Unit 4

1. Unit 4 • Proteins • Transcription (DNA to mRNA) • Translation (mRNA to tRNA to proteins) • Gene expression/regulation (turning genes on and off) • Viruses 1

2. Today’s Exit Ticket The final product of transcription is mRNA. The template used for transcription is DNA. The first step of the process is called initiation and involves transcription factors binding to the promoter region. This allows RNA polymerase to bind to the DNA and begin transcribing, in a process called elongation. During that process, the enzyme reads from the 3’ to 5’ direction and builds the new strand from 5’ to 3’. The last step of transcription is called termination. In eukaryotes, there is another step before translation. This is called RNA processing and involves removing introns and adding a 5’ cap and 3’ poly-A tail. 2

3. Unit 4 • Proteins • Transcription (DNA to mRNA) • Translation (mRNA to tRNA to proteins) • Gene expression/regulation (turning genes on and off) • Viruses 3

4. Today’s Agenda • Transcription practice • Translation in detail • Mutations 4

5. The template strand of a given gene includes the sequence 3′-G C C A C G T A T C A G-5′. • What is the sequence of the non-template strand? 5’– C G G T G C A T A G T C – 3’ • What is the mRNA sequence made? 5’– C G G U G C A U A G U C – 3’ For each one, be sure to indicate 5′ and 3′ ends. 5

6. The template strand of a given gene includes the sequence 3′-G C C A C G T A T C A G-5′. Non-template strand: 5’– C G G T G C A T A G T C – 3’ mRNA sequence: 5’– C G G U G C A U A G U C – 3’ What is the amino acid sequence produced from this DNA? Arg-Cys-Ile-Val 6

7. Today’s Agenda • Transcription practice • Translation in detail • Mutations 7

8. Transcription vs. Translation DNA RNA Proteins Hello สวัสดีครับ Hullo Transcription: • Like copying info from a book in the reserved section of the library • Using the same language Translation: • Literally translating between two different languages • Take the copied info from the library and translate it into French/Spanish/Mandarin 8

9. Translation U U U G U G C G G The major players in translation 9

10. Translation Translation: • The structure of tRNA • The ribosome • initiate • elongate • terminate 10

11. 11

12. Translation a) tRNA For accurate translation, the tRNA HAS to have the right amino acid! 1 20 different synthetases  20 different amino acids 12

13. Translation a) tRNA 2 3 13

14. Translation a) tRNA 4 14

15. Translation Translation: • The structure of tRNA • The ribosome • initiate • elongate • terminate 15

16. Translation • The ribosome • What is a ribosome? • Made of proteins and rRNA (ribosomal RNA) • Where are ribosomes? • In the nucleus • Loose in the cytoplasm • On the Golgi body • On the ER • More than one of the above is correct 16

17. All those RNA molecules… • RNA= ribonucleic acid • pre-mRNA = the RNA transcript produced initially during transcription in eukaryotes • mRNA = messenger RNA = the (processed) RNA transcript molecule that will actually be translated • tRNA = transfer RNA = the RNA molecule that brings amino acids to the ribosome • rRNA = ribosomal RNA = RNA that forms the structure of the ribosome 17

18. Translation b) the ribosome • The ribosome • What does it do? • Serves as the site of matching mRNA codons with tRNA anticodons • Catalyzes formation of peptide bonds to form proteins 18

19. Translation b) the ribosome Growing polypeptide Next amino acid to be added to polypeptide chain 19

20. Translation Translation: • The structure of tRNA • The ribosome • initiate • elongate • terminate 20

21. 5. Translation A G U (i) Initiation of translation • Small ribosomal subunit binds mRNA. • Scans for start codon (sets reading frame). • Initiator tRNA binds to start codon. 21

22. Translation A G U b) the ribosome: initiation  Final step of initiation: large ribosomal subunit binds. 22

23. Translation Translation: • The structure of tRNA • The ribosome • initiate • elongate • terminate 23

24. E, P, and A sites • A site: where new aminoacyl tRNAs enter • P site: • Location of peptidyl tRNA • Where peptide bonds are made • E site: Exit site 24

25. Elongation 25

26. Termination Also, don’t forgetHank’s crash course on gene expression! One more good video: http://www.dnalc.org/resources/3d/16-translation-advanced.html 26

27. USE THE GENETIC CODE TABLE TO TRANSLATE 5 DIFFERENT CODONS into AMINO ACIDS: RNA: 5’ CGC 3’ = ___________ 5’ UAU 3’ = ___________ NOTE: technically “Codon” refers to the 3 letters in the mRNA that are translated. 27

28. USE THE GENETIC CODE TABLE TO TRANSLATE 5 DIFFERENT CODONS into AMINO ACIDS: RNA: 5’ CGC 3’ = ___ Arg ___ 5’ UAU 3’ = ___ Tyr___ NOTE: technically “Codon” refers to the 3 letters in the mRNA that are translated. 28

29. USE THE GENETIC CODE TABLE TO TRANSLATE 5 DIFFERENT CODONS into AMINO ACIDS: DNA (template strand): 3’ TTG 5’ = ___________ 3’ ACT 5’ = ___________ NOTE: technically “Codon” refers to the 3 letters in the mRNA that are translated. 29

30. USE THE GENETIC CODE TABLE TO TRANSLATE 5 DIFFERENT CODONS into AMINO ACIDS: DNA (template strand): 3’ TTG 5’ RNA 5’ AAC 3’ = Asn DNA 3’ ACT 5’ RNA 5’ UGA 3’ = Stop NOTE: technically “Codon” refers to the 3 letters in the mRNA that are translated. 30

31. USE THE GENETIC CODE TABLE TO TRANSLATE 5 DIFFERENT CODONS into AMINO ACIDS: Brain twister: DNA NON-template strand: 5’ ATG 3’ = __________ NOTE: technically “Codon” refers to the 3 letters in the mRNA that are translated. 31

32. USE THE GENETIC CODE TABLE TO TRANSLATE 5 DIFFERENT CODONS into AMINO ACIDS: Brain twister: DNA NON-template strand: 5’ ATG 3’ = _______ DNA template strand = 3’ TAC 5’ = RNA 5’ AUG 3’ = Met (start) NOTE: technically “Codon” refers to the 3 letters in the mRNA that are translated. 32

33. How DNA mutations can alter proteins Mutations in protein coding DNA sequences (exons) can alter protein structure and function in several ways. 33 Fanpop.com

34. 5) How DNA mutations can alter proteins 5) Mutations in protein coding DNA sequences (exons) can alter protein structure and function in several ways. a) Substitution - Switching one nucleotide for another b) Insertion/deletion- Adding or removing a nucleotide  can create a frameshift 34

35. 5) How DNA mutations can alter proteins A U G A A G U U U G G C U A A A U G A A G U U U A G C U A A a) Substitution- Switching one nucleotide for another can cause different amino acid to be attached. 35

36. 5) How DNA mutations can alter proteins A U G A A G U U U G G C U A A a) Substitution- Switching one nucleotide for another can cause NO CHANGE in the protein. How? 36

37. 5) How DNA mutations can alter proteins A U G A A G U U U G G C U A A a) Substitution- Switching one nucleotide for another can cause NO CHANGE in the protein. How? 37

38. 5) How DNA mutations can alter proteins A U G A A G U U U G G C U A A A U G U A A G U U U G G C U A A b) Insertions or Deletions - Inserting an extra nucleotide, or deleting a nucleotide causes a frameshift. 38

39. 5) How DNA mutations can alter proteins A U G A A G U U U G G C U A A A U G A A G U U G G C U A A b) Insertions or Deletions - Inserting an extra nucleotide, or deleting a nucleotide causes a frameshift. U 39

40. 5) How DNA mutations can alter proteins b) Insertions or Deletions - Inserting an extra nucleotide, or deleting a nucleotide causes a frameshift. 40

41. 5) How DNA mutations can alter proteins c) Gene duplications: a duplicate copy of an exon or whole gene is created in the genome • this is largely how NEW proteins arise in evolution: once a gene has been duplicated, one copy can evolve, while the other one maintains the original function. Gene DNA Exon 1 Intron Exon 2 Intron Exon 3 Exon 3 Exon 1 Exon 2 Exon 2 mRNA 41

42. Today’s Exit Ticket • Fill in the blanks in the DNA/RNA chart below. • What is the amino acid sequence corresponding to the DNA and RNA sequences below? 42