BIOLOGY 111
CHAPTER 5: Life's Border:
The Plasma Membrane
Life’s Border:
THE PLASMA MEMBRANE
5.1 The Nature of the Plasma Membrane
 5.2 Diffusion, Gradients, and Osmosis
 5.3 Moving Smaller Substances In and Out
 5.4 Moving Larger Substances In and Out

Life’s
Life’sBorder:
Border:
THE
THEPLASMA
PLASMAMEMBRANE
MEMBRANE
•
The Plasma Membrane is constructed of
two phospholipid layers
This is called a Phospholipid Bilayer
•
The exterior and interior are Polar
(Phosphate Heads)
•
The interior is Nonpolar (Fatty Acids)
Life’s Border:
THE PLASMA MEMBRANE
Life’s Border:
THE PLASMA MEMBRANE
COMPONENTS OF THE PLASMA MEMBRANE

•
•
•
•
The Plasma Membrane has 4 components:
First Component: The Phospholipid Bilayer
Second Component: Cholesterol
Third Component: Proteins
Fourth Component: The Glycocalyx
COMPONENTS OF THE PLASMA MEMBRANE

•
The First Component: The Phospholipid Bilayer
Been there, done that!
COMPONENTS OF THE PLASMA MEMBRANE

Second Component: Cholesterol:
•
Cholesterol is a lipid (nonpolar)
Located in the interior nonpolar region
•
Cholesterol helps give the plasma membrane its fluid
characteristics
•
Cholesterol also helps keep the phospholipid bilayer intact at
different temperatures
COMPONENTS OF THE PLASMA MEMBRANE

Third Component: Proteins: (2 main types of membrane proteins)
•
Some proteins in the plasma
membrane are Integral (span
the membrane)
•
Others are Peripheral
(temporarily attached to the
polar regions of the membrane
or integral proteins)
COMPONENTS OF THE PLASMA MEMBRANE

•
Third Component: Proteins: (2 main types of membrane proteins)
Some proteins in the plasma membrane are Integral
These are “inside” or integrated with the plasma membrane. These proteins have both
polar and nonpolar regions
•
Polar regions are on the exterior boundaries of the PM (facing H2O)
•
Nonpolar regions tend to be
on the interior of the PM
COMPONENTS OF THE PLASMA MEMBRANE

•
Third Component: Proteins:
Some proteins in the plasma membrane are peripheral
These are primarily “exterior” and do not span the plasma membrane
•
•
These proteins are mostly Polar and tend to be on the outside or inside of the
PM (facing H2O) or attached
to integral proteins
COMPONENTS OF THE PLASMA MEMBRANE

Third Component: Proteins:
Different
roles for Plasma
Membrane
Proteins
COMPONENTS OF THE PLASMA MEMBRANE

•
Third Component: Proteins:
There are 4 different roles that proteins play that are
critical to the function of the plasma membrane
COMPONENTS OF THE PLASMA MEMBRANE

•
Third Component: Proteins:
1. Proteins offer Structural Support
These proteins attach to the Cytoskeleton
This connects the cytoskeleton to the plasma membrane,
keeping the internal structure of the cell connected to
the plasma membrane
COMPONENTS OF THE PLASMA MEMBRANE

•
Third Component: Proteins:
2. Proteins play a role of Recognition
These proteins identify other cells by interacting with
unique proteins on their cell surface
•
This mechanism is similar to how cells in our immune
system communicate with each other or ‘recognize’
invaders
COMPONENTS OF THE PLASMA MEMBRANE

•
Third Component: Proteins:
3. Proteins help with Intra-cellular Communication
•
Receptor proteins can recognize molecules in their
environment that are close to the cell.
•
This kind of molecular signal can trigger a response
within the cell
•
Example: Insulin tells cells that blood glucose is high
and to construct channels to bring glucose into the cell
COMPONENTS OF THE PLASMA MEMBRANE

•
Third Component: Proteins:
4. Proteins help with Transport
•
Transport proteins help molecules or ions (charged
atoms) move from one side of the plasma membrane
to the other
•
Very small molecules (like CO2 and O2) or nonpolar
molecules generally don’t require transport proteins to
get in or out of the cell (they use diffusion)
COMPONENTS OF THE PLASMA MEMBRANE

•
Fourth Component: Glycocalyx:
Carbohydrate chains that extend from proteins on the
Plasma Membrane
The glycocalyx helps signaling
proteins to better recognize
specific molecules
Life’s Border:
THE PLASMA MEMBRANE
COMPONENTS OF THE PLASMA MEMBRANE

•
•
•
•
The Plasma Membrane has 4 components:
First Component: The Phospholipid Bilayer
Second Component: Cholesterol
Third Component: Proteins
Fourth Component: The Glycocalyx
Click on these informational videos and interactive self tests!
Cell membranes: (first 9:25 minutes)
Plasma membrane (animated summary)
Plasma membrane: (interactive self quiz)
Life’s Border:
THE PLASMA MEMBRANE
5.1 The Nature of the Plasma Membrane
 5.2 Diffusion, Gradients, and Osmosis
 5.3 Moving Smaller Substances In and Out
 5.4 Moving Larger Substances In and Out

DIFFUSION, GRADIENTS, AND OSMOSIS

•
From Concentrated to Dispersed: Diffusion
Diffusion is the movement of molecules or ions from
areas of greater concentration to areas of lesser
concentration.
DIFFUSION, GRADIENTS, AND OSMOSIS

From Concentrated to
Dispersed:
Constant movement and
collisions between molecules
cause them to gradually move
away from each other.
Molecules that are very close
together will have more
collisions and will move more
quickly away from each other
than those that are further
apart.
DIFFUSION, GRADIENTS, AND OSMOSIS

From Concentrated to
Dispersed:
Molecules that are
concentrated have more
energy than molecules
that are dispersed!
Energy systems will
always spontaneously go
from high energy to low
energy – this is why
diffusion occurs.
THERE IS ENERGY IN A
DIFFUSION GRADIENT!
These
molecules
have more
energy!
These
molecules
have less
energy!
DIFFUSION, GRADIENTS, AND OSMOSIS
From Concentrated to Dispersed: Osmosis
•
Osmosis is the diffusion of water across a semipermeable
membrane (from an area of lower solute concentration to an area of higher
solute concentration)
Solute, is something that is dissolved in water – like salt or
glucose
•
•
Try these video links:
Video: http://www.youtube.com/watch?v=w3_8FSrqc-I
Video: http://www.youtube.com/watch?v=eQsAzXr0U
DIFFUSION, GRADIENTS, AND OSMOSIS

Osmosis:
•
Water diffuses across a
semipermeable membrane
•
Water moves towards a
higher solute concentration
•
This is done to balance out
the concentration of free H2O
molecules on both sides of
the membrane
DIFFUSION, GRADIENTS, AND OSMOSIS

Water Balance:
•
Hypertonic: High Solute concentration on one side

Water will move towards this direction
•
Isotonic: Equal Solute concentrations on both sides

Water will not move in either direction
•
Hypotonic: Lower Solute Concentration on one side
Water will move away from this solution

DIFFUSION, GRADIENTS, AND OSMOSIS

How Solutes Affect the
Balance of H20:
•
Hypertonic
•
Isotonic
•
Hypotonic
Check these videos on osmosis:
Osmosis and Cells (interactive video)
Osmosis 1
Osmosis 2 (Mr. Anderson – Bozeman)
DIFFUSION, GRADIENTS, AND OSMOSIS

How Solutes Affect the
Balance of H20:
•
Hypertonic
•
Isotonic
•
Hypotonic
Life’s Border:
THE PLASMA MEMBRANE
5.1 The Nature of the Plasma Membrane
 5.2 Diffusion, Gradients, and Osmosis
 5.3 Moving Smaller Substances In and Out
 5.4 Moving Larger Substances In and Out

DIFFUSION, GRADIENTS, AND OSMOSIS

•
Moving Smaller Substances In and Out:
Diffusion and Osmosis are how small (uncharged)
molecules move in and out of cells
•
These things will move from a location of higher
concentration to a location of lower concentration
•
If there is a high concentration of O2 outside a cell, the
O2 will move into the cell by diffusion
Life’s Border:
THE PLASMA MEMBRANE
5.1 The Nature of the Plasma Membrane
 5.2 Diffusion, Gradients, and Osmosis
 5.3 Moving Smaller Substances In and Out
 5.4 Moving Larger Substances In and Out

MOVING LARGE SUBSTANCES IN AND OUT

•
Integral Proteins:
Some integral proteins can act like tunnels to let specific
substances in and out of the cell
The shape of the substance has to align with the particular
‘tunnel’ (protein) for it to pass through
•
This specificity is referred to as “Selective Permeability”
Check this video on Selective Permeability: http://www.bozemanscience.com/015-cell-membrane
Life’s Border:
THE PLASMA MEMBRANE
3 Types of Transport
Simple Diffusion
1)
-
With Gradient
2) Facilitated Diffusion
-
With Gradient
Transport Protein
3) Active Transport
Transport Protein
- Against Gradient
- Requires ATP
-