C replicative cycle

Question 1

1 attachment

Answer 1

SU binds to receptor CD4, found on t-helper cells and some other cells. this produces a conformational change in SU allowing it to bind to a coreceptor

Question 2

1. what is used as a coreceptor by R5 strains

Answer 2

R5 strains of HIV uses CCr5, a chemokine receptor. people who are CCr5 -ive are resistant to infection by 5R strains of HIV

Question 3

1. what is used as a coreceptor by X4 strains

Answer 3

CXCR4

Question 4

2. entry

Answer 4

attachment to receptor and coreceptor causes SU to move to side permitting the fusion peptide of TM to inserted into host’s PM. membrane fuse and capisd released into cytoplasm

Question 5

3. reverse transcriptase

Answer 5

+ive strand RNA genome is not translated. genome is used as template to make dsDNA. carried out by reverse transciptase, an enzyme w/3 catalytic activity

Question 6

3. 3 catalytic activity of reverse transcriptase

Answer 6

1. RDDP uses tRNA as primer to synthesize -ive DNA
2. RNAse H has exo and endonuclease fn. removes RNA including the tRNA
3. DDDP uses -ive DNA as template and pieces of RNA as primer

Question 7

what is produced at the end of reverse transcriptase activity

Answer 7

dsDNA w/long terminal repeat at each end. sequences are required for integration into host genome and for transcription. present as such on the viral genome

Question 8

4. genome

Answer 8

U means unique to 5’ or 3’ end

Question 9

5. integration

Answer 9

dsDNA is transported into nucleus. integrase also transported makes cut in host DNA and ligates in the viral DNA. now called a provirus

Question 10

6. the genes

Answer 10

Gag stands for group specific antigen. this region encodes CA, MA, NC, and a protease. pol endoces reverse transcriptase and integrate. env encodes for SU and TM

Question 11

7. transcription

Answer 11

a host DDRP begins transcription at the junction of the left UTR. host enzymes will splice, cap, polyadenylate the primary transcript producing mRNA. mRNA is transported to cytoplasm

Question 12

7. how does some transcript compared to original genome

Answer 12

some are full length and identical to original genome. others have gag and pol spiced out

Question 13

8. translation

Answer 13

mRNA encoding env only is translated on RER producing SU-TM precursor. SU-TM is cleaved in the golgi apparatus to produce SU and TM. inserted in the PM

Question 14

8. Translation full length mRNA

Answer 14

can be translated or fn as new genomes. when translated 90% of time ribosome begins translation at 5’ end of gag and stops at stop codon at 3’ end of gag. ribosome falls off. 10% of time synths contd. producing gag, pol polyprotein

Question 15

8. how does gag pol polyprotein occur

Answer 15

ribosomal shifting, ribosome stalls before stop codon at end of gag and slips back by one nucleotide. changes reading frame, no stop codon at end of gag. ribosome now stops at end of pol

Question 16

9. Assembly

Answer 16

full length transcripts have a packaging signal near 5’ end. recognized and bound by NC which is still part of gag. other NC binds non specifically to genome. full length viral RNA coated w/NC.

Question 17

9. why are eukaroytic and env mRNA not coated w/NC

Answer 17

do not have packaging signal. mean they will not be into the capsid

Question 18

9. associations

Answer 18

tRNA is associated w/NC. CA capsid is part of gag and gagpol self assembles enclosing NC, genome and tRNA. MA proteins still part of gag and gagpol bind to inner doian of TM

Question 19

10. Exit and maturation

Answer 19

by budding. then part of gag becomes active protease which cuts gag and gagpol into diff proteins. capsid encloses genome and 3 enzyme. particle is infectious

Question 20

10. why

Answer 20

prevents reverse transcriptase from producing DNA inside cell. having polyportein ensure all components are package and that reverse transcriptase cannot convert genome into dsDNA until it infects next cell