2-2 - Bacterial Cytoplasmic Membranes.pdf

2-2: Bacterial Cytoplasmic Membrane Lecture Overview: • The concept of the “cell envelope” and the structure and function of the bacterial cytoplasmic membrane • Textbook: Chapter 2.1 Cell envelope Gram-positive bacterium no Gram-negative bacterium outer-membrane - I i I Outer outer membra...

2-2: Bacterial Cytoplasmic Membrane Lecture Overview: • The concept of the “cell envelope” and the structure and function of the bacterial cytoplasmic membrane • Textbook: Chapter 2.1 Cell envelope Gram-positive bacterium no Gram-negative bacterium outer-membrane - I i I Outer outer membrane ↳ Cell wall Textbook, Fig 2.7 membrane & Cell envelope o Generic term used to describe the structures surrounding the cytoplasm o Major structures can include: Cytoplasmic membrane, cell wall, outer membrane, S-layers, more o Many roles: o Maintains barrier with environment o Protects cell from stress o Allows transport of nutrients into cell and waste out of cell o Energy conservation/production o And much more! Where much of the “action” takes place in a bacterium! Cytoplasmic (cell) membrane • All cells have a cytoplasmic membrane (AKA “cell membrane”. In Gram negative bacteria, AKA “inner membrane”) • Primary barrier between the inner workings of the cell & its environment ↳ important for PH ↳ toxin bulane protection Textbook, Fig 2.4 Cytoplasmic membrane Electron micrograph of a bacterial cell membrane Lipid bilayer Two “sheets” of phospholipids together tail to tail Textbook, Fig 2.1 Cytoplasmic membrane Hydrophilic “water loving” molecules (or moieties). Ionic and/or polar. Hydrophobic “water fearing” molecules (or moieties) – non-polar. Generally, hydrophobic molecules/moieties preferentially interact with other hydrophobic molecules and exclude hydrophilic ones. Phospholipids have: Hydrophilic head group (blue circles) Hydrophobic tails (gold) Textbook, Fig 2.1 Cytoplasmic membrane Side chain is variable Hydrophilic head group Glycerol phosphate backbone is conserved in bacteria (& Eukarya) Different fatty acids can be incorporated into phospholipids that have different properties. Hydrophobic tail Phosphatidylethanolamine Textbook, Fig 2.1 E.g. unsaturated fatty acids (contain double bonds) increase fluidity (decrease rigidity) of membrane. Cytoplasmic membrane: Proteins o Peripheral membrane proteins (loosely attached) & integral membrane proteins (embedded in membrane) and transmembrane proteins (are integral membrane proteins that pass all the way through membrane) found throughout phospholipid bilayer. o Play a wide range of essential roles for the cell Textbook, Fig 2.2 Cytoplasmic membrane: Proteins Textbook, Fig 2.2 o Proteins embedded in membranes (integral or transmembrane) have specific topologies. o Inserted such that specific parts (ranging from short loops to large domains) face either cytoplasm or periplasm/cell wall. o Amino acids that reside within the membrane typically hydrophobic o Hydrophilic side chains often surfaceexposed in cytoplasm or periplasm Periplasm cytoplasm Cytoplasmic membrane: The two “faces” o Note that one side of cytoplasmic membrane faces the cytoplasm (cytoplasmic face) and the other faces outward (sometimes called periplasmic face). o Two faces not identical. E.g., many proteins embedded such that certain domains face one compartment or the other periplasm (cell wall) cytoplasm Textbook, Fig 2.2