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Cell MembraneThe cell membrane is a semi-permeable lipid bilayer. – Semi-permeable means it lets some things pass
through it. – Lipid means fat (phospholipid to be exact) – Bilayer means there are 2 layers
Cell Membrane
Cell Membrane
Cell Membrane
The cell membrane maintains the internal environment of the cell, by moving molecules from one side to the other.
PhospholipidThe cell membrane is composed phospholipids, which have hydrophilic heads and hydrophobic tails.
Cell membrane
Proteins
Protein channel Lipid bilayer
Carbohydrate chains
Lipid Bilayer
Phospholipids spontaneously arrange into a double layered membrane in a fluid environment.
Membrane ProteinsProteins embedded within the membrane allow materials to move in and out of the cell.
Classes of membrane proteins – peripheral proteins
• loosely bound to surface of membrane • ex: cell surface identity marker (antigens)
– integral proteins • penetrate through the cell membrane • ex: transport proteins
Membrane Proteins
Passive TransportDiffusion is the movement of molecules from an area of high concentration to an area of low concentration.
Passive TransportIn a cell... Diffusion moves small, uncharged molecules across the cell membrane until equilibrium is reached.
Facilitated Diffusion
High Concentration
Low Concentration
Cell Membrane
Facilitated diffusion is the movement of large or charged particles such as ions, sugars, and salts through protein channels across the cell membrane.
High Concentration to Low Concentration
Osmosis: Facilitated DiffusionOsmosis is the diffusion of water through a selectively permeable membrane. Many cells contain water channel proteins called aquaporins that allow water to pass directly through the membrane.
Osmosis: Facilitated DiffusionThere is a net movement of water from low to high solute concentration, or high to low water concentration.
The net movement of water into or out of a cell produces a force known as osmotic pressure.
Osmotic Pressure
Osmotic PressureOsmosis is a force that exerts a pressure on the more concentrated side of a cell membrane.
Solution ConcentrationsTonicity is a measure of the osmotic pressure gradient of two solutions separated by a semipermeable membrane. • Hypertonic - Having a higher concentration than another
solution. • Hypotonic - Having a lower concentration than another
solution. • Isotonic - Having the same amount of dissolved solute as
another solution.
Comparing Solutions• A cell placed in a hypertonic solution will decrease
in volume. • A cell placed in a hypotonic solution will increase in
volume. • A cell placed in an isotonic solution will not change
in volume.