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Chapter 5b
Membrane
Dynamics
Energy Transfer in Living Cells
Glucose
Energy is imported into the cell as
energy stored in chemical bonds
of nutrients such as glucose.
Glucose
Glycolysis
ATP
Pyruvate
Metabolism
The chemical bond energy is converted
into high-energy bonds of ATP through
the process of metabolism.
Heat
CA
cycle
H2O
ETS
CO2
Primary active transport
Na+
ATP
K+
ATP
O2
ADP+Pi
High [K+] Low [K+]
Low [Na+] High [Na+]
Na+
K+
2 Cl–
KEY
CA
= Citric acid cycle
cycle
The energy in the high-energy phosphate
bond of ATP is used to move K+ and Na+
against their concentration gradients.
This creates potential energy stored
in the ion concentration gradients.
Secondary active transport
The energy of the Na+ gradient can be
used to move other molecules across
the cell membrane against their
concentration gradients.
ETS = Electron transport system
Figure 5-16
Carrier-Mediated Transport
• Specificity
• Competition
• Saturation
• Transport maximum
Carrier-Mediated Transport Competition
Figure 5-17
Carrier-Mediated Transport Competition
Extracellular fluid
Glucose
Glucose
Maltose
GLUT
transporter
Intracellular fluid
(a) The GLUT transporter
(b) Maltose
Figure 5-18
Carrier-Mediated Transport Saturation
Figure 5-19
Vesicular Transport
• Phagocytosis
• Cell engulfs bacterium or other particle into
phagosome
• Endocytosis
• Membrane surface indents and forms vesicles
• Active process that can be nonselective
(pinocytosis) or highly selective
• Potocytosis uses caveolae
• Receptor-mediated uses clathrin-coated pits
Phagocytosis
Bacterium
Phagocyte
Lysosome
1 The phagocytic white blood
cell encounters a bacterium
that binds to the cell
membrane.
2 The phagocyte uses its
cytoskeleton to push its
cell membrane around the
bacterium, creating a large
vesicle, the phagosome.
3 The phagosome containing
the bacterium separates
from the cell membrane and
moves into the cytoplasm.
4 The phagosome fuses with
lysosomes containing
digestive enzymes.
5 The bacterium is killed
and digested within the
vesicle.
Figure 5-20
Phagocytosis
Bacterium
Phagocyte
Lysosome
1 The phagocytic white blood
cell encounters a bacterium
that binds to the cell
membrane.
Figure 5-20, step 1
Phagocytosis
Bacterium
Phagocyte
Lysosome
1 The phagocytic white blood
cell encounters a bacterium
that binds to the cell
membrane.
2 The phagocyte uses its
cytoskeleton to push its
cell membrane around the
bacterium, creating a large
vesicle, the phagosome.
Figure 5-20, steps 1–2
Phagocytosis
Bacterium
Phagocyte
Lysosome
3 The phagosome containing
the bacterium separates
from the cell membrane and
moves into the cytoplasm.
1 The phagocytic white blood
cell encounters a bacterium
that binds to the cell
membrane.
2 The phagocyte uses its
cytoskeleton to push its
cell membrane around the
bacterium, creating a large
vesicle, the phagosome.
Figure 5-20, steps 1–3
Phagocytosis
Bacterium
Phagocyte
Lysosome
1 The phagocytic white blood
cell encounters a bacterium
that binds to the cell
membrane.
3 The phagosome containing
the bacterium separates
from the cell membrane and
moves into the cytoplasm.
4 The phagosome fuses with
lysosomes containing
digestive enzymes.
2 The phagocyte uses its
cytoskeleton to push its
cell membrane around the
bacterium, creating a large
vesicle, the phagosome.
Figure 5-20, steps 1–4
Phagocytosis
Bacterium
Phagocyte
Lysosome
1 The phagocytic white blood
cell encounters a bacterium
that binds to the cell
membrane.
2 The phagocyte uses its
cytoskeleton to push its
cell membrane around the
bacterium, creating a large
vesicle, the phagosome.
3 The phagosome containing
the bacterium separates
from the cell membrane and
moves into the cytoplasm.
4 The phagosome fuses with
lysosomes containing
digestive enzymes.
5 The bacterium is killed
and digested within the
vesicle.
Figure 5-20, steps 1–5
Receptor-Mediated Endocytosis and Exocytosis
1 Ligand binds to membrane receptor.
9 Exocytosis
Extracellular fluid
2 Receptor-ligand migrates to clathrin-coated pit.
8 Transport vesicle
and cell membrane
fuse (membrane
recycling).
Clathrin-coated
pit
3 Endocytosis
Receptor
Clathrin
4 Vesicle loses
clathrin coat.
7 Transport vesicle
with receptors moves
to the cell membrane.
5 Receptors
and ligands
separate.
To lysosome or
Golgi complex
6 Ligands go to lysosomes
or Golgi for processing.
Endosome
Intracellular fluid
Figure 5-21
Receptor-Mediated Endocytosis and Exocytosis
1 Ligand binds to membrane receptor.
Extracellular fluid
Receptor
Intracellular fluid
Figure 5-21, step 1
Receptor-Mediated Endocytosis and Exocytosis
1 Ligand binds to membrane receptor.
Extracellular fluid
2 Receptor-ligand migrates to clathrin-coated pit.
Clathrin-coated
pit
Receptor
Clathrin
Intracellular fluid
Figure 5-21, steps 1–2
Receptor-Mediated Endocytosis and Exocytosis
1 Ligand binds to membrane receptor.
Extracellular fluid
2 Receptor-ligand migrates to clathrin-coated pit.
Clathrin-coated
pit
3 Endocytosis
Receptor
Clathrin
Intracellular fluid
Figure 5-21, steps 1–3
Receptor-Mediated Endocytosis and Exocytosis
1 Ligand binds to membrane receptor.
Extracellular fluid
2 Receptor-ligand migrates to clathrin-coated pit.
Clathrin-coated
pit
3 Endocytosis
Receptor
Clathrin
4 Vesicle loses
clathrin coat.
Intracellular fluid
Figure 5-21, steps 1–4
Receptor-Mediated Endocytosis and Exocytosis
1 Ligand binds to membrane receptor.
Extracellular fluid
2 Receptor-ligand migrates to clathrin-coated pit.
Clathrin-coated
pit
3 Endocytosis
Receptor
Clathrin
4 Vesicle loses
clathrin coat.
5 Receptors
and ligands
separate.
Endosome
Intracellular fluid
Figure 5-21, steps 1–5
Receptor-Mediated Endocytosis and Exocytosis
1 Ligand binds to membrane receptor.
Extracellular fluid
2 Receptor-ligand migrates to clathrin-coated pit.
Clathrin-coated
pit
3 Endocytosis
Receptor
Clathrin
4 Vesicle loses
clathrin coat.
5 Receptors
and ligands
separate.
To lysosome or
Golgi complex
6 Ligands go to lysosomes
or Golgi for processing.
Endosome
Intracellular fluid
Figure 5-21, steps 1–6
Receptor-Mediated Endocytosis and Exocytosis
1 Ligand binds to membrane receptor.
Extracellular fluid
2 Receptor-ligand migrates to clathrin-coated pit.
Clathrin-coated
pit
3 Endocytosis
Receptor
Clathrin
4 Vesicle loses
clathrin coat.
7 Transport vesicle
with receptors moves
to the cell membrane.
5 Receptors
and ligands
separate.
To lysosome or
Golgi complex
6 Ligands go to lysosomes
or Golgi for processing.
Endosome
Intracellular fluid
Figure 5-21, steps 1–7
Receptor-Mediated Endocytosis and Exocytosis
1 Ligand binds to membrane receptor.
Extracellular fluid
2 Receptor-ligand migrates to clathrin-coated pit.
8 Transport vesicle
and cell membrane
fuse (membrane
recycling).
Clathrin-coated
pit
3 Endocytosis
Receptor
Clathrin
4 Vesicle loses
clathrin coat.
7 Transport vesicle
with receptors moves
to the cell membrane.
5 Receptors
and ligands
separate.
To lysosome or
Golgi complex
6 Ligands go to lysosomes
or Golgi for processing.
Endosome
Intracellular fluid
Figure 5-21, steps 1–8
Receptor-Mediated Endocytosis and Exocytosis
1 Ligand binds to membrane receptor.
9 Exocytosis
Extracellular fluid
2 Receptor-ligand migrates to clathrin-coated pit.
8 Transport vesicle
and cell membrane
fuse (membrane
recycling).
Clathrin-coated
pit
3 Endocytosis
Receptor
Clathrin
4 Vesicle loses
clathrin coat.
7 Transport vesicle
with receptors moves
to the cell membrane.
5 Receptors
and ligands
separate.
To lysosome or
Golgi complex
6 Ligands go to lysosomes
or Golgi for processing.
Endosome
Intracellular fluid
Figure 5-21, steps 1–9
Transepithelial Transport
• Polarized cells of transporting epithelia
Lumen of intestine
or kidney
Apical
membrane
Tight junction
Transporting
epithelial cell
Basolateral
membrane
Extracellular
fluid
Transport proteins
Figure 5-22
Transepithelial Transport of Glucose
[Glucose] low
[Na+] high
1 Na+-glucose symporter
brings glucose into cell
against its gradient using
energy stored in the Na+
concentration gradient.
Lumen of kidney
or intestine
1
Apical
membrane
2 GLUT transporter
transfers glucose to ECF
by facilitated diffusion.
[Na+] low
[Glucose] high
3 Na+-K+- ATPase pumps
Na+ out of the cell, keeping
ICF Na+ concentration low.
Epithelial
cell
Basolateral
membrane
2
3
Extracellular
fluid
[Glucose] low
[Na+] high
Figure 5-23
Transepithelial Transport of Glucose
[Glucose] low
[Na+] high
1 Na+-glucose symporter
brings glucose into cell
against its gradient using
energy stored in the Na+
concentration gradient.
Lumen of kidney
or intestine
1
Apical
membrane
[Glucose] high
[Na+] low
Epithelial
cell
Basolateral
membrane
Extracellular
fluid
Figure 5-23, step 1
Transepithelial Transport of Glucose
[Glucose] low
[Na+] high
1 Na+-glucose symporter
brings glucose into cell
against its gradient using
energy stored in the Na+
concentration gradient.
Lumen of kidney
or intestine
1
Apical
membrane
2 GLUT transporter
transfers glucose to ECF
by facilitated diffusion.
[Glucose] high
[Na+] low
Epithelial
cell
Basolateral
membrane
2
Extracellular
fluid
[Glucose] low
Figure 5-23, steps 1–2
Transepithelial Transport of Glucose
[Glucose] low
[Na+] high
1 Na+-glucose symporter
brings glucose into cell
against its gradient using
energy stored in the Na+
concentration gradient.
Lumen of kidney
or intestine
1
Apical
membrane
2 GLUT transporter
transfers glucose to ECF
by facilitated diffusion.
[Na+] low
[Glucose] high
3 Na+-K+- ATPase pumps
Na+ out of the cell, keeping
ICF Na+ concentration low.
Epithelial
cell
Basolateral
membrane
2
3
Extracellular
fluid
[Glucose] low
[Na+] high
Figure 5-23, steps 1–3
Transcytosis Across the Capillary Endothelium
Red
blood
cell
Plasma proteins
Caveolae
Capillary
endothelium
Endocytosis
1
1 Plasma proteins are concentrated
in caveolae, which then undergo
endocytosis and form vesicles.
2
2 Vesicles cross the cell with help
Vesicular
transport
from the cytoskeleton.
3
Exocytosis
3 Vesicle contents are released into
interstitial fluid by exocytosis.
Interstitial fluid
Figure 5-24