The Plasma Membrane also called the cell membrane - 1/18/2019 The Plasma Membrane also called the cell membrane - Gateway to the Cell copyright cmassengale G. Podgorski, Biol. 1010

Photograph of a Cell Membrane The Plasma Membrane 1/18/2019 Photograph of a Cell Membrane copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane 1/18/2019 Cell Membrane The cell membrane is flexible and allows a unicellular organism to move copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane 1/18/2019 Homeostasis Balanced internal condition of cells Also called equilibrium Maintained by plasma membrane controlling what enters & leaves the cell copyright cmassengale G. Podgorski, Biol. 1010

Functions of Plasma Membrane The Plasma Membrane 1/18/2019 Functions of Plasma Membrane Protective barrier Regulate transport in & out of cell (selectively permeable) Allow cell recognition Provide anchoring sites for filaments of cytoskeleton copyright cmassengale G. Podgorski, Biol. 1010

Functions of Plasma Membrane The Plasma Membrane 1/18/2019 Functions of Plasma Membrane Provide a binding site for enzymes Interlocking surfaces bind cells together (junctions) Contains the cytoplasm (fluid in cell) copyright cmassengale G. Podgorski, Biol. 1010

Structure of the Cell Membrane The Plasma Membrane 1/18/2019 Structure of the Cell Membrane copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale Membrane Components The Plasma Membrane 1/18/2019 Phospholipids Proteins (peripheral and integral) Cholesterol copyright cmassengale Carbohydrates (glucose) G. Podgorski, Biol. 1010

copyright cmassengale

copyright cmassengale The Plasma Membrane 1/18/2019 Phospholipids Make up the cell membrane Contains 2 fatty acid chains that are nonpolar Head is polar & contains a –PO4 group & an alcohol (glycerol) copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane 1/18/2019 FLUID MOSAIC MODEL FLUID- because individual phospholipids and proteins can move side-to-side within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above. copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane Cell Membrane 1/18/2019 Polar heads are hydrophilic “water loving” Nonpolar tails are hydrophobic “water fearing” Makes membrane “Selective” in what crosses copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane 1/18/2019 copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane Cell Membrane 1/18/2019 The cell membrane is made of 2 layers of phospholipids called the lipid bilayer Hydrophobic molecules pass easily; hydrophilic DO NOT copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane 1/18/2019 Solubility Materials that are soluble in lipids can pass through the cell membrane easily copyright cmassengale G. Podgorski, Biol. 1010

Semipermeable Membrane The Plasma Membrane Semipermeable Membrane 1/18/2019 Small molecules and larger hydrophobic molecules move through easily. e.g. O2, CO2, H2O copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane Semipermeable Membrane 1/18/2019 Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own. copyright cmassengale G. Podgorski, Biol. 1010

The Fluidity of Membranes Phospholipids in the plasma membrane Can move within the bilayer two ways Lateral movement (~107 times per second) Flip-flop (~ once per month)

The Fluidity of Membranes The type of hydrocarbon tails in phospholipids Affects the fluidity of the plasma membrane Fluid Viscous Unsaturated hydrocarbon tails with kinks Saturated hydro- Carbon tails

The Fluidity of Membranes The steroid cholesterol Has different effects on membrane fluidity at different temperatures Figure 7.5 Cholesterol

Membrane Proteins and Their Functions A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer Fibers of extracellular matrix (ECM)

Types of Membrane Proteins Integral proteins Penetrate the hydrophobic core of the lipid bilayer Are often transmembrane proteins, completely spanning the membrane EXTRACELLULAR SIDE

Transport Proteins Transport proteins Allow passage of hydrophilic substances across the membrane

Types of Membrane Proteins Peripheral proteins Are appendages loosely bound to the surface of the membrane

The Role of Membrane Carbohydrates in Cell-Cell Recognition Is a cell’s ability to distinguish one type of neighboring cell from another Membrane carbohydrates Interact with the surface molecules of other cells, facilitating cell-cell recognition