Cell Membranes & Movement Across Them 2006-2007

Lipids of cell membrane Membrane is made of special kind of lipid phospholipids “split personality” Membrane is a double layer Membrane is semi-permeable “attracted to water” Hydrophilic phosphate inside cell outside cell Fatty acid Hydrophobic “repelled by water”

Passive Transport – No Energy Diffusion Osmosis Facilitated Diffusion

Molecules move from high to low Diffusion move from HIGH to LOW concentration Movement from high concentration of that substance to low concentration of that substance.

Diffusion Move from HIGH to LOW concentration diffusion passive transport no energy needed EXAMPLE diffusion

Crossing the cell membrane What molecules can get through the cell membrane directly? Oxygen, fats and oils can pass directly through inside cell outside cell lipid salt waste but… what about other stuff? sugar aa

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 salt outside cell waste

Facilitated Diffusion Move from HIGH to LOW through a channel sugar sugar sugar sugar inside cell sugar sugar LOW Which way will sugar move? HIGH outside cell sugar sugar sugar sugar sugar sugar sugar

Simple vs. facilitated diffusion simple diffusion facilitated diffusion O2 inside cell outside cell sugar inside cell outside cell protein channel sugar

Osmosis diffusion of water Water is very important, so we talk about water separately diffusion of water

Osmosis Osmosis diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane

Active transport Cells may need molecules to move from LOW to HIGH concentration requires energy (ATP) ATP Plants have nitrate & phosphate pumps in their roots. Why? Nitrate for amino acids Phosphate for DNA & membranes Not coincidentally these are the main constituents of fertilizer.

ANALOGY: ENERGY NEEDED: Active Transport NO ENERGY NEEDED: Diffusion Osmosis Facilitated Diffusion ENERGY NEEDED: Active Transport

Endocytosis and Exocytosis is how very large molecules (such as food, wastes and some protiens) get into and out of the cell Food is moved into the cell by Endocytosis Wastes are moved out of the cell by Exocytosis animation

Cystic Fibrosis CFTR Protein Mutations in the DNA Doesn’t make it to membrane Channel won’t open How is homeostasis affected? Cystic Fibrosis Video (5:08-6:32)