Membrane Structure and Transport

Membrane Structure Phospholipid bilayer (nonpolar) Membrane proteins – act as transport channels Carbohydrate chains –act as “ID” tags for the cell Cholesterol – provides stability for the membrane http://library.thinkquest.org/C004535/media/cell_membrane.gif

Fluid Mosaic Model http://biologyisaprocess.wordpress.com/2011/10/1 5/the-fluid-mosaic-model/

Membrane Functions Provides a selectively permeable barrier around the cell Controls the passage of substances in and out of the cell. Polar and charged substances can pass through the membrane proteins (“gates”) Maintains homeostasis for the cell helping it meet its needs.

Types of Cellular Transport ACTIVE Requires energy from ATP Goes against the concentration gradient (low to high) Active Transport, Endocytosis, Exocytosis PASSIVE Does not require energy Goes with the concentration gradient (high to low) Simple Diffusion, Osmosis, Facilitated Diffusion

Passive Transport: Simple Diffusion http://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter 2/ Simple diffusion is when a small, 
non-polar molecule passes through a lipid bilayer.  
.

Passive Transport: Osmosis Osmosis is the diffusion of water through a selectively permeable membrane. Water will move to the side of the membrane that has the higher solute concentration.

Osmosis (Cont.) Cells will shrivel when put into a solution with MORE SOLUTE. Ex) salt water If solute concentration is equal on both sides of the membrane, the cell does not change. Cells will swell or burst when put into a solution with LESS SOLUTE Ex) Fresh water

Tonicity

Passive Transport: Facilitated Diffusion Particles are moving through a transport protein from high to low concentration Particles that are polar are charged must move through a protein channel Glucose and ions enter the cell in this way.

Facilitated diffusion Hypertonic Hypotonic Isotonic Vocabulary Lipid bilayer Passive Transport Diffusion Osmosis Facilitated diffusion Hypertonic Hypotonic Isotonic

Active Transport Particles move from low to high concentration against concentration gradient Requires ATP energy The sodium / potassium pump is an example.

Active Transport: Endocytosis The plasma membrane surrounds and brings large particles into the cell Phagocytosis – cell “eating” Pinocytosis – cell “drinking” Requires energy

Active transport: Exocytosis The export of large particles such as waste out of the cell Proteins, hormones, and other substances are secreted from cells in this manner Nerve cells release neurotransmitters in this manner

Vocabulary Active Transport Endocytosis Exocytosis