DNA and chromosomes

• DNA is stored in the nucleus of eukaryotic cells
• Chromosome


  Tightly coiled DNA
• Histone proteins


  Proteins that DNA is wrapped around to prevent tangling
• Nucleosome


  Complex of DNA wrapped around histone proteins
• In prokaryotic cells, DNA is circular and not wrapped around histones
• Mitochondria and chloroplasts contain their own circular, histone-free DNA</b>
• Mitochondrial and chloroplast DNA is similar to prokaryotic DNA
• Gene


  Short section of DNA that codes for a polypeptide and functional RNA
• Allele


  Different form/version of the same gene
• Locus


  Location of a gene on a chromosome
• Homologous pair


  Pair of chromosomes with the same genes
• Humans have 23 pairs of chromosomes
• The 23rd chromosome pair are the sex chromosomes (X and Y)
• Compacting DNA into chromosomes

  DNA double helix tightly coils around histone proteins
• Function of histone proteins


  Allow DNA to tightly coil and fit into the nucleus
• All body cells in humans have the same 2.3 meters of DNA