2. Surface view of
monolayers.
This sketch of a freeze-
fractured membrane
shows electron
micrographs of the E and
P faces from the plasma
membrane of a mouse
kidney tubule cell.
Individual proteins
imbedded in either face
show up as small
particles (TEMs).
Freeze-Fracture Analysis of a
Membrane.
Lecture 8 Biological Membranes
3. Figure 7-17 Freeze-fracture electron micrograph
of human red blood cells.
Note that the density of intramembrane particles
on the cytosolic (P) face is higher than on the
external (E) face.
4. Lecture 8 Biological Membranes
Fluid mosaic model of membranes
Three classes of membrane proteins:
Protein class Location Interactions
Integral
proteins (Y)
Embedded
within lipid
bilayer
Held in place by
the
hydrophobic
interactions
Peripheral
Proteins
(Z)
Located on
surface of
membrane
Linked
noncovalently
to the polar
groups of
phospholipids
and proteins
Lipid anchored
Proteins
(X)
On the
periphery but
anchored in the
lipid layer
hydrophilic
5. 11_21_proteins.associ.jpg
Lecture 8 Biological Membranes
Membrane proteins can associate with the lipid bilayer in
several different ways
(A) Transmembrane proteins can extend across the bilayer as a single a helix,
as multiple a helices, or as a rolled-up b sheet (called a b barrel).
(B) Some membrane proteins are anchored to the cytosolic surface by an
amphipathic a helix.
(C) Others are attached to either side of the bilayer solely by a covalent
attachment to a lipid molecule (red zigzag lines).
(D) Finally, many proteins are attached to the membrane only by relatively
6. Figure 7-19 The Main Classes of Membrane Proteins
Membrane proteins are classified according to their mode of attachment to the membrane. Integral
membrane proteins contain one or more hydrophobic regions that are embedded within the lipid
bilayer. Peripheral membrane proteins are too hydrophilic to penetrate into the membrane but are
attached to the membrane by electrostatic and hydrogen bonds that link them to adjacent
membrane proteins or to phospholipid head groups. Lipid-anchored proteins are hydrophilic and do
not penetrate into the membrane; they are covalently bound to lipid molecules that are embedded
in the lipid bilayer. (f) Proteins on the inner surface of the membrane are usually anchored by either a
fatty acid or a prenyl group. (g) On the outer membrane surface, the most common lipid anchor is
glycosylphosphatidylinositol (GPI).
Lecture 8 Biological Membranes
7. Transmembrane protein
Lecture 8 Biological Membranes
Hydrophobic amino acid
residues span membrane
Hydrophilic domains on both
sides of membrane
Only outer domain has
covalently attached carbohydrates
Extracted with detergents
Glycophorine one transmembrane span
9. Integral membrane protein
Lecture 8 Biological Membranes
Most membrane proteins have multiple
transmembrane spans.
More difficult to work with than water soluble
protein
Bacteriorodpsin
10. Peripheral protein
Lecture 8 Biological Membranes
No transmembrane spans.
Located on surface of membrane .
Usually bound electrostatically to membrane.
11. Peripheral protein
Lecture 8 Biological Membranes
No hydrophobic interactions with interior of
membrane
bind to other proteins
bind to lipid head groups.
Peripheral proteins much easier to isolate (like
water soluble protein)
12. Lipid anchored proteins
Lecture 8 Biological Membranes
Hydrophilic proteins that don’t penetrate into the
membranes.
Covalently bound to lipid molecules that are
embedded in lipid bilayer.
16. Figure 11–20 Plasma membrane
proteins have a variety of
functions.
Lecture 10, membranes
17. Light transduction
Lecture 10, membranes
Absorb light:
Rhodopsin: absorbed light triggers nervous
impulse.
Bacteriorhodopsin: uses light energy to
transport H+ across membrane.
Light harvesting proteins
Reaction center proteins
Transfer light
energy to other
protein
18. Electron transport proteins
Lecture 10, membranes
Transfer e- from one molecule to another
molecule
examples:
Cytochrome C
Ferredoxin
Plastocyanin
20. Membrane carbohydrates
Lecture 10, membranes
Approximately 2-10 % of mass
Confined mainly to the non-cytosolic surface:-
- On the extracellular surface of the cells
- Inward toward the lumen of the compartment
23. In many animal cells, the carbohydrate groups of
plasma membrane glycoproteins and glycolipids
protrude from the cell surface and form a surface coat
called the glycocalyx (meaning “sugar coat”).
they are important components of the recognition
sites of membrane receptors, in antibody-antigen
reactions, and in intercellular adhesion to form tissues.
Glycocalyx surrounding
animal egg cell
26. Glycocalyx of Streptococcus enables it to escape
detection & destruction by immune system
Lecture 10, membranes
27. Membrane carbohydrates bound to
the internal surface of lipid bilayer
Lecture 10, membranes
Covalently bound carbohydrates to the
internal surface of
Golgi vesicles
Secretion vesicles
Lysosomes also have
28. RBC plasma membrane composition
(by weight)
Lecture 10, membranes
1. 52% protein
2. 40% lipid
3. 8% carbohydrate by weight
Note: Most of the membrane mass IS NOT due to
lipids!!!
An erythrocyte is a small, disk-shaped cell with a diameter of
about 7 μm. A mammalian erythrocyte contains no nucleus or
other organelles, which makes it easy to obtain very pure
plasma membrane preparations without contamination by
organelle membranes.
30. Structural Features of the Erythrocyte
Plasma Membrane
Lecture 10, membranes
integral proteins
a.Glycophorin
b.Anion channel
peripheral
proteins
a)Spectrin
b)Ankyrin
c)Actin
d)Band 4.1
31. Lecture 10, membranes
FIGURE 7-28
demonstration of the
mobility of membrane
proteins by cell fusion.
The mobility of
membrane proteins
can be shown
experimentally by the
mixing of membrane
proteins that occurs
when cells from two
different species
(mouse and human)
are fused and the
membrane proteins
are labeled with
specific fluorescent
antibodies.
33. Lecture 10, membranes
Critical thinking
The effects of temperature and lipid composition on
membrane fluidity are often studied by using artificial
membranes containing only one or a few kinds of
lipids and no proteins. Assume that you have made
the following artificial membranes:
Membrane 1: Made entirely from
phosphatidylcholine with saturated 16-carbon fatty
acids.
Membrane 2: Same as membrane 1, except that
each of the 16-carbon fatty acids has a single cis
double bond.
Membrane 3: Same as membrane 1, except that
each of the saturated fatty acids has only 14
carbon atoms.
34. Lecture 10, membranes
After determining the transition temperatures of
samples representing each of the membranes, you
discover that your lab partner failed to record which
membranes the samples correspond to. The three
values you determined are –36°C, 23°C, and 41°C.
Assign each of these transition temperatures to the
correct artificial membrane, and explain your
reasoning.
