Transport Across Cell Membranes

1. Transport Across Cell Membranes

2. CELL MEMBRANES I. Cell membranes A. Function – barrier that separates inside of cell from the external environment B. Cell membranes made mainly of: 1. Phospholipids – form bilayer a. Hydrophilic heads b. Hydrophobic fatty acid tails 2. Proteins a. Some have sugar groups bound to them – glycoproteins 3. Cholesterol (animal cells only) C. Consistency similar to olive oil

3. MEMBRANE STRUCTURE

4. Membrane Permeability D. Permeability - what is allowed to cross a barrier 1. Impermeable – nothing gets through 2. Permeable – anything gets through 3. Cell membranes are semipermeable - a. Some molecules cross freely b. Some must be transported across

5. Membrane Permeability

6. Membrane Permeability a. Molecules that pass freely: 1. Small uncharged molecules like glycerol, ethanol 2. Small hydrophobic molecules like oxygen, carbon dioxide b. Molecules that must be transported: • Water • Macromolecules (proteins, sugars, etc..) too large 3. Ions like H+, Na+, Cl-, Ca++

7. MEMBRANES • For cells to survive they must be able transport materials (water, oxygen, food, waste products, ions) into and out of the cells. II. Transport mechanisms used by cells include (handout): A. Passive mechanisms (require no energy expenditure) 1. Diffusion 2. Osmosis 3. Facilitated diffusion B. Active transport (requires energy output) 1. Active transport 2. Endocytosis and exocytosis

8. Diffusion A. Passive mechanisms – fueled by concentration gradient - Difference in concentration across a given space

9. Diffusion 1. Diffusion - movement of a substance from a place of higher concentration to a place of lower concentration a. Remember, all molecules in constant, random motion unless at absolute zero b. If concentration gradient exists, there will be net movement of substance in greater concentration until equilibrium (equal concentration ) is reached.

10. Diffusion • Animation http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ce/m3/s2/index.htm

11. Diffusion c. Example – American pioneers d. Rate of diffusion is related to kinetic energy and the size of the gradient 1) Increased kinetic energy… 2) Large concentration gradient… e. Demonstration

12. Diffusion f. Diffusion is one way materials are moved in and out of cells. - Cytoplasm is mostly water containing dissolved solutes (salts)

13. Diffusion Gas exchange in the lungs: 1) Oxygen follows its concentration gradient into the capillary 2) Carbon dioxide (waste) follows its concentration gradient into the lung, is exhaled

14. Diffusion g. Diffusion works very well over short distances 1) As size of cell increases, volume increases faster than surface area 2) Cells remain relatively small because center of large cells would not get adequate gas exchange, would die. 3) Multicellular organisms made up of many small cells because they can be efficiently supplied by circulatory system, even if deep inside organism.

15. Osmosis 2. Osmosis - diffusion (movement) of water (only) across a semipermeable membrane a. Water moves along its concentration gradient from an area of high water concentration (less solute) to an area of lower water concentration (more solute)

16. Potato demonstration

17. Osmosis • Animation: http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ce/m3/s3/index.htm b. Can generate significant osmotic pressure -Turgor pressure in plants

18. Osmosis c. 3 possibilities for direction of water movement in living cells: 1) Hypotonic environment: greater concentration of water outside the cell than inside. Water enters, cell swells. a) Animal cell bursts (lysis, rupture) b) Plant cell – water pushes against cell wall, creating turgor pressure. - Helps plants stand up against gravity - Cell wall protects from bursting

19. Osmosis 2) Hypertonic environment: greater concentration of water inside cell. Water moves out, cell shrinks a) Animal cell – shrivels up (crenation) b) Plant cell – plasmolysis (low turgor pressure). Cell membrane draws away from cell wall, plant wilts.

20. Osmosis 3) Isotonic:solute and water concentration is the same inside and outside cell a) At equilibrium, molecules continue to move across membranes evenly (but there is no net movement) b) Cell size and volume do not change

21. Osmosis http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ce/m3/s3/index.htm

23. Osmosis 4) How do organisms that live in water deal with osmosis? a) Freshwater animals…? b) Marine (saltwater) organisms…? c) Plants…?

24. FACILITATED DIFFUSION 3. Facilitated diffusion - passive transport of specific substances down their concentration gradient by a carrier protein a. Examples: water, glucose

25. ACTIVE TRANSPORT B. Active transport - uses energy (ATP) and a membrane protein to move materials against their concentration gradient from an area of lower to higher concentration 1. Used to move ions (Na+, Ca++, Cl-, K+), amino acids, nucleotides across the cell membrane

26. Active Transport • Animation - http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ce/m3/s5/index.htm

27. Membrane-Assisted Transport C. Membrane-assisted transport uses energy to move large, complex molecules across the cell membrane 1. Large molecules like proteins, food, or fluid droplets are packaged in vesicles, then sent into or out of the cell 2. Exocytosis – large products removed from cell a) Vesicle from inside cell fuses with cell membrane to secrete its contents b) Examples: insulin, mucus

28. Membrane-Assisted Transport 3. Endocytosis moves large particles into a cell a) Phagocytosis – particles 1) Cell membrane extends out, surrounds the material & pinches off inside the cell making a vesicle2) Used by amoeba to feed & white blood cells to kill bacteria b) Pinocytosis - Cell membrane surrounds fluid droplets

29. Membrane-Assisted Transport Animation -http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ce/m3/s6/index.htm

30. Transport review

31. Membrane Transport III. Real world examples: A. Fresh produce B. Wrinkled fingers and toes when swimming C. Lungs D. Destruction of bacteria, viruses by immune system

32. Membrane Transport

33. Membrane Transport E. Cystic fibrosis – remember symptoms? Cause? a. Genetic mutation changes membrane protein controlling Cl- ion exchange b. Cl- ions retained in cell, along with water

34. Membrane Transport c. Mucus too thick, clogs lungs (infections), pancreas (trouble with digestion, poor growth), usually fatal by 20-40 years old d. Treatment – antibiotics, physical therapy (vest), diet, enzymes, transplants

35. Membrane-assisted transport activity

36. Homeostasis • Homeostasis - maintaining a stable internal environment even when external conditions change • Homes – furnace, a/c • Cells – membrane transport • Organisms – have systems that help maintain relatively constant conditions inside the organism • Examples?

37. Homeostasis • Temperature (sweat when hot, shiver when cold) • pH (buffers) • Nutrients (maintain level blood sugar) • Blood pressure • O2/CO2 levels (gas exchange, respiratory system) • Concentration of waste products (urinary system)

38. Homeostasis • Maintaining homeostasis is critical to survival of organisms! • Look at 2 organ systems used by body to maintain homeostasis • Respiratory system (gas exchange) • Excretory system (waste removal)

39. Respiration I. Introduction A. All organisms need constant supply of energy for… B. Energy from food released through cellular respiration (in the form of ???) 1. Requires O2 2. Generates CO2. C. Organisms need a steady supply of O2 and a way to get rid of CO2. This is called respiration = breathing = gas exchange

40. Respiration II. Water-dwelling organisms A. Breathing (movement of O2 and CO2) happens by diffusion across a membrane B. Some O2 dissolved in water, but concentration low (<1%), so organisms need very efficient breathing mechanism - Large surface area to volume ratio required for efficient diffusion of O2

41. Respiration C. Gills have very large surface area 1. Made of fine, threadlike filaments 2. Allow high rate of water flow and close contact between water and gill surface

42. Respiration 3. Constant flow of water over gills + huge surface area allows O2 to diffuse into extensive blood supply, while CO2 diffuses out along concentration gradients. 4. Blood then flows via circulatory system to all cells in organism

43. Respiration II. Land (terrestrial) organisms A. Differences/challenges 1. Air has 25-50 times higher O2 concentration than water 2. But gases (O2 and CO2) must be dissolved in water for diffusion to occur 3. Therefore, gas exchange can occur only on moist surfaces 4. Land organisms must battle water loss by evaporation from moist respiratory surfaces.

44. Respiration B. Human respiratory system 1. To minimize water loss, many land animals internalize respiratory surface (lungs) - Found in thoracic cavity with heart - Air is filtered, warmed and humidified before entering lungs

45. Respiration • www.youtube.com/watch?v=DoSTehS7iq8

46. Respiration 2. Structures and functions a. Trachea (windpipe) – tube reinforced with cartilage that carries air from pharynx to bronchi. b. Bronchi – branching tubes that carry air into (and out of) the lungs

47. Respiration c. Alveoli (folds or pockets) that maximize respiratory surface area (thus diffusion) - Each lung has hundreds of million alveoli - Total surface area of all alveoli in 1 person’s lungs would cover a tennis court! - Respiratory surfaces very thin with many capillaries to maximize diffusion of O2 and CO2

48. Respiration d. Diaphragm contracts, rib cage expands to create larger volume and thus negative pressure in thoracic cavity. Air rushes in to fill space. As muscles relax, exhalation occurs.

49. Respiration 3. Respiratory system disorder – asthma a. Airway walls become irritated, swollen and very sensitive b. Exposure to triggers (allergens, smoke, perfume, exercise or illness) causes airways to react and become narrower. c. Lungs get less air, causing wheezing, coughing, chest tightness and difficulty breathing

50. Respiration d. Treatments (often inhaled medicines) - Fast acting medicines that dilate the airways - Longer acting medicines like steroids to stabilize airways, make them less reactive