March 19, 2010 What is the point of a cell membrane? What is the difference between a prokaryote and a eukaryote?

Demo w/ Food Coloring If I add in one drop of food coloring, draw what the beaker will look like at time 0 sec. Use “x” to represent molecules of food coloring PREDICT what it will look like after 30 sec Draw your prediction PREDICT what it will look like in 15 min

Demo w/ Food Coloring Why does it happen like this? (30 sec) Food coloring molecules are heavier than water, so fall to bottom. Molecules like to be spread out Since they are always moving, they bump into each other and they don’t like it.

Demo w/ Food Coloring How does this relate to cells? Particles need to get into and out of cells When there is too much waste inside, they want to spread out so need to leave the cell! When there is not enough nutrients (ex. Glucose, oxygen) in the cell, it needs to enter! Cell membrane controls enter/exit of things

Important Information Relating to Discovery of Cells Discovery of cells goes along with developments of microscope 1590 = Janssen make compound microscope (more than one lens) 1667 Hooke = studies cork under microscope Calls compartments “cells” since they look like jail cells 1675 Leeuwenhoek = “father of microscope” Discovered bacteria and microscopic animals (zooplankton)

Statements of Cell Theory Plant Cells Statements of Cell Theory All living things are made of cells Cells are the basic building blocks of life. Schleiden and Schwann (1840ish) New cells are made from pre-existing cells One cell grows and splits into two Virchow (1858) Bacteria Cell Cell reproducing

Ideas for Cell Membrane Danielli & Dawson (1935) Lipids on inside, proteins on outside Singer & Nicolson (1970) current model

Cell Membrane Currently known as the Fluid Mosaic Model “Fluid” because it moves “mosaic” because it is made of many different parts Mosaic is usually connected with art, many small parts making up a bigger image, such as the frog above EVERY cell has one! (even if there is a cell wall, like in plants.) Prokaryotes & Eukaryotes Sometimes called the plasma membrane

Cell Membrane Protects the cell Composed of mainly Allows only some things in (like glucose for energy) and some things out (like wastes), based on need of cell We say it is selectively permeable Composed of mainly Lipids Proteins Also have some carbohydrates (for recognition) and cholesterol (for stability)

Lipids of Cell Membrane Phospholipids Phosphate head Likes water Called Hydrophillic – “hydro” = water, “phillic” = loving Lipid tails Don’t like water (imagine: oil, a lipid, and water do not mix!) Hydrophobic – “hydro” = water, “phobic” = fear

Lipids Form a lipid bilayer (2 layer) Outside of cells = lots of water Inside of cells = lots of water So tails face toward each other, heads face toward water Some small molecules can make it in between phospholipids PASSIVE transport (doesn’t use energy)

Proteins of Cell Membrane External (peripheral) Sit on outside of membrane Serve as receptors for the cell, receive chemical messages from outside Channels allow molecules that wouldn’t mix with lipid tails thru Not much bigger than space between phospholipids PASSIVE transport (doesn’t use energy) Pumps Allow ions thru (charged atoms) Force things thru, even if they don’t want to ACTIVE transport (uses energy!)

Cell Membrane Draw a picture of a cell membrane in your notes. Label phospholipid, lipid bilayer, protein channel, protein pump, hydrophobic, and hydrophillic regions

Why would molecules move without being forced to? They get crowded Move from high concentration (where there’s a lot of them) to low concentration (where there’s not as many of them) Remember: all molecules are constantly moving. When they bump into each other, they move away. More bumping = more likely to be pushed/move away.

Why would molecules move without being forced to? Will continue to move until equal amounts of molecules on both sides of membrane Called dynamic equilibrium When equilibrium is reached, they don’t stop moving. Instead, one molecule goes in and one comes out.

Why would molecules move without being forced to? Movement from high to low concentration is called diffusion Form of PASSIVE transport, b/c energy isn’t required Occurs between phospholipids (diffusion) & in channel proteins (called facilitated diffusion)

Passive Transport Label on your cell membrane picture where diffusion and facilitated diffusion occur

What happens if molecules are too big to move across membrane? Sometimes water will move to help even out concentration Move from high water concentration to low water concentration (just like diffusion) Diffusion of water is called OSMOSIS

Factors that Affect Diffusion Lab Be careful! 2 bottles of SAME color! 150 – 200 mL of water is fine, make sure you have same amount of water in each beaker.