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

Cell membrane

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!) 3

Overview of Cell Membrane The plasma (cell) membrane – the boundary that separates living cell from its nonliving surroundings – Also called the phospholipid bilayer

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 5

Phospholipids

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

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

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. Selective Permeability Small polar molecules must pass through proteins Large molecules must be moved with vesicles

Membrane Proteins and Their Functions A membrane A membrane – Includes different proteins embedded in the fluid lipid bilayer FUNCTION: 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

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 the bilayer Proteins

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 Cholesterol

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

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

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

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! 16 be.com/video/36 0/Fluid-Mosaic- Model