Part I- Fluid Mosaic Model

Phospholipid Bilayer

Held together by the hydrophobic effect.

Phospholipids and the bilayer they create are amphipathic- they contain hydrophobic and hydrophilic regions.

Approximately 60-100 A thick

Membrane Components Phospholipids- main component

Glycoproteins (a carbohydrate attached to a protein)- cell membrane surface signals

Cholesterol (lipid)- in the hydrophobic core

Transport Proteins- span the bilayer for transport

Structural Proteins- provide structure and support to the membrane.

Properties of the Plasma Membrane

Flexibility- affected by cholesterol

Fluidity- affected by temp, cholesterol, and saturation

Self-Sealing- governed by the hydrophobic effect.

Functions of the Plasma Membrane The cell membrane regulates what enters and leaves

the cell (transport)- passive and active transport.

Cell to cell communication/recognition- gap junctions

Barrier- selectively permeable

Compartmentalization- internal membranes

Signaling/Receptors- glycoproteins

Fluid Mosaic Model The fluid-mosaic model encompasses our current

understanding of membrane structure. It describes both the "mosaic" arrangement of proteins embedded throughout the lipid bilayer as well as the "fluid" movement of lipids and proteins alike.

What affects fluidity? Increase Decrease

Cholesterol Decrease fluidity Increase fluidity

Temperature Increase fluidity Decrease fluidity

Saturation Decrease fluidity Increase fluidity

Fluidity is controlled by the temperature, the amount of cholesterol, and the degree of saturation in the FA tails of phospholipids.

Fluid Mosaic Video In the fluid mosaic model

membrane components are free to rotate along a vertical axis and move laterally within a layer of the bilayer.

Membrane components can not flip from one layer to the other without using energy so it doesn’t happen unless a membrane is being repaired.

http://www.youtube.com/watch?v=Qqsf_UJcfBc

Selective Permeability

Moves across freely Needs a pore or channel

Oxygen (O2)

Carbon dioxide (CO2)

Water

Urea

Glycerol

SMALL and

HYDROPHOBIC!

Glucose

Ions

Proteins

Lipids

Carbohydrates

LARGE or CHARGED!

Specificity Substances that can’t move

freely across the membrane need a protein channel of pore that spans the length of the bilayer, this is called an integral protein

Protein pores and channels are specific for certain substances. Pores= water pore

Pores are specific for small uncharged molecules like water and are shaped like an open tube across the membrane.

Channels are specific for the large molecule or charged ion they allow to pass through and involve a change of shape to transport across the membrane. (conformational change)

Transport Substances can move into and out of a cell in three

ways: Passive transport- diffusion and osmosis- moves freely

with the concentration gradient. (moves from high to low)

Active transport- uses energy to move substances against their concentration gradient. (moves low to high)

Cytosis- when the cell needs to get substances across the membrane it coats them in a phospholipid vesicle. (think about in the lab where you had to coat the paperclip in soap before passing it through the membrane.)

Cell to cell communication and self recognition All cells in an organism need to recognize other cells in

the same organism as “self” or “non-self”.

All cells in an organism need to be tagged as that kind of cell (ex. Tagged as a liver cell vs. a nerve cell)

All cells in an organism need to communicate with other cells.

All cells in an organism need receptors for other cells, and substances.

THIS IS DONE BY GLYCOPROTEINS!

Cell to Cell / SignalingExamples

Glycoproteins in the membrane are responsible for receiving information from other cells, foreign invaders, chemicals, hormones, and a variety of other signals.