2. Outline for Today Protein Synthesis Overview of Information Transfer Transcription Translation Protein Trafficking What goes where and why care? Ribosome role Pathway of secreted protein
4. Overview What is a gene? Gene = sequence of nucleotides that codes for the synthesis of a piece of RNA (simplified version) http://library.thinkquest.org/19037/genome.html
6. mRNA Patterned from DNA in the nucleus Moves to the cytoplasm 10% of RNA is of this type 3 base sequence constitutes a codon Overview http://www.alumni.ca/~mcgo4s0/t3/RNA.html
7. tRNA Carries the amino acid from the cytoplasm to the ribosome Anticodon is a recognition area Complimentary to the codon of the mRNA Specific for an amino acid 10% of the RNA is of this type Fig. 4.8 Overview
8. rRNA The RNA portion of ribosomes 80% of RNA is of this type Fig. 4.9 Overview
9. Protein Synthesis Overview Information transfer from nucleus to cytoplasm Culminates in protein formation
10. Stages Two stages to protein synthesis Transcription Translation Overview 3rd. Ed Fig. 4.6
11. Stages Transcription DNA to mRNA code Not all of the DNA is transcribed at once Language of the nucleotides Overview http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/nucleic/chpt15/transcription.gif
12. Stages Translation Translate the code from “A, C, G, and U” to amino acid language Nucleic acid language to amino acid language Overview 3rd. Ed Fig. 4.6
13. Transcription DNA to mRNA nucleus Stretch of DNA helix unwinds RNA polymerase DNA rules of complimentarity apply DNA RNA G C C G T A A U Transcription http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/nucleic/chpt15/transcription.gif
14. Transcription Separation of strands Enzymes link nucleotides together based upon laws of complementarity Russo, handout
15. What are introns?(intervening regions) Consider the following inthebekweoitwoenasdfginninggodcreatedtheheavensdsjfaoiqwerjwqandtheearth inthebekweoitwoenasdfginninggodcreatedtheheavensdsjfaoiqwerjwqandtheearth inthebeginninggodcreatedtheheavensandtheearth
16. mRNA Processing Trans-Trans link Don’t confuse introns and exons (expressed regions). Finished mRNA http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/nucleic/chpt15/intron.htm
18. Overview mRNA leaves the nucleus and goes to the cytoplasm Is recognized by the ribosomal subunit Translation Russo, handout
19. Overview Binding of subunits (amino acids) to get the polypeptide Translation Russo, handout
20. Role of tRNA “transfers” or carries the amino acid from the cytoplasm to the ribosome Anti-codon 3 nucleotide base sequence Complimentary to the codon Translation http://www.alumni.ca/~mcgo4s0/t3/RNA.html
21. Codon Triplet sequence on mRNA 1 codon codes for 1 amino acid Remember this was coded from the DNA Translation Russo, handout
23. All RNA’s involved rRNA makes up the ribosome tRNA brings the amino acid to the ribosome mRNA carries the message from the nucleus (DNA) The three types of RNA together carry out translation Translation http://www.cancerquest.org/index.cfm?page=45
24. Let’s Watch a Video https://paris.mcgraw-hill.com/sites/0073525693/student_view0/chapter4/how_translation_works.html
25. Steps Initiation tRNA with amino acid binds to ribosome subunit AUG is start codon Therefore UAC is the anti-codon Other subunit comes in Another tRNA comes in with an aminio acid Form the first peptide bond Ribosome shifts a distance of 1 codon How is the correct amino acid brought to the ribosome? Translation http://kvhs.nbed.nb.ca/gallant/biology/translation_initiation.jpg
26. The genetic code Translation This lets you determine what amino acid is brought to the ribosome. (read in mRNA) Campbell et al., Fig. 10.11
27. Steps Elongation Ribosome moves along the mRNA Bond forms between 2 adjacent amino acids Bond breaks between amino acid and tRNA Process keeps going like a ticker tape Translation http://www.science.siu.edu/microbiology/micr302/figure%207.25.JPG
29. Steps Termination The process stops because the protein is complete Get one of the 3 stop codons UAA UAG UGA Translation Campbell et al., Fig. 10.11
30. Translation Termination = addition of amino acids stops Stop Codon = Codon for which there is no complementary anticodon
31. Overview of the process Campbell et al., Fig. 10.20 Translation
33. = amino acid Ribosome Translation mRNA message is “read” as triplet sequence of nucleotides: CODON
34. Mutations Mutation is a change in the base of the DNA At least one type of mutation is this type (There are others that involve an addition or a deletion of a base Sickle cell disease is caused by one change in the DNA bases resulting in an improper amino acid in the hemoglobin A mistake at either transcription or translation can result in problems Protein Synthesis Campbell et al., Fig. 10.21
36. What goes where Protein Trafficking Way of determining what protein goes where in the cell Tay-Sachs disease the proteins are supposed to go to the lysosome but they don’t Get fatty acids accumulations http://medgen.genetics.utah.edu/photographs/pages/tay.htm http://www.dynagene.com/education/tay.html
37. Ribosome location Free ribosomes Protein will stay in the cytoplasm or move to the nucleus or mitochondria Stays in the cell Anchored (to er) Associated with the ER Proteins destined for the plasma membrane , the lysosome,or released from the cell (secretion) Fig. 3.26a Protein Trafficking Fig. 3.26b
38. Pathway Fig. 4.11 Protein Trafficking Initial sequence of amino acids is a signal Called the signal sequence Signal is recognized by a particle in the cytoplasm Signal recognition particle (SRP) SRP pulls the complex to the endoplasmic reticulum Signal peptide goes into the lumen of the ER
39. Synthesis begins Initial sequence of amino acids is a SIGNAL that directs protein to the ER whole protein threads into the interior of the ER Signal sequence is translocated across membrane of the ER to the inside Protein Trafficking “element” in cytoplasm recognizes signal and moves whole complex to the surface of the RER RER
40. Protein Trafficking Inside the ER the signal sequence is cleaved Can be altered in the ER Remove some aa’s, folding, stabilizing with S-S bridges, adding carbs, etc. Insulin starts out as 1 chain of 86 aa’s but ends up as 2 chains of 21 and 30 aa’s. Protein put into a bud of the ER that forms a transport vesicle Transport vesicle goes to the Golgi Fuses with Golgi Protein is liberated into the Golgi Fig. 4.11 Protein Trafficking
41. Completed protein inside ER Stimulus Applied Immediate secretion Regulated secretion Protein Trafficking RER Signal is removed “budding” Transport vesicle “shuttle” to Golgi “budding” Fusion with Golgi Golgi “modifications” occur that provide sorting signals “shuttle” to membrane Secretory vesicle Storage vesicle Fate #2 Fate #1
42. Pathway In the Golgi it is modified and sorted Bud forms from the Golgi Secretory vesicle Leaves via exocytosis Fig. 4.11 Protein Trafficking
43. Pathway Two possibilities for secretion Immediate release Regulated storage Vesicles stay in cell for a while as storage vesicles e.g. neurons and endocrine cells Fig. 4.11 Protein Trafficking
44. DNA mRNA mRNA Signal sequence whole protein threads into the interior of the ER Signal sequence is translocated across membrane of the ER to the inside Protein Trafficking Synthesis begins Free ribosomal subunits in the cytoplasm Ribosome subunits associate with mRNA Initial sequence of amino acids is a SIGNAL that directs protein to the ER “element” in cytoplasm recognizes signal and moves whole complex to the surface of the RER RER
45. Eventually the protein is moved into a membrane “bud” which will generate a transport vesicle Transport vesicle The transport vesicle fuses with the Golgi and releases the protein inside Secretory vesicle The ribosome dissociates from the mRNA RER An enzyme inside the RER will cleave off the signal sequence The signal piece will be degraded; the remainder of the protein will be further processed Protein is liberated into the interior of the RER once translation ends After more processing, the protein is moved into a membrane “bud” which will generate a secretory vesicle The transport vesicle shuttles the protein to the Golgi Golgi
46. Storage vesicle Plasma membrane Plasma membrane Secretory vesicle Fate of the Secretory Vesicle In some cases the secretory vesicle will transition to the plasma membrane for immediate secretion of the contents into the extracellular space Regulated Secretion requires that a stimulus (trigger event) be applied to the cell to make the storage vesicle release its contents into the extracellular space In some cells the vesicle can remain as a storage vesicle for a period of time; this is true in cells that have Regulated Secretion STIMULUS! Secretion into the extracellular space Regulated secretion
