Transcript RESPIRATORY SYSTEM - Bowie High School

UNIT 4 CHAPTER 4:
Cell Transport
The Cell
Chapter 4 Vocabulary
1. passive transport
2. concentration gradient
3. equilibrium
4. diffusion
5. osmosis
6. hypertonic solution
7. hypotonic solution
8. isotonic solution
9. ion channel
10. carrier protein
11. facilitated diffusion
12. active transport
13. sodium-potassium pump
14. endocytosis
15.
16.
17.
18.
19.
20.
21.
22.
phagocytosis
pinocytosis
exocytosis
receptor protein
beta blockers
macrophages
negative feedback loop
positive feedback loop
The Cell
SECTION 1:
TYPES OF TRANSPORT -PASSIVE TRANSPORT
The Cell
Types of Transport Across
Cell Membranes
• There are two basic types of transport across cell
membranes: passive transport and active transport.
• Passive transport is the movement across the cell
membrane that does not require energy. Passive
transport relies on the kinetic energy of motion of the
molecules themselves.
• Active transport is the movement across the cell
membrane that requires energy. The cell must use
some form of energy other than kinetic energy for
active transport to occur.
The Cell
Passive Transport -- Diffusion
• Particles of a substance in a solution tend to
move around randomly or scatter until
equilibrium is reached.
• If there is a concentration gradient in the
solution, the substance will move from an area of
higher concentration to an area of lower
concentration in an attempt to reach a state of
equilibrium.
• A concentration gradient is a difference in the
concentration of a substance across a space or
distance.
The Cell
How Cells Move Substances Around
Diffusion
Diffusion is the movement of molecules from an area
of higher concentration to an area of lesser
concentration until the molecules reach equilibrium.
Semipermeable membrane
The Cell
• Equilibrium is a condition in which the
concentration of a substance is equal
throughout a space.
• Many substances, such as molecules and
ions dissolved in the cytoplasm and in the
fluid outside cells, enter or leave cells by
diffusing across the cell membrane.
• The concentrations of most substances
inside the cell are different from the
concentrations of substances outside the
cell.
The Cell
• For each of these substances, a
concentration gradient exists across the cell
membrane.
• To diffuse “down” its concentration gradient
– from an area of high concentration to an
area of lower concentration – a substance
must be able to pass through the cell
membrane.
• The cell membrane is selectively permeable
to certain substances – which means it allows
some substances to enter, but not others.
The Cell
When molecules diffuse, they move down
a concentration gradient -- from and area
of high concentration to an area of low
concentration.
The Cell
• The nonpolar interior of the lipid bilayer repels
ions and most polar molecules, preventing
these substances from diffusing across the cell
membrane.
• Molecules that are either very small or nonpolar
can diffuse across the cell membrane down
their concentration gradient. Examples would
be gas molecules and water molecules.
• The diffusion of such molecules across the cell
membrane is the simplest type of passive
transport.
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•Heads are polar.
•Tails are nonpolar.
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The Cell
Diffusion Through A
Semipermeable Membrane
Dialysis tubing is a manmade semi-permeable
membrane that is often used to illustrate diffusion.
Consider what happens in the following example:
A few drops of Lugol's iodine solution placed in a
beaker of water will turn the water red. A starch
solution was poured into length of dialysis tubing
and the ends were tied. The starch solution was
white.
The tubing was then dropped into the beaker of
iodine solution. After 10 minutes, the white starch
solution turned black and the iodine water remained
red.
Why did this occur?
The Cell
Passive Transport -- Osmosis
• Osmosis is the diffusion of WATER through a
selectively permeable membrane from an area of
higher concentration to an area of lesser
concentration, until the molecules reach
equilibrium.
• Osmosis involves the movement of WATER down
its concentration gradient.
• Osmosis is a type of passive transport because it
requires only the kinetic energy of motion of the
water molecules.
The Cell
How Cells Move Substances Around
Osmosis
Osmosis is the diffusion of water molecules from an area
of higher concentration to an area of lesser concentration, until
the molecules reach equilibrium.
sugar
molecules
water
molecules
Semipermeable membrane
Water molecules pass
through, but not the sugar!
The Cell
• Solutions on either side of the cell
membrane will have different
concentrations of “free” water molecules
which are water molecules not dissolved
with other substances that are free to
move around.
• Osmosis occurs because these “free”
water molecules move into the solution
with the lower concentration of free
water molecules in an attempt to reach
equilibrium.
The Cell
• The direction of water movement across the
cell membrane depends on the relative
concentrations of free water molecules in
the cytoplasm and in the fluid outside the
cell.
•
•
•
•
Water can do one of three things:
(1) It can move out of the cell.
(2) It can move into the cell.
(3) There will be NO net movement of water
into or out of the cell.
The Cell
The Cell
How Cells Move Substances Around
Hypotonic Solutions
• A hypotonic solution contains a lesser
concentration of impermeable solutes
than the solution on the other side of
the membrane.
• When a cell’s cytoplasm is bathed in a
hypotonic solution, the water will be
drawn out of the solution and into the
cell by osmosis. The cell will plump up.
The Cell
How Cells Move Substances Around
• If water
molecules
continue to
diffuse into the
cell, it will cause
the cell to swell,
up to the point
that lysis (which
means to rupture
or burst) may
occur.
The Cell
How Cells Move Substances Around
Hypertonic Solutions
A hypertonic solution
contains a greater
concentration of impermeable
solutes than the solution on
the other side of the
membrane.
When a cell’s cytoplasm is
bathed in a hypertonic
solution, the water will be
drawn into the solution and
out of the cell by osmosis.
The cell will eventually shrink,
or crenate.
The Cell
How Cells Move Substances Around
• In eukaryotic animal
cells, a hypertonic
environment forces
water to leave the
cell so that the
shape of the cell
becomes distorted
and wrinkled, a
state known as
crenation. The cell
shrinks.
The Cell
How Cells Move Substances Around
In plant cells, the effect is more
dramatic. The flexible cell membrane
pulls away from the rigid cell wall, but
remains joined to the cell wall at points
called plasmodesmata.
The cell takes on the appearance of a
pincushion, and the plasmodesmata
almost cease to function because they
become constricted — a condition
known as plasmolysis.
The Cell
How Cells Move Substances Around
Isotonic Solutions
An isotonic solution is a condition in
which the concentration of solute
molecules is the same in the internal
environment of a cell and in the external
environment.
There is no change in the cell or in its
outside environment because both are in
a state of equilibrium.
The Cell
How Cells Move Substances Around
The Cell
Animal Cells in Solutions
The Cell
Plant Cells In Solution
plasmolysis – plasma membrane pulls away from the cell wall
because water moves out of the cell, so the cell shrinks or
crenates
flaccid – same as isotonic – same concentration inside and
outside of cell
turgid – vacuole takes on water, has turgor pressure, pushes
against the plasma membrane, so the cell plumps up The Cell
The Cell
hypotonic
hypertonic
isotonic
hypertonic
isotonic
hypotonic
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The Cell
http://www.youtube.com/watch?v=2Th0PuORsWY
You Tube Video Diffusion Through A Dialysis Membrane
http://www.youtube.com/watch?v=aubZU0iWtgI
Khan Academy video on diffusion
The Cell
How Cells Move Substances Around
Passive Transport by PROTEINS
• Some compounds are too large to pass
through the cell membrane by diffusion.
• Transport proteins or carrier proteins help
these substances move in or out of the cell.
• Transport proteins, also called ion channel
proteins, provide polar passageways through
which ions and polar molecules can move
across the cell membrane.
The Cell
Diffusion Through Ion Channels
• Ions such as sodium (Na+), potassium (K+),
calcium (Ca2+), and chloride (Cl-) are involved in
many important cell functions.
• Although ions cannot diffuse through the
nonpolar interior of the lipid layer, they can cross
the cell membrane by diffusing through special
openings in the transport proteins called ion
channels.
• An ion channel, or channel protein, is a transport
protein with a polar pore through which ions can
pass.
The Cell
• The pores of some ion channels are always open.
In other ion channels, the pores can be closed by
ion channel gates.
• Ion channel gates may open or close in response
to different kinds of stimuli.
• These stimuli include the stretching of the cell
membrane, a change in electrical charge, or the
binding of specific molecules to the ion channel.
• In this way, the stimuli are able to affect the
ability of particular ions to cross the cell
membrane.
The Cell
• The diffusion of ions through ion
channels is a form of passive transport.
• No use of energy by the cell is required
because the ions move down their
concentration gradients.
• The rate of movement of a substance
across the cell membrane is generally
determined by the concentration gradient
of the substance.
The Cell
Electrical Charge and
Ion Transport
• The inside of a typical cell is negatively charged
with respect to the outside of the cell which is
positively charged.
• Opposite charges attract, and like charges repel.
• A more positively charged ion located outside the cell
is more likely to diffuse into the cell, where the charge
is negative. The reverse is also true.
• An ion’s electrical charge often affects the diffusion of
the ion across the cell membrane.
The Cell
Facilitated Diffusion
• Facilitated diffusion is a type of passive transport that
involves the use of carrier proteins (or transport
proteins) to move substances down their concentration
gradient without using the cell’s energy.
• STEP 1: The carrier protein binds a specific molecule on
one side of the cell membrane.
• STEP 2: A change in the shape of the carrier protein
exposes the molecule to the other side of the cell
membrane.
• STEP 3: The carrier protein shields the molecule from the
interior of the lipid bilayer. The molecule is then released
from the carrier protein, which returns to its original
shape.
The Cell
VIDEO: How Facilitated
Diffusion Works
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation
__how_facilitated_diffusion_works.html
The Cell
The Cell
Molecules will randomly move through
the pores in channel proteins.
The Cell
Carrier proteins bind to specific substances
on the outside of the cell, and then change
shape as they move the substances past the
cell membrane and release them into the
cytoplasm.
The Cell
FACILITATED DIFFUSION
• Facilitated diffusion
provides a means for the
transport of large
molecules, such as
proteins and glucose
that are too large to
pass through membrane
pores, to enter the cell.
• Proteins in the plasma
membrane act as
carriers to move these
large molecules
passively across the cell
membrane.
The Cell
The Cell
SECTION 2:
ACTIVE TRANSPORT
The Cell
How Cells Move Substances Around
Active Transport
•Active transport is the movement across the
cell membrane that requires energy.
•A cell can move substances from an area of lesser
concentration to an area of greater concentration,
but it must expend energy to do so.
•This type of movement goes against a
concentration gradient.
•The energy needed for active transport is usually
supplied directly or indirectly by ATP.
The Cell
The Sodium-Potassium Pump
• The sodium-potassium pump is a type of
solute pump that carries sodium ions
out of the cell and potassium ions into the
cell, and is absolutely necessary for normal
transmission of impulses by nerve cells.
• Because there are more sodium ions (Na+)
outside the cell, the sodium ions inside the
cell tend to remain inside the cell unless
the cell uses ATP to force, or “pump” them
out.
The Cell
• Likewise, there are more potassium ions inside
cells than in interstitial (extracellular) fluid, and
potassium ions that leak out of cells must be
actively pumped back inside.
• Solute pumping allows the cell to be very selective
in cases where substances cannot pass by
diffusion.
• No pump means no transport.
• REMEMBER: there is more sodium outside, and
more potassium inside – the cell must reverse this
order.
The Cell
• The sodium-potassium
pump is an example of
counter-transport in
which two kinds of particles
are transported at the
same time in opposite
directions by the same
mechanism.
Substances are moved
against the
concentration gradients,
which is opposite the
normal direction by
diffusion – thus the cell will
need energy in the form of
ATP.
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The Cell
BULK TRANSPORT Transport of Large Particles
• Bulk transport is a type of active transport that
moves large molecules, and involves the use of
ATP to move these substances through the plasma
membrane.
• Two types of bulk transport are exocytosis and
endocytosis.
• Because the types of bulk transport use energy to
move substances through the plasma membrane,
they are both types of active transport.
The Cell
Transport of Large Particles - Endocytosis
Endocytosis is a type
of active transport by
which a cell surrounds
and takes in material
from its environment.
The cell forms a pouch
around a substance,
which then closes and
pinches off from the
membrane to form a
vesicle.
The Cell
Endocytosis
Two types of endocytosis are phagocytosis and
pinocytosis.
Phagocytosis is the ingestion (taking in) of large solid
particles by cells such as bacteria, foreign debris, and
worn out cell parts.
Phagocytosis means “cell eating.”
A macrophage or a phagocyte is any large
phagocytic cell occurring in the blood, lymph, and
connective tissue of vertebrates that ingests and
destroys foreign particles, bacteria, and cell debris.
The Cell
Endocytosis
Pinocytosis
involves engulfing
extracellular fluid
into the cell, and
is a routine
activity of most
cells.
Pinocytosis is
sometimes called
“cell drinking.”
The Cell
Based on the definitions
of the two types of
endocytosis, is the
animation illustrating
phagocytosis or
pinocytosis? The
particles on the outside of
the membrane are large
solid particles.
The animation is
illustrating phagocytosis,
the ingestion of large
solid particles by cells
such as bacteria, foreign
debris, and worn out cell
parts.
Phagocytosis means
“cell eating.”
The Cell
Transport of Large Particles
Exocytosis is a type of
active transport that
involves the movement of
a substance by a vesicle
to the outside of a cell.
Exocytosis is used to
expel wastes, export
proteins, or secrete
substances such as
hormones.
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Inside Cell
Cell environment
The Cell
How Cells Move Substances Around
Because
endocytosis and
exocytosis both
require energy to
move material,
they are both
forms of active
transport.
The Cell
Transport of Large Particles
Food particles
Endocytosis
Food vacuole
Lysosomes
Digestive vacuole
Exocytosis and
elimination
The Cell
Three Forms of Transport Across the Membrane
59
The Cell
Proteins Are Critical to
Membrane Function
60
The Cell
Membrane Receptor Proteins
• Cells that do not lie next to each other
cannot communicate directly.
• These cells must release signal molecules
that carry information to nearby cells and
throughout the body.
• Hormones are specialized types of protein
molecules that act as signal molecules and
are carried through the bloodstream to
other areas, where they have their effects.
The Cell
Membrane Receptor Proteins
• Cells can receive the messages carried by
certain signal molecules because the cell
membrane contains specialized proteins
that bind these signal molecules.
• An example is a receptor protein.
• A receptor protein is a protein that binds
to a specific signal molecule, enabling the
cell to respond to the signal molecule.
The Cell
Membrane Receptor Proteins
• Most receptor proteins are embedded in the lipid
bilayer of the cell membrane.
• The part of the protein that fits the signal molecule
faces the outside of the cell.
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Membrane Receptor Proteins
• The binding of a signal molecule by its
complementary receptor protein cause a
change in the receiving cell.
• The change can occur in three ways:
• 1) by causing changes in the permeability of
the receiving cell,
• 2) by triggering the formation of second
messengers inside the cell, and
• 3) by activating enzymes inside the cell.
The Cell
Membrane Receptor Proteins
• The binding of a signal molecule to the receptor
protein can cause an ion channel to open,
allowing specific ions to cross the cell
membrane.
• The receptor protein may cause the formation of
a second messenger inside the cell that acts as a
signal molecule in the cytoplasm and amplifies
the signal of the original signal molecule.
• The receptor protein may act as an enzyme that
may function to speed up chemical reactions
inside the cell.
The Cell
Beta Blockers
• Some drugs have been created to block or
interfere with receptor proteins, thus
preventing signal molecules from binding to
the receptor proteins.
• Beta blockers are an example of a drug that
interferes with the binding of signal molecules
to the receptor proteins, preventing the heart
rate from increasing too rapidly.
• Beta blockers are a class of drug used
particularly for the management of cardiac
arrhythmias.
The Cell
Feedback Mechanisms
• The cell uses various methods to
maintain a state of equilibrium inside
and outside the cell by controlling
what enters and leaves the cell.
• Living organisms use two main
homeostatic control mechanisms to
maintain a balance within the
organism:
1. negative feedback loops and
2. positive feedback loops
The Cell
Negative Feedback Loops
• In a negative feedback loop, the
net effect of the response to the
stimulus is to shut off the original
stimulus or reduce its intensity,
and bring the situation back to
normal (homeostatic balance).
• This is similar to a home heating
system connected to a
thermostat.
The Cell
Negative Feedback Loops
• An example of a negative feedback loop
within the human body would be the
hypothalamus helping to regulate body
temperature.
• The release of gastric fluids to maintain
a consistent pH level in the stomach is
also an example of a negative feedback
loop.
• Another example of a negative feedback
loop would be the regulation of blood
glucose levels within the body.
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Positive Feedback Loops
• A positive feedback loop tends to
increase the original disturbance
(stimulus) and to push the
variable farther from its original
value, or to amplify (or increase)
the stimulus.
• Examples of these mechanisms are
much more rare in the body, such as
blood clotting and the birth of a baby.
The Cell
Positive Feedback Loops
• During blood clotting, the positive
feedback loop is initiated when injured
tissue releases signal chemicals that
activate platelets in the blood.
• An activated platelet releases chemicals
to activate more platelets, causing a rapid
cascade and the formation of a blood clot.
The Cell
Positive Feedback Loops
• Another example of a positive feedback loop
occurs during childbirth.
•
• During childbirth, when a contraction occurs,
the hormone oxytocin is released into the body,
which stimulates further contractions. This
results in contractions increasing in amplitude
and frequency to hasten childbirth.
• Most homeostatic control mechanisms are
negative feedback mechanisms.
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an example
of negative
feedback in
the human
body
The Cell