dna and chromosome structure

• Gene


  A short section of DNA that codes for a polypeptide and a functional RNA
• Locus


  The location of where a gene is found
• Allele


  A different form or version of the same gene
• Chromosome


  • Tightly coiled DNA located in the nucleus of eukaryotic cells
  • Humans have 23 pairs of chromosomes (46 total)
• Homologous pair


  A pair of chromosomes that have exactly the same genes
• Karyotype is an image showing all the chromosomes in a cell organised into homologous pairs
• How DNA is stored in eukaryotic cells

  1. DNA is wrapped around histone proteins to form nucleosomes

  2. Nucleosomes are tightly coiled to form chromosomes
• DNA in prokaryotic cells


  • Shorter and circular, not wrapped around histones
• DNA in mitochondria and chloroplasts

  • Similar to prokaryotic DNA - shorter, circular, not histone bound
• The human genome contains approximately 3 billion base pairs
• If DNA is equally distributed between 46 chromosomes

  Each chromosome would have 6.5 x 10^7 base pairs
• In every body cell, the DNA content is the same