Transport Across the Plasma Membrane

1. Transport Across the Plasma Membrane

2. Plasma Membrane Transport • Molecules move across the plasma membrane by: Active Transport Passive Transport

3. What are three types of passive transport? • Diffusion • Facilitated Diffusion • Osmosis Passive Transport ATP energy is not needed to move the molecules through.

4. Passive Transport 1: Diffusion • Molecules can move directly through the phospholipids of the plasma membrane This is called … DIFFUSION

5. What is Diffusion? • Diffusion is the net movement of molecules from a high concentration to a low concentration until equally distributed. • Diffusion rate is related to temperature, pressure, state of matter, size of concentration gradient, and surface area of membrane. http://www.biologycorner.com/resources/diffusion-animated.gif

6. What molecules pass through the plasma membrane by diffusion? • Gases (oxygen, carbon dioxide) • Water molecules (rate slow due to polarity) • Lipids (steroid hormones) • Lipid soluble molecules (hydrocarbons, alcohols, some vitamins) • Small noncharged molecules (NH3)

7. Why is diffusion important to cells and humans? • Cell respiration • Alveoli of lungs • Capillaries • Red Blood Cells • Medications: time-release capsules

8. Passive Transport 2: Facilitated Diffusion • Molecules can move through the plasma membrane with the aid of transport proteins This is called … FACILITATED DIFFUSION

9. What is Facilitated Diffusion? • Facilitated diffusion is the net movement of molecules from a high concentration to a low concentration with the aid of channel or carrier proteins.

10. What molecules move through the plasma membrane by facilitated diffusion? • Ions (Na+, K+, Cl-) • Sugars (Glucose) • Amino Acids • Small water soluble molecules • Water (faster rate)

11. How do molecules move through the plasma membrane by facilitated diffusion? • Channel and Carrier proteins are specific: • Channel Proteins allow ions, small solutes, and water to pass • Carrier Proteins move glucose and amino acids • Facilitated diffusion is rate limited, by the number of proteins channels/carriers present in the membrane.

12. Specific Types of Facilitated Diffusion • Counter Transport – the transport of two substances at the same time in opposite directions, without ATP. Protein carriers are called Antiports. • Co-transport – the transport of two substances at the same time in the same direction, without ATP. Protein carriers are called Symports. • Gated Channels – receptors combined with channel proteins. When a chemical messenger binds to a receptor, a gate opens to allow ions to flow through the channel.

13. Why is facilitated diffusion important to cells and humans? • Cells obtain food for cell respiration • Neurons communicate • Small intestine cells transport food to bloodstream • Muscle cells contract

14. Passive Transport 3: Osmosis • Water Molecules can move directly through the phospholipids of the plasma membrane This is called … OSMOSIS

15. What is Osmosis? • Osmosis is the diffusion of water through a semipermeable membrane. Water molecules bound to solutes cannot pass due to size, only unbound molecules. Free water molecules collide, bump into the membrane, and pass through.

16. Why is osmosis important to cells and humans? • Cells remove water produced by cell respiration. • Large intestine cells transport water to bloodstream • Kidney cells form urine

17. Osmosis and Tonicity • Tonicity refers to the total solute concentration of the solution outside the cell. • What are the three types of tonicity? • Isotonic • Hypotonic • Hypertonic

18. Isotonic • Solutions that have the same concentration of solutes as the suspended cell. • What will happen to a cell placed in an Isotonic solution? • The cell will have no net movement of water and will stay the same size. • Ex. Blood plasma has high concentration of albumin molecules to make it isotonic to tissues.

19. Hypotonic • Solutions that have a lower solute concentration than the suspended cell. • What will happen to a cell placed in a Hypotonic solution? • The cell will gain water and swell. • If the cell bursts, then we call this lysis. (Red blood cells = hemolysis) • In plant cells with rigid cell walls, this creates turgor pressure.

20. Hypertonic • Solutions that have a higher solute concentration than a suspended cell. • What will happen to a cell placed in a Hypertonic solution? • The cell will lose water and shrink. (Red blood cells = crenation) • In plant cells, the central vacuole will shrink and the plasma membrane will pull away from the cell wall causing the cytoplasm to shrink called plasmolysis.

21. Review: Passive Transport • Diffusion – O2 moves in and CO2 moves out during cell respiration • Facilitated Diffusion – glucose and amino acids enter cell for cell respiration • Osmosis – cell removal or addition of water

22. Review Tonicity • What will happen to a red blood cell in a hypertonic solution? • What will happen to a red blood cell in an isotonic solution? • What will happen to a red blood cell in a hypotonic solution?

23. What are three types of Active transport? 1) Active Transport 2) Exocytosis 3) Endocytosis • Phagocytosis • Pinocytosis • Receptor-Mediated endocytosis Active Transport ATP energy is required to move the molecules through.

24. Active Transport • Molecules move from areas of low concentration to areas of high concentration with the aid of ATP energy. • Requires protein carriers called Pumps.

25. The Importance of Active Transport • Bring in essential molecules: ions, amino acids, glucose, nucleotides • Rid cell of unwanted molecules (Ex. sodium from urine in kidneys) • Maintain internal conditions different from the environment • Regulate the volume of cells by controlling osmotic potential • Control cellular pH • Re-establish concentration gradients to run facilitated diffusion. (Ex. Sodium-Potassium pump and Proton pumps)

26. The Sodium-Potassium Pump • 3 Sodium ions move out of the cell and then 2 Potassium ions move into the cell. • Driven by the splitting of ATP to provide energy and conformational change to proteins by adding and then taking away a phosphate group. • Used to establish an electrochemical gradient across neuron cell membranes. http://www.biologie.uni-hamburg.de/b-online/library/biology107/bi107vc/fa99/terry/images/ATPpumA.gif

27. Active Transport 2: Exocytosis • Movement of large molecules bound in vesicles out of the cell with the aid of ATP energy. Vesicle fuses with the plasma membrane to eject macromolecules. • Ex. Proteins, polysaccharides, polynucleotides, whole cells, hormones, mucus, neurotransmitters, waste

28. Active Transport 3: Endocytosis • Movement of large molecules into the cell by engulfing them in vesicles, using ATP energy. • Three types of Endocytosis: • Phagocytosis • Pinocytosis • Receptor-mediated endocytosis

29. Phagocytosis • “Cellular Eating” – engulfing large molecules, whole cells, bacteria • Ex. Macrophages ingesting bacteria or worn out red blood cells. • Ex. Unicellular organisms engulfing food particles.

30. Pinocytosis • “Cellular Drinking” – engulfing liquids and small molecules dissolved in liquids; unspecific what enters. • Ex. Intestinal cells, Kidney cells, Plant root cells