Biology 4.2 Active Transport

1. Biology 4.2 Active Transport Active Transport in Cells

2. Biology 4.2 Active Transport Low concentration Movement Against a Concentration Gradient • A concentration gradientis the difference in the amount of diffusion of a substance between two areas: an area of low concentration and an area of high concentration. • Look at the illustration at right. • The top part has no red in it (0% diffusion). • The very bottom has all red (100% diffusion). • In between we have a gradient as the amount of red diffuses from 100% to 0%. gradient High concentration

3. Biology 4.2 Active Transport Low concentration red Movement Against a Concentration Gradient • One area may have a high concentration of a solution. • Another area may have a low concentration of the same solution. • The diffusion across the area where the two connect is the concentration gradient Gradient High concentration red

4. Biology 4.2 Active Transport • Sometimes the concentration of a substance • outside a cell moves through the cell’s membrane • from an area of high concentration of the substance • toward an area of lower concentration. • This is called movement across a concentration gradient. Yellow dye diffuses into water

5. Active Transport • In passive transport, no energy is required to move substances across a concentration gradient. • Substances are also moved across cell membranes by a system called active transport. • Active transport requires energy.

6. Active Transport • Passive transport is like swimming downstream with a current pushing you. • No energy is needed. • Active transport is like swimming upstream against a current. • You use energy to go against the current.

7. Active Transport • Active transport allows substances to move • from an area of low concentration • to an area of high concentration, • against the concentration gradient.

8. Active Transport low • Unlike passive transport, active transport requires the cell to use energy because the substance is being moved against it’s concentration gradient. • Most often, the energy needed for active transport is supplied by ATP. high

9. Active Transport • Some active processes involve carrier proteins. • Carrier proteins used in active transport • bind to specific substances on one side of the cell membrane • and release them on the other side of the cell membrane. • Think of a carrier protein as a small motor boat with an engine that carries you up the river “against the current” using it’s energy to move you.

10. Active Transport • But in active transport, substances bind to carrier proteinswhere they are low in concentration and are released where they are high in concentration. • Carrier proteins in active transport function as “pumps” that move substances across the cell membrane against their concentration gradient.

11. Sodium-Potassium Pump • One of the most important membrane pumps in animal cells is a carrier protein called the sodium-potassium pump. • The energy needed to power sodium-potassium pumps is supplied by ATP. • The sodium-potassium pump transports • three sodium ions out of a cell • and two potassium ions into the cell. • Thus, both sodium ions and potassium ions move against their concentration gradients.

12. Movement in Vesicles Vesicle forms around substance • Many substances, such as proteins and polysaccharides, are too large to be transported by carrier proteins. • In these cases, vesicles move these substances into cells through the membrane. Vesicle pulls substance through membrane

13. Movement in Vesicles Vesicle forms around substance • The movement of a substance into a cellby a vesicle is called endocytosis. • During endocytosis, the cell membrane forms a pouch around a substance. • The pouch than closes up and pinches off from the membrane to form a vesicle inside the cell. Vesicle pulls substance through membrane Into the cell

14. Movement in Vesicles • The movement of a substance by a vesicle to the outside of a cell is called exocytosis. • During exocytosis, vesicles in the cell fuse with the cell membrane, releasing their contents.

15. Membrane Receptor Proteins • The cells of your body must communicate with each other. • Some cells release signal molecules that carry information to nearby cells and throughout the body. • Hormones are one familiar example of signal molecules. • Cells can receive the messages carried by certain signal molecules because the cell membrane contains specialized proteins that bind to these signal proteins. • These proteins are called receptor proteins.

16. Membrane Receptor Proteins • A receptor proteinis a protein that binds to a specific signal molecule, enabling the cell to respond to the signal molecule. • For example, the muscles of a person exercising could not contract without receptor proteins and signal molecules that tell the muscles when to contract and when to relax.

17. Functions of Receptor Proteins • A signal molecule is bound by a receptor protein that fits that molecule. • Within the lipid bilayer, the part of the receptor protein that fits the signal molecule faces the outside of the cell. • The receiving and binding of a signal molecule triggers a change in the receiving cell.

18. Functions of Receptor Proteins • This change in the cell can happen in three ways: • By causing changes in the permeability of the receiving cells. (what can move in/out) • By triggering the formation of second messengers inside the cell. (passing on the message) • By activating enzymes inside the cell. (trigger a response inside the cell)

19. Changes in Permeability • The receptor protein may be coupled with an ion channel. • The binding of a signal molecule to the receptor protein causes the ion channel to open. • This type of receptor protein is very important to the nervous system.

20. Second Messengers • The receptor proteins may also cause the formation of a second messenger inside the cell. • 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, passing the signal along.

21. Second Messengers • Some second messengers activate enzymes, triggering changes in the cell. • Others change how or what the cell allows in by opening ion channels in the cell’s membrane. • The diagram at right shows a signal molecule triggering an ion channel to open. • Once opened, ions flood in attracted by ions of the opposite charge.

22. Enzyme Action • The receptor protein may act as an enzyme. • This means that when a signal molecule binds to the receptor protein, the receptor protein may speed up chemical reactions within the cell. • Receptor proteins may also activate other enzymes within the cell or in the cell membrane, triggering chemical reactions within the cell.

23. 4.2 Review: Major Concepts • Active Transport is the movement of a substance against the concentration gradient of the substance. • Active transport requires cells to use energy. • In animal cells, the sodium-potassium pump uses energy supplied by ATP to transport sodium ions out of the cell and potassium ions into the cell simultaneously.

24. 4.2 Review: Major Concepts • During endocytosis, substances are moved into the cell by a vesicle that pinches off from a cell membrane. • During exocytosis, substances move out of a cell as materials inside a vesicle are released from a cell as the vesicles fuse with the cell membrane.

25. 4.2 Review: Major Concepts • Communication between cells often involves signal molecules that are bound to receptor proteins on cells. • Asignal molecule that is bound by a receptor protein on a cell can change the activity of the cell in three ways: • by enabling specific ions to cross the cell membrane, • by causing the formation of a second messenger, • or by speeding up the chemical reactions of a cell