Lecture 8 and 7

• Gene Expression (Protein Biosynthesis)

  Transcription and Translation

  
• In a eukaryotic cell, the nuclear envelope separates transcription from translation

  
• Extensive RNA processing occurs in the nucleus

  
• Translation


  RNA-directed synthesis of a polypeptide chain (Protein)

  
• Translation


  1. mRNA

  2. Ribosomes - Ribosomal RNA

  3. Transfer RNA

  4. Genetic coding – codons

  
• Codon


  3 bases that code for the production of a specific amino acid
• There are 64 possible codons but only 20 amino acids, therefore most have more than 1 codon
• 3 of the 64 codons are used as STOP signals, 1 codon is used as a START signal
• Transfer RNA


  Single RNA strand about 80 nucleotides long, has a specific amino acid on one end and anticodon on the other end, brings the amino acids to the ribosomes

  
• Anticodon


  3 RNA bases that matches the 3 bases of the codon on the mRNA molecule
• Ribosomes


  Facilitate the specific coupling of tRNA anticodons with mRNA codons during protein synthesis, constructed of proteins and RNA molecules (ribosomal RNA or rRNA)

  
• Translation Stages


  1. Initiation

  2. Elongation

  3. Termination
• Post-translation Modifications


  • New polypeptide floating loose in the cytoplasm or inserted into a membrane, polypeptides fold spontaneously into their active configuration, other molecules like sugars, lipids, phosphates attached for protein function
• Transferase is an enzyme that transfers a group (such as a phosphate or methyl) from one compound to another.