Movement across the Cell Membrane

Diffusion  Diffusion  movement from HIGH → LOW concentration  Down the concentration gradient  Diffusion  movement from HIGH → LOW concentration  Down the concentration gradient Is this a passive or active process? Is this a passive or active process? What did it take to make the concentration gradient?

The concentration gradient stores potential energy It takes energy to generate the gradient The process is still considered passive

Facilitated Diffusion Diffusion through protein channels –highly specific –passive process “The Bouncer” HIGHLOW what sort of molecules will use this process?

Active Transport “The Doorman” Cells may need to move molecules against concentration gradient –conformational shape change transports solute from one side of membrane to other –protein “pump” –“costs” energy = ATP ATP LOWHIGH Once completed, where has the energy for the active transport gone?

symportantiport Active transport Many models & mechanisms ATP

Getting through cell membrane Passive Transport –Simple diffusion nonpolar, hydrophobic molecules –HIGH → LOW concentration gradient –Facilitated transport polar, hydrophilic molecules through a protein channel –HIGH → LOW concentration gradient Active transport –against concentration gradient LOW → HIGH –uses a protein pump (requires ATP) ATP

Transport summary simple diffusion facilitated diffusion active transport ATP

What about large molecules? Moving large molecules into & out of cell –through vesicles & vacuoles –endocytosis phagocytosis = “cellular eating” pinocytosis = “cellular drinking” –exocytosis exocytosis

Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific process triggered by molecular signal

What about Osmosis? Diffusion of water from HIGH concentration of water to LOW concentration of water –across a semi-permeable membrane Why does osmosis need a membrane?

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 hypotonichypertonic water net movement of water

13 Hypotonic, Hypertonic, Isotonic How does sugar concentration lead to water movement?

14 Which way would water move if oil was added to the left side of the tube? Let’s watch the video

Managing water balance Hypotonic Animal cell/protist cell problem? Solutions? Plant cells.... turgid = full cell wall protects from bursting freshwater No problem, here KABOOM!

Managing water balance Hypertonic Animal cells: How can they adjust: Take up water or pump out solutes. –plant cells plasmolysis = wilt saltwater I will survive! I’m shrinking, I’m shrinking! Why do people make beef jerky, and add syrup to preserve canned fruit?

Managing water balance Isotonic –Animal cell problems: –none –solutes are equally concentrated on both sides of membranes –Plant cell problems –flaccid cells lose structure. balanced I could be better… That’s perfect!

Aquaporins Water moves rapidly into & out of cells –evidence that there were water channels protein channels allowing flow of water across cell membrane Peter Agre John Hopkins Roderick MacKinnon Rockefeller

.05 M.03 M Which way will water move?

Hey...watch this