Transcript Active Transport (con`t)

Active Transport
Section 4-2
Some substances are transported
against a concentration gradient.
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Facilitated diffusion moves sugars and amino
acids across the cell membrane DOWN their
concentration gradient.
Cells must transport certain amino acids,
sugars, and other substances into the
cytoplasm where the concentration of that
substance is higher in the cell than outside
the cell. TRANSPORTING AGAINST THE
CONCENTRATION GRADIENT
REMEMBER….
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DOWN the concentration gradient → going
from a high concentration to a low
concentration
AGAINST the concentration gradient →
going from a low concentration to a high
concentration
Active Transport
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The transport of a substance across the cell
membrane AGAINST its concentration gradient
ACTIVE TRANSPORT REQUIRES ENERGY!
Most often, the energy used is in the form of
ATP
Some active transport processes involve carrier
proteins. These proteins bind to specific
substances on one side of cell and releases it on
the other/opposite side of cell.
Active Transport (con’t)
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The difference in active transport is that
substance is moving against its concentration
gradient (low to high). In facilitated diffusion,
the substance moves down its concentration
gradient (high to low).
Carrier proteins in active transport act as
pumps that move substances against
concentration gradient. This is why they are
often called membrane pumps.
Sodium-Potassium Pump
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One of the most important membrane pumps in
animal cells.
Transports 3 sodium ions (Na+) out of the cell
and 2 potassium ions (K+) into the cell.
Sodium Ions – usually the concentration outside
of cell is higher, so it is against its concentration
gradient.
Potassium Ions – concentration is usually higher
on the inside of the cell than on the outside of the
cell.
Sodium-Potassium Pump (con’t)
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The sodium-potassium pump actively transports Na+ and
K+ against their concentration gradients through the use of
ATP.
Reason for Importance of Pump
1. prevents Na+ from accumulating in the cell. If
accumulates in the cell, can cause cell to burst.
2. helps maintain the concentration gradients of Na+ and
K+ across the cell membrane. Can be used to help
transport other substances across cell membrane.
Vesicles move substances ACROSS
membranes
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Endocytosis – movement of a substance
into a cell by a vesicle.
Exocytosis – movement of a substance by a
vesicle to the outside of a cell.
Membrane Receptor Proteins Receive
Information
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Some cells release signal molecules to carry
information to nearby cells and through the body.
(Example: Hormones)
Cells must respond to important information and
filter out unimportant information.
Receptor Proteins – protein that binds to a
specific signal molecule, enabling the cell to
respond to the signal molecule, which is located in
the cell membrane
Functions of Receptor Proteins
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When a signal molecule encounters a cell, the
signal molecule binds to the receptor protein.
Receptor protein is specialized to fit the specific
signal molecule.
Receptor proteins are embedded in the lipid
bilayer of the cell membrane, and the part of the
protein that fits the signal molecules faces the
outside of the cell.
Functions of Receptor Proteins (con’t)
The binding of a signal molecule to its matching
receptor protein causes a change in the activity of the
receiving cell. This change can occur in 3 ways.
1. By causing changes in the permeability of the
receiving cell.
2. By triggering the formation of second messengers
inside the cell.
3. By activating enzymes inside the cell.
Changes in Permeability
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Receptor protein may be coupled with an ion
channel.
Binding of a signal molecule to the receptor
protein causes the ion channel to open,
allowing specific ions to cross the cell
membrane.
Second Messengers
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Receptor protein may cause the formation of
a second messenger
When it is activated, a second messenger
acts as a signal molecule in the cytoplasm.
The second messenger amplifies the signal
of the first (messenger) signal molecule.
Second Messengers (con’t)
Second Messengers can change the
functioning of a cell in several ways
1. Some second messengers activate
enzymes, triggering a series of
biochemical reactions in the cell.
2. Other second messengers change the
permeability of the cell by opening ion
channels in the cell membrane.
Enzyme Action
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Receptor protein may act as an enzyme
When a signal molecule binds to the receptor
protein, the receptor protein speeds up chemical
reactions inside the cell.
Receptor proteins may also trigger other
enzymes inside the cell or cell membrane. This
triggers chemical reactions in the cell.
The signal molecule causes changes in the
functioning of the receiving cell.
Drugs can affect the binding of signal
molecules to a receptor protein
Heroin
1. imitates signal molecules by binding to
receptor proteins on a receiving cell
2. alters function of cell
Beta Blockers
1. Bind receptor proteins
2. prevent heart rate from increasing too
rapidly by blocking the signal molecules.
Conclusion
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Active Transport requires energy – ATP.
Carrier Proteins in Active Transport – called
membrane pumps.
Sodium-Potassium Pump – transports 3 Na+
out of cell and 2 K+ into cell
Conclusion (con’t)
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Endocytosis – brings substance into cell
Exocytosis – takes substance out of cell
Receptor Protein – binds to a specific
substance and then enables cell to respond
appropriately.
Second Messengers – amplifies the signal
from the first messenger
Homework
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Section 4-2 Review Questions
Page 86
Questions 1-5