3.6. Prokaryotic Cells and Viruses

• Eukaryotic cells are large and have a nucleus bounded by nuclear membranes, also known as the nuclear envelope
• Prokaryotic cells are smaller and have no nucleus or nuclear envelope
• Bacteria are versatile, adaptable and successful as a result of their small size, ranging from 0.1 to 10 micrometres in length
• All bacteria possess a cell wall, which is made up of murein, which is a polysaccharide with peptide bonds. Many bacteria protect themselves with a capsule of mucilaginous slime around this wall
• Inside the bacterial cell wall, there is a cell-surface membrane, within which is the cytoplasm that contains 70S ribosomes. These ribosomes are smaller than those found in eukaryotic cells but these still synthesise proteins
• Bacteria store food reserves as glycogen granules and oil droplets. The genetic material in bacteria is in the form of a circular strand of DNA
• Plasmids reproduce themselves independently and give the bacterium resistance to harmful chemicals such as antibiotics. They are also used as carriers of genetic material in genetic engineering
• Another name given to murein is peptidoglycan
• Bacteria do not have chloroplasts, only bacterial chlorophyll associated with the cell-surface membrane in some bacteria
• Viruses are acellular, non-living particles. They are smaller than bacteria ranging from 20-300nm
• They contain nucleic acids such as DNA and RNA as genetic material but can only multiply inside living host cells. The nucleic acid is enclosed within a protein coat called the capsid
• Some viruses, like HIV are further surrounded by a lipid envelope. The lipid envelope or capsid have attachment proteins which are essential to allow the virus to identify and attach to the host cell
• HIV: Human immunodeficiency virus, a virus that attacks the immune system and causes AIDS
• Flagellum is used for locomotion. Some species contain multiple, some have none
• Reverse transcriptase is an enzyme that catalyzes the conversion of RNA to DNA. Viruses do this to replicate their genome
• Attachment proteins can be viewed as the key that opens the cellular door to allow the virus to enter the cell