Transcript Chapter 3 PowerPoint

Chapter 3 Part B
Cells:
The Living
Units
© Annie Leibovitz/Contact Press Images
© 2016 Pearson Education, Inc.
PowerPoint® Lecture Slides
prepared by
Karen Dunbar Kareiva
Ivy Tech Community College
3.4 Active Membrane Transport
• Two major active membrane transport
processes
– Active transport
– Vesicular transport
• Both require ATP to move solutes across a
plasma membrane for any of these reasons:
– Solute is too large for channels, or
– Solute is not lipid soluble, or
– Solute is not able to move down concentration
gradient
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Active Transport
• Requires carrier proteins (solute pumps)
– Bind specifically and reversibly with substance
being moved
– Some carriers transport more than one
substance
• Antiporters transport one substance into cell while
transporting a different substance out of cell
• Symporters transport two different substances in the
same direction
• Moves solutes against their concentration
gradient (from low to high)
– This requires energy (ATP)
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Active Transport (cont.)
• Two types of active transport:
– Primary active transport
• Required energy comes directly from ATP hydrolysis
– Secondary active transport
• Required energy is obtained indirectly from ionic
gradients created by primary active transport
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Active Transport (cont.)
• Primary active transport
– Energy from hydrolysis of ATP causes change in
shape of transport protein
– Shape change causes solutes (ions) bound to
protein to be pumped across membrane
– Example of pumps: calcium, hydrogen (proton),
Na+-K+ pumps
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Active Transport (cont.)
• Sodium-potassium pump
– Most studied pump
– Basically is an enzyme, called Na+-K+ ATPase,
that pumps Na+ out of cell and K+ back into cell
– Located in all plasma membranes, but especially
active in excitable cells (nerves and muscles)
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Active Transport (cont.)
• Leakage channels located in membranes result
in leaking of Na+ into the cell and leaking of K+
out of cell
– Both travel down their concentration gradients
• Na+-K+ pump works as an antiporter that pumps
Na+ out of cell and K+ back into cell against their
concentration gradients
• Maintains electrochemical gradients, which
involve both concentration and electrical charge
of ions
– Essential for functions of muscle and nerve
tissues
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Figure 3.1 Cell diversity.
Erythrocytes
Fibroblasts
Skeletal
muscle
cell
Smooth
muscle cells
Epithelial cells
Cells that connect body parts, form linings,
or transport gases
Cells that move organs and body parts
Macrophage
Fat cell
Cell that stores
nutrients
Nerve cell
Cell that fights
disease
Sperm
Cell of reproduction
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Cell that gathers information and controls
body functions
Focus Figure 3.1 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using
energy supplied directly by ATP. The action of the Na+-K+ pump is an important example of primary active transport.
Extracellular fluid
Na+
Na+ –K+
pump
ATP
ATP-binding site
K+
Cytoplasm
1 Three cytoplasmic Na+ bind to
pump protein.
© 2016 Pearson Education, Inc.
Slide 2
Focus Figure 3.1 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using
energy supplied directly by ATP. The action of the Na+-K+ pump is an important example of primary active transport.
Extracellular fluid
Na+
Na+ –K+
pump
ATP
ATP-binding site
K+
Na+ bound
Cytoplasm
1 Three cytoplasmic Na+ bind to
pump protein.
P
ADP
2 Na+ binding promotes hydrolysis
of ATP. The energy released during this
reaction phosphorylates the pump.
© 2016 Pearson Education, Inc.
Slide 3
Focus Figure 3.1 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using
energy supplied directly by ATP. The action of the Na+-K+ pump is an important example of primary active transport.
Extracellular fluid
Na+
Na+ –K+
pump
ATP
ATP-binding site
K+
Na+ bound
Cytoplasm
1 Three cytoplasmic Na+ bind to
pump protein.
P
ADP
2 Na+ binding promotes hydrolysis
of ATP. The energy released during this
reaction phosphorylates the pump.
Na+
released
P
3 Phosphorylation causes the
pump to change shape, expelling
Na+ to the outside.
© 2016 Pearson Education, Inc.
Slide 4
Focus Figure 3.1 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using
energy supplied directly by ATP. The action of the Na+-K+ pump is an important example of primary active transport.
Extracellular fluid
Na+
Na+ –K+
pump
ATP
ATP-binding site
Na+ bound
K+
Cytoplasm
1 Three cytoplasmic Na+ bind to
pump protein.
P
ADP
2 Na+ binding promotes hydrolysis
of ATP. The energy released during this
reaction phosphorylates the pump.
Na+
released
P
K+
3 Phosphorylation causes the
pump to change shape, expelling
Na+ to the outside.
P
4 Two extracellular K+ bind to pump.
© 2016 Pearson Education, Inc.
Slide 5
Focus Figure 3.1 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using
energy supplied directly by ATP. The action of the Na+-K+ pump is an important example of primary active transport.
Extracellular fluid
Na+
Na+ –K+
pump
ATP
ATP-binding site
Na+ bound
K+
Cytoplasm
1 Three cytoplasmic Na+ bind to
pump protein.
P
ADP
2 Na+ binding promotes hydrolysis
of ATP. The energy released during this
reaction phosphorylates the pump.
Na+
released
K+ bound
P
Pi
5 K+ binding triggers release of
the phosphate. The dephosphorylated
pump resumes its original
conformation.
K+
3 Phosphorylation causes the
pump to change shape, expelling
Na+ to the outside.
P
4 Two extracellular K+ bind to pump.
© 2016 Pearson Education, Inc.
Slide 6
Focus Figure 3.1 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using
energy supplied directly by ATP. The action of the Na+-K+ pump is an important example of primary active transport.
Extracellular fluid
Na+
Na+ –K+
pump
ATP
ATP-binding site
Na+ bound
K+
Cytoplasm
1 Three cytoplasmic Na+ bind to
pump protein.
ATP
P
K+ released
ADP
6 Pump protein binds ATP; releases
K+ to the inside, and Na+ sites are ready
to bind Na+ again. The cycle repeats.
2 Na+ binding promotes hydrolysis
of ATP. The energy released during this
reaction phosphorylates the pump.
Na+
released
K+ bound
P
Pi
5 K+ binding triggers release of
the phosphate. The dephosphorylated
pump resumes its original
conformation.
K+
3 Phosphorylation causes the
pump to change shape, expelling
Na+ to the outside.
P
4 Two extracellular K+ bind to pump.
© 2016 Pearson Education, Inc.
Slide 7
Active Transport (cont.)
• Secondary active transport
– Depends on ion gradient that was created by
primary active transport system
– Energy stored in gradients is used indirectly to
drive transport of other solutes
• Low Na+ concentration that is maintained inside cell
by Na+-K+ pump strengthens sodium’s drive to want to
enter cell
• Na+ can drag other molecules with it as it flows into
cell through carrier proteins (usually symporters) in
membrane
– Some sugars, amino acids, and ions are usually
transported into cells via secondary active transport
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Slide 2
Figure 3.10 Secondary active transport is driven by the concentration gradient created by primary active transport.
Extracellular fluid
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
Na+-K+
pump
ATP
Cytoplasm
1 Primary active transport
The ATP-driven Na+-K+ pump
stores energy by creating a steep
concentration gradient for Na+
entry into the cell.
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Na+
Na+
Slide 3
Figure 3.10 Secondary active transport is driven by the concentration gradient created by primary active transport.
Extracellular fluid
Na+
Na+
Na+-glucose
Na+
Na+
Na+
Glucose
Na+
Na+
Na+
K+
Na+-K+
pump
symport
transporter
loads glucose
from extracellular
fluid
Na+
Na+
Na+-glucose
symport transporter
releases glucose
into the cytoplasm
Na+
ATP
Cytoplasm
1 Primary active transport
Na+-K+
The ATP-driven
pump
stores energy by creating a steep
concentration gradient for Na+
entry into the cell.
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2 Secondary active transport
As Na+ diffuses back across the membrane
through a membrane cotransporter protein, it
drives glucose against its concentration gradient
into the cell.
Vesicular Transport
• Involves transport of large particles,
macromolecules, and fluids across membrane
in membranous sacs called vesicles
• Requires cellular energy (usually ATP)
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Vesicular Transport (cont.)
• Vesicular transport processes include:
– Endocytosis: transport into cell
• 3 different types of endocytosis: phagocytosis,
pinocytosis, receptor-mediated endocytosis
– Exocytosis: transport out of cell
– Transcytosis: transport into, across, and then out
of cell
– Vesicular trafficking: transport from one area or
organelle in cell to another
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Vesicular Transport (cont.)
• Endocytosis
– Involves formation of protein-coated vesicles
– Usually involve receptors; therefore can be a
very selective process
• Substance being pulled in must be able to bind to its
unique receptor
– Some pathogens are capable of hijacking
receptor for transport into cell
– Once vesicle is pulled inside cell, it may:
• Fuse with lysosome or
• Undergo transcytosis
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Figure 3.11 Events of endocytosis mediated by protein-coated pits.
1 Coated pit
ingests substance.
Extracellular fluid
Plasma
membrane
Protein coat
(typically clathrin)
Cytoplasm
2 Protein-coated
vesicle detaches.
3 Coat proteins are recycled
to plasma membrane.
Transport
vesicle
Uncoated
endocytic
vesicle
Endosome
4 Uncoated vesicle fuses with
a sorting vesicle called an
endosome.
Lysosome
5 Transport vesicle
containing membrane
components moves to
the plasma membrane
for recycling.
6 Fused vesicle may (a) fuse
(a)
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with lysosome for digestion of
its contents, or (b) deliver its
contents to the plasma
membrane on the opposite
side of the cell (transcytosis).
(b)
Slide 2
Figure 3.11 Events of endocytosis mediated by protein-coated pits.
1 Coated pit
ingests substance.
Protein coat
(typically clathrin)
(a)
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Extracellular fluid
Plasma
membrane
Cytoplasm
(b)
Slide 3
Figure 3.11 Events of endocytosis mediated by protein-coated pits.
1 Coated pit
ingests substance.
Protein coat
(typically clathrin)
Extracellular fluid
Plasma
membrane
Cytoplasm
2 Protein-coated
vesicle detaches.
(a)
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(b)
Slide 4
Figure 3.11 Events of endocytosis mediated by protein-coated pits.
1 Coated pit
ingests substance.
Protein coat
(typically clathrin)
Extracellular fluid
Plasma
membrane
Cytoplasm
2 Protein-coated
vesicle detaches.
3 Coat proteins are recycled
to plasma membrane.
(a)
© 2016 Pearson Education, Inc.
(b)
Slide 5
Figure 3.11 Events of endocytosis mediated by protein-coated pits.
1 Coated pit
ingests substance.
Protein coat
(typically clathrin)
Extracellular fluid
Plasma
membrane
Cytoplasm
2 Protein-coated
vesicle detaches.
3 Coat proteins are recycled
to plasma membrane.
Uncoated
endocytic
vesicle
Endosome
4 Uncoated vesicle fuses with
a sorting vesicle called an
endosome.
(a)
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(b)
Slide 6
Figure 3.11 Events of endocytosis mediated by protein-coated pits.
1 Coated pit
ingests substance.
Protein coat
(typically clathrin)
Extracellular fluid
Plasma
membrane
Cytoplasm
2 Protein-coated
vesicle detaches.
3 Coat proteins are recycled
to plasma membrane.
Transport
vesicle
Uncoated
endocytic
vesicle
4 Uncoated vesicle fuses with
a sorting vesicle called an
endosome.
(a)
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Endosome
5 Transport vesicle
containing membrane
components moves to
the plasma membrane
for recycling.
(b)
Slide 7
Figure 3.11 Events of endocytosis mediated by protein-coated pits.
1 Coated pit
ingests substance.
Extracellular fluid
Plasma
membrane
Protein coat
(typically clathrin)
Cytoplasm
2 Protein-coated
vesicle detaches.
3 Coat proteins are recycled
to plasma membrane.
Transport
vesicle
Uncoated
endocytic
vesicle
Endosome
4 Uncoated vesicle fuses with
a sorting vesicle called an
endosome.
Lysosome
5 Transport vesicle
containing membrane
components moves to
the plasma membrane
for recycling.
6 Fused vesicle may (a) fuse
(a)
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with lysosome for digestion of
its contents, or (b) deliver its
contents to the plasma
membrane on the opposite
side of the cell (transcytosis).
(b)
Vesicular Transport (cont.)
• Phagocytosis: type of endocytosis that is
referred to as “cell eating”
– Membrane projections called pseudopods form
and flow around solid particles that are being
engulfed, forming a vesicle which is pulled into
cell
– Formed vesicle is called a phagosome
– Phagocytosis is used by macrophages and
certain other white blood cells
• Phagocytic cells move by amoeboid motion where
cytoplasm flows into temporary extensions that allow
cell to creep
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Figure 3.12a Comparison of three types of endocytosis.
Receptors
Phagosome
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Phagocytosis
The cell engulfs a large particle by forming
projecting pseudopods (“false feet”) around
it and enclosing it within a membrane sac
called a phagosome. The phagosome is
combined with a lysosome. Undigested
contents remain in the vesicle (now called a
residual body) or are ejected by exocytosis.
Vesicle may or may not be protein-coated
but has receptors capable of binding to
microorganisms or solid particles.
Vesicular Transport (cont.)
• Pinocytosis: type of endocytosis that is
referred to as “cell drinking” or fluid-phase
endocytosis
– Plasma membrane infolds, bringing extracellular
fluid and dissolved solutes inside cell
• Fuses with endosome
– Used by some cells to “sample” environment
– Main way in which nutrient absorption occurs in
the small intestine
– Membrane components are recycled back to
membrane
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Figure 3.12b Comparison of three types of endocytosis.
Pinocytosis
The cell “gulps” a drop of extracellular fluid
containing solutes into tiny vesicles. No receptors
are used, so the process is nonspecific. Most
vesicles are protein-coated.
Vesicle
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Vesicular Transport (cont.)
• Receptor-mediated endocytosis involves
endocytosis and transcytosis of specific molecules
– Many cells have receptors embedded in clathrin-coated
pits, which will be internalized along with the specific
molecule bound
• Examples: enzymes, low-density lipoproteins (LDL), iron,
insulin, and, unfortunately, viruses, diphtheria, and cholera
toxins may also be taken into a cell this way
– Caveolae have smaller pits and different protein coat
from clathrin, but still capture specific molecules (folic
acid, tetanus toxin) and use transcytosis
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Figure 3.12c Comparison of three types of endocytosis.
Vesicle
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Receptor-mediated endocytosis
Extracellular substances bind to specific receptor
proteins, enabling the cell to ingest and concentrate
specific substances (ligands) in protein-coated
vesicles. Ligands may simply be released inside
the cell, or combined with a lysosome to digest
contents. Receptors are recycled to the plasma
membrane in vesicles.
Exocytosis
• Process where material is ejected from cell
– Usually activated by cell-surface signals or
changes in membrane voltage
• Substance being ejected is enclosed in
secretory vesicle
• Protein on vesicle called v-SNARE finds and
hooks up to target t-SNARE proteins on
membrane
– Docking process triggers exocytosis
• Some substances exocytosed: hormones,
neurotransmitters, mucus, cellular wastes
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Figure 3.13a Exocytosis.
Extracellular
fluid
Secretory
vesicle
Plasma membrane
SNARE (t-SNARE)
Vesicle
SNARE
(v-SNARE)
Molecule to
be secreted
Cytoplasm
Fused
v- and
t-SNAREs
The process of
exocytosis
1 The membranebound vesicle migrates
to the plasma
membrane.
2 There, proteins at
the vesicle surface
(v-SNAREs) bind with
t-SNAREs (plasma
membrane proteins).
Fusion pore formed
3 The vesicle and
plasma membrane fuse
and a pore opens up.
4 Vesicle contents
are released to the cell
exterior.
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Slide 2
Figure 3.13a Exocytosis.
Extracellular
fluid
Secretory
vesicle
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Plasma membrane
SNARE (t-SNARE)
Vesicle
SNARE
(v-SNARE)
Molecule to
be secreted
Cytoplasm
The process of
exocytosis
1 The membranebound vesicle migrates
to the plasma
membrane.
Slide 3
Figure 3.13a Exocytosis.
Extracellular
fluid
Secretory
vesicle
Plasma membrane
SNARE (t-SNARE)
Vesicle
SNARE
(v-SNARE)
Molecule to
be secreted
Cytoplasm
Fused
v- and
t-SNAREs
© 2016 Pearson Education, Inc.
The process of
exocytosis
1 The membranebound vesicle migrates
to the plasma
membrane.
2 There, proteins at
the vesicle surface
(v-SNAREs) bind with
t-SNAREs (plasma
membrane proteins).
Slide 4
Figure 3.13a Exocytosis.
Extracellular
fluid
Secretory
vesicle
Plasma membrane
SNARE (t-SNARE)
Vesicle
SNARE
(v-SNARE)
Molecule to
be secreted
Cytoplasm
Fused
v- and
t-SNAREs
The process of
exocytosis
1 The membranebound vesicle migrates
to the plasma
membrane.
2 There, proteins at
the vesicle surface
(v-SNAREs) bind with
t-SNAREs (plasma
membrane proteins).
Fusion pore formed
3 The vesicle and
plasma membrane fuse
and a pore opens up.
© 2016 Pearson Education, Inc.
Slide 5
Figure 3.13a Exocytosis.
Extracellular
fluid
Secretory
vesicle
Plasma membrane
SNARE (t-SNARE)
Vesicle
SNARE
(v-SNARE)
Molecule to
be secreted
Cytoplasm
Fused
v- and
t-SNAREs
The process of
exocytosis
1 The membranebound vesicle migrates
to the plasma
membrane.
2 There, proteins at
the vesicle surface
(v-SNAREs) bind with
t-SNAREs (plasma
membrane proteins).
Fusion pore formed
3 The vesicle and
plasma membrane fuse
and a pore opens up.
4 Vesicle contents
are released to the cell
exterior.
© 2016 Pearson Education, Inc.
Figure 3.13b Exocytosis.
Photomicrograph
of a secretory
vesicle releasing
its contents
by exocytosis
(100,000)
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3.5 Membrane Potential
• Resting membrane potential (RMP)
– Electrical potential energy produced by
separation of oppositely charged particles across
plasma membrane in all cells
• Difference in electrical charge between two points is
referred to as voltage
• Cells that have a charge are said to be polarized
– Voltage occurs only at membrane surface
• Rest of cell and extracellular fluid are neutral
• Membrane voltages range from –50 to –100 mV in
different cells (negative sign (–) indicates inside of cell
is more negative relative to outside of cell)
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K+ is Key Player in RMP
• K+ diffuses out of cell through K+ leakage
channels down its concentration gradient
• Negatively charged proteins cannot leave
– As a result cytoplasmic side of cell membrane
becomes more negative
• K+ is then pulled back by the more negative
interior because of its electrical gradient
• When drive for K+ to leave cell is balanced by its
drive to stay, RMP is established
– Most cells have an RMP around –90 mV
• Electrochemical gradient of K+ sets RMP
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K+ is Key Player in RMP (cont.)
• In many cells, Na+ also affects RMP
– Na+ is also attracted to inside of cell because of
negative charge
• If Na+ enters cell, it can bring RMP up to –70 mV
– Membrane is more permeable to K+ than Na+, so
K+ primary influence on RMP
• Cl– does not influence RMP because its
concentration and electrical gradients are
exactly balanced
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Figure 3.14 The key role of K+ in generating the resting membrane potential.
Extracellular fluid
Na+
K+
K+
+
+



+
K+


A
© 2016 Pearson Education, Inc.

K+
K+
A
Na+
Cytoplasm
+
because they are attracted to the
negative charge established on
the inner plasma membrane face.
3 A negative membrane potential
K+
K+
concentration gradient (out of the
cell) via leakage channels. Loss of
K+ results in a negative charge on
the inner plasma membrane face.
2 K+ also move into the cell
+

K+
K+
K+
+
Potassium
leakage
channels
K+
K+
Na+
CI
+

Na+
Na+
CI
K+
Na+
Na+
Na+
K+
+
Na+
1 K+ diffuse down their steep
Protein anion (unable
to follow K+ through the
membrane)
(–90 mV) is established when the
movement of K+ out of the cell
equals K+ movement into the cell.
At this point, the concentration
gradient promoting K+ exit exactly
opposes the electrical gradient for
K+ entry.
Figure 3.14 The key role of K+ in generating the resting membrane potential.
Extracellular fluid
Na+
K+
K+
K+
+
+



+
K+


+

K+
K+
A
A
© 2016 Pearson Education, Inc.
K+
K+
Na+
Cytoplasm
+

K+
K+
K+
+
Potassium
leakage
channels
K+
K+
Na+
CI
+

Na+
Na+
CI
1 K+ diffuse down their steep
Na+
Na+
Na+
K+
+
Na+
Slide 2
Protein anion (unable
to follow K+ through the
membrane)
concentration gradient (out of the
cell) via leakage channels. Loss of
K+ results in a negative charge on
the inner plasma membrane face.
Figure 3.14 The key role of K+ in generating the resting membrane potential.
Extracellular fluid
Na+
K+
K+
K+
+
+



+
K+



K+
A
A
© 2016 Pearson Education, Inc.
+
K+
K+
Na+
Cytoplasm
K+
concentration gradient (out of the
cell) via leakage channels. Loss of
K+ results in a negative charge on
the inner plasma membrane face.
2 K+ also move into the cell
+

K+
K+
K+
+
Potassium
leakage
channels
K+
K+
Na+
CI
+

Na+
Na+
CI
1 K+ diffuse down their steep
Na+
Na+
Na+
K+
+
Na+
Slide 3
Protein anion (unable
to follow K+ through the
membrane)
because they are attracted to the
negative charge established on
the inner plasma membrane face.
Figure 3.14 The key role of K+ in generating the resting membrane potential.
Extracellular fluid
Na+
K+
K+
K+
+
+



+
K+


A
© 2016 Pearson Education, Inc.

K+
K+
A
Na+
Cytoplasm
+
because they are attracted to the
negative charge established on
the inner plasma membrane face.
3 A negative membrane potential
K+
K+
concentration gradient (out of the
cell) via leakage channels. Loss of
K+ results in a negative charge on
the inner plasma membrane face.
2 K+ also move into the cell
+

K+
K+
K+
+
Potassium
leakage
channels
K+
K+
Na+
CI
+

Na+
Na+
CI
1 K+ diffuse down their steep
Na+
Na+
Na+
K+
+
Na+
Slide 4
Protein anion (unable
to follow K+ through the
membrane)
(–90 mV) is established when the
movement of K+ out of the cell
equals K+ movement into the cell.
At this point, the concentration
gradient promoting K+ exit exactly
opposes the electrical gradient for
K+ entry.
Active Transport Maintains Electrochemical
Gradients
• RMP is maintained through action of the Na+-K+
pump, which continuously ejects 3Na+ out of cell
and brings 2K+ back inside
• Steady state is maintained because rate of
active pumping of Na+ out of cell equals the rate
of Na+ diffusion into cell
• Neuron and muscle cells “upset” this steady
state RMP by intentionally opening gated Na+
and K+ channels
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3.6 Cell-Environment Interactions
• Cells interact with their environment by
responding directly to other cells, or indirectly to
extracellular chemicals
• Interactions always involves glycocalyx
– Cell adhesion molecules (CAMs)
– Plasma membrane receptors
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Role of Cell Adhesion Molecules (CAMs)
• Every cell has thousands of sticky glycoprotein
CAMs projecting from membrane
• Functions:
– Anchor cell to extracellular matrix or to each
other
– Assist in movement of cells past one another
– Attract WBCs to injured or infected areas
– Stimulate synthesis or degradation of adhesive
membrane junctions (example: tight junctions)
– Transmit intracellular signals to direct cell
migration, proliferation, and specialization
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Roles of Plasma Membrane Receptors
• Membrane receptor proteins serve as binding
sites for several chemical signals
– Contact signaling: cells that touch recognize
each other by each cell’s unique surface
membrane receptors
• Used in normal development and immunity
– Chemical signaling: interaction between
receptors and ligands (chemical messengers)
that cause changes in cellular activities
• In some cells, binding triggers enzyme activation; in
others, it opens chemically gated ion channels
• Examples of ligands: neurotransmitters, hormones,
and paracrines
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Roles of Plasma Membrane Receptors (cont.)
– Chemical signaling (cont.):
• Same ligand can cause different responses in different
cells depending on chemical pathway that the receptor
is part of
• When ligand binds, receptor protein changes shape
and thereby becomes activated
• Some activated receptors become enzymes; others
act to directly open or close ion gates, causing
changes in excitability
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Roles of Plasma Membrane Receptors (cont.)
– Chemical signaling (cont.):
• Activated G protein–linked receptors indirectly
cause cellular changes by activating G proteins,
which in turn can affect ion channels, activate other
enzymes, or cause release of internal second
messenger chemicals such as cyclic AMP or calcium
© 2016 Pearson Education, Inc.
Focus Figure 3.2 G proteins act as middlemen or relays between extracellular first messengers and intracellular second messengers that cause responses within
the cell.
2nd
Ligand Receptor G protein Enzyme
messenger
(1st messenger)
1 Ligand*(1st
messenger) binds to
the receptor. The
receptor changes shape
and activates.
2 The activated receptor binds
to a G protein and activates it.
The G protein changes shape (turns
“on”), causing it to release GDP
and bind GTP (an energy source).
3 Activated G protein
activates (or inactivates)
an effector protein by
causing its shape to
change.
Extracellular fluid
Effector protein
(e.g., an enzyme
Ligand
Receptor
GTP
GTP
G protein
GDP GTP
4 Activated effector
enzymes catalyze reactions
that produce 2nd
messengers in the cell.
(Common 2nd messengers
include cyclic AMP and Ca2+.)
Inactive 2nd
messenger
Active 2nd
messenger
5 Second messengers
activate other enzymes or
ion channels. Cyclic AMP
typically activates protein kinase
enzymes.
Activated
Kinase
enzymes
* Ligands include
hormones and
neurotransmitters.
© 2016 Pearson Education, Inc.
Cascade of cellular
Responses
(The amplification
effect is tremendous.
Each enzyme catalyzes
hundreds of reactions.)
6 Kinase enzymes activate
other enzymes. Kinase
enzymes transfer phosphate
groups from ATP to specific
proteins and activate a series of
other enzymes that trigger
various metabolic and structural
changes in the cell.
Intracellular fluid
Focus Figure 3.2 G proteins act as middlemen or relays between extracellular first messengers and intracellular second messengers that cause
responses within the cell.
2nd
Ligand Receptor G protein Enzyme
messenger
(1st messenger)
1 Ligand*(1st
messenger) binds to
the receptor. The
receptor changes shape
and activates.
Extracellular fluid
Effector protein
(e.g., an enzyme
Ligand
Receptor
GTP
GTP
G protein
GDP GTP
Inactive 2nd
messenger
Active 2nd
messenger
Activated
Kinase
enzymes
* Ligands include
hormones and
neurotransmitters.
© 2016 Pearson Education, Inc.
Cascade of cellular
Responses
(The amplification
effect is tremendous.
Each enzyme catalyzes
hundreds of reactions.)
Intracellular fluid
Slide 2
Focus Figure 3.2 G proteins act as middlemen or relays between extracellular first messengers and intracellular second messengers that cause
responses within the cell.
2nd
Ligand Receptor G protein Enzyme
messenger
(1st messenger)
1 Ligand*(1st
messenger) binds to
the receptor. The
receptor changes shape
and activates.
2 The activated receptor binds
to a G protein and activates it.
The G protein changes shape (turns
“on”), causing it to release GDP
and bind GTP (an energy source).
Extracellular fluid
Effector protein
(e.g., an enzyme
Ligand
Receptor
GTP
GTP
G protein
GDP GTP
Inactive 2nd
messenger
Active 2nd
messenger
Activated
Kinase
enzymes
* Ligands include
hormones and
neurotransmitters.
© 2016 Pearson Education, Inc.
Cascade of cellular
Responses
(The amplification
effect is tremendous.
Each enzyme catalyzes
hundreds of reactions.)
Intracellular fluid
Slide 3
Focus Figure 3.2 G proteins act as middlemen or relays between extracellular first messengers and intracellular second messengers that cause
responses within the cell.
2nd
Ligand Receptor G protein Enzyme
messenger
(1st messenger)
1 Ligand*(1st
messenger) binds to
the receptor. The
receptor changes shape
and activates.
2 The activated receptor binds
to a G protein and activates it.
The G protein changes shape (turns
“on”), causing it to release GDP
and bind GTP (an energy source).
3 Activated G protein
activates (or inactivates)
an effector protein by
causing its shape to
change.
Extracellular fluid
Effector protein
(e.g., an enzyme
Ligand
Receptor
GTP
GTP
G protein
GDP GTP
Inactive 2nd
messenger
Active 2nd
messenger
Activated
Kinase
enzymes
* Ligands include
hormones and
neurotransmitters.
© 2016 Pearson Education, Inc.
Cascade of cellular
Responses
(The amplification
effect is tremendous.
Each enzyme catalyzes
hundreds of reactions.)
Intracellular fluid
Slide 4
Focus Figure 3.2 G proteins act as middlemen or relays between extracellular first messengers and intracellular second messengers that cause
responses within the cell.
2nd
Ligand Receptor G protein Enzyme
messenger
(1st messenger)
1 Ligand*(1st
messenger) binds to
the receptor. The
receptor changes shape
and activates.
2 The activated receptor binds
to a G protein and activates it.
The G protein changes shape (turns
“on”), causing it to release GDP
and bind GTP (an energy source).
3 Activated G protein
activates (or inactivates)
an effector protein by
causing its shape to
change.
Extracellular fluid
Effector protein
(e.g., an enzyme
Ligand
Receptor
GTP
GTP
G protein
GDP GTP
4 Activated effector
enzymes catalyze reactions
that produce 2nd
messengers in the cell.
(Common 2nd messengers
include cyclic AMP and Ca2+.)
Inactive 2nd
messenger
Active 2nd
messenger
Activated
Kinase
enzymes
* Ligands include
hormones and
neurotransmitters.
© 2016 Pearson Education, Inc.
Cascade of cellular
Responses
(The amplification
effect is tremendous.
Each enzyme catalyzes
hundreds of reactions.)
Intracellular fluid
Slide 5
Focus Figure 3.2 G proteins act as middlemen or relays between extracellular first messengers and intracellular second messengers that cause
responses within the cell.
2nd
Ligand Receptor G protein Enzyme
messenger
(1st messenger)
1 Ligand*(1st
messenger) binds to
the receptor. The
receptor changes shape
and activates.
2 The activated receptor binds
to a G protein and activates it.
The G protein changes shape (turns
“on”), causing it to release GDP
and bind GTP (an energy source).
3 Activated G protein
activates (or inactivates)
an effector protein by
causing its shape to
change.
Extracellular fluid
Effector protein
(e.g., an enzyme
Ligand
Receptor
GTP
GTP
G protein
GDP GTP
4 Activated effector
enzymes catalyze reactions
that produce 2nd
messengers in the cell.
(Common 2nd messengers
include cyclic AMP and Ca2+.)
Inactive 2nd
messenger
Active 2nd
messenger
5 Second messengers
activate other enzymes or
ion channels. Cyclic AMP
typically activates protein kinase
enzymes.
Activated
Kinase
enzymes
* Ligands include
hormones and
neurotransmitters.
© 2016 Pearson Education, Inc.
Cascade of cellular
Responses
(The amplification
effect is tremendous.
Each enzyme catalyzes
hundreds of reactions.)
Intracellular fluid
Slide 6
Focus Figure 3.2 G proteins act as middlemen or relays between extracellular first messengers and intracellular second messengers that cause
responses within the cell.
2nd
Ligand Receptor G protein Enzyme
messenger
(1st messenger)
1 Ligand*(1st
messenger) binds to
the receptor. The
receptor changes shape
and activates.
2 The activated receptor binds
to a G protein and activates it.
The G protein changes shape (turns
“on”), causing it to release GDP
and bind GTP (an energy source).
3 Activated G protein
activates (or inactivates)
an effector protein by
causing its shape to
change.
Extracellular fluid
Effector protein
(e.g., an enzyme
Ligand
Receptor
GTP
GTP
G protein
GDP GTP
4 Activated effector
enzymes catalyze reactions
that produce 2nd
messengers in the cell.
(Common 2nd messengers
include cyclic AMP and Ca2+.)
Inactive 2nd
messenger
Active 2nd
messenger
5 Second messengers
activate other enzymes or
ion channels. Cyclic AMP
typically activates protein kinase
enzymes.
Activated
Kinase
enzymes
* Ligands include
hormones and
neurotransmitters.
© 2016 Pearson Education, Inc.
Cascade of cellular
Responses
(The amplification
effect is tremendous.
Each enzyme catalyzes
hundreds of reactions.)
6 Kinase enzymes activate
other enzymes. Kinase
enzymes transfer phosphate
groups from ATP to specific
proteins and activate a series of
other enzymes that trigger
various metabolic and structural
changes in the cell.
Intracellular fluid
Slide 7