MBIO 1010 Lecture 6

• You cannot determine a common ancestor with cell morphology
• 0.15 micrometers = 150nm
• In gram positive doesn't have periplasm space, so it would be the outside of the cell
• Archaeal membranes

  Ether linkages in phospholipids of archaea

  Bacteria and Eukarya that have ester linkages in phospholipids

  archaeal lipids lack fatty acids; have isoprenes instead

  Major lipids are glycerol diethers and tetraethers

  can exist as lipid monolayer, bilayer or mixture
• membrane structure

  • in contrast to lipid bilayers, lipid monolayer membranes are extremely heat resistant
  • commonly found in hyperthermophilic Archaea (grow best at temperatures above 80 degrees Celsius
• Hyperthermophilic

  • hyper: more, a lot, increase (inverse is hypo)
  • thermo: heat
  • philic: loving
• despite the advantages of a monolayer, they are similar to bacterial membranes and eukaryal membranes - have hydrophilic components that protects it from the hydrophobic
• instead of fatty acids, archaeal membranes have isoprenes, look similar to fatty acids

  • diethers (phytanyl - have 20 carbon side chains)
  • tetraethers (biphytanyl - have 40 carbon side chains and 2 glycerol groups)
• Membrane function

  Permeability barrier

  protein anchor

  energy conservation
• Permeability barrier

  • polar and charged molecules must be transported
  • transport proteins accumulate solutes against the concentration gradient
  • through the membrane
  • We don't want the solution to be all the same concentration and hence the movement against the concentration gradient in order to do this we need transport proteins - come can't cone because they are too big or what not
  • prevents leakage and function as a gateway for transport of nutrients into, and wastes out of the cell
• Protein anchor

  • holds transport proteins in place
  • site of many proteins that participate in transport, bioenergetics and chemotaxis
• Energy conservation

  • generation of proton motive force
  • site of generation and dissipation of the proton motive force
• Carrier-mediated transport systems

  • using the transport proteins
  • show saturation effect
  • highly specific - won't transport just anything - controls what comes in and out
  • some hydrophobic can pass with diffusion, hydrophilic cannot pass
  • help things move that pass on their own - outside the cell
  • rate of solution entry - time component
  • simple diffusion - slow entry
  • transport proteins have a limit on how fast they can go
• Three major classes of transport systems in prokaryotes

  • simple transport
  • group translocation
  • ABC system
• All three major classes of transport systems require energy in some form, usually proton motive force or ATP
• Due to the major classes of transport systems in prokaryotes requiring energy, we call it active transport because they need energy to be able to move against the concentration gradient
• Simple transport

  • driven by the energy in the proton motive force
  • solute moving in as well as a proton and vice versa
  • involves 1 transport protein
• Group translocation

  • Chemical modification of the transported substances driven by phosphoenolpyruvate
  • solute moves into the cell or out
  • as its being transported it is also being chemically modified
  • more than one at play - series of proteins involved
• ABC transporter

  • Periplasmic binding proteins are involved and energy comes from ATP
  • 3 parts
• Simple transport and ABC transporters have the same things from beginning to the end
• Passive transport is simple diffusion
• Three transport events are possible

  • uniport
  • symport
  • antiport
• Uniporters transport in one direction across the membrane
• symporters function as co-transporters
• antiporters transport a molecules across the membrane while simultaneously transporting another molecule in the opposite direction
• Simple transport

  • Common example
  • lac permease of Escherichia coli
  • lactose is transported in to E.coli by the simple transporter lac permease, a symporter - two molecules move across membrane in same direction
  • activity of lac permease is energy-driven
  • transport lactose and a H+ into the cell simultaneously
• Ending in ASE - enzyme
• Group translocation

  • Phosphotransferase system in E.coli
  • sugar is phosphorylated during transport across the membrane
  • moves glucose, fructose and mannose
  • phosphoenolphyruvate (PEP) donates a P to a phosphorelay system
  • P is transferred through a series of carrier proteins and deposited onto the sugar as it is brought into the cell
  • Enzyme 1 and HBr will do any sugar
  • Enzyme 2 and 2b are specific - different sets for each sugar being transported
• ABC (ATP-binding cassette) transport systems

  • involved in uptake of organic compounds (sugar, amino acids) inorganic nutrients (sulfate, phosphate) and trace metals
  • typically display high substrate specificity
  • gram-negative employ periplasmic-binding proteins and ATP-driven transport proteins
  • Gram positive employ substrate-binding lipoproteins (anchored to external surface of cell membrane) and ATP-driven transport proteins
  • solute binding protein
  • periplasm
  • binds specific substrate
  • integral membrane proteins
  • transporter
  • ATP-hydrolyzing proteins
  • supply energy for the transport event