Viruses Objective: 1.Explain reverse transcription and how retroviruses use it during infection, as well as how it is used in biotechnology. Task: 1.Please copy two key definitions into your notes: 2.Reverse Transcription: making a dsDNA molecule from an RNA template 3.Gene splicing: inserting DNA from one organism into another. The result is a transgenic organism

Ebola Zaire Most lethal viral infection known to science ( > 85% of cases fatal) Antisense ssRNA virus (ss = singlestranded) 19 kbp genome (human = 3.1 Gbp) codes for 8 proteins

Today’s Big Ideas Viruses are small genetic entities that are obligate pathogens. (the only way they can survive is through other cells) They are not cells, and contain no ribosomes. Most viruses defy the normal rules of DNA  RNA  Protein, –some of them store information as RNA –Some can perform reverse transcription –High diversity and mutation rate Virus may follow a lytic lifecycle or a lysogenic one –Lytic cycle = makes new viruses directly –Lysogenic cycle = inserts genetic info into host.

The Lytic Cycle: viral genes translated immediately

Lysogenic Cycle: viral RNA reverse transcribed into host DNA ex: HIV, HPV, others

Important Characteristics RNA virus H & N refer to different versions of viral proteins. ~100 nm (0.1 μm) diameter. spherical

Transmission: Aerosol or hand-mouth

Step 1: Hemagglutinin Protein Binds to Epithelial Cell in Nose or Lungs Lung Cell H Protein

Holsberry/FRAMES/start.htm Hemagglutinin

Step 2: Endocytosis of Virus by Cell

Step 2: another view

Step 3: Viral Genes Enter Cytoplasm

Step 4: vRNA Enters Nucleus, Begins making virus materials vRNA and vRNA polymerase begin replicating and transcribing the virus genes. Viral genes are transcribed by host cell ribosomes, producing proteins that take over the cell: –Break down cell mRNAs for parts –Use the nucleotides to copy genetic material –Build proteins with cell ribosomes for new viruses

Step 5: Virus Assembly

Step 6: Release of Viruses

6 Steps of Viral Infection 1.Attachment 2.Endocytosis 3.Unpackaging 4.Viral Synthesis 5.Assembly 6.Release

Human Immunodeficiency Virus: HIV Do Now: Begin reading the background information about HIV/AIDS. We will complete flu presentations momentarily.

9 genes, 19 proteins, 2.5 million deaths per year.

Where HIV Strikes

Who HIV Strikes: High Risk Behaviors Transmission Category Estimated # of AIDS Cases, Through 2007* Adult and Adolescent Male Adult and Adolescent Female Total Male-to-male sexual contact 487,695- Injection drug use175,70480,155255,859 Male-to-male sexual contact and injection drug use 71,242- High-risk heterosexual contact** 63,927112,230176,157 Other *** 12,1086,15818,266 *Includes persons with a diagnosis of AIDS from the beginning of the epidemic through **Heterosexual contact with a person known to have, or to be at high risk for, HIV infection. *** Includes hemophilia, blood transfusion, perinatal exposure, and risk not reported or not identified.

HIV Demographics Race or Ethnicity Estimated # of HIV/AIDS Cases in 2007 American Indian/Alaska Native228 Asian a 455 Black/African American21,549 Hispanic/Latino b 7,484 Native Hawaiian/Other Pacific Islander46 White12,556

US Demographics RacePercentageNumber WhiteWhite alone (Not including the 23.2 million White Hispanic and Latino Americans: 66% or million) White Hispanic and Latino Americans 74%221.3 million Hispanic or LatinoHispanic or Latino ethnicity, of any race14.8% about 44.3 million Black or African AmericanBlack or African American alone13.4%40.9 million Some other raceSome other race alone6.5%19 million AsianAsian alone4.4%13.1 million Two or more races2.0%6.1 million American Indian or Alaska NativeAmerican Indian or Alaska Native alone0.68%2.0 million Native Hawaiian or other Pacific IslanderNative Hawaiian or other Pacific Islander alone0.14%0.43 million

RNA Virus HIV stores its genes in the form of RNA. Each free virus has 2 identical copies of the same molecule.

HIV is a Retrovirus A retrovirus is a type of virus which inserts its genetic material into the DNA of the host cell it infects. Because the viral genes become part of cell’s own DNA, it is nearly impossible to completely get rid of an HIV infection. This is also the reason HIV infection may take years to cause AIDS

STEP 1: Gp120 protein on virus attaches to CD4 protein on white blood cell

STEP 2: Reverse Transcriptase makes DNA copy of vRNA DNA-RNA Hybrid Molecule vRNA Reverse Transcriptase

Reverse Transcription: A Powerful Tool for Humanity & Viruses Remember that transcription is the process by which a cell makes an RNA copy of a gene stored as DNA. The RNA molecule produced provides the instructions for protein synthesis to the ribosomes.

Transcription: Forward and Backwards Transcription: DNA  RNA Reverse Transcription: RNA  DNA REVERSE TRANSCRIPTION is the process by which a DNA copy of an RNA molecule is made. The ability to make double stranded DNA from single stranded RNA is how retroviruses insert themselves into host DNA It is also a key tool of biotechnology, allowing for the study and storage of all genes being expressed in a cell.

STEP 3: Integrase inserts DNA copy of viral genes into host DNA. Integrase protein Virus DNA Host DNA

STEP 4: Proviral DNA is transcribed into mRNA. Proviral mRNA proviral DNA Host DNA

STEP 5: Viral Proteins are made and processed Protease Viral pre-protein Finished viral protein

STEP 6: Viral RNA and proteins assemble into a capsid Protease Viral RNA Reverse Transcriptase

Step 7: New virus buds from cell