Transport Across Cell Membrane, by Dr. Baqir Naqvi.pptx

Transport Across Cell Membrane

1. DAKSON Institute of Health Sciences, Islamabad Lecture by Dr. Syed Baqir Raza Naqvi BSc. (English), Pharm-D , M. Phil (Pharmacology) Subject – Physiology Topic – Transport Across Cell Membrane 1

2. TOPICS OF DISCUSSION A. Factors affecting transport Cell membrane Chemical gradient Electrical gradient Rate of transport B. Passive transport Diffusion Osmosis Facilitated diffusion C. Active transport Pumps phagocytosis Endocytosis/exocytosis 2

3. A. Factors affecting transport: cell membrane The cell needs to absorb and excrete various compounds throughout its life. These compounds need to pass through the membrane which is made from a phospholipid bilayer. The phospholipid bilayer is formed by phospholipid molecules. B ipolar molecule: the fatty acid side is hydrophobic, the phosphoric side is hydrophilic. 3

4. The membrane is permeable to : The membrane is impermeable to: H2O Gases (O2, CO2, N2) Lipids Small, neutral molecules (such as urea) Small, charged molecules “large molecules” such as amino acids, glucose and larger These compounds must go through channels present in the membrane in order to enter or exit the cell 4

5. Factors affecting transport: Chemical gradient Compound moves from an area of high concentration to low concentration (or concentration gradient) All compounds permeable to the phospholipid bilayer will move this way. 5

6. Factors affecting transport: Electrical force Positive ions are attracted to negative ions and vice versa. Ions are repelled by ions of the same charge (+ against + and – against -). 6

7. Movement across the cell membrane Both chemical and electrical forces (electrochemical force) drive the movement of compounds across the cell membrane. 7

8. Factors affecting the R ate of Transport The rate of transport will depend on: The concentration gradient The compound permeability to the membrane The type and number of charges present on the compound 8

9. Crossing the cell membrane fats and oils can pass directly through inside cell outside cell waste lipid Fats sugar A.A H 2 O 9

10. Types of Transport Proteins Channel proteins are embedded in the cell membrane & have a pore for materials to cross. Carrier proteins can change shape to move material from one side of the membrane to the other. 10

11. Cell membrane channels Need to make “doors” through membrane protein channels allow substances in & out specific channels allow specific materials in & out H 2 O channel, salt channel, sugar channel, etc. inside cell outside cell 11

12. Protein channels Proteins act as doors in the membrane. channels to move specific molecules through cell membrane. HIGH LOW 12

13. 13 ( A) Passive transport

14. Passive transport Compounds will move from area of high concentration toward area of lower concentration No ATP is needed for this type of transport Passive transport mainly TWO types A- Osmosis B- Diffusion -diffusion again two types; a- S imple diffusion- no energy needed b- F acilitated diffusion- no energy needed -help through a protein channel 14

15. 1. Osmosis Each compound obeys the law of diffusion. diffusion of water from HIGH concentration of water to LOW concentration of water a cross a semi-permeable membrane. However, some compounds are unable to cross the cell membrane (glucose, electrolytes …). 15

16. where is osmosis important 16

17. Cells in Solutions 17

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19. PLASMOLYSIS Isotonic Solution NO NET MOVEMENT OF H 2 O (equal amounts entering & leaving) Hypotonic Solution CYTOLYSIS (Cell Burst) Hypertonic Solution PLASMOLYSIS (Cell Shrink) 19

20. 2. Diffusion Simple diffusion - no energy needed. Movement across higher to lower concentration gradient. F acilitated diffusion- Some compounds are unable to diffuse through the membrane. They will be allow to cross if the membrane has proteins that can bind these compounds and enable to cross toward the area of lower concentration. 20

21. Simple and facilitated diffusion inside cell outside cell lipid inside cell outside cell A.A simple diffusion facilitated diffusion A.A protein channel 21

22. i . Simple Diffusion Doesn’t require energy. Moves high to low concentration. Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out. 22

23. Factors Affecting Simple Diffusion The rate of diffusion will be increased when there is : Concentration : the difference in between two areas (the gradient) causes diffusion. The greater the difference in concentration, the faster the diffusion . Molecular size : smaller substances diffuse more quickly. Large molecules (such as starches and proteins) simply cannot diffuse through. Shape of Ion/Molecule : a substance’s shape may prevent it from diffusing rapidly, where others may have a shape that aids their diffusion . Viscosity of the Medium : the lower the viscosity, the more slowly molecules can move through it. 23

24. Movement of the Medium : currents will aid diffusion. Like the wind in air, cytoplasmic steaming (constant movement of the cytoplasm) will aid diffusion in the cell . Solubility: lipid - soluble molecules will dissolve through the phospholipid bilayer easily, as will gases like CO 2 and O 2 . Polarity : water will diffuse, but because of its polarity, it will not pass through the non-polar phospholipids. Instead, water passes though specialized protein ion channels 24

25. ii. Facilitated diffusion Doesn’t require energy. Uses transport proteins to move high to low concentration. Examples: Glucose or amino acids moving from blood into a cell. 25

26. where is facilitated transport important 26

27. 27

28. 28 ( B ) Active Transport

29. 29 Active Transport - Pumps - phagocytosis - Endocytosis/exocytosis

30. Active transport ATP (energy) is needed  pump Moves materials from LOW to HIGH concentration AGAINST concentration gradient . 30

31. 1. ATPase pumps Example-1 The most common: Na/K pumps reestablish membrane potential. Present in all cells. Two K + ions are exchanged with 3 Na + ions 31

32. EXAMPLES OF ACTIVE TRANSPORT Through ATPase Pumps Example 2 T he thyroid gland accumulates iodine as it is needed to synthesize the hormone thyroxin . The iodine concentration can be as much as 25 times more concentrated in the thyroid than in blood. 32

33. Example 3 : In order to make ATP in the mitochondria , a proton pump (hydrogen ion) is required. 33

34. where is active transport important 34

35. Endocytosis Endocytosis : (“Endo” means “in” ). Endocytosis is the taking in of molecules or particles by invagination of the cell membrane forming a vesicle. Integrity of plasma membrane is maintained. This requires energy. 35

36. Types of endocytosis 36 1. Pinocytosis (cell drinking ): Small molecules are ingested and a vesicle is immediately formed. Example: This is seen in small intestine cells (villi). There are two Types of endocytosis

37. 37 2 . Phagocytosis (cell eating): L arge particles, (visible with light microscope) are invaginated into the cell. Example: white blood cells ‘eat’ bacteria). Types of endocytosis

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39. Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles. Called “Cell Eating 39

40. Capture of a Yeast Cell (Greenish) by Membrane Extensions of an Immune System Cell (blue) 40

41. Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize & take in hormones , cholesterol, etc. 41

42. Exocytosis Exocytosis : (“ Exo ” means “out” .) Exocytosis is the reverse of endocytosis. This is where a cell releases the contents of a vesicle outside of the cell. These contents may be wastes, proteins, hormones , or some other product for secretion. This also requires energy. Example: vesicles from the Golgi fuse with the plasma membrane and the proteins are released outside of the cell. 42

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44. Fusion of vesicle with plasma membrane is mediated by a number of accessory proteins- SNARE protein. They Require stimulus and increased intracellular Ca . Exceptions- Renin from JG cells and PTH from parathyroid gland by decrease in intracellular Ca . Constitutive Secretion- Immunoglobulin from plasma Cells and collagen from fibroblast. Regulated by- endocrine gland, pancreatic acinar cells. 44 This figure provides a simple overview of the interaction of SNARE proteins with vesicles during exocytosis . It Shows SNARE complex assembly, zippering, and disassembly. Process of Exocytosis

45. Membrane Transport Proteins 1. Water Channels or Aquaporin's (AQPs) – 12 types Amount of water is regulated by No. of AQPs They are known as gated channel although they are pores. Two types a ) Aquaporin's- only for water. b ) Aqua- glyceroporins - also for small molecules. 45

46. 2- Ion Channels- All cells specially on excitable cells – Neurons and muscle cells, They may be Selective and non selective. Gated – voltage gated and extracellular agonist or antagonist gated, for example – acetylcholine gated cationic specific channel at motor end plate of skeletal muscle. Conductance- 1-2 picosimens and > 100 picosimens . Examples;- Na, K, Ca , Cl , Anion , cation . 46

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48. 3 . Solute Carriers- > 40 types , > 300 transporters. three groups- 1 . Uniporters- single molecule across the membrane (GLUT ) 2 . Symporters- Two or more molecules. For Example- Na-k-cl Symporter (Kidney) Na - Glucose Co-transporter. 3 . Antiporters- Two or more molecules but in opposite directions. For Example: Na-H anti porter ( pH regulation) Na- Ca , Cl - HCO3 48

49. 4.ATP DEPENDENT TRANSPORTERS 1. ATPase Ion Transporters 1 . P- Type- gate phosphorylted during transport . e..g ; Na- K ATP ase . 2 . V- Type- Vacuolar H- ATPase – For urine acidification on Vacules like endosomes and lysosomes . 49

50. 50 2. ATP – binding cassette (ABC) transporters – 7 subgroups transport diverse group of ions ex- Cl , Cholesterol, bile acids, drugs, iron and organic anions. EX :- Cystic fibrosis transmembrane regulator. Multidrug Resistance Protein, organic Anions. https:// www.sciencedirect.com/science/article/abs/pii/S1087184521000347#preview-section-snippets

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52. 52 Practice MCQ’s 

53. Q-1 all membrane processes, such as pumping and channelling of molecules are carried out by. a-lipid b-carbohydrate c-nucleic acid d-protein 53

54. 54 Q-3 Diffusion across the plasma membrane is more rapid if a substance is a-a protein b-hydrophilic c-high in its oil : water partition coefficient d-larger and globular in shape

55. 55 Q-2 Which of the following statement about membrane transport protein is incorrect a-carrier proteins are similar to enzymes in that they show saturation b-carrier protein can facilitate both active and passive transport c-channel protein can facilitate both active and passive transport d-the Na + /Glucose transport protein carries out secondary active transport.

56. 56 Q-4 the difference between simple diffusion and facilitated transport is that facilitated transport. a-is concentration dependent b-occurs across plasma membrane c-require membrane protein d-utilize a substance moving with its concentration gradient

57. 57 Q-5 Erythrocyte glucose transporter specifically transports glucose down its concentration gradient and exhibit hyperbolic saturation kinetics .This is an example of a-active mediated transport b-passive mediated transport c-non- mediated transport d-group translocation

58. 58 Q-6 which one of the following is a correct statement for Na-K ATPase. a-it gives out 3 Na-ions and takes in 2 K-ions b- it gives out 2 Na-ions and takes in 3 K-ions c- it gives out 3 Ca-ions and takes in 2 K-ions d-it gives out 3 Na-ions and takes in 2 Ca-ions

59. 59 Q7-which of the following effects of the steroid digitalis is observed after treatment of congestive heart failure. a-decrease in cytosolic sodium levels b-inhibition of Na-K ATPase c-decrease in the force of heart muscle contraction d-stimulation of the plasma membrane ion pump.

60. 60 Q8-you wish to design a new drug which will act as an ionophore to deliver Ca 2+ across the nerve cell membrane .This drug would most likely be a-hydrophobic on the outside and hydrophilic on inside b-insoluble in lipid c-soluble in proteins d-smaller than 0.001 nm in diameter

61. 61 Q9- the process by which a cell secretes macro-molecule by fusing a vesicle to the plasma membrane is called a-endocytosis b-exocytosis c-pinocytosis d-phagocytosis

62. 62 Q10- free fatty acids enter cell by a-passive diffusion b-active diffusion c- through carrier protein d – Active transport

63. 63 Q-11 Aquaporins transport- a. Water only b. water and small molecules. c. Water and Glucose d. Water and salt.

64. 64 Q-12 Which of the fallowing is responsible for PH Regulation- a. Antiporters. b. Symporters c. Uniporters. d. Co-porters.

65. 65 Q-13 V type – transporters are a. ATPase dependent. b. Symporters. c. Carrier Proteins. d. Receptor Proteins.

66. 66 Q-14 .GLUT is an example of- a. Antiporters. b. Symporters c. Uniporters. d. Co-porters.

67. 67 Q-15 Presence of Ion channels are must on a. Excitable tissue. b. Non excitable tissue. c. Renal tissue d. Cardiac muscle.

68. 68 Q-16 Na- K ATPase transport Na- a. Towards Concentration gradient. b. Against Concentration gradient. c. Towards electro chemical gradient. d. Against electrochemical gradient.

69. 69 Q-17. Rennin secretion from JG cells is an example of- a.) Exocytosis b.) pincocytosis c.) Vacular movement. d.) Transcytosis.

70. 70 Q.- 18. PTH secretion fro parathyroid glands require- a.) low intracellular Ca. b.) high Intracellular Ca. c.) Low intracellular K. d.) high Intracellular K.

71. 71 Q-19. Transcytosis incudes- a. Endocytosis and phagocytosis. b. Endocytosis and pincocytosis. c. Endocytosis and exocytosis. d. Endocytosis only.

72. 72 Q-20. Transcytosis occurs at a). Epethelial Cells. b). Endocrine Cells. c). Nerve cells. d). None of the above.

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