Cell Membrane Structure / Function and Cell Transport Ms. Kim Honors Biology

1. Cell Membrane Structure/ Function and Cell Transport Ms. Kim Honors Biology

2. Cell membrane

3. The Cell Membrane • Thin, flexible, surround all cells • Controls the traffic of molecules into and out of the cell (school doors/fence/security guards) • Takes in substances & takes out the cell’s waste • Allows substances through by either passive transport(no energy) or active transport (energy required!)

4. Overview of CellMembrane • The plasma (cell) membrane • the boundary that separates living cell from its nonliving surroundings • Also called the phospholipidbilayer

5. Structure of Plasma Membrane • Made of phospholipids • Phosphate head and 2 fatty acid chains are the tail • Arranged in a bilayer • Heads (polar)– hydrophilic • Tails (nonpolar) – hydrophobic • Roots: • Phospho- polar phosphate group • Lipid- non-polar fat • Bi- two • Layer- sheet or quantity covering a surface

6. Phospholipids

7. Polar heads love water & dissolve. Fluid Mosaic Model of the cell membrane Membrane movement animation Non-polar tails “hide” from water. Carbohydrate cell markers Proteins

8. The phospholipidbilayeris a selectively permeable membrane. It is semi-permeable. • Only allows certain substances to cross it more easily than others.

9. Selective Permeability • Selective Permeability: • Allows some materials, but not all, to cross through • Small, non-polar, hydrophobic, neutral molecules can pass easily through membrane • Although polar, water is SO small that it can move through the cell membrane. • Small polar molecules must pass through proteins • Large molecules must be moved with vesicles

10. Membrane Proteins and Their Functions • A membrane • Includes different proteins embedded in the fluid lipid bilayer • FUNCTION: • Help move molecules and ions across the membrane • They help cells communicate between the cell’s internal and external environments 2 major types of membrane proteins

11. Proteins • Integral • Permanently attached to the membrane • Are often transmembrane • found throughout the entire bilayer • Peripheral • Are appendages loosely bound to the surface of the membrane • Only found “outside” of thebilayer

12. Cholesterol • Cholesterol stabilizes (stiffens) the membrane • Integrates between phospholipids • Without cholesterol, cell membranes would be too fluid, not firm enough (very mushy). • Cholesterol also helps maintain the fluidity • Also helps separate the phospholipids so that the fatty acid chains can’t come together and crystallize. • Therefore, cholesterol helps prevent extremes—whether too fluid, or too firm—in the consistency of the cell membrane. • Present in animal cell membranes • Absent in bacteria and most plants where the cell wall provides stability

13. Why have Carbohydrates on Cell Membrane proteins? • Cell-cell recognition • Is a cell’s ability to distinguish one type of neighboring cell from another • It’s their “ID” tag

14. Carbohydrates (Oligosaccharides) • Carbs found on the outside for identification • Glycolipids and Glycoproteins serve as recognition sites for other cells Glycolipids Glycoprotein

15. 2 different types membrane carbohydrates • Glycolipids • Carbohydrates covalently attached to lipids • Glycoproteins • Carbohydrates covalently attached to proteins (most abundant)

16. Fluid Mosaic Model • Description of arrangement of molecules that make up the cell membrane • Cell Membrane is flexible, not rigid • Phospholipids can move from side to side and slide past each other • Variety of molecules studding the membrane is similar to arrangement of tiles with different textures and patterns Know this picture! http://www.dnatube.com/video/360/Fluid-Mosaic-Model