Textbook Notes (363,149)
Canada (158,223)
Biology (305)
BIOL 103 (103)
Chapter 16


8 Pages
Unlock Document

Queen's University
BIOL 103
Virginia K Walker

BOAG CHAPTER 16 (pg 390-395, 403-406) VIRUS REPRODUCTION -when a virus infects a host cell; results in the production of new viruses 1. Attachment -virus attaches to surface of host cell; attachment usually specific for 1/few cells (virus proteins recognize cell membrane components) 2. Entry -viral genome enters host cell -one/several viral genes are expressed immediately b/c of action of host cell enzymes + ribosomes -expression of key genes leads to step 3 or step 4 of virus reproductive cycle -virus genome integrates into host cell --> step 2 to 3 (delaying production of new viruses) -step 3--> immediate production of new viruses 3. Integration Lysogenic cycle: dormancy; no new viruses made, host cell not destroyed -viruses carry a gene for integrase; genen is expressed soon after entry and the enzyme is made -viral genome copied from RNA into complimentary DNA, then uses DNA strand as a template to make double-stranded viral DNA w/ reverse transcriptase from the virus itself -->reverse transcription creates virus DNA called prophase -viral DNA enters host nucleus -integrase cuts host's DNA and inserts viral DNA into host DNA -once integrated, phage DNA + host DNA = provirus 4. Synthesis of Viral Components -production of new viruses in host cell involves replication of viral genome + synthesis of capsid proteins to make the viral coat -if integration occurred, prophage must be excised before synthesis of new viral components can happen -excisionase excises the virus DNA from host's DNA -host cell enzymes make lots of copies of the phage DNA and transcribe them into mRNA -host cell ribosomes translate the viral mRNA into viral proteins -expression of phage genes leads to degradation of host chromo DNA 5. Viral Assembly -after all necessary parts have been made, viruses are put together -some can self-assemble; components spontaneously bind to each other to form a complete virus -non-self-assembly viruses need noncapsid proteins to help; they f'n as enzymes, serve as scaffolding, etc 6. Release -phages burst/lyse their host cell to escape -after phage is assembled, phage-encoded lysozyme digests the bacterial host cell wall; cell bursts -Lytic cycle: active virus reproduction cycle, steps 1,2,4,5,6 LATENCY IN BACTERIOPHAGES -during lysogenic cycle the prophage/provirus is inactive -most of the viral genes are silent; viral reprod doesn't progress to step 4 -when a lysogenic host cell divides, it copies the prophage along w/ its own DNA: each daughter cell inherits a copy of the prophage -prophage can be replicated continually w/o killing the host -temperate phage: virus that spends some of its time in the lysogenic phase -will switch into lytic phase if there's enough nutrients in cell to make virus parts -virulent phage: virus that only uses the lytic cycle; genome incapable of integrating into host chromo -episome: a genetic element that can replicate independently of the chromo DNA but also can occasionally integrate into chromo DNA; switches back and forth b/w lysogenic and lytic HIV VIRUS -causative agent of AIDS -primarily spread by sexual contact b/w infected + noninfected individuals -effects of AIDS results from viral destruction of helper-T cells : supposed to interact w/ other leukocytes in the immune system to facilitate production of antibodies and molecules that target+kill antigens in the body -lots of helper-T cells destroyed = immune system weakened, individual becomes easy target for infectious diseases that would not normally happen to a healthy person -HIV virus has 2 copies of single-stranded RNA and 2 molecules of reverse transcriptase --> characteristic of retroviruses: use reverse trans to produce viral DNA that can be integrated into host cell DNA 1. HIV binds to surface of a helper-T: spike glycoproteins in viral envelope (has proteins gp41 and gp120) recognize helper-T receptors on membrane surface (CD4) 2. viral envelope fuses w/ helper-T membrane, capsid released into cytosol, releasing HIV RNA and reverse trans. 3. reverse transcription occurs; HIV DNA enters host nucleus + integrates into host chromo -->reverse trans lacks proofreading f'n: makes more errors + tends to create mutant strains of HIV very quickly -->undermines body's ability to combat HIV and catch up to it ; difficult to create a vaccine; HIV can become quickly immune by just mutating 4. Later, the proviral DNA is transcribed into viral RNA in the nucleus w/o getting excised -->viral RNA enters cytosol, translated into new virus parts
More Less

Related notes for BIOL 103

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.