1. Active Transport
Section 4-2

2. Some substances are transported against a concentration gradient.
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

3. REMEMBER….
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

4. Active Transport
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.

5. Active Transport (con’t)
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.

7. Sodium-Potassium Pump
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.

8. Sodium-Potassium Pump (con’t)
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.

10. Vesicles move substances ACROSS membranes
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.

12. Membrane Receptor Proteins Receive Information
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

13. Functions of Receptor Proteins
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.

14. 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.

16. Changes in Permeability
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.

17. Second Messengers
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.

18. 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.

20. Enzyme Action 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.

21. 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.

22. Conclusion 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

23. Conclusion (con’t) 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

24. Homework
Section 4-2 Review Questions
Page 86
Questions 1-5