Plasma Membrane

Plasma Membrane (AKA Cell Membrane)

• What is the plasma membrane?

• What does it do?

• What is its composition?

http://en.wikipedia.org/wiki/File:Cell_membrane_detailed_diagram_4.svg

• Plasma membrane = the flexible boundary between the cell and its environment

• Allows:• Things in the cell• Things out of the cell• Maintains BALANCE in the cell

• What is maintaining balance in the cell called?

• Homeostasis!

How does the plasma membrane maintain homeostasis?

• Plasma membranes are selectively permeable

• Selective permeability = process in which a membrane allows some molecules to pass while keeping others in/out.

Plasma membranes are regulators…

How is a screened window similar to a cell membrane?

Plasma Membrane Structure

Structure is the KEY!

• The specific structure of the plasma membrane allows it to be selectively permeable

Plasma Membrane Structures:

• Thin layer of phosopholipds, proteins, and cholesterol

• Phospholipid = kind of lipid found in the cell membrane– Glycerol, 2 fatty acids,

and phosphate (PO4) – Phospholipids have 2

parts

http://en.wikipedia.org/wiki/File:Cell_membrane_detailed_diagram_4.svg

Each part has a different property in water!

1. Phosphate Head– Hydrophilic – Can dissolve in water

2. Lipid tails (x2)– Hydrophobic– Cannot dissolve in water

http://en.wikipedia.org/wiki/File:Cell_membrane_detailed_diagram_4.svg

What does the polarity mean about the passage of water in/out of the cell?

• Water CAN pass through the polar part, but CANNOT pass through the nonpolar part.

• This allows the cell to prevent water loss and prevent “drowning”

• Cell membranes consist of 2 phospholipid layers called a bilayer (think bicycle has 2 wheels)

Plasma Membrane

• Made of: phospholipid bilayer– Phosphate head hydrophilic– Lipid tail hydrophobic– Carrier proteins– Cholesterol (good kind)

• Called the fluid mosaic model– Moves fluidly– Mosaic of proteins scattered in membrane– http://www.youtube.com/watch?v=Qqsf_UJcfBc&featur

e=related

Cell Transport

Cell Transport

• Diffusion = movement across a plasma membrane from HI to LO concentration

• Osmosis = diffusion of water across a plasma membrane from HI to LO concentraion

Solution

• Solution = homogeneous mixture of 2 or more substances

• Made up of:– Solute = part that gets dissolved– Solvent = part that does the dissolving

• Water is the UNIVERSAL SOLVENT

Types of Cell Transport

• Water can move freely through the plasma memebrane, but can Solute???

• NO!• Water will move to reach equilibrium since the

solute cannot• Which way will the water move?• Depends on the TYPE OF SOLUTION the cell is

in

Types of Solution

• Hypertonic– Solute concentration is higher in solution than cell– Water moves OUT– Cell shrinks

• Hypotonic– Solute concentration is lower in solution than cell– Water moves IN– Cell Swells

• Isotonic– Solute concentration is equal in solution and in cell– Water moves IN and OUT– Cell stays the same

Hypertonic Solution Hypotonic Solution

Cell Transport

• Active transport = movement of substances across membrane; requires ATP

• Passive transport = movement of substances across membrane; does NOT require ATP

Active Transport

• Goes against concentration gradient• Exocytosis = move particles OUT of cell• Endocytosis = move particels IN cell– 2 kinds of endocytosis:– Pinocytosis = movement of liquid IN cell– Phagocytosis = movement of solids IN cell– http://www.youtube.com/watch?v=4gLtk8Yc1Zc&NR=1

Exocytosis

Endocytosis

Passive Transport

• Goes with concentration gradient• Osmosis = movement of water across a

membrane with concentration gradient• Facilitated Transport = movement of

substances across a membrane with concentration gradient with the help of a carrier protein

• http://www.youtube.com/watch?v=s0p1ztrbXPY&feature=related

Facilitated Transport

Turgor Pressure and Plasmolysis

• http://www.youtube.com/watch?v=GOxouJUtEhE&feature=related