Cell Biology: The Cell Membrane

1. Cell Biology:The Cell Membrane Lesson 1 – Structure and Function of the Cell Membrane (Inquiry into Life pg. 67-69)

2. Today’s Objectives • Analyze the structure and function of the cell membrane, including: • Apply knowledge of organic molecules such as phospholipids, proteins, glycoproteins, glycolipids, carbohydrates, and cholesterol, to explain the structure and function of the fluid-mosaic membrane model • Identify the hydrophobic and hydrophilic regions of the phospholipid bilayer • Explain why the cell membrane is described as “selectively permeable”

3. Cell (Plasma) Membrane Function • The cell membrane regulates the entrance and exit of molecules into and out of the cell

4. Cell Membrane Function • Impermeable – nothing can pass through • Permeable – most things can pass through • Semi-permeable – smaller molecules pass through but not larger molecules • Selectively permeable – only certain small molecules and certain large molecules can pass through • Cell membranes are selectively permeable • Also called differentially permeable

5. Cell Membrane Structure • Early Theory: • Proteins were sandwiched between 2 layers of phospholipid molecules • Problem: Since the phospholipid tails are hydrophobic (hate water) this theory did not explain how water (or other polar molecules) can travel freely through membranes

6. Cell Membrane Structure • Accepted Theory: Fluid-Mosaic Model • There is a double layer of phospholipids but the proteins are scattered through the membrane (mosaic) • The proteins float among the semi-fluid phospholipids Polar molecules can travel through the pores in the proteins

7. Proteins in the Cell Membrane • The proteins have polar and non-polar regions, which accounts for their placement among the phospholipid bilayer • Proteins imbedded in the membrane are called integral proteins (can move freely) • Proteins partially imbedded in the membrane (on one side) are called peripheral proteins • Peripheral proteins help maintain membrane shape and are often held in place by cytoskeletal filaments Peripheral Protein Integral Protein

8. Proteins in the Cell Membrane • Some of the proteins and phospholipids have carbohydrate chains attached to them (always on outer side of the cell membrane) • Protein + Carbohydrate chain = glycoprotein • Protein + Carbohydrate chain = glycolipid • These carbohydrate chains function as cell identification markers • They help identify pathogens (germs) and tell the body to attack them • An example of this is when a body rejects an organ transplant

9. Glycoproteins and Glycolipids • Think of the carbohydrate chains as antennae such as on an insect: • Just like the antennae, the carbohydrate chains can detect things either harmful or beneficial to the cell

10. Types of Proteins in the Cell Membrane • There are several different types of proteins in the cell membrane, each with a different function • Control what enters and exits the cell • Detect harmful pathogens • Function as enzymes that catalyze specific reactions • We will learn more about some of these proteins in the next lesson, but for now, here is a quick introduction

11. Types of Proteins • 1) Channel Protein • Allow particular molecules or ions to cross the plasma membrane

12. Types of Proteins • 2) Carrier Protein • Selectively interacts with a specific molecule or ion so that it can cross the plasma membrane

13. Types of Proteins • 3) Cell Recognition Protein • Cell recognition proteins are glycoproteins • Help the body recognize when it is being invaded by pathogens so that the immune system can destroy them

14. Types of Proteins • 4) Receptor Protein • Shaped in such a way that a specific molecule can bind to it • The binding of the molecule causes the protein to change its shape, bringing about a cellular response (reaction)

15. Types of Proteins • 5) Enzymatic Protein • Catalyze specific metabolic reactions