Unformatted text preview: 204-325 1 Summary of the Last Lecture Genes are transcribed into RNA first in order to be expressed. Transcription is regulated by promoter sequence and catalyzed by a single RNA polymerase in prokaryotes. In eukaryotes, transcription is regulated by promoter, enhancer, as well as internal control region and upstream activator sequence; and is catalyzed by three RNA polymerases. RNA can be modified by capping, poly A tailing, splicing, editing and base modification after transcription.
2 The Central Dogma Replication DNA
Transcription Gene Expression RNA
3 Today's Topics 1. Protein Structure 2. Genetic Code 3. Translation: Protein Synthesis 4. Protein Sorting in Eukaryotes 4 Topic 1 Protein Structure
5 General Structural Formula for an Amino Acid (Residue) 6 20 Naturally Occurring Amino Acids 7 20 Naturally Occurring Amino Acids (Continued) 8 20 Naturally Occurring Amino Acids (Continued) 9 Peptide Bond Formation in Polypeptide 10 Four Levels of Protein Structure
sequence conformation (shape) function 1-D sequence if multisubunit (such as 3-D local NH, CO binding 11 Topic 2 Genetic Code 12 Theoretical Consideration for Genetic Code How do 4 bases code for 20 amino acids? 4 4X4 = 16 4x4x4= 64 Not enough codons Not enough codons More than enough codons Continuous or punctuated ?
13 Reversion of a Frameshift Mutation 14 Three Addition Mutations can Restore the Reading Frame 15 The Genetic Code 16 Degeneracy : More than one Codons for one Amino Acid 17 Features of the Genetic Code Triplet code: Codon No comma (continuous) Non-overlapping Universal (almost) Start and stop signals Degenerate Wobble
18 Condon and Anti-codon 19 Wobble Position of the Anticodon 20 Wobble Rules 21 Wobble Rules 22 Example of Base-pairing Wobble 23 Another Example of Base-pairing Wobble 24 Topic 3 Translation: Protein Synthesis 25 Charging of tRNA by Aminoacyl-tRNA Synthetase
1 2 4 3 26 Attachment of an Amino Acid to a tRNA Molecule 27 Ribosome 28 E. coli Ribosome 50S 30S 20 nm S (Svedberg coefficient) depends on molecule's density, mass, and shape
29 E. coli Ribosome 30S 50S 30 Crystal Structure of the 70s Ribosome 31 Initiation of Protein Synthesis in Prokaryotes 32 Sequences of Some Prokaryotic Ribosome-binding Sites Shine-Delgarno Sequence: AGGAGG 33 Base Pairing between Shine-Dalgarno Sequence and rRNA 34 Elongation Stage of Translation in Prokaryotes
EF-Tu GTP 35 Peptide Bond Formation Catalyzed by Peptidyl Transferase (a ribozyme) 36 Elongation 37 Translation Termination: Release Factor Recognizes Stop Codon (by peptidyl transferase) 38 Polysome: Several Ribosomes Translating the Same mRNA 39 Animation 1: Translation Initiation 40 Animation 2: Translation Elongation 41 Animation 3: Translation Termination 42 Topic 4 Protein Sorting in Eukaryotes
43 Movement of Secretory Proteins in Eukaryotes 44 Protein Sorting Without Signal peptide With Signal peptide Cytoplasm Nucleus Mitochondrion Chloroplasts
45 Membrane Secreted Translocation of Proteins into the Endoplasmic Reticulum 46 Destination of Proteins 47 Summary Proteins are built from amino acids held together by peptide bonds. Genetic codes are triplets, comma free and nonoverlapping. The code is almost universal. Wobble base pairing contributes to the degeneracy of the code. Translation initiation involves Shine-Delgarno sequence in prokaryotes and AUG scanning in eukaryotes. Elongation of peptide chain includes repetitions of 3 steps: aminoacyl-tRNA binding, peptide bond formation, and translocation. Proteins are sorted to organelles based on their signal sequences in eukaryotes.
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