BIOC20 LEC 10 RETROVIRUSES & HIV EXAM QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS LATEST UPDATE GRADED A++

BIOC20 LEC 10 RETROVIRUSES & HIV EXAM QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS LATEST UPDATE GRADED A++ HIV replicates in and kills.... lymphocytes and macrophages - both cells are CD4+, glycoprotein found on immune cell surface) Cd4+ is a.... Cd4+ is a glycoprotein found in immune cell surfaces Infection results in •Infection results in depletion of CD4+ T cells, rendering the host immunocompromised Phases of HIV infection 1) Acute Infection 2) Clinical latency 3) AIDS Explain Acute Infection •flu-like symptoms, infection of gut-associated lymphoid tissue (GALT) results significant drop in CD4+ cells Explain Clinical latency •Cytotoxic T lymphocytes (CTLs) and antibodies respond to infection but virus replication persists in lymph nodes resulting in gradual depletion in CD4+ T cells Explain AIDS •Acquired Immunodeficiency Syndrome •High levels of virus in blood and opportunistic infections If left untreated, what are phases HIV can take several courses after an acute infection •Rapid progressors: (10-15%) develop late-stage symptoms in 2 to 3 years •Slow progressors: (70-80%) develop late-stage symptoms in 8 to 10 years •Long-term nonprogressors: (5%) show no decline in CD4+ T cell levels Describe retroviruses •5' cap and poly(A) tail •150-200 nt repeated sequences on 5' and 3' end of genome RNA (labelled R in figure) •Adjacent to R, there are unique regions designated U5 (untranslated 5', 80-200 nt) and U3 (untranslated 3', 240-1200 nt) •A specific cellular tRNA is bound to genomic RNA by base pairing with primer binding sequence (PBS) downstream of U5 •Ψ packaging sequence •5'SS and 3'SS are splice sites •Ppt is polypurine tract •Used during reverse transcription What is tRNA used for in retroviruses tRNA is used for a primer for synthesis in retroviruses, polymerases need primers to extand the nucleotide chain Explain 1) Synthesis of minus-strand strong-stop DNA •Extends from tRNA primer to 5' end of viral RNA template, short sequence of R+U5 • •Strong stop: DNA synthesis stops abruptly in vitro • •100-400 nt DNA copy of R + U5 (labelled R' and U5' in figure) How many steps in Retrovirus reverse transcription Nine steps 1) Synthesis of minus-strand strong-stop DNA 2) Removal of template RNA 3) First-strand transfer 4) Copying of full-length genome 5) Removal of template RNA 6) Synthesis of plus-strand strong-stop DNA 7) Removal of tRNA and ppt primer by RNase H 8) Second strand transfer 9) Extension of both DNA strands by RT Explain 2) Removal of template RNA •RNase H digests RNA in DNA:RNA hybrid