Basic Principles of Transcription and Translation - Computer ...

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Protein Folding and Post-Translational Modifications During and after synthesis, a polypeptide chain spontaneously coils and folds into its three-dimensional shape Proteins may also require post-translational modifications before doing their job Some polypeptides are activated by enzymes that cleave them Other polypeptides come together to form the subunits of a protein Targeting Polypeptides to Specific Locations Two populations of ribosomes are evident in cells: free ribsomes (in the cytosol) and bound ribosomes (attached to the ER) Free ribosomes mostly synthesize proteins that function in the cytosol Bound ribosomes make proteins of the endomembrane system and proteins that are secreted from the cell Ribosomes are identical and can switch from free to bound
Polypeptide synthesis always begins in the cytosol Synthesis finishes in the cytosol unless the polypeptide signals the ribosome to attach to the ER Polypeptides destined for the ER or for secretion are marked by a signal peptide A signal-recognition particle (SRP) binds to the signal peptide The SRP brings the signal peptide and its ribosome to the ER 1) Polypetide synthesis begins on a free ribosomo in the cytosol. 2) An SRP binds to the signal peptide. halting synthesis momentarily 3) The SRP binds to a receptor protein in the ER membrane. This receptor is part of a protein complex (a translocation complex) that has a membrane pore and a signal cleaving enzyme 4) The SRP leaves and 5) The signal polypetides synthesis cleaving resumes with enzyme simultaneous cuts off the translocation across the signal membrane (The signal peptide peptide stays attached to the translocation complex) 6) The rest of the completed polypeptide leaves the ribosome and folds into its final conformation Ribosome Signal peptide Signalrecognition particle (SRP) CYTOSOL ER LUMEN mRNA Translocation complex SRP receptor protein Signal peptide removed ER membrane Protein The signal mechanism for targeting proteins to the ER. A polypeptide destined for the endomembrane system or for secretion from the cell begins with a signal peptide a series of amino acids that targets it for the ER. This figure shows the synthesis of a secretory protein and its simultaneous import into the ER. In the ER and then in the Golgi, the protein will be processed further. Finally a transport vesicle will convey it to the plasma membrane for release from the cell
Page 1 and 2: The Flow of Genetic Information Th
Page 3 and 4: TRANSCRIPTION DNA mRNA (a) Bacteria
Page 5 and 6: The Genetic Code How are the instr
Page 7 and 8: Cracking the Code All 64 codons we
Page 9 and 10: Molecular Components of Transcripti
Page 11 and 12: RNA Polymerase Binding and Initiati
Page 13 and 14: Eukaryotic cells modify RNA after t
Page 15 and 16: 5′ Exon Intron Exon Intron Pre-mR
Page 17 and 18: The Functional and Evolutionary Imp
Page 19 and 20: Polypeptide Trp Phe Ribosome Amino
Page 21 and 22: Amino acid P P P ATP Adenosine Amin
Page 23 and 24: Building a Polypeptide The three s
Page 25 and 26: The elongation cycle of translation
Page 27: Growing polypeptides Completed poly
Page 31 and 32: Type of RNA Small nucleolar RNA (sn
Page 33 and 34: RNA polymerase RNA polymerase Polyr
Page 35 and 36: Individual bacteria respond to envi
Page 37 and 38: Eukaryotic gene expression can be r
Page 39 and 40: CYTOPLASM mRNA in cytoplasm Degrada
Page 41 and 42: Histone tails DNA double helix Amin
Page 43 and 44: Epigenetic Inheritance Although th
Page 45 and 46: The Roles of Transcription Factors
Page 47 and 48: Mechanisms of Post-Transcriptional
Page 49 and 50: Initiation of Translation The init
Page 51 and 52: Noncoding RNAs play multiple roles
Page 53: Chromatin Remodeling and Silencing

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