Transcript Membrane Structure and Function

Chapter 8
Membrane Structure
and Function
Plasma Membrane
Membrane
Composition
Question:
How are the materials
arranged?
Lipid Bilayer
Phospholipids
Hydrophilic
heads
Hydrophobic
tails
Membrane Models
Davson-Danielli Model
1935
Lipid
bilayer.
Proteins coat the surfaces.
Sometimes called the
“sandwich” model.
Evidence
Biochemical
work.
TEM pictures show the
membrane as a double line.
Problems
Not
all membranes in a cell
were the same.
How could the proteins stay
in place?
Result - the model was
questioned and tested by
scientific process.
Fluid Mosaic Model
1972
New
model to fit the new
evidence with membranes.
Example of
“Science as a Process”.
Fluid Mosaic Model
“Fluid”
Ways to keep the
membrane “fluid”
“Mosaic”
Evidence
TEM
pictures of fractured
membranes.
Cell fusion studies.
Tagging of membrane
proteins by antibodies.
Protein Function in
Membranes
Types of Membrane
Proteins
Integral
–
Peripheral
-
Question?
How
do the integral proteins
stick to the membrane?
Hydrophilic
Amino Acids
Hydrophobic
Amino Acids
Hydrophilic
Amino Acids
Membranes are Bifacial
Carbohydrates
Membrane
Carbohydrates
Question
How
do materials get across
a cell's membrane?
Problems
Lipid
bilayer is hydrophobic.
Hydrophilic materials don't
cross easily.
Large molecules don't cross
easily. Too big to get through
the membrane.
Mechanisms
1.
2.
Passive Transport
Types of Passive
Transport
1.
2.
3.
Diffusion
Equilibrium
Factors that Effect
Diffusion
1.
Osmosis
Tonicity
Isotonic
Hypotonic
Hypertonic
.
Facilitated Diffusion
Aquaporins
Newly
found channels for
osmosis.
GFP labeled
Aquaporins
Active Transport
Types of Active
Transport
1.
Carrier-Mediated
Transport
Examples
1.
+
Na -
+
K
pump
Electrogenic or
H+ pumps
.
Cotransport
Exocytosis
Endocytosis
.
Types
1.
Carbohydrates
Forming vesicles
Summary
Know
membrane structure.
Be able to discuss the
various methods by which
cells move materials through
membranes.
Be able to solve problems in
osmosis.