10.2.2 Reproduction and replication

• Reproduction


  The processes that make more of the same kind of organism
• Reproduction in fungi


  • Can be both sexual and asexual
  • Usually involves spores
  • Asexual spores may be free at the tips of hyphae (budding)
  • Asexual spores may also be formed within a sac (sporangiospores)

  
• Yeasts


  Microscopic, unicellular fungi with a single nucleus and eukaryotic organelles
• Asexual reproduction in yeasts

  1. Budding

  2. A new cell forms at the surface of the original cell, enlarges, and then breaks free

  3. The new yeast cell is genetically identical
• Asexual reproduction in bacteria (binary fission)

  1. DNA uncoils and duplicates

  2. DNA is pulled to separate poles as the cell increases in size

  3. New cell wall begins to separate the bacterium

  4. New daughter cells have tightly coiled DNA rods, ribosomes and plasmids
• E.coli cells typically divide about every 20 minutes at 37 °C
• Bacterial growth curve


  • Lag phase
  • Log/exponential phase (birth rate > death rate)
  • Stationary phase (birth rate = death rate)
  • Death phase (birth rate < death rate)

  
• Limiting factors in the stationary phase are nutrients (e.g. glucose and oxygen) running out and metabolites building up and becoming toxic
• Virus replication


  1. Virus attaches to cell

  2. Virus injects DNA/RNA into cell

  3. Uses host cell machinery to replicate its own DNA/RNA

  4. Makes copies of protein coat

  5. Viruses are 'put together' (DNA/RNA inside protein coat)

  6. Viruses are released, often destroying the host cell

  
• Difference between binary fission and budding

  • In binary fission, the parent organism is divided into two daughter organisms by evenly splitting the cytoplasm
  • In budding, the parent organism forms a new organism by sprouting out and unevenly separating the cytoplasm
• Asexual reproduction


  • Can start a new population from only one individual (no need to find another organism to reproduce with)
• Advantages of asexual reproduction 


  • Large populations can form quickly and easily (make copies of the adding organisms quickly)
  • New cells are genetically identical
  • Can start a new population from only one individual (no need to find another organism to reproduce with)
• Disadvantages of asexual reproduction 


  • Lack of genetic variation (DNA is copied exactly)