1. Reverse Transcription

2. POINT > Describe the process of reverse transcription POINT > Discuss the role of reverse transcription in retroviral infection POINT > Describe the advantage of using cDNA in recombinant DNA research POINT > Define what a cDNA library is

3. Central Dogma

4. POINT > Describe the process of reverse transcription Normal transcription involves synthesis of mRNA from DNA Reverse transcription is the transcription of single stranded mRNA back into double stranded DNA Reverse transcriptase is the enzyme that can make this happen

5. POINT > Describe the process of reverse transcription Reverse Transcriptase was discovered by Howard Temin and David Baltimore in 1970, independently Controversial discovery at the time, because it challenged Central Dogma They shared the Nobel Prize in Medicine for their discovery

6. WB CHECK: What happens in reverse transcription? What enzyme performs reverse transcription?

7. POINT > Discuss the role of reverse transcription in retroviral infection A class of viruses called retroviruses utilize this process, most notably HIV (the cause of AIDS) These viruses inject RNA into a host cell along with the reverse transcriptase enzyme Reverse transcriptase synthesizes cDNA (complementary DNA) from the RNA strand The cDNA is then incorporated into the host cell DNA and expressed to make more virus

8. WB CHECK: What kind of viruses use reverse transcription? What 2 things does a retrovirus inject into a host cell?

9. cDNA is very useful in biotech research. What is the advantage of cDNA over DNA from the nucleus? To make cDNA, mRNA is extracted from a cell and treated with reverse transcriptase Since mRNA contains no introns, this allows researchers to clone cDNA gene sequences that are also without introns

10. This powerpoint was kindly donated to www.worldofteaching.com http://www.worldofteaching.com Is home to well over a thousand powerpoints submitted by teachers. This a free site. Please visit and I hope it will help in your teaching POINT > Describe the advantage of using cDNA in recombinant DNA research

11. If we take DNA from the nucleus, we get sequences of exons and introns Problem: Bacterial DNA doesn’t have introns, so bacteria don’t recognize them Expressing nuclear DNA in bacteria won’t result in useful proteins. The amino acid sequence will include “intron amino acids”

12. This powerpoint was kindly donated to www.worldofteaching.com http://www.worldofteaching.com Is home to well over a thousand powerpoints submitted by teachers. This a free site. Please visit and I hope it will help in your teaching POINT > Describe the advantage of using cDNA in recombinant DNA research

13. WB CHECK: Why is nuclear DNA no good for expressing proteins in bacteria? What would be wrong with a protein produced in bacteria from nuclear DNA? Why is cDNA better to use in bacteria?

14. POINT > Describe the use of reverse transcription in recombinant DNA research A cDNA allows bacterial expression of DNA sequences that code for the correct amino acid sequence only- no introns To produce human proteins in bacterial cells (insulin, HGF, etc), researchers must have cDNA (from reverse transcriptase)

15. WB CHECK: Why

16. POINT > Define what a cDNA library is Scientists can now isolate all of the different mRNAs from a cell and make a cDNA for each one This collection of cDNAs is called a cDNA library A cDNA library contains the genetic code to build all of the proteins that particular cell type produces

17. WB CHECK: What is a cDNA library made from? Would a cDNA library made from one of your muscle cells be the same as a cDNA library made from one of your nerve cells? Why or why not?

18. Homework: Workbook Pages 258-260, 267-270