Protein synthesis

• How DNA is stored in eukaryotes

  • Long, linear DNA molecules are wound around proteins called histones and then coil up to form compact chromosomes, which are stored in the nucleus
• How DNA is stored in prokaryotes

  • DNA molecules are shorter and circular. They condense by supercoiling and aren't associated with histone proteins
• The DNA in mitochondria and chloroplasts in eukaryotic cells is similar to prokaryotic DNA in its structure
• Gene


  Base sequences of DNA that code for a polypeptide or a functional RNA
• Triplet (or codon)


  A sequence of three DNA bases that codes for one amino acid in a polypeptide
• Genome


  The complete set of genes in a cell
• Proteome


  The full range of proteins that a cell is able to produce
• Much of the nuclear DNA in eukaryotic cells doesn't code for polypeptides
• Within genes that code for polypeptides, only the exons code for amino acids
• Introns


  Non-coding DNA within genes in eukaryotes
• Multiple repeats


  Non-coding DNA between genes in eukaryotes
• Alleles


  Different versions of the same gene
• Alleles coding for the same characteristic are found at the same position (locus) on each chromosome in a homologous pair
• mRNA (messenger RNA)


  Made of a single polynucleotide strand
• tRNA (transfer RNA)


  Made of a single polynucleotide strand folded into a clover shape
• Transcription


  Production of an mRNA copy of a gene from DNA
• Transcription in prokaryotes


  Direct production of mRNA from DNA
• Transcription in eukaryotes


  Production of pre-mRNA from DNA, which is then spliced to form mRNA
• Translation


  Amino acids are joined together by ribosomes to make a polypeptide strand (protein) based on the order of codons in mRNA
• tRNA molecules carry amino acids to the ribosomes during translation
• ATP is needed to provide the energy for the bond formation between the amino acid and the tRNA molecule
• Genetic code


  • Universal (the same base pairs code for the same amino acids in all living things)
  • Non-overlapping (codons do not share triplets)
  • Degenerate (there are more possible combinations of triplets than there are amino acids)