Translation in eukaryotes

• Translation is more complex in eukaryotes
• In eukaryotes

  • The ribosomes are larger and longer lived than in bacteria
  • Transcription occurs in the nucleus
  • The 5’ end of mRNA is capped with a 7-methylguanosine residue at maturation, which is essential for translation
  • A poly-A tail is added at the 3’ end of the mRNA
  • Translation occurs in the cytoplasm
• Many eukaryotic mRNAs contain a purine (A or G) 3 bases upstream from the AUG initiator codon, which is followed by a G
• This Kozak (Marilynn) sequence is considered to increase the efficiency of translation by interacting with the initiator tRNA
• Translation in eukaryotes generally requires more factors for initiation, elongation, and termination than translation in bacteria does
• Many ribosomes aren’t free-floating as in bacteria but instead are associated with the endoplasmic reticulum
• The initial insight that proteins are important in heredity was provided by the study of inborn errors of metabolism
• Alkaptonuria and phenylketonuria result from mutation that lead to metabolic blocks
• Hundreds of medical conditions are caused by errors in metabolism resulting from mutant genes
• Pedigree analysis of these diseases indicated that human diseases can have a genetic basis
• PKU results when phenylalanine isn’t converted to tyrosine
• Phenylalanine hydroxylase is inactive in affected individuals
• Phenylalanine and its derivatives enter the cerebrospinal fluid with elevated levels, resulting in mental retardation
• Newborns are routinely screened throughout the US, with afflicted babies put on special diets