Protein Synthesis
and the Genetic Code
The
Genetic Code Has Been Solved
The
Genetic Code Has Several Important
Characteristics
Wobble
Allows Some tRNAs to Recognize More than One
Codon
BOX 26-1
Translational Frameshifting and RNA Editing: mRNAs That
Change Horses in Midstream
Overlapping
Genes in Different Reading Frames Are Found in
Some Viral DNAs
Protein Synthesis
BOX 26-2 Natural
Variations in the Genetic Code
The
Ribosome Is a Complex Molecular Machine
Transfer
RNAs Have Characteristic Structural Features
Aminoacyl-tRNA
Synthetases Attach the Correct Amino Acids to
Their tRNAs
Some
Aminoacyl-tRNA Synthetases Are Capable of
Proofreading
The
Interaction between Aminoacyl-tRNA Synthetase and
tRNA Constitutes a "Second Genetic
Code"
Polypeptide
Synthesis Begins at the Amino-Terminal End
A
Specific Amino Acid Initiates Protein Synthesis
Initiation
of Polypeptide Synthesis Has Several Steps
Peptide
Bonds Are Formed during the Elongation Stage
Proofreading
on the Ribosome Is Limited to Codon-Anticodon
Interactions
Termination
of Polypeptide Synthesis Requires a Special
Signal
Fidelity
in Protein Synthesis Is Energetically Expensive
BOX 26-3 Induced
Variation in the Genetic Code: Nonsense Suppression
Polysomes
Allow Rapid Translation of a Single Message
Polypeptide
Chains Undergo Folding and Processing
Modification
of Individual Amino Acids
Attachment
of Carbohydrate Side Chains
Addition
of Isoprenyl Groups
Addition
of Prosthetic Groups
Proteolytic
Processing
Formation
of Disulfide Cross-Links
Protein
Synthesis Is Inhibited by Many Antibiotics and
Toxins
Protein Targeting
and Degradation
Posttranslational
Modification of Many Eukaryotic Proteins Begins
in the Endoplasmic Reticulum
Bacteria
Also Use Signal Sequences for Protein Targeting
Cells
Import Proteins by Receptor-Mediated Endocytosis
Protein
Degradation Is Mediated by Specialized Systems in
All Cells
Summary
Further Reading
Problems
