The membrane is semipermeable (imagine a fence or screen door) The Plasma Membrane -  S.J. Singer proposed the Fluid Mosaic Model to describe the cell membrane The membrane is semipermeable (imagine a fence or screen door) Pg 84 The phospholipid bilayer

Fluid Mosaic Model Phospholipids are made up of a phosphate head that is polar and hydrophilic (water loving), as well as two fatty acid tails that are non-polar and hydrophobic (water "fearing").  When put into an aqueous environment, phospholipids automatically form the structure of a bilayer with the hydrophilic phosphate heads facing the aqueous environment, and the hydrophobic fatty acid chains facing each other. Aqueous environments contain water, so the water loving phosphate heads stay on the outside, whilst the water fearing fatty acid tails stay on the inside AWAY from the water.  They form a bilayer in aqueous environments because one component of phospholipids does not like interacting with water whilst the other component does, and forming this bilayer allows both components to be "happy". 

Jobs of the Cell Membrane Isolate the cytoplasm from the external environment Regulate the exchange of substances Communicate with other cells Identification

1.  The plasma membrane is a phospholipid bilayer with embedded proteins.  Figure 5.2

What does the cell membrane do? acts as a boundary layer to contain the cytoplasm (fluid in cell) 2) Regulates interactions between the cell and the environment. Selective Permeability: The ability to allow certain substances through a membrane while keeping others out. Our cells need certain macromolecules/ions to enter and needs to keep wastes out.

Channel Proteins - form small openings for molecules to diffuse through Carrier Proteins- binding site on protein surface "grabs" certain molecules and pulls them into the cell Gated Channels - similar to carrier proteins, not always "open" Receptor Proteins - molecular triggers that set off cell responses (such as release of hormones or opening of channel proteins), binding site Recognition Proteins - ID tags, to identify cells to the body's immune system Enzymatic Proteins – carry out specific reactions

Figure 5.4a Figure 5.4a

Figure 5.4b Figure 5.4b

Figure 5.4c Figure 5.4c

Figure 5.4d Figure 5.4d

Figure 5.4e Figure 5.4e

Membrane Permeability à   Transport Across Membrane *Selectively or Differentially permeable – some things can cross, not others What things can pass? What cannot pass? Figure 5.5

Cell Membrane and Transport Notes Mr Walker Biology Class

Passive Transport DOES NOT USE ENERGY!!!! Diffusion: The movement of a particle from an area of a high concentration to that of a low concentration. Remember….Salt Sucks….Sugar sucks. Equilibrium: the same amount of particles per space on both sides.

Osmosis Osmosis is the diffusion of water through a membrane. ISOTONIC: water will move through the membrane at the same rate. HYPOTONIC: More water outside the cell than inside. So water moves into the cell causing the cell to SWELL! HYPERTONIC: More water inside the cell than outside. So water moves out of the cell causing the cell to SHRINK!

Proteins in the cell membrane Channels proteins allow particles to diffuse into the cell. Facilitated Diffusion: A channel protein which allows large particles to enter the cell. PASSIVE TRANSPORT

Active Transport Active transport is the movement of particles from an area of a LOW concentration to an area of a HIGH concentration. USES ENERGY!!!!!!!

Na+ K+ Pump A carrier protein which uses energy to pump in 2 potassium ions and pump out 3 sodium ions

Endocytosis The movement of the cell membrane around a large particle to help bring the particle INTO the cell

Exocytosis The movement of the cell membrane around a large particle to help bring it out of the cell.