Cell Membrane

• Cell membrane

  Mediates isolation of cell contents from the external environment, transport of nutrients into the cell, solute transport, oxidative phosphorylation through electron transport, photosynthetic electron transport (in photosynthetic eukaryotes), maintenance of electrochemical gradients and ATP synthesis, motility, signal transduction, synthesis of cell surface structures and protein secretion

  
• Cell membrane


  • Consists of 35-50% phospholipids which provide the isolation property, and 50-65% proteins which are involved in membrane functions

  
• Phospholipids


  Amphipathic compounds with hydrophobic hydrocarbon chains and a hydrophilic head group in a single molecule
• Phospholipids


  • Sterols, Hopanoids, Glycerophospholipids, Sphingolipids

  
• Membrane proteins

  Integral and peripheral

  
• Membrane proteins

  • Aquaporin, Enzymes responsible for turnover of surface structures, ATP synthase (ATPase) enzyme complex

  
• Archaeal membranes


  The lipids contain ether bonds between glycerol and their hydrophobic side chains, Isoprenoid side chains

  
• Fluid mosaic model


  The hydrocarbon part of phospholipids is in a semi-solid state at physiological temperature, The proteins in the membrane are clustered in functional aggregates, with the aggregates floating around the membrane

  
• Electrochemical gradient


  Measure of the free energy available to carry out the useful work of transporting the molecule across the membrane, Determines the direction an ion moves by diffusion or active transport across a membrane
• Cytoplasmic constituents

  • Cytoplasm, cytoskeleton, intracytoplasmic membrane, mesosomes, nucleoid, genetic material, plasmid, ribosomes, inclusion bodies, storage granules

  
• Cytoplasm


  Consists of aqueous solution of macromolecules, small organic molecules, various inorganic ions and ribosome, Soluble part: cytosol

  
• Prokaryotic cytoskeletal filaments


  • FtsZ - cell division, MreB - cell shape, Crescentin - cell shape, similar to intermediate filaments

  
• Intracytoplasmic membrane (ICM)


  Lipidic structures connected to plasma membrane, Present in methanotrophs, nitrosifters, nitrifiers, phototrophs, and N fixers

  
• Mesosomes


  Invaginations of plasma membrane in the shape of vesicles, tubules, and lamellae, Believed to be involved in cell septum formation, electron transport, photosynthesis, cell wall formation, DNA replication and segregation, sporulation

  
• Nucleoid


  DNA containing region of the cell, Irregularly shaped, some appear coralline in structure, Envelope-associated nucleoid (with large amounts of RNA, proteins, lipids, and peptidoglycan), Envelope-free (lesser amount of non-DNA components)

  
• Bacterial chromosome


  • Mostly circular, Very tightly coiled, No association in histone-like proteins
• Archaeal chromosome


  • Circular, Associated with histone-like proteins
• Plasmid


  Small, independent dsDNA molecules, Non-essential, Replication: cell-independent, Confers enhanced survivability, Classified based on mode of existence, spread, and function
• Ribosomes


  Complex of protein and RNA, Present in cytoplasmic matrix or loosely attached to plasma membrane, Protein synthesis, ~50 different proteins, 70S, 3 RNA (23S, 16S, 5S)
• Inclusion bodies


  Dense, spherical particles of stainable substances (usually aggregated proteins), Formed from overexpression of heterologous proteins, Represent sites of viral multiplication, often with viral capsid proteins
• Storage granules


  Excess carbon - polyhydroalkanoates, glycogen, Sulfur - stored as elemental form, deposited either intra- or extracellularly