DNa

• DNA

  Linear DNA molecules that exist as chromosomes
• Chromosomes


  • Thread-like structures each made up of a DNA molecule and its associated proteins
• DNA molecule


  Very long, has to be wound around histone proteins to fit into the nucleus
• Histone proteins


  Help to support the DNA
• Chromosome


  A compound made up of DNA and histone proteins
• Mitochondria and chloroplasts


  • Have their own DNA, similar to prokaryotic DNA
• Prokaryotic DNA


  Shorter and circular, not wound around histones
• Gene


  A sequence of DNA bases that codes for either a polypeptide or a functional RNA
• Polypeptide


  A sequence of amino acids, the primary structure of a protein
• Amino acid


  Coded to by a sequence of 3 DNA bases
• Protein synthesis


  1. Transcription: DNA copied into mRNA

  2. Translation: mRNA used to synthesise a protein
• mRNA


  Carries the genetic code from DNA to the ribosome to make a protein
• tRNA


  Involved in translation, carries the amino acids used to make proteins to the ribosome
• Transcription


  RNA polymerase attaches to DNA, separates the strands, and uses one strand as a template to make mRNA
• Translation


  mRNA attaches to a ribosome, tRNA molecules carry amino acids to the ribosome, amino acids are joined together to make a polypeptide
• Genetic code


  The sequence of base triplets (codons) in mRNA that code to specific amino acids
• Stop signals


  Specific codons that tell the cell to stop production of a protein
• The genetic code is universal, the same specific base triplet codes for the same amino acid in all living things
• There are more possible combinations of codons than there are amino acids
• Not all codons code for amino acids, some are used as start and stop signals
• Eukaryotic DNA contains non-coding regions (introns) that are removed during protein synthesis
• Eukaryotic DNA also contains multiple repeating sequences that do not code for amino acids
• Alleles


  Different versions of the same gene that code for slightly different versions of the same polypeptide
• Homologous chromosomes


  • Matching pairs of chromosomes in a eukaryotic cell nucleus, containing the same genes but potentially different alleles