cell membranes and movement across them

Bellringer Review of organelles and cells

Remember: oil & water don’t mix!! Building a membrane How do you build a barrier that keeps the watery contents of the cell separate from the watery environment?  FATS   LIPIDS  Remember: oil & water don’t mix!! What substance do you know that doesn’t mix with water?

Cell Membrane Structure Main components: Phospholipids-transport of small molecules Proteins- transport of large molecules Carbohydrate chains- identification and communication

Lipids of cell membrane Membrane is made of special kind of lipid phospholipids “split personality” Membrane is a double layer phospholipid bilayer “attracted to water” phosphate inside cell outside cell lipid “repelled by water”

Semi-permeable membrane Cell membrane controls what gets in or out Need to allow some materials — but not all — to pass through the membrane semi-permeable or selectively permeable Selective with material passing in and out So what needs to get across the membrane? sugar lipids aa O2 H2O salt waste

Crossing the cell membrane What molecules can get through the cell membrane directly? (non-polar and very small polar) fats and oils can pass directly through lipid inside cell outside cell salt waste but… what about other stuff? sugar aa H2O

Diffusion Movement of molecules from HIGH to LOW concentration Simple diffusion- directly through membrane Passive diffusion (no energy needed) Facilitated diffusion- help through a protein channel HIGH LOW

Simple Diffusion LOW HIGH Move from HIGH to LOW fat fat fat fat Which way will fat move? inside cell fat fat LOW HIGH fat outside cell fat fat fat fat fat fat fat

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

Simple vs. facilitated diffusion simple diffusion facilitated diffusion lipid inside cell outside cell inside cell outside cell H2O protein channel H2O

Active transport Cells may need molecules to move against concentration gradient need to pump “uphill” from LOW to HIGH using energy protein pump requires energy (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. ATP

Transport summary simple diffusion facilitated diffusion ATP active transport

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

Keeping balance Cell survival depends on balancing water uptake & water loss freshwater balanced saltwater

Concentration of water Direction of osmosis is determined by comparing total solute concentrations Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water hypotonic hypertonic water net movement of water

Keeping right amount of water in cell 1 Keeping right amount of water in cell KABOOM! freshwater Freshwater high concentration of water around cell cell gains water example: Paramecium problem: cells gain water, swell & can burst water continually enters Paramecium cell solution: contractile vacuole pumps water out of cell No problem, here HYPOTONIC

Keeping right amount of water in cell 2 Keeping right amount of water in cell I’m shrinking, I’m shrinking! saltwater Saltwater a cell in salt water low concentration of water around cell cell loses water example: shellfish problem: cell loses water in plants: plasmolysis in animals: shrinking cell solution: take up water I will survive! HYPERTONIC

Keeping right amount of water in cell 3 Keeping right amount of water in cell balanced Balanced conditions no difference in concentration of water between cell & environment cell in equilibrium example: blood problem: none water flows across membrane equally, in both directions volume of cell doesn’t change ISOTONIC

How to Remember: HypER = highER HighER solute. Brrr, makes cells shrink HypO = lOw lOwer solute. Makes cells explOde

Large Molecules Endocytosis: taking IN material Moving large molecules into & out of cell Endocytosis: taking IN material phagocytosis = “cellular eating” (material) pinocytosis = “cellular drinking” (liquid) Exocytosis: sending OUT material

receptor mediated endocytosis fuse with lysosome for digestion phagocytosis non-specific process pinocytosis receptor mediated endocytosis

Cytoskeleton and Movement Microtubules that aide in the movement of the cell -Examples: cilia and flagella