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DNA

Join a collaborative exploration of cellular structures and transport mechanisms. In this activity, students will compare prokaryotic and eukaryotic cells while engaging in hands-on demonstrations of diffusion, osmosis, and membrane permeability. Participants will work in pairs to simulate cellular interactions and observe how different molecules cross cell membranes. Through PhET simulations and guided discussions, we will learn about the critical roles of membranes in maintaining cellular environments and the processes of passive and active transport.

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DNA

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  1. DNA • Compare and contrast prokaryotes and eukaryotes with your groupmates • Put away everything but a pen or pencil

  2. When Finished with Quiz… • Grab a computer for you and the person sitting next to you • Log in – if it says you can’t shut off the computer, turn it on and try again • Google “PHET simulations” and play around with one of the simulations until everyone is done

  3. Crossing the Membrane

  4. Osmosis/Diffusion Activity • Work as partners – we’ll begin as a class

  5. Activity 1 • Start in one corner • Try to move randomly- when you (Carefully) bump into somebody “bounce” the other direction • What happens?

  6. Diffusion • We call this phenomenon diffusion • Things naturally bounce off each other and spread apart – if they can • We say things move from “high concentration” to “low concentration”

  7. What does this have to do with cells? • Lots of things enter and exit this cell by this process • However, they must be able to somehow cross the membrane Cytosol

  8. General Membrane Structure • Phospholipids with proteins embedded in the membrane • Different membranes have different proteins

  9. PhospholipidBilayer

  10. Observation 1 • Watch the water and oil, do they mix? • What happens when we drop food coloring into the oil layer?

  11. Hydrophilic and Hydrophobic Don’t Mix • The inside of the membrane is hydrophobic (oily) • Which means polar things will not mix well with it • Ions will definitely not mix well

  12. Membranes Keeps Cells Separate • Most things are either too big to cross the membrane • OR they are polar and won’t mix with the membrane • Creates an internal environment different from the outside world(i.e. it has enzymes, proteins, sugars, ATP, NADH, FADH etc. floating around)

  13. Simple Diffusion • Very small hydrophobic (non-polar) molecules can simply slip between the membranes and cross the hydrophobic layer • Water is small enough that some of it can slip through

  14. Facilitated Diffusion • Other small molecules need to move through a protein channel (small, polar or ionic compounds)

  15. Observe the Facilitated Diffusion • What will happen when we put a channel in the membrane?

  16. Concentration Gradient High Concentration Low Concentration

  17. Equilibrium / No Concentration Gradient • No net change in concentration. Molecules still move but on average the concentrations stay the same Medium Concentration Medium Concentration

  18. Facilitated Diffusion – 2 molecules

  19. What if We Want to Move Things Against the Gradient? • Active Transport! • We must invest energy to “pump” molecules

  20. Review • Small, non-charged molecules can simply diffuse • Small, polar or charged molecules can pass through a protein • Energy must be invested to move things against the gradient

  21. Endo/Exocytosis • Big things must enter through endocytosis and form a vesicle • Big things must exit by exocytosis, where the vesicle becomes part of the plasma membrane

  22. Selective Permeability • Membranes control what gets in and what gets out of the cell • Protein channels or pumps can be opened and closed

  23. Osmosis • Special name for diffusion of water • When molecules can’t diffuse, water does • Water diffuses towards the more concentrated side until the concentrations are balanced* • *or another force is applied

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