Membrane
Structure &
Function
AP Biology
Chapter 7
Cellular membranes are fluid
mosaics of lipids and
proteins
7.1
Fibers of extracellular matrix (ECM)
Glycoprotein
Carbohydrate
Glycolipid
EXTRACELLULAR
SIDE OF
MEMBRANE
Cholesterol
Microfilaments
of cytoskeleton
Peripheral
proteins
Integral
protein
CYTOPLASMIC SIDE
OF MEMBRANE
Membrane structure results
in selective permeability
7.2
Selective Permeability

Cell membrane is “picky”
about what is allowed to
pass


Related to
hydrophobic/hydrophilic
nature of phospholipids
Transport proteins, carrier
proteins, aquaporins assist
in movement across
membrane
Learning Targets – Membrane
Function





I can explain how water will move if a cell is
placed in an isotonic, hypotonic or hypertonic
solution and predict the effect of these different
environments on cells with and without cell walls.
I can explain how materials move into and out of
cells both passively and actively
I can describe how a concentration gradient
represents potential energy.
I can explain how electrochemical gradients are
formed and function in cells.
I can describe how endocytosis and exocytosis
move large molecules into and out of the cell
respectively.
Passive transport is diffusion
of a substance across a
membrane with no energy
investment
7.3
Passive Transport
 Movement
of materials
across membrane
without using energy
 With the concentration
gradient
 3 types
1.
2.
3.
Diffusion
Osmosis
Facilitated diffusion
1. Diffusion
 Movement
of
molecules from
high to low
concentration

Ex: O2, CO2
2. Osmosis



Movement of water across a selectively
permeable membrane
Passive transport – high to low concentration,
no energy required
3 osmotic environments
A. Hypotonic
 Higher
concentration of
water/lower
concentration of solute
outside the cell
 Water moves into the cell
 Animal cells – cytolysis

Contractile vacuole
(Paramecium)
 Plant
cells – turgor pressure
B. Hypertonic
 Lower
concentration of
water/higher concentration
of solute outside of the cell
 Water moves out of the cell
 Animal cells – plasmolysis
 Plant cells – plasmolysis
C. Isotonic
 Concentration
of water and
solute is equal on both sides
of the membrane
 No net movement of water
(still moves)
 Animal cells – normal
 Plant cells – flaccid
3. Facilitated Diffusion

1.
Transport proteins open to allow diffusion of
molecules too large to fit otherwise
Channel proteins

2.
Channel allows molecules to pass
Carrier proteins

Change shape to bind and allow molecules to
pass
Active transport uses energy
to move substances against
their gradients
7.4
Active Transport
 Against
concentration
gradient, therefore
requiring energy (ATP)
 2 types


Ion pumps
Cotransport
Ion Pumps



Example: sodium-potassium pump
Establish gradient across the membrane for neurons to “fire”
ATP energy used to:


move 3 Na+ ions out of the cell while simultaneously moving 2 K+
ions into the cell
Animation
Cotransport
 Membrane
protein
enables the
“downhill” diffusion of
one molecule to drive
the “uphill” transport
of another
 Sucrose transport in
plants
Bulk transport across the
plasma membrane occurs
by exocytosis and
endocytosis
7.5
Endocytosis
 Bringing
materials into
cell
1. Receptormediated
2. Pinocytosis
3. Phagocytosis
 Animation
Exocytosis
 Secreting
materials out of cell
 Animation