3.3 Cell Membrane KEY CONCEPT The cell membrane is a barrier that separates a cell from the external environment.

3.3 Cell Membrane Cell membranes are composed of two layers of phospholipids (phospholipid bilayer)

3.3 Cell Membrane Cell membrane has two major functions. 1. forms a boundary between inside and outside of cell 2.controls passage of materials in and out of cell cell membrane outside cell inside cell

3.3 Cell Membrane Cell membrane is made of a phospholipid bilayer. Phospholipids have hydrophobic and hydrophilic ends. Hydrophobic: repel H 2 0; non-polar fatty acid tails Hydrophilic heads face out. Hydrophobic tails are in the middle. Water is inside and outside cell. Hydrophobic middle keeps things from seeping through. Hydrophilic: attracted to H 2 0; polar phosphate heads

3.3 Cell Membrane Phosphate group (head; hydrophilic) Glycerol (holds parts together) Two fatty acid chains (tail; hydrophobic) Phosphate group glycerol Fatty acid chains Hydrophobic: repel H 2 0; non-polar fatty acid tails Hydrophilic: attracted to H 2 0; polar phosphate heads Cell membrane is made of a phospholipid bilayer. Phospholipids have hydrophobic and hydrophilic ends. Phospholipids are made of:

3.3 Cell Membrane Other molecules are embedded in cell membrane. Cholesterol Strengthen the membrane Proteins Help materials cross membraeCarbohydrates Attached to proteins to serve as ID tags which enable cell to distinguish one type from another carbohydrates proteins cholesterol

3.3 Cell Membrane cell membrane The fluid mosaic model describes how things move in the cell membrane. Cell membrane is flexible, not rigid. Parts move around within cell membrane. Bubble Demonstration: rubber band could float around on bubble surface. Hole in rubber band is like a protein channel protein cholesterol protein carbohydrate chain protein channel

3.3 Cell Membrane Fluid Mosaic Video

3.3 Cell Membrane Cell membranes are selectively permeable. Some molecules can pass, but others cannot. Diffusion: Some small molecules can slip through (H 2 0, O 2, CO 2 ) Active Transport: Larger molecules pass through protein channels if cell lets them. Requires energy. Semi-permeable membrane

3.3 Cell Membrane Chemical signals are transmitted across the cell membrane by receptors. Receptors are proteins that bind with ligands and change shape. This causes other molecules to send a message inside cell. Type 1: Intracellular receptors Located inside the cell Bind with ligands that can pass through the cell membrane

3.3 Cell Membrane Chemical signals are transmitted across the cell membrane by receptors. Receptors are proteins that bind with ligands and change shape. This causes other molecules to send a message inside cell. Type 2: Membrane Receptors Embedded in cell membrane Ligand binds with protein on outside of cell Receptor changes shape causing chain of events that tells cell what to do

3.3 Cell Membrane Two Different Types of Receptors Membrane Receptor –Ligand cannot cross the membrane but binds to receptor proteins within the cell membrane, entire protein will change shape –Receptor then sends a message to the cell interior –Changed shape of protein causes molecules inside the cell to respond and start a chain of events to tell cell what to do –Ex: red blood cells have a membrane protein receptor that triggers the process that carries CO2 out of the body through the lungs

3.3 Cell Membrane