Prokaryotic cells and viruses

• Prokaryotes: Capsule

  Protection - secretes substances to protect bacterium from environment. SOMETIMES present
• Prokaryotes: Cell wall

  Made of a peptidoglycan called murein. Protects against damage e.g. osmotic damage. ALWAYS present
• Prokaryotes: Cell-surface membrane

  Controls exactly what enters and exits the cell (differentially permeable is the term). ALWAYS present
• Prokaryotes: Cytoplasm

  Contains 70S ribosomes. Ribosomes and cytoplasm are ALWAYS present
• Prokaryotes: Circular strands of DNA

  The form of genetic material. Useful for replication of bacterial cells. ALWAYS present
• Prokaryotes: Plasmids

  Circular pieces of DNA. Helps in antibiotic resistance by producing enzymes that break down antibodies. ALWAYS present
• Prokaryotes: Pilli

  Hair-like structures. Helps prokaryotes to attach to other bacterial cells. Sometimes pilli exchange DNA. SOMETIMES present
• Prokaryotes: Flagella

  Used in locomotion (the flagella rotates to move the cell). SOMETIMES present
• Eukaryotes vs Prokaryotes

  Eukaryotes - larger, contains nucleus, contains membrane-bound organelles

  Prokaryotes - smaller, no nucleus, contains no membrane-bound organelles
• Binary fission

  1. Circular DNA loops replicate and the 2 copies then attach to the cell membrane. Plasmids also replicate
  2. Cell elongates (the cell wall and cell membrane elongates)
  3. The cell membrane pinches inward (think: body SNATCHED!) which divides the cytoplasm into two.
  4. A new cell wall forms between the two DNA loops. This divides the original cell into 2 identical daughter cells (these daughter cells have one copy of the circular DNA, and many different numbers of copies of plasmids)

  
• What is the equation for binary fission maths questions?

  Total time bacteria are producing cells / mean division time (usually 20 minutes in ideal conditions) = number of divisions (n)

  Original population x 2^n = number of bacteria cells
• 4 properties of viruses:

  • Acellular (no cells) - This is because they have no cell-surface membrane. They are considered particles instead
  • Non-living
  • Very small (20-300nm)
  • Requires a host to replicate
• Viruses: capsid

  Made of protein, for protection
• Viruses: genetic material

  Enclosed by the capsid. Either DNA or RNA
• Viruses: reverse transcriptase enzymes

  Only present if RNA is present
• Viruses: matrix

  A virus' cytoplasm, essentially (do not say this in exam)
• Viruses: lipid envelope

  Only some viruses have it, e.g. HIV
• Viruses: attachment proteins

  These proteins allow viruses to identify and attach to a host cell
• Do viruses undergo cell division?

  No, because they are non-living. Instead, they inject their nucleic acid (DNA or RNA) into a host cell which then replicates the virus particles.
• How could we increase the growth rate of cells?

  Increase the temperature to increase enzyme activity

  Increase the concentration of glucose or oxygen to increase respiration