Chapter 17: From Gene to Protein
Figure 17-01
LE 17-2 Class I Mutants (mutation In gene A) Wild type Class II Mutants (mutation In gene B) Class III Mutants (mutation In gene C) Precursor Ornithine A Enzyme A Citrulline Arginine Gene A Gene B Gene C Precursor AA BBB Ornithine Enzyme B Enzyme C Arginine CCC Citrulline Minimal Medium (MM) (control) Wild type Class I Mutants Class II Mutants Class III Mutants MM + Ornithine MM + Citrulline MM + arginine (control)
LE 17-4 DNA molecule Gene 1 Gene 2 Gene 3 DNA strand (template) 3 TRANSCRIPTION Codon mRNA TRANSLATION Protein Amino acid 3 5 5
DNA vs. RNA (review from chapter 5) Activity: (16) DNA and RNA Structure
LE TRANSCRIPTION DNA Prokaryotic cell Ribosome Polypeptide mRNA Prokaryotic cell
Activity: Overview of Protein Synthesis
20 amino acids
LE 17-5 Second mRNA base First mRNA base (5 end) Third mRNA base (3 end)
LE 17-7 Elongation Non-template strand of DNA RNA polymerase RNA nucleotides 3 end Newly made RNA Template strand of DNA Direction of transcription (“downstream”) Promoter 5 3 RNA polymerase Start point DNA Transcription unit Unwound DNA RNA tran- script Template strand of DNA Initiation Elongation Termination Rewound DNA RNA transcript 5 Completed RNA transcript Activity: Transcription Transcription
LE 17-7a-1 Promoter Transcription unit RNA polymerase Start point DNA
DNAi.org
LE Protein-coding segment 5 Start codon Stop codon Poly-A tail Polyadenylation signal 5 3 Cap UTR Activity: RNA Processing mRNA processing (eukaryotes only)
LE ExonIntronExonIntronExon 3 Pre-mRNA Coding segment Introns cut out and exons spliced together Cap Poly-A tail 5 3 UTR
LE Exon 1 5 IntronExon 2 Other proteins Protein snRNA snRNPs RNA transcript (pre-mRNA) Spliceosome 5 components Cut-out intron mRNA Exon 1Exon 2 5
LE Gene Transcription RNA processing Translation Domain 2 Domain 3 Domain 1 Polypeptide Exon 1IntronExon 2IntronExon 3 DNA
Activity: Overview of Protein Synthesis
Protein Synthesis Polypeptide tRNA with amino acid attached Ribosome tRNA Anticodon 3 5 mRNA Amino acids Codons
LE 17-14a Amino acid attachment site Hydrogen bonds 3 5 Two-dimensional structure Anticodon Amino acid attachment site 3 5 Hydrogen bonds Anticodon Symbol used in this book Three-dimensional structure 35 tRNA
LE Amino acid Aminoacyl-tRNA synthetase (enzyme) Pyrophosphate Phosphates tRNA AMP Aminoacyl tRNA (an “activated amino acid”)
LE Amino end mRNA 5 3 Growing polypeptide Next amino acid to be added to polypeptide chain tRNA Schematic model with mRNA and tRNA Computer model of functioning ribosome 5 3 E Codons Schematic model showing binding sites Small subunit Large subunit A site (Aminoacyl- tRNA binding site) E site (Exit site) EPA mRNA binding site P site (Peptidyl-tRNA binding site) Small subunit Large subunit Exit tunnel Growing polypeptide tRNA molecules E P A mRNA Activity: Translation
LE Met GTP Initiator tRNA mRNA 5 3 mRNA binding site Small ribosomal subunit Start codon P site 5 3 Translation initiation complex E A Large ribosomal subunit GDP Met Translation: Initiation
LE Ribosome ready for next aminoacyl tRNA mRNA 5 Amino end of polypeptide E P site A site GDP E PA GTP GDP E PA E PA Elongation
LE 17-5 Second mRNA base First mRNA base (5 end) Third mRNA base (3 end)
LE Release factor Stop codon (UAG, UAA, or UGA) Free polypeptide 3 When a ribosome reaches a stop codon on mRNA, the A site of the ribosome accepts a protein called a release factor instead of tRNA. The release factor hydrolyzes the bond between the tRNA in the P site and the last amino acid of the polypeptide chain. The polypeptide is thus freed from the ribosome. The two ribosomal subunits and the other components of the assembly dissociate. Termination DNAi.org
LE Ribosomes mRNA This micrograph shows a large polyribosome in a prokaryotic cell (TEM). An mRNA molecule is generally translated simultaneously by several ribosomes in clusters called polyribosomes. Incoming ribosomal subunits Growing polypeptides End of mRNA (3 end) Start of mRNA (5 end) Polyribosome Completed polypeptides m 0.1
LE Ribosomes mRNA Signal peptide Signal- recognition particle (SRP) SRP receptor protein CYTOSOL ER LUMEN Translocation complex Signal peptide removed ER membrane Protein
LE RNA polymerase DNA Polyribosome RNA polymerase Direction of transcription mRNA 0.25 DNA Polyribosome Polypeptide (amino end) Ribosome mRNA (5 end) m
LE Wild-type hemoglobin DNA mRNA Mutant hemoglobin DNA mRNA Normal hemoglobinSickle-cell hemoglobin
LE Base-pair substitution No effect on amino acid sequence U instead of C Missense A instead of G Nonsense U instead of A Stop Amino end Protein 53 Carboxyl end Stop mRNA Wild type
LE Base-pair insertion or deletion Frameshift causing immediate nonsense Extra U Missing Frameshift causing extensive missense Insertion or deletion of 3 nucleotides: no frameshift but extra or missing amino acid Missing Stop Amino end Carboxyl end Stop Wild type mRNA Protein 53
LE TRANSCRIPTION RNA PROCESSING RNA transcript 5 Exon NUCLEUS FORMATION OF INITIATION COMPLEX CYTOPLASM 3 DNA RNA polymerase RNA transcript (pre-mRNA) Intron Aminoacyl-tRNA synthetase Amino acid tRNA AMINO ACID ACTIVATION 3 mRNA A P E Ribosomal subunits 5 Growing polypeptide E A Activated amino acid Anticodon TRANSLATION Codon Ribosome
Noncoding segments… Follow up to the Unseen Genome: Gems Among the Junk ENCODE ENCODE