The Cell Membrane aka Plasma Membrane

Function Regulates the movement of materials from one environment to the other. Transports raw materials into the cell and waste out of the cell. Prevents the entry of unwanted matter and the escape of needed materials. Maintain a steady environment: Homeostasis Unwanted matter: toxins in the bloodstream Escape of needed materials: muscle cells releasing stored up glucose into the bloodstream when you exercise

Cell (plasma) membrane IN food - sugars - proteins - fats salts O2 H2O OUT waste - ammonia - salts - CO2 - H2O products - proteins Questions: How do sugars, proteins, fats, salts, oxygen and water go in and ammonia, salts, carbon dioxide, water, proteins and other wastes go out? cell needs materials in & products or waste out

Why Called Fluid Mosaic Model?

What is a Mosaic?

Structure: Composed of a phospholipid bilayer with a mosaic (or collage) of many different proteins, lipids and carbohydrates. A Phospholipid is composed of 1 glycerol molecule, 2 fatty acids and 1 phosphate group. This structure causes hydrophilic and hydrophobic regions. Bilayer meaning there are two layers that come together to make one structure Glycerol is made of 3 carbon atoms, with a hydroxyl group Fatty acid: made of hydrocarbon chain and carboxyl group (COOH)

Lipids of cell membrane Membrane is made of special kind of lipid Phospholipids Membrane is a double layer phospholipid bilayer “attracted to water” phosphate inside cell outside cell Questions: What are phospholipids? What does it mean to be attracted to water? What does it mean to be repelled by water? lipid “repelled by water”

Hydrophilic vs. Hydrophobic Hydrophilic: attracted to water Hydrophobic: repelled by water

The Fluid-Mosaic Membrane Model Membranes are not static; they have a fluid consistency. Most membrane lipids and proteins can drift about laterally in the plane of the membrane. Cholesterol enhances membrane fluidity, allows animal membranes to function in a wide range of temperatures and also makes the membrane less permeable to biological molecules. Illustration: static and inflexible vs. fluid (sheet of paper or ruler) Drift laterally: means they can move side to side Cholesterol is also found in cell membrane Let’s talk about permeability real quick

Semi-permeable membrane Cell membrane controls what gets in or out Need to allow some materials — but not all — to pass through the membrane semi-permeable only some material can get in or out So what needs to get across the membrane? Questions: What is does semi-permeable mean? How does the membrane decide what materials go in and which ones go out? Why do sugars, lipids, amino acids, oxygen, water, salt and waste have to get across the membrane? sugar lipids aa O2 H2O salt waste

Crossing the cell membrane What molecules can get through the cell membrane directly? fats and oils can pass directly through lipid inside cell outside cell salt waste Questions: Why can fats and oils pass directly through the membrane? How do wastes and salts pass through? How do sugars, amino acids and water pass through? but… what about other stuff? sugar aa H2O

Membrane Proteins: Two Types: Integral: Proteins that are embedded in the membrane (transmembrane proteins) Peripheral: Proteins attached to the surface of the cell membrane. Function: Transportation Enzymes Receptor sites Cell adhesion Attachment to the cytoskeleton

Cell membrane channels Need to make “doors” through membrane protein channels allow substances in & out specific channels allow specific material in & out H2O channel, salt channel, sugar channel, etc. inside cell H2O aa sugar Questions: How can I reframe this so it flows better? These doors are also known as protein channels, which allow substances in and out 1st period- guys I had a really cool idea! So save the packets I gave you. At the end of our lesson on cell membranes, I want you to make a physical model of the cell membrane (which means I have to make one myself over the weekend) So I’m going to modify this assignment So it looks like in addition to protein channels, there are other channels that allow certain substances out. So there’s a sugar channel? salt outside cell waste

Carbohydrates: Usually branched molecules of 15 or less sugar units. Some are bonded to lipids: Glycolipids. Most are bonded to proteins: Glycoproteins. Function: Cell-cell recognition.