From Gene to Protein

1. From Gene to Protein Chapter 17

2. The Central Dogma of Molecular Biology • Dogma: (n), [dawg-muh] a specific tenet or doctrine authoritatively laid down.

3. The central dogma of molecular biology REPLICATION (= make more DNA before cell divides) DNA  RNA  Protein TRANSCRIPTION (copy DNA encoded message into RNA encoded message) TRANSLATION (the RNA message directs the Ribosome in making the protein into a protein)

4. Gene: a sequence of bases on DNA that codes for a specific protein HOW????? By transcribing message on RNA, which then translates it into a protein

5. An Overview of the Central Dogma

6. The Triplet code: The mRNA transcript is read in groups of three.

7. DNA two antiparallel strands BasesA T C G deoxyribose RNA single strand U uracyl instead of T thymine ribose instead of deoxyribose

8. Three types of RNA: Messenger RNA mRNA (the photocopy, disposable) Transfer RNA  tRNA (Think of this as a translator at United Nations conference) Ribosomal RNA  rRNA (Actually part of the ribosome structure itself)

9. RNA Types: Transfer RNA (tRNA)

10. Anatomy of a ribosome Ribosomes “make”protein by decoding the mRNA into the amino acid language.

11. Let’s put it together and see where mRNA, tRNA, rRNA and the ribosome act together.

13. CODONS on mRNA

14. Start Stop

15. The genetic code is UNIVERSAL Same from bacteria to humans! = Evolved early in the history of life

16. A closer look 1 The enzymes that makes RNA are called: RNA polymerases NOTE RNA-polymerase can add nucleotides ONLY to the 3’ end RNA thus grows FROM the 5’ in the 3’ direction REMEMBER  DNA strands are antiparallel

17. A closer look 2 • Transcription has three stages: • Initiation • RNA polymerase attaches to a site on DNA called  PROMOTER REGION • Initiation factors necessary to start • First amino acid codon is for Methionine • 2. Elongation • RNA polymerase “unzips” the DNA exposing the coding strand • Only one of the two strands is used (called TEMPLATE strand) • A primary RNA is made as the enzyme moves along the DNA template.

18. 3. Termination • When the RNA polymerase reaches the terminator region • The RNA is released from the DNA • Other enzymes are also involved: • * in unzipping the DNA • * in stabilizing the unzipped regions • * in reassembling the DNA after transcription

21. 3 A closer look In eukaryotes RNA is modified after transcription (1) 5’ cap cap of modified nucleotides (methyl-guanine, mG) to protect from degradation  “attach here” sign for ribosomes (2) 3’ tail tail of about 100 adenines nucleotides (poly-A tail)  protection from enzymes  helps export RNA from nucleus (3) RNA splicinggenes and their RNA have long non-coding sections these sections are removed Example: Primary RNA has about 8000 nucleotides Only 1200 needed to code for a 400 amino acid protein

22. Non-coding segments on RNA called INTRONS on the DNA Coding sequences on the RNA called EXONS on the DNA (=expressed) SPLICING = to cut out a piece and put the ends together again (movies) Primary RNA is SPLICED: Pieces cut out, ends put back together

24. Why all this? Hypothesis Introns have sequences that control gene activity in some way and are not needed to make proteins

25. TRANSCRIPTION RNA PROCESSING TRANSLATION

26. A closer look 4 Building a Protein is Translation

27. STAGES • Initiation AUG (codon) • a.a.??? _________

28. 2. Elongation: Peptide bonds - Dehydration synthesis

29. 3. Termination: stop codon (UAA, UAG, UGA)

30. Some proteins are translated directly into the ER for intracellular transport or export outside of the cell.

31. Putting it all together… • Transcription • Intron splicing • Translation • The whole central dogma

32. Sometimes things go wrong. What’s happening?