Membranes

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Membranes
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Cell membrane

• Happened early in evolution.
• Separate cell from its surroundings
• Selective permeability allows only certain
  things to cross

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Cell membranes

• Membranes fluid mosaics of lipids and proteins
• Amphipathic molecule phospholipids have both a
  hydrophilic (head) and hydrophobic (tail) region
  also membrane proteins
• Hydrophobic portions are hidden in the middle of
  the bilayer membrane

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Lateral movement

• Proteins and lipids can move laterally within the
  membrane
• Seem to move with specific direction.driven
  along cytoskeletal fibers by motor proteins.

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• Membranes must be fluid to work properly.
• Salad oil
• Cholesterol hinders closeness of the
  phospholipids making membrane slightly less fluid
  but maintaining fluidness into lower temperatures.

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Membranes differ

• Membranes with different functions differ in
  their makeup.
• Mitochondria have more embedded proteins

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Membrane transport

• Hydrophobic not charge can dissolve partially
  cross
• Hydrophilic more difficult

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Cell Wall plants

• Cell wall
• Cellulose
• Proteins
• Polysaccharides
• Pectin (starch)

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Cell Membrane

• Cell Membrane (animal)
• Phospholipid bilayer
• Imbedded proteins protein channels
• Cholesterol
• Glycoproteins cell to cell recognition

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Membrane transport

• Hydrophobic no charge, non polar
• If small CO2, O2 can dissolve and cross easily
• Hydrophilic polar more difficult H2O, glucose

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Passive transport

• Passive transport diffusion, osmosis,
  facilitated diffusion (uses transport protein)
• Diffusion tendency of molecules to spread out
  due to their kinetic energy.
• Substances will diffuse down their concentration
  gradient
• Unaffected by the concentration of other
  substances.

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Membrane transport Facilitated

• Facilitated diffusion H2O, glucose
• Transport Proteins may be hydrophilic inside
• Carrier may physically move substrate
• Aquaporins for H2O
• May be substrate specific or may just span the
  membrane

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Membrane Transport facilitated

• Transport protein
• Protein channel
• Ion channels usually gated. Need chemical or
  electrical stimulus
• Protein carrier

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Osmosis

• Osmosis diffusion of water passive
• Water down its concentration gradient
• Hypotonic to Hypertonic less
  solute(more water) more solute

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• Cell wall lets in only so much water until cell
  is turgid (healthy for plant)
• Animal cell with no wall will burst if put in
  hypotonic solution.

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Active transport

• Sodium potassium pump
• Pumping solutes against their concentration
  gradient.
• Cell inside K high Na low
• Must use energy to maintain this balance
• ATP phos. Group might bind directly to the
  transport protein

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Na K pump

• Na binds with protein causes ATP to ADP
• The added phosphate changes protein shape
• So, protein spits Na out the other side and
  grabs K
• K binding releases the Phosphate
• 3 Na out and 2 K in

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Voltage

• Cell membrane have voltage
• Membrane potential electrical potential energy
  due to the charges in and out of cell ( - inside
  outside)
• Animal electrogenic pump (Na, K)
• Plants use proton pump

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• 2 forces drive diffusion
• Membrane potential electrical energy
• Concentration gradient chemical energy

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Cotransport

• Plant pumps H out
• When it diffuses back in it can carry sucrose
  with it. (even against concentration gradient)

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Exocytosis

• Exocytosis vesicle fuses with cell membrane to
  release it secretions outside

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Endocytosis

• Membrane forms vesicle with something from
  outside
• 1. phagocytosis pseudopodium then fuse with
  lysosome
• 2. pinocytosis wrap around drop of
  extracellular fluid
• 3. receptor mediated humans- cholesterol ligand
  any molecule that binds to receptor