3.6 - Prokaryotic cells and viruses

• prokaryotic cells are smaller than eukaryotic cells and have no nucleus or nuclear envelope
• Structure of a bacterial cell:

  cell wall made of murein - physical barrier that excludes certain substances and protects against mechanical damage and osmotic lysis

  capsule - (of slime) protects bacterium from other cells and helps groups of bacteria stick together for further protection

  cell surface membrane - acts as a differentially permeable layer which controls the entry and exit of chemicals

  circular DNA - possesses the genetic information for the replication of bacterial cells

  plasmid - possesses the genes that may aid the survival of bacteria in adverse conditions
• plasmids are used in genetic engineering as vectors
• bacterial cells contain 70s ribosomes, which are smaller than the 80s ribosomes found in eukaryotic cells, but can synthesise proteins
• viruses and bacteria are types of prokaryotic cells
• viruses are acellular, non living particles. they are smaller than bacteria (20-300 nm)
• viruses contain nucleic acids but rely on host cells to replicate. their nucleic acids are enclosed within a protein coat called a capsid, which has attachment proteins on it, allowing the virus to identify and attach to a host cell