The Cell Membrane 3.3 E.Q.: How is the structure of the cell membrane important for its function?

Cell Membrane Function Forms a boundary between inside & outside of cell Controls what goes in & out of cell

The cell membrane is selectively permeable meaning that it allows some things to pass through but not others This helps the cell maintain homeostasis

Cell Membrane Structure Consist of a phospholipid bilayer Phospholipids are composed of three parts: 1. a charged phosphate group 2. glycerol 3. two fatty acid chains Phospholipids have a polar hydrophilic head (phosphate group) & nonpolar hydrophobic tails (fatty acids)

Phospholipid Phospholipid

Cell membrane Phospholipid bilayer

Other molecules in membrane: Cholesterol: strengthen the cell membrane Proteins: help materials cross the membrane and make up cytoskeleton Carbohydrates: identification tag for cell

carbohydrates protein cholesterol protein protein

Scientists use the fluid mosaic model to describe the cell membrane because 1. membrane is flexible 2. membrane contains a variety of molecules

Chemical signals are transmitted across the cell membrane via receptors. Receptor: protein that detects a signal & performs an action in response Receptors bind with a molecule called a ligand and the two change shape

Two types of Receptors: 1. Intracellular receptor: receptor located inside the cell -small molecules such as some hormones are able to cross the cell membrane and bind to intracellular receptors

2. Membrane receptor: receptor located within cell membrane -molecules that can’t pass through membrane bind to these receptors with send signals to the inside of the cell