CELL MEMBRANE NOTES Cell Membrane is also known as the Plasma Membrane

It’s role in Homeostasis Directly controls what materials ENTER and LEAVE the cell. It allows oxygen and nutrients to enter, and removes wastes that build up inside

The Fluid-Mosaic Model FLUID – Means the materials in the membrane can freely move MOSAIC – Means the membrane is made out of more than one type of molecule

The cell membrane consists of: lipids, proteins, and carbohydrates The cell membrane consists of TWO (2) layers of LIPIDS called the LIPID BILAYER  1  2 Carbohydrate molecules sometimes extend from the protein molecules on OUTER surface of the cell membrane.

PROTEINS ARE EMBEDDED WITHIN THE LIPID BILAYER Some proteins extend through both lipid layers, while some only extend through the outermost layer.

All of the molecules “float” around, giving the membrane great flexibility.

The microscopic spaces between the lipids allow SMALL molecules to easily DIFFUSE across the barrier.

Since some materials can enter while others cannot, the membrane is called “Selectively Permeable” or “Semi- Permeable.” Large molecules are BLOCKED while small molecules can pass through.

Some molecules need the help of TRANSPORT PROTEINS to pass through the cell membrane.

Other proteins on the cell membrane’s surface act as RECEPTOR MOLECULES. Receptor molecules have SPECIFIC SHAPES to allow materials to communicate with other cells.

The cell membrane has three (3) important jobs 1) Identification – CARBOHYDRATES act like chemical ID cards. 2) Communication – PROTEIN receptor molecules allow cells to respond to messages from other cells, tissues, or organs. 3) Transport – Small molecules are able to pass through the LIPIDS while larger molecules may be transported through transport PROTEINS.

QUESTIONS 1. How many layers of lipids make up the cell membrane?2 2. What type of molecules are embedded in the lipid bilayer?Protein 3. What does the term “fluid” mean?Able to move/flow 4. Name 2 things that can diffuse through the pores of the lipid bilayer? Oxygen, Carbon Dioxide 5. How do larger molecules move across the cell membrane? Through TRANSPORT PROTEINS

6. Name three (3) main jobs of the cell membrane * IDENTIFICATION* COMMUNICATION * TRANSPORT 7. Why can only specific substances react with certain cells? Receptor molecules have SPECIFIC SHAPES so they will FIT only with certain substances. 8. With regard to the cell membrane, what does the term “mosaic” mean? Mosaic means that the cell membrane is made of more than one type of molecule.