Active Transport, Endocytosis,
and Exocytosis
Section 3.5
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Objectives
• SWBAT describe active transport.
• SWBAT distinguish among endocytosis,
exocytosis, and phagocytosis.
• Main Ideas
– Proteins can transport materials against a
concentration gradient.
– Endocytosis and exocytosis transport materials
across the cell membrane in vesicles.
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Vocabulary Section 3.5
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Endocytosis (endocitosis)
Exocytosis (exocitosis)
Phagocytosis (fagocitosis)
Active transport (transporte activo)
ATP (adenosine triphosphate)
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Starter
• Small lipid molecules are in high concentration
outside a cell. They slowly cross the
membrane into the cell. What term describes
this action? Does it require energy?
• Diffusion and no.
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Two Types of Transport
• There are two ways of transporting materials
across a cell membrane. They are:
– Passive Transport – we have already looked at this.
– Active Transport – actively drives molecules
across the cell membrane from a region of lower
concentration to a region of higher
concentration. Requires energy input.
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Active Transport
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Active Transport
Active transport drives
molecules across a membrane
from region of lower
concentration to a region of
higher concentration
(remember our bicycle
example).
There are transport proteins
that allow diffusion but there
are others, often called
pumps, that move materials
against the concentration
gradient.
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Active Transport
Active transport requires
energy input from a cell and
enables a cell to move a
substance against its
concentration gradient.
Cells use active transport to
get needed molecules
regardless of the
concentration gradient to
maintain homeostasis.
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Sodium/Potassium Pump
Both facilitated diffusion
and active transport are
used in neurons (brain cells)
to propagate action
potentials (electrical
impulses). The sodium and
potassium channels allow
sodium ions and potassium
ions to move across the cell
membrane by facilitated
diffusion. The movement of
the ions is what allows the
action potential to
propagate along the
neurons axon.
To move the sodium and potassium ions back to the sides of the neuron
from which the came (sodium on the inside and potassium on the outside),
a sodium potassium pump (using ATP) is employed by the cell. The return of
sodium and potassium to their original sides of the cell membrane “resets”
the neuron – preparing it for the next action potential.
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Question
• Are the protein pumps, like the Na/K pump in
neurons, active or passive transport?
• Explain how a protein pump works?
• What kind of energy does it use?
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ATP (Adenosine Triphosphate)
ATP is chemical energy made in a cell’s
mitochondria.
Besides in neurons, like we have already
seen, ATP is needed to drive many other
processes – including the making of ATP.
ATP is used in the mitochondrial proton
pump, moving hydrogen ions (H+) across
the inner mitochondrial membrane. This
proton pump is essential for the creation
of ATP.
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ATP
Like with sodium and potassium
in the neuron, the hydrogen ions
are “pumped,” using ATP, across
the mitochondrial inner
membrane (against the H+
gradient).
They then diffuse across the
membrane through a protein
channel (an enzyme called ATP
Synthase).
The enzyme uses the movement
of the H+ to create ATP from a
precursor called ADP.
ATP spent in
active
transport
ATP created via
diffusion through
protein channel
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ATP Video
• http://highered.mcgrawhill.com/sites/9834092339/student_view0/ch
apter38/proton_pump.html
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Transport Proteins
• All transport proteins/enzymes (which are
proteins) span a membrane.
• Most change shape when they bind to a target
molecule or molecules.
• As we have seen, some transport proteins bind to
only one type of molecule.
• Others bind to 2 different types.
– Those that bind to two types can move both types of
molecules either one way or opposite directions (like
the sodium/potassium pump we saw in the neuron.
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Question
• How do transport proteins that are pumps
differ from those that are channels?
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Endocytosis
• Endocytosis – the process of taking liquids or
fairly large molecules into a cell by engulfing
them in a membrane.
– The cell membrane makes a pocket around the
substance.
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Endocytosis
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Endocytosis
• The pocket breaks off inside the cell and forms
a vesicle.
– The vesicle then fuses with a lysosome.
Lysosomal enzymes
break down the vesicle
membrane and the
vesicle’s contents are
release into the cell.
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Phagocytosis
• Phagocytosis – the word literally means “cell
eating.”
• It is a special type of endocytosis which plays a
major role in your immune system.
• White blood cells find foreign materials, such
as bacteria, engulf them and destroy them.
– They are your body’s enforcers.
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Exocytosis
Exocytosis is the opposite of
endocytosis. It is the release of
substances out of a cell by the
fusion of a vesicle with the cell
membrane.
Note how the vesicle pinches off
from the Golgi Apparatus.
Remember that the Golgi Apparatus
is the cell’s “storage, packing, and
shipping center.”
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Exocytosis
1. The cell forms a vesicle
around material that needs
to be removed or secreted.
2. The vesicle is transported
to the cell membrane.
3. The vesicle membrane
fuses with the cell
membrane and releases
the contents.
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Exocytosis in Neuron
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Exocytosis in Neuron
The neurotransmitter is stored in vesicles in
the terminus of the axon of the neuron.
When the action potential arrives, the
vesicles, via exocytosis, release their
neurotransmitter (for example,
acetylcholine) into the synaptic cleft.
Membrane receptors on the neuron on the
other side of the synaptic cleft stimulate is
stimulated by the neurotransmitter to “fire”
– transferring the action potential from one
neuron to the other.
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Exocytosis – Neuron to Muscle
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Questions
• How do endocytosis and exocytosis differ
from one another?
• List one function that exocytosis carries out
in the human body?
• List one function that endocytosis carries
out?
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Questions
• What might happen if vesicles in your
neurons were suddenly unable to fuse with
the cell membrane?
• How do endocytosis and exocytosis differ
from diffusion?
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