Prokaryotic cells and viruses ppt

• Prokaryotic cells


  • Much smaller than eukaryotic cells - only a few µm long/wide
  • Have a cell surface membrane and cytoplasm
  • Have a cell wall made of MUREIN (a glycoprotein)
  • Have smaller ribosomes than eukaryotic cells
  • Have a single circular DNA molecule not associated with proteins
  • Do not have a nucleus or any other membrane-bound organelles
• Some prokaryotic cells have

  • One or more plasmids - extra circles of DNA
  • One or more flagella
  • A capsule surrounding the cell/cells
• Both prokaryotic and eukaryotic cells have

  • Cell surface membrane
  • Cytoplasm
  • Ribosomes
  • DNA
  • Plant, algal, fungal cells also have a cell wall like prokaryotes
• Plant, algal, fungal cells also have a cell wall like prokaryotes
• Prokaryotic cells reproduce by Binary fission

  1. Circular DNA and plasmids replicate (make exact copies)

  2. Cell grows in size and DNA and plasmids move to each side

  4. Cytoplasm divides and a new cell wall begins to form

  6. Cells separated by new cell wall

  7. Each new cell has a single copy of circular DNA & a variable number of plasmids

  (the doubling of the cells after each cycle leads to exponential growth)
• Antibiotic resistant genes are often found on plasmid DNA and plasmids can be transferred between bacteria of the same and different species
• Viruses


  • Acellular (not cells) & non-living
  • Have a simple structure with a capsid (protein coat) surrounding genetic material (DNA or RNA) and attachment proteins (to allow entry into host cells)
  • Viral DNA or RNA contains the codes for making the viral proteins
  • Once inside the host cell, new virus proteins can be made using these codes and new viruses are assembled
  • The host cell also makes copies of the viral DNA or RNA
• Virus reproduction- they can only reproduce inside of a host cell


  1. Inject their nucleic acid into the host cell

  2. Incorporate DNA into host cell DNA

  3. Take over protein synthesis

  4. This allows more new virus particles to be made

  5. These then leave the cell to infect new host cells (often killing the cell)
• Some viruses are called enveloped viruses

  • These take a layer of host cell membrane around them as they leave
  • This gives them some protection against our immune system as they are covered with our antigens, hiding their own antigens (antigens are often surface proteins/glycoproteins)
• What are the 4 types of eukaryotic cells?

  Plant, animal, fungi, algal
• All eukaryotic cells contain what?


  A membrane bound nucleus, (organelles in the cytoplasm such as)mitochondria, vacuoles, golgi, ER, ribosomes (not membrane bound)
• Describe the size of prokaryotic cells

  Much smaller than eukaryotic cells- only a few micrometres long/wide
• Prokaryotic cells

  
• Comparing eukaryotic and prokaryotic cell structure

  
• Prokaryotes have no membrane bound organelles like mitochondria, chloroplasts etc.
• Most bacteria have a rigid cell wall which provides structural support and protects from osmosis
• Equation for calculating number of bacterial cells after binary fission

  $(N)2^n$N= number of cells at beginning

  n= number of generations (divisions)
• Antibiotic resistant genes


  • Often found on plasmid DNA
  • Plasmids can be transferred between bacteria of the same and different species
• Virus structure

  
• Virus structure

  
• HIV- Attachment proteins

  • Glycoproteins
  • Act as antigens
  • They attach to specific receptor proteins on Th cells-HIV capsid then enters Th cells
• HIV envelope

  • Lipid coat (extra layer)
  • Membrane taken from host cells when new HIV viruses emerge
• HIV capsid 


  Protein coat surrounding genetic material
• HIV genetic material- RNA

  • RNA
  • Carry the base sequences coding for new HIV proteins/ enzymes
• HIV enzyme- reverse transcriptase

  • Enzyme (not found in human cells)
  • Allows HIV‘s RNA to be copied into DNA by the host cell
  • The cell then uses the DNA codes to make more viral proteins to assemble new HIV viruses
• Replication of HIV inside host cells

  1. Attachment proteins bind to specific receptor proteins on Th cell. Capsid enters Th cell and releases RNA and reverse transcriptase into cell
  2. Reverse transcriptase makes a single stranded DNA copy from the viral RNA then a double strand DNA copy is made (using DNA polymerase),viral DNA then inserted into host cell DNA in the nucleus
  3. Cell enzymes and organelles are used to make viral proteins, new viruses are assembled, viruses leave the cell-killing it in the process, picking up a layer of cell membrane
  4. Viruses infect other Th cells
• How does HIV cause aids?

  1. HIV replicates inside helper T-cells (Th cells), leading to the destruction of the Th cells
  2. Less Th cells so less B-cells/ Tc cells are activated (less B-cells divide so less antibodies)
  3. Less pathogens destroyed so replicate too fast, causing damage to body cells/tissues
• Why don’t antibiotics work for viral infections?

  • Antibiotics target enzymes/ ribosomes of bacteria and viruses do NOT contain these
  • Antivirals target enzymes that are specific to viruses