Transcription & HIV/AIDS

1. Transcription & HIV/AIDS May, 2013

2. HIV • HIV – Human Immunodeficiency Virus • Weakens the immune system by infecting leukocytes (Helper T cells/CD4) • Compromised immune system make people vulnerable to other infections • Opportunistic infections • Cancers

3. HIV into AIDS • AIDS – Acquired Immunodeficiency Syndrome

4. HIV Transmission • 3 conditions: • HIV must be present • In sufficient quantity • It must get into the bloodstream • Activities: • Unprotected sex (anal, vaginal, oral) • Sharing needles • Pregnancy and Breastfeeding

6. Structure of HIV • Outer membrane • Proteins and lipids • Inner membrane • Protein • Genetic info • RNA (retrovirus) • Enzymes • Reverse transcriptase • Integrase

8. Mechanism of Infection • HIV binds to specific protein receptors on helper T cells; cell membranes fuse • The virus enters and the RNA is set free • Reverse transcriptase converts RNA into DNA • Viral DNA enters the nucleus and is spliced into the host’s DNA by integrase – provirus • Activation of the helper T cell results in transcription of viral DNA  produce HIV

9. Treatment • Drugs targeting multiple viral enzymes (reverse transcriptase, integrase, etc) – HAART highly active antiretroviral therapy • Expensive ($12000/year) • Side effects (nausea, fatigue, diarrhea, bone loss) • Strict adherence to drugs • HIV vaccine • Mutations and Drug-resistance • Variations

10. Translation March 26, 2012

11. The Central Dogma DNA Transcription RNA Translation Protein

12. The Ribosome • mRNA transcript exits the nucleus into the cytoplasm • Ribosomes in the cytoplasm and the ER recognizes the 5’ cap and binds to the mRNA • Eukaryotic ribosomes consists of 2 subunits: • 60S = large subunit • 40S = small subunit • “S” = Svedberg unit, rate of sedimentation 80S 60S 40S

13. The Ribosome • The ribosome moves along the mRNA in a 5’ to 3’ direction • Adds a new amino acid each time it reads a codon to create a polypeptide chain • Each amino acid has its own tRNA • Reading frame = 1 of 3 ways to read the mRNA

14. tRNA • tRNA delivers the correct amino acids to the ribosome • Clover-leaf structure, small, single-stranded • Anticodon recognizes the codon on the mRNA • 3’ end carries the correct amino acid

15. Aminoacyl-tRNAsynthetase • Aminoacyl-tRNAsynthetase adds the appropriate amino acid to the tRNA molecule • Creates an aminoacyl-tRNA (tRNA with amino acid attached)

16. Ribosomal Sites • Ribosome has 3 sites for tRNA • A (acceptor) site: where tRNA brings in an amino acid • P (peptide) site: where peptide bonds are formed between amino acids on a polypeptide chain • E (exit) site: where tRNA exits

17. Initiation • The first codon is the start codon AUG (methionine) • Ensures that the correct reading frame is used • tRNA carrying methionine is loaded onto the 40S subunit first • Moves along the mRNA searching for the first AUG • Once AUG is found, 60S subunit is added

19. Elongation • Next tRNA carrying the corresponding amino acid enters the A site • Ribosome moves one codon (3bp) over creating a peptide bond at the P site • tRNA (without amino acid) leaves the E site to be recycled

20. Elongation • Repeat the process until the ribosome reaches a stop codon • N-terminal of protein is made first

21. Termination • Stop codons = UGA, UAG, UAA • These codons do not code for an amino acid • Release factor realizes the ribosome has stalled and helps to release the polypeptide chain from the ribosome • Ribosome dissociates

22. Polyribosomes • 1 mRNA is translated by multiple ribosomes • Ribosomes are spaced 80 nucelotides apart • Ensures a large quantity of protein is made

23. Functional Protein • Polypeptide chain needs to fold correctly and be modified (glycosylation, acetylation, phosphorylation) before it becomes a functional protein • Combines with other proteins

24. RNA in Translation

25. Summary Translation: http://www.youtube.com/watch?v=5bLEDd-PSTQ Super-Mario Version: http://www.youtube.com/watch?v=ZPlnDzkBrpc&feature=related (*prokaryotic translation)