DNA

• features of DNA in prokaryotic cells:

  Supercoiled

  • Prokaryotic chromosomes coil around themselves in a process called supercoiling.
  • Supercoiling condenses the circular chromosomes so that they can fit inside the cell.
• features of DNA in prokaryotic cells:

  Short and circular

  • The chromosomes in prokaryotes are short and circular.
• features of DNA in prokaryotic cells:

  Located in the cytoplasm

  • Prokaryotes have no nucleus.
  • DNA is located in the cytoplasm of prokaryotes
• features of DNA in eukaryotic cells:

  Located in the nucleus

  • Eukaryotes have a nucleus.
  • DNA in eukaryotes is located in the nucleus.
• features of DNA in eukaryotic cells:

  Long and linear

  • Chromosomes in eukaryotic cells are long and linear
• features of DNA in eukaryotic cells:

  Homologous pairs of chromosomes

  • Diploid eukaryotes have homologous pairs of chromosomes.
  • The number of pairs varies for a species.
  • Humans have 23 pairs of chromosomes.
  • Homologous here means that the chromosome from the mother and father have the same genes at the same loci but alleles might be different at those loci.
• features of DNA in eukaryotic cells:

  Histones

  • The DNA in eukaryotes is tightly wrapped around proteins called histones.
  • DNA then coils around the histones and is condensed in the chromosome.
• DNA

  • Prokaryotes vs eukaryotes
  • Prokaryotes
  • Short and circular
  • Supercoiled
  • No nucleus
  • Eukaryotes
  • Long and linear
  • Histones
  • Located in the nucleus
• A small amount of DNA is present in the mitochondria of eukaryotes and the chloroplasts of plant cells.
• Endosymbiotic theory

  • The presence of DNA in mitochondria and chloroplasts is explained by the endosymbiotic theory.
  • The endosymbiotic theory states that bacterial cells were engulfed by a larger cell during evolution.
  • The bacteria and host cell formed a beneficial symbiotic relationship.
  • The bacterial cell became incorporated into the larger cell to become organelles.
• Mitochondria and chloroplasts

  • It is thought that the bacterial cells that became incorporated into a host cell are mitochondria and chloroplasts.
  • When mitochondria and chloroplasts were free-living bacteria, they needed their own DNA to survive.
  • This explains why there is still some DNA in mitochondria and chloroplasts.
• Role of the DNA

  • The DNA that is found in mitochondria encodes enzymes that are used in respiration.
  • The DNA that is found in chloroplasts encodes enzymes that are used in photosynthesis.
  • The enzymes needed for these two reactions are readily available in the organelles.
• endosymbiotic theory:

  the endosymbiotic theory states that a bacteria cell was englufed by a larger cell.
• symbiosis:

  after the cell was engulfed, the bacteria and host cell formed a beneficial symbiotic relationship.
• incorporation:

  the bacteria cell became incorporated into the large cell to become an organelle.
• evolution:

  the bacteria cells evolved as organelles with their host cells to give rise to mitochondria and chloroplasts.
• what is the name given to chromosomes in diploid eukaryotes ?

  Homologous pairs.