

A
  • Binds to RNA in duplex (either RNA:RNA or RNA:DNA) and makes internal cleavages to break apart RNA template
  • Essential in synthesis of complimentary dsDNA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

First 5 steps of reverse transcription in HIV-1

A
  1. (First strand (-) cDNA synthesis is initiated in a 5’ direction.
  2. RNase H activity degrades the small fragment of complimentary template RNA
  3. This allows for the first jump to occur. Complimentary R
    (R’) within the newly synthesised (-)cDNA is complimentary to R in the 3’ end of the RNA template, allowing for RT extension
  4. (-)cDNA extension occurs towards the 5’ end of the template
  5. With RNase H activity degrading the template RNA, leaving behind only the RNA complimentary to PPT
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Steps 6-8 of reverse transcription in HIV-1

A
  1. PPT’ provides a primer for the synthesis of ds CDNA (+), complimentary to the (-)cDNA
  2. RNase H activity removes all remaining RNA template, allowing for the second jump, with PBS from the second
    strand complimenting the PBS’ of the 5’ end of the (-)cDNA template
  3. Result is dsDNA with long terminal repeats (LTRs) at both ends, containing U3, R and U5
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Comparison of HIV RNA genome and proviral DNA

A
  • 5’ end of the genome differs in sequence from the 5’ LTR
  • The 3’ end of the genome is poly-adenylated, while in
    the provirus there is another copy of the LTR.
  • The provirus is flanked by host DNA
17
Q

HIV-1 cDNA integration into host cell DNA by viral integrase

A
  • One DNA produced from 2 genomic RNAs by viral RT
  • Viral LTR (U3, R and UF domains) is promoter
  • Proviral DNA (ie. Integrated viral DNA) directs the host transcription machinery to synthesise many copies of viral mRNA
  • Viral mRNA is translated into viral proteins OR encapsidated into new viral particles
  • No mechanism for excision of integrated provirus
18
Q

LTRs

A
  • Essential for transcription
  • Many sequences in LTR that interact with host TFs
  • Core promoter in composed of TATA box and many transcription binding sites
  • The 5’ and 3’ LTRs are identical, but serve different functions
19
Q

3’ LTR

A

Regulates 3’ end processing of the pre mRNA affecting polyadenylation and transcription termination

20
Q

HIV-1 accessory TAT protein

A
  • Transcription initiation is not sufficient to produce mRNA
  • Transcription elongation, involving host pol II must also
    occur
  • Tat, promotes elongation through interaction with a stem-loop structure called the Tar element, found in all HIV-1 mRNA
21
Q

Event following Tar binding to Tat

A
  • The whole complex then binds to host proteins including a kinase
  • The kinase phosphorylates Pol 2 which promotes elongation
22
Q

Five non enzymatic structural subunits expressed by all retroviruses

A
  • SU
  • TM
  • MA
  • CA
  • NC
23
Q

SU

A

The surface protein for receptor binding

24
Q

TM

A

Transmembrane protein found in viral envelope

25
Q

MA

A

MAtrix protein, between capsid and envelope

26
Q

CA

A

CApsomer

27
Q

NC

A

Nucleoprotein, associated with RNA genome

28
Q

Three enzymes encoded for by all retroviruses

A
  • Reverse transcriptase
  • Integrase
  • Protease
29
Q

Protease

A

Processes three seperate polyproteins:
- Gag
- Gag-pol
- Env

30
Q

Hepadnaviruses

A
  • Enveloped viruses,
  • Circular genomes (3.3kb) with both DNA and RNA-
  • dsDNa with gap of ssDNA
  • The longer DNA strand has terminal protein (P) attached at 5’ end
  • Shorter DNA is a DNA-RNA chimera, small number of RNA nts at 5’ end
  • Triplex DNA region
  • Use reverse transcription to amplify their genomes, even though their genomes are predominately DNA
  • No genome integration
31
Q

Example of hepadnavirus

A

Hepatitis B

MICR3320 (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions