AP Biology

Fluid Mosaic Model:  States that membranes are composed of a lipid bilayer containing various proteins and glycoproteins some of which are mobile while others are stationary

Fluid Mosaic Model:  Fluid?  molecules are continuously removed and replaced with newly made molecules  Can stretch  Can reseal itself

Fluid Mosaic Model:  Mosaic?  proteins embedded in or attached to a phospholipid bilayer

Fluid Mosaic Model:  Composed of?  1. Lipids  2. Proteins  3. Carbohydrates (glycoproteins, glycolipids)

Fluid Mosaic Model:  Lipids??  Phospholipids more specifically  Composed of:  Compounds with nitrogen  Phosphate group  Glycerol  Saturated and unsaturated fatty acid chains

Fluid Mosaic Model:  Amphiphathic molecule:

Fluid Mosaic Model:

Fluidity of Membranes:  membranes are not static  hydrophobic and hydrophilic interactions  proteins and lipids can drift, laterally in the membrane  temperature does play a role on membrane fluidity, permeability, enzyme activity  cholesterol  fluidity and function

Roles of Membrane  1.Containment and Separation  2. Material Exchange  3. Information Detection  4. Identification  5. Attachment reinforcement  6. Movement and Metabolism

Membrane Proteins and their Functions:  Proteins determine most of the membranes specific functions  Bound to cytoskeleton on cytoplasmic side and ECM on extracellular side

Membrane Proteins and their Functions:  Two major types of membrane proteins:  Integral  peripheral

Integral Proteins:  penetrate the hydrophobic core of the lipid bilayer  consists of one or more stretches of nonpolar amino acids  hydrophilic parts are exposed on either end of the bilayer

Peripheral Proteins:  not embedded in the membrane  loosely bound to the surface of the membrane  often bound to exposed parts of integral proteins

Functions of Membrane Proteins: 11. Transport 22. Enzyme activity 33. Cell to cell recognitions 44. Signal transduction 55. Intercellular joining 66. Attachment (cytoskeleton and ECM)

The Permeability of the lipid bilayer:  Hydrophobic molecules(hydrocarbons), CO2, O2  Dissolve in the membrane and pass with ease  polar, hydrophilic molecules such as ions  Have trouble passing through the membrane because of the hydrophobic core  Glucose, water(polar molecules)  Pass slowly through the membrane

The Permeability of the lipid bilayer:  Transport Proteins  Enhance the permeability of membrane  Substance specific  Span the width of the membrane  Two types:  Channel proteins  Carrier proteins

The Permeability of the lipid bilayer:  channel proteins:  having a hydrophilic channel  certain molecules and ions use to pass through the membrane  carrier proteins:  transmit molecules through the membrane by changing shape

Passive Transport:  Diffusion  the tendency for molecules of a substance to spread out evenly into the available space  Osmosis:  diffusion of water across a semi-permeable membrane

Passive Transport:  Facilitated Diffusion  passive diffusion of polar molecules and ions with the help of transport proteins  gated channels: need a stimulus to open((electrical or chemical stimulus)

Energy driven transport:  Active Transport:  using energy to move a substance against a concentration gradient  uses carrier proteins  energy is supplied by ATP  See sodium/ potassium pump

 hill.com/sites/ /student_view0/cha pter2/animation__how_the_sodium_potassiu m_pump_works.html hill.com/sites/ /student_view0/cha pter2/animation__how_the_sodium_potassiu m_pump_works.html

Bulk Transport  Passing through membrane by molecules too large to fit through proteins.  Relies on ability of membrane to change shape and create vesicles and reseal itself

Endocytosis  Take large molecules in  Cell membrane pinches in and surrounds molecule in membrane

Phagocytosis  “Cell eating”: engulfing entire cell; done by some white blood cells

Receptor-mediated Endocytosis  Allows smaller molecules to enter  Molecules bind to specific receptor proteins  Egg cells take in yolk protein by this method

Pinocytosis  “Cell drinking”; cells take in fluid and the solutes it contains

Exocytosis  Expelling large molecules; reverse of endocytosis

Cells transport substances across their membranes. Choose ONE of the following four types of cellular transport.  Osmosis  Active Transport  Facilitated Diffusion  Endocytosis/exocytosis  For the transport type you choose,  Describe the transport process and explain how the organization of cell membranes functions in the movement of specific molecules across membranes