DNACompare and contrast prokaryotes and eukaryotes with your groupmates

Put away everything but a pen or pencil

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

Crossing the Membrane

Osmosis/Diffusion ActivityWork as partners – we’ll begin as a class

Activity 1Start in one cornerTry to move randomly- when you (Carefully) bump into somebody “bounce” the other direction

What happens?

DiffusionWe 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”

What does this have to do with cells?Lots of things enter and exit this cell

by this processHowever, they must be able to

somehow cross the membraneCytosol

General Membrane StructurePhospholipids with proteins embedded in

the membraneDifferent membranes have different

proteins

Phospholipid Bilayer

Observation 1Watch the water and oil, do they

mix?

What happens when we drop food coloring into the oil layer?

Hydrophilic and Hydrophobic Don’t MixThe inside of the membrane is hydrophobic

(oily)Which means polar things will not mix well

with itIons will definitely not mix well

Membranes Keeps Cells SeparateMost 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)

Simple DiffusionVery 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

Facilitated DiffusionOther small molecules need to move

through a protein channel (small, polar or ionic compounds)

Observe the Facilitated DiffusionWhat will happen when we put a channel in

the membrane?

Concentration Gradient

High Concentration

Low Concentration

Equilibrium / No Concentration GradientNo net change in concentration. Molecules

still move but on average the concentrations stay the same

Medium Concentration

Medium Concentration

Facilitated Diffusion – 2 molecules

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

molecules

ReviewSmall, 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

Endo/ExocytosisBig things must

enter through endocytosis and form a vesicle

Big things must exit by exocytosis, where the vesicle becomes part of the plasma membrane

Selective PermeabilityMembranes control what gets in and what gets out of the cell

Protein channels or pumps can be opened and closed

OsmosisSpecial name for

diffusion of waterWhen molecules can’t

diffuse, water doesWater diffuses

towards the more concentrated side until the concentrations are balanced*

*or another force is applied