The Plasma Membrane AP Biology

Selective Permeability Brings in certain substances Releases or keeps out certain substances Maintains water balance Essential for life

Structure of the membrane Composed largely of phospholipids Arranged in a bilayer The hydrophilic heads face the outside of the membrane The hydrophobic tails are inside the membrane away from water

Phospholipid Bilayer Water bathes the outside of the cell and makes up most of the cytoplasm

Fluid Mosaic Model The membrane has a fluid quality: will ooze if punctured Parts move and interact Mosaic means many parts or components

Components of the Mosaic Phospholipids Glycolipids Sterols Proteins Glycoproteins

Types of Proteins Transport proteins Receptor proteins Recognition proteins Adhesion proteins Cell to cell communication proteins

Transport Proteins Allows water soluble molecules to move through membrane Binds substance on one side, and releases it on the other Glucose, ions, large polar molecules May be active or passive

Receptor Proteins Bind substances outside the cell which triggers some cellular activity Hormones Perfect fit: lock and key

Recognition Proteins Identify each person’s cells as their own Must be matched in transplants, blood transfusions, etc.

Adhesion Proteins Help cells of the same type stick together in tissues These are glycoproteins with oligosaccharides attached.

Cell to Cell Communication Proteins Cell to cell communication proteins: match up with another cell to pass on a signal

Permeability Some substances move across easily These include substances which are soluble in lipids (non-polar) CO2, O2, and some H2O.

Permeability Glucose, amino acids, and other large molecules that do not dissolve in lipids cannot pass through Most water molecules, and ions such as H+, NA+, K+, and Ca+ cannot pass through Need transporter proteins