Prokaryotic Cells

• Prokaryotic - Smaller and simpler cells with no true nucleus and include bacteria and archaebacteria
• Ancient (4 billion years old), diverse and numerous kingdoms of organisms, two domains: Eubacteria (Bacteria) and Archaebacteria (Archaea) and some can live in any habitat (extremophiles)
• They don’t divide by mitosis but instead, binary fission and may also do conjunction, DNA/genes are transferred sexually between cells
• Not all bacteria are pathogenic - some of it is good for the body, and the majority are neither
• Super Small, 1-10 μm (0.001-0.01mm),15,000x smaller that the average eukaryotic cells, and are all Unicellular - can form clusters/chains
• Structurally very simple, but they are metabolically and biochemically more versatile than eukaryotic cells, they have no nucleus or any membrane-bound organelles
• They have a singular circle of chromosomes, and always have a cell wall (made of peptidoglycan), some respire aerobically and others anaerobically
• Bacteria is split into two groups, gram-positive and gram-negative
• Gram-positive - A thick layer of peptidoglycan and certain acids, it appears blue/violet under a light microscope (stained with the gram stain)
• Gram-negative - A thinner layer of peptidoglycan which is surrounded by a second membrane, it contains lipopolysaccharides or lipoproteins, and they do not take up gram stain and appear red/pink under a light microscope
• Cell walls: Located outside the plasma membrane and made of polysaccharides, the main one is peptidoglycan - provides shape and rigidity to the cell
• Mesosome: Reminiscent of mitochondria and chloroplasts; they are a tightly folded region of the cell membrane containing many membrane-bound proteins giving a large internal surface area
• Mesosome 2: Location of aerobic respiration, does photosynthesis in cyanobacteria, and also involved with cell division
• Nucleoid: Always circular (closed loop) double-stranded DNA associated with proteins (not histones), sometimes called bacterial chromosome and have all genes to code for all bacterial proteins
• Ribosomes: Same as in eukaryotes but 70s size and all free in the cytoplasm and never attached to membranes (used for protein synthesis)
• Flagellum: A rotating helical-shaped tail made of the protein flagellin, attached to a membrane-bound motor protein (bacteria can have one or many); used for movement
• Pili/Fimbriae: Protein filaments sticking out from the cell wall, pili helps in conjunction and fimbriae helps bacteria stick to each other, form colonies, or to other surfaces, form biofilms
• Capsule/Slime layer: Common but not always present, it's thick polysaccharide layer outside of the cell wall that protect against desiccation and phagocytosis
• Plasmids: Small circle of DNA (separate from main loop) and can be transferred between bacteria cells during conjugation - antibiotic resistance genes often occur on plasmids, they are also used extensively as vectors in genetic engineering
• Endospores: Unique to bacteria (circumstantial structure), allow for a certain level of dormancy, a tough, non-reproductive system
• Endospores 2: Formed by some gram-positive when environmental conditions are unfavourable, for survival and protection of dormant bacteria from high temperature, desiccation and UV radiation
• Cyanobacteria: Contains Chlorophyll and other photosynthetic pigments, the most abundant photosynthesising organisms on earth (first to produce oxygen; gigantic role in the evolution of the Earth’s atmosphere)