Chapter 5: Cellular Membranes
CHAPTER 5
Cellular Membranes
Chapter 5: Cellular Membranes
Chapter 5: Cellular Membranes
Membrane Composition and Structure
Cell Adhesion
Passive Processes of Membrane Transport
Active Transport
Chapter 5: Cellular Membranes
Chapter 5: Cellular Membranes
Endocytosis and Exocytosis
Membranes Are Not Simply Barriers
Membranes Are Dynamic
Chapter 5: Cellular Membranes
Membrane Composition and
Structure
• Biological membranes consist of lipids,
proteins, and carbohydrates.
• The fluid mosaic model describes a
phospholipid bilayer in which membrane
proteins move laterally within the
membrane.
Review Figures 5.1, 5.2
4
Chapter 5: Cellular Membranes
figure 05-01.jpg
5.1
Figure 5.1
Chapter 5: Cellular Membranes
figure 05-02.jpg
5.2
Figure 5.2
Chapter 5: Cellular Membranes
Membrane Composition and
Structure
• Integral membrane proteins are partially
inserted into the phospholipid bilayer.
• Peripheral proteins attach to its surface by
ionic bonds.
Review Figure 5.1
7
Chapter 5: Cellular Membranes
Membrane Composition and
Structure
• The two surfaces of a membrane may have
different properties due to different
phospholipid compositions, exposed integral
membrane proteins, and peripheral
membrane proteins.
• Defined regions of a plasma membrane may
have different membrane proteins.
Review Figures 5.1, 5.2
8
Chapter 5: Cellular Membranes
Membrane Composition and
Structure
• Carbohydrates attached to proteins or
phospholipids project from the external
surface of the plasma membrane and
function as recognition signals between
cells.
Review Figure 5.1
9
Chapter 5: Cellular Membranes
Cell Adhesion
• In an organism or tissue, cells recognize
and bind to each other by means of
membrane proteins protruding from the cell
surface.
Review Figure 5.5
10
Chapter 5: Cellular Membranes
figure 05-05.jpg
5.5
Figure 5.5
Chapter 5: Cellular Membranes
Cell Adhesion
• Tight junctions prevent passage of
molecules through space around cells, and
define functional regions of the plasma
membrane by restricting migration of
membrane proteins over the cell surface.
• Desmosomes allow cells to adhere strongly
to one another.
• Gap junctions provide channels for chemical
and electrical communication between cells.
Review Figure 5.6
Chapter 5: Cellular Membranes
figure 05-06a.jpg
5.6 – Part 1
Figure 5.6 – Part 1
Chapter 5: Cellular Membranes
figure 05-06b.jpg
5.6 – Part 2
Figure 5.6 – Part 2
Chapter 5: Cellular Membranes
Passive Processes of Membrane
Transport
• Substances can diffuse passively across a
membrane by:
•
•
•
unaided diffusion through the
phospholipid bilayer
facilitated diffusion through protein
channels
carrier proteins.
Review Table 5.1
15
Chapter 5: Cellular Membranes
table 05-01.jpg
Table 5.1
Table 5.1
Chapter 5: Cellular Membranes
Passive Processes of Membrane
Transport
• Solutes diffuse across a membrane from a
region with a greater solute concentration to
a region of lesser.
• Equilibrium is reached when the
concentrations are identical on both sides.
Review Figure 5.7
17
Chapter 5: Cellular Membranes
figure 05-07.jpg
5.7
Figure 5.7
Chapter 5: Cellular Membranes
Passive Processes of Membrane
Transport
• The rate of simple diffusion of a solute
across a membrane is directly proportional
to the concentration gradient across the
membrane.
• A related important factor is the lipid
solubility of the solute.
19
Chapter 5: Cellular Membranes
Passive Processes of Membrane
Transport
• In osmosis, water diffuses from regions of
higher water concentration to regions of
lower concentration across a membrane.
20
Chapter 5: Cellular Membranes
Passive Processes of Membrane
Transport
• In hypotonic solutions, cells tend to take up
water while in hypertonic solutions, they
tend to lose it.
• Animal cells must remain isotonic to the
environment to prevent destructive loss or
gain of water.
Review Figure 5.8
21
Chapter 5: Cellular Membranes
figure 05-08.jpg
5.8
Figure 5.8
Chapter 5: Cellular Membranes
Passive Processes of Membrane
Transport
• The cell walls of plants and some other
organisms prevent cells from bursting under
hypotonic conditions.
• Turgor pressure develops under these
conditions and keeps plants upright and
stretches the cell wall during cell growth.
Review Figure 5.8
23
Chapter 5: Cellular Membranes
Passive Processes of Membrane
Transport
• Channel proteins and carrier proteins
function in facilitated diffusion.
Review Figures 5.9, 5.10
24
Chapter 5: Cellular Membranes
figure 05-09.jpg
5.9
Figure 5.9
Chapter 5: Cellular Membranes
figure 05-10.jpg
5.10
Figure 5.10
Chapter 5: Cellular Membranes
Passive Processes of Membrane
Transport
• The rate of carrier-mediated facilitated
diffusion is at maximum when solute
concentration saturates the carrier proteins
so that no rate increase is observed with
further solute concentration increase.
27
Chapter 5: Cellular Membranes
Active Transport
• Active transport requires energy to move
substances across a membrane against a
concentration gradient.
Review Table 5.1
28
Chapter 5: Cellular Membranes
table 05-01.jpg
Table 5.1
Table 5.1
Chapter 5: Cellular Membranes
Active Transport
• Active transport proteins may be uniports,
symports, or antiports.
Review Figure 5.11
30
Chapter 5: Cellular Membranes
figure 05-11.jpg
5.11
Figure 5.11
Chapter 5: Cellular Membranes
Active Transport
• In primary active transport, energy from the
hydrolysis of ATP is used to move ions into
or out of cells against their concentration
gradients.
Review Figure 5.12 & Table 2.
32
Chapter 5: Cellular Membranes
figure 05-12.jpg
5.12
Figure 5.12
Chapter 5: Cellular Membranes
Active Transport
• Secondary active transport couples the
passive movement of one solute with its
concentration gradient to the movement of
another solute against its concentration
gradient.
• Energy from ATP is used indirectly to
establish the concentration gradient
resulting in movement of the first solute.
Review Figure 5.13
34
Chapter 5: Cellular Membranes
figure 05-13.jpg
5.13
Figure 5.13
Chapter 5: Cellular Membranes
Endocytosis and Exocytosis
• Endocytosis transports macromolecules,
large particles, and small cells into
eukaryotic cells by means of engulfment
and by vesicle formation from the plasma
membrane.
Review Figures 5.14
36
Chapter 5: Cellular Membranes
figure 05-14.jpg
5.14
Figure 5.14
Chapter 5: Cellular Membranes
Endocytosis and Exocytosis
• In receptor-mediated endocytosis, a specific
membrane receptor binds to a particular
macromolecule.
38
Chapter 5: Cellular Membranes
Endocytosis and Exocytosis
• In exocytosis, materials in vesicles are
secreted from the cell when the vesicles
fuse with the plasma membrane.
Review Figure 5.14 again.
39
Chapter 5: Cellular Membranes
Membranes Are Not Simply
Barriers
• Membranes function as sites for recognition
and initial processing of extracellular signals,
for energy transformations, and for
organizing chemical reactions.
Review Figure 5.17
40
Chapter 5: Cellular Membranes
figure 05-17a.jpg
5.17 –
Part 1
Figure 5.17 – Part 1
Chapter 5: Cellular Membranes
figure 05-17b.jpg
5.17 –
Part 2
Figure 5.17 – Part 2
Chapter 5: Cellular Membranes
Membranes Are Dynamic
• Although not all cellular membranes are
identical, ordered modifications in
membrane composition accompany the
conversions of one type of membrane into
another type.
Review Figure 5.18
43
Chapter 5: Cellular Membranes
figure 05-18.jpg
5.18
Figure 5.18