What do you know so far about the cell membrane?
What do you want to know about the cell membrane?

Cell Membrane Structure & Function
• Phospholipid Bi-layer (hydrophilic heads, hydrophobic tails)
– Fluid-Mosaic Model
– Proteins & cholesterol embedded within the phospholipid bi-layer
– Selectively Permeable – controls was enters and exits the cell

• Channel Proteins:
– Allow molecules, such as water, to pass through the cell membrane
• Recognition/ID Protein:
– Has carbohydrate chains attached that are used as ID markers
– Allow cells to communicate with eachother and identify foreign invaders (other blood type, virus)

• Protein Pump:
– Use ATP (energy) to pump substance across the membrane
• Cholesterol:
– Lipid that controls the
fluidity of the cell membrane

• There are 2 types of cell membrane transport:
– Passive Transport
• Things flow from
High to low
– Active Transport
• Things flow from
Low to high

Another perspective on passive and active transport

• Diffusion
– The movement of particles from areas of high concentration to low concentration
– http://www.indiana.edu/~phys215/lecture/lecnotes/diff.html
– http://www.biosci.ohiou.edu/introbioslab/Bios170/diffusion/Diffusion.html

• When is equilibrium reached when discussing cell membrane transport?
– When the concentrations of particles are the same on both sides

• Particles flow from high concentration to low concentration but this time they need the help of proteins to get through the cell membrane.

• Osmosis
– The diffusion of water across a selectively permeable membrane
– Important in maintaining cell homeostasis
– Water flows to side of membrane where the water concentration is lower until equilibrium is reached

• Osmosis is controlled by the amount of solutes on either side of a membrane

Osmosis – Types of Solutions
• When dealing with osmosis, water can either move into the cell or out of it.
• The solute can not move to equal out the solution so the water has to.
90%
What are the concentrations?
40%
• We describe the solutions that cells are in as either hypotonic, isotonic, or hypertonic.

• Isotonic solution – Concentration of solute is the same in the cell and the area around the cell.
• Give me an example of an isotonic solution that some of you use everyday

• Hypotonic Solution – Concentration of solute is lower in the solution than in the cell.
• Where is water going to move in order to reach equilibrium (Equal concentrations)?
– Inside the cell

• Since water moves into the cell the cell can explode
• http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
• So, Hypotonic solution, low concentration of solute, cell can explode

Plant and animal cells in a hypotonic solution

• Hypertonic solution – concentration of solute is higher in the solution than in the cell.
• Where is water going to move in order to reach equilibrium (Equal concentrations)?
– Outside the cell

• Since water moves out of the cell the cell will shrink
• http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
• So, Hypertonic solution, high concentration of solute, cell will shrink

Plant and animals cells in a Hypertonic
Solution

• http://www2.nl.edu/jste/osmosis.htm
• http://www.coolschool.ca/lor/BI12/unit4/U04
L06/rbc.html

• Molecules move from low concentration to high concentration
– Requires energy….why?

• Molecular Transport –
– Protein Pumps
• Small molecules and ions carried across the cell membrane by proteins in the membrane that act like pumps
• Bulk Transport
– Endocytosis – in!
– Exocytosis – out!

Other membrane transport activities that require energy
• Endocytosis
– Engulfing of large particles or liquids from outside the cell

• Phagocytosis
– Engulfing of large particles from outside the cell
• Pinocytosis
– Engulfing of liquids from outside the cell

Other membrane transport activities that require energy
• Exocytosis
– Release of large particles or liquids from inside the cell
Inside the cell
Outside the cell