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CELL MEMBRANES. The Fluid-Mosaic Model. This is an introduction to the structure and function of cell membranes. It is designed to be a self-contained unit with links to other, related material. THE FUNCTION OF CELL MEMBRANES. Compartmentalization of tissues Regulation of cell contents

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cell membranes
CELL MEMBRANES
  • The Fluid-Mosaic Model

This is an introduction to the structure

and function of cell membranes. It is

designed to be a self-contained unit with

linksto other, related material.

the function of cell membranes
THE FUNCTION OF CELL MEMBRANES
  • Compartmentalization of tissues
  • Regulation of cell contents
  • Provides surface for enzymes, receptors, recognition, etc.

It is thought by some that the spontaneous organization of membranes played an important role in the evolution of life.

phospholipids the backbone of the membrane

PHOSPHOLIPIDS: The “Backbone” of the Membrane

Cartoon of a phospholipid molecule

This cartoon depicts the basic

amphipathic* structure common

to all phospholipids

Glycerol

plus

polar side

group

Fatty acids

* both polar and non-polar regions

water molecules are polar
WATER MOLECULES ARE POLAR
  • Structure of water and the Cartoon version
  • Water is a dipole

d/2

+

H

d

+

O

d/2

+

H

Oxygen pulls electrons towards itself

causing a charge imballance (d-)

water is a good solvent for polar molecules and ions

-

Cl

+

Na

- +

- +

- +

- +

- +

- +

Water is a good solvent for polar molecules and ions

- +

Hydration Shells

- +

- +

- +

- +

- +

- +

- +

- +

- +

- +

- +

- +

- +

- +

- +

- +

- +

- +

- +

phospholipids
PHOSPHOLIPIDS
  • Cartoon of a phospholipid molecule

Non-polar tail

(Hydrophobic-

hates water)

Polar head

(Hydrophilic-

likes water)

oil water partition the kitchen experiment

OIL

WAIT

OIL/WATER PARTITION: THE “KITCHEN” EXPERIMENT

MIX OIL WATER AND TEST SUBSTANCE

CONCENTRATION OF TEST SUBSTANCE IN

OIL/ CONCENTRATION OF TEST SUBSTANCE

IN WATER = OIL WATER PARTITION COEFFICIENT (OWPC=K)

K > 1 HYDROPHOBIC (NON-POLAR)

K < 1 HYDROPHILIC (POLAR)

WATER

mixing phospholipids and water spontaneous self organization
MIXING PHOSPHOLIPIDS AND WATER: Spontaneous Self-Organization

Click to next slide to see the spontaneous self-organization

mixing phospholipids and water spontaneous self organization1
MIXING PHOSPHOLIPIDS AND WATER: Spontaneous Self-Organization

Click ahead

mixing phospholipids and water spontaneous self organization2
MIXING PHOSPHOLIPIDS AND WATER: Spontaneous Self-Organization

Click ahead

phospholipids plus water make a self organizing system
Phospholipids plus water make a self-organizing system
  • Low lipid/water ratio - micelles
  • High lipid/water ratio - lamellae
  • Single lamellae = bilayer or sheet
slide13

Sheet

Micelle

the black lipid membrane blm
The Black Lipid Membrane (BLM)
  • Formed across a small hole in a teflon beaker using a sable artist’s brush
  • Viewed with an optical system
  • Looks like a soap bubble with large patches of black where the bilayer forms
  • Used as a laboratory model of the cell membrane
the black lipid membrane blm1
The Black Lipid Membrane (BLM)
  • Experimental Setup

Microscope

Outer Beaker

Inner Beaker

What you see

Light Source

the black lipid membrane could be used to show what else is in cell membranes
The Black Lipid Membrane Could be used to Show what else is in Cell Membranes
  • It has too low permeability for ions- it needs protein and polypeptide to help them get through (channels and carriers)
  • It needs cholesterol for proper “fluidity”
  • It needs carbohydrate to provides cell recogtnition properties
proteins can span the bilayer
Proteins can span the bilayer

Hydrophilic

Hydrophobic

the fluid mosaic model
The fluid-mosaic model
  • Lipid bilayer
  • Cholesterol between tails
  • Protein, Glycoprotein, Lipoprotein “dissolved” in the lipid portion
cell membranes become network elements in tissue membranes
Cell Membranes Become Network Elements in Tissue Membranes
  • Epithelia are tissue membranes made up of cells
  • Network Thermodynamics provides a way of modeling these composite membranes
  • Often more than one flow goes through the tissue
a network model of coupled salt and volume flow through an epithelium
A Network Model of Coupled Salt and Volume Flow Through an Epithelium

CL

PL

LUMEN

AM

TJ

BL

CELL

BM

BLOOD

PB

CB

what to do now
What to do now?
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