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Transport across cell membrane by Vani Gupta

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1 Transport across cell membrane by Vani Gupta

2 Types of cell membrane transport
Factors affecting transport Cell membrane Chemical gradient Electrical gradient Rate of transport Passive transport Diffusion Osmosis Facilitated diffusion Active transport Pumps phagocytosis Endocytosis/exocytosis

3 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 bipolar molecule: the fatty acid side is hydrophobic, the phosphoric side is hydrophilic

4 The membrane is impermeable to: The membrane is permeable to:
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 H2O Gases (O2, CO2, N2) Lipids Small, neutral molecules (such as urea)

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

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 -)

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

8 Factors affecting the rate 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

9 Crossing of cell membrane
fats and oils can pass directly through lipid inside cell sat waste sugar aa H2O outside cell

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

11 Cell membrane channels
Need to make “doors” through membrane protein channels allow substances in & out specific channels allow specific material in & out H2O channel, salt channel, sugar channel, etc. inside cell outside cell

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

13 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-simple diffusion- no energy needed b- facilitated diffusion- no energy needed -help through a protein channel

14 Osmosis Each compound obeys the law of diffusion
diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane However, some compounds are unable to cross the cell membrane (glucose, electrolytes…) Water can cross  will enter or exit the cell depending its concentration gradient.

15 where is osmosis important

16 Cells in Solutions

17 NO NET MOVEMENT OF H2O (equal amounts entering & leaving)
PLASMOLYSIS Isotonic Solution Hypotonic Solution Hypertonic Solution NO NET MOVEMENT OF H2O (equal amounts entering & leaving) CYTOLYSIS PLASMOLYSIS

18 Diffusion Simple diffusion- no energy needed
Movement across higher to lower concentration gradient. Facilitated 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

19 facilitated diffusion
Simple and facilitated diffusion simple diffusion facilitated diffusion lipid inside cell outside cell inside cell outside cell H2O protein channel H2O

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

21 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.

22 Movement of the Medium: currents will aid diffusion
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 CO2 and O2. 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

23 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.

24 where is facilitated transport important


26 Active Transport - Pumps - phagocytosis - Endocytosis/exocytosis

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

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

Example 2: the thyroid gland accumulates iodine as it is needed to manufacture the hormone thyroxin. The iodine concentration can be as much as 25 times more concentrated in the thyroid than in blood.

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

31 where is active transport important

32 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. Endocytosis is fallowed by exocytosis on the other side. – Transcytosis, vesicle trafficking, or cytopempsis.

33 Types of endocytosis 1. pinocytosis (cell drinking): small molecules are ingested and a vesicle is immediately formed. This is seen in small intestine cells (villi) 2. phagocytosis (cell eating): large particles, (visible with light microscope) are invaginated into the cell (ie: white blood cells ‘eat’ bacteria


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

36 Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)

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

38 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.


40 Fusion of vesicle with plasma membrane is mediated by a number of accessory proteins- SNARE protein.
Require stimulus and Ca. Exception- 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- endocrine gland, pancreatic acinar cells

41 Membrane Transport Proteins
1. Water Channels or Aquaporins (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) Aquaporins- only water. b) Aquaglyceroporins- also for small molecules.

42 2- Ion Channels- All cells specially on excitable cells – Neurons and muscle cells Selective and non selective Gated – voltage gated and extracellular agonist or antagonist gated ex – acetylcholine gated cationic specific channel at motor end plate of skeletal muscle. Conductance- 1-2 picosimens and > 100 picosimens. Ex- Na, K, Ca, Cl, Anion , cation.

43 3.Solute Carriers- > 40 types , > 300 transporters.
three gps-1. Uniporters- single molecule across the membrane (GLUT ) 2. Symporters- Two or more molecules Ex- Na-k-cl Symporter (Kidney) Na - Glucose Cotransporter. 3. Antiporters- Two or more molecules in opposite directions Ex :Na- H antiporter ( PH regulation) 3Na- Ca , Cl- HCO3

1. ATPase Ion Transporters 1. P- Type- gate phosphorylted during transport. Na- K ATP ase. 2. V- Type- Vacuolar H- ATPase – urine acidification on Vacules like endosomes and lysosomes. 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. .

45 Molecular Motors: Kinesin- over the microtubule Dynein- retrogate transport Myosin- over the microfilaments.- 18 types a

46 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 Ans- d Difficulty Index- Pre Lecture- 54 % Post Lecture- 100%

47 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. Ans- C Difficulty Index- Pre Lecture- 55 % Post Lecture- 96%

48 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 Ans- C Difficulty Index- Pre Lecture- 49 % Post Lecture- 87%

49 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 Ans- C Difficulty Index- Pre Lecture- 25 % Post Lecture- 98%

50 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 Ans- b Difficulty Index- Pre Lecture- 14 % Post Lecture- 76%

51 Q-6 which one of the following is a correct statement for Na-K ATPase
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 Ans- a Difficulty Index- Pre Lecture- 69 % Post Lecture- 99%

52 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. Ans- b Difficulty Index- Pre Lecture-12 % Post Lecture- 78%

53 Q8-you wish to design a new drug which will act as an ionophore to deliver Ca2+ 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 nm in diameter Ans- a Difficulty Index- Pre Lecture- 26 % Post Lecture- 89%

54 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 Ans- b Difficulty Index- Pre Lecture- 59 % Post Lecture- 98%

55 Q10- free fatty acids enter cell by a-passive diffusion b-active diffusion c- through carrier protein d – Active transport Ans- a Difficulty Index- Pre Lecture- 29 % Post Lecture- 88%

56 Q-11 Aquaglyceroporins transport- a. Water only
b. water and small molecules. c. Water and Glucose d. Water and salt. Ans- b Difficulty Index- Pre Lecture- 06 % Post Lecture- 78%

57 Q-12 Which of the fallowing is responsible for PH Regulation-
a. Antiporters. b. Symporters c. Uniporters. d. Co-porters. Ans- a Difficulty Index- Pre Lecture- 29 % Post Lecture- 92%

58 Q-13 V type – transporters are a. ATPase dependent. b. Symporters.
c. Carrier Proteins. d. Receptor Proteins. Ans- a Difficulty Index- Pre Lecture- 18 % Post Lecture- 76%

59 Q-14 .GLUT is an example of- a. Antiporters. b. Symporters
c. Uniporters. d. Co-porters. Ans- C Difficulty Index- Pre Lecture- 18 % Post Lecture- 89%

60 Q-15 Presence of Ion channels are must on a. Excitable tissue.
b. Non excitable tissue. c. Renal tissue d. Cardiac muscle. Ans- a Difficulty Index- Pre Lecture- 12 % Post Lecture- 84%

61 Q-16. Na- K ATPase transport Na- a. Towards Concentration gradient. b
Q-16. Na- K ATPase transport Na- a. Towards Concentration gradient. b. Against Concentration gradient. c. Towards electro chemical gradient. d. Against electrochemical gradient. Ans- C Difficulty Index- Pre Lecture- 41 % Post Lecture- 98%

62 Q-17. Rennin secretion from JG cells is an example of- a.) Exocytosis
b.) pincocytosis c.) Vacular movement. d.) Transcytosis. Ans- a Difficulty Index- Pre Lecture- 38 % Post Lecture- 94%

63 Q.- 18. PTH secretion fro parathyroid glands require-
a.) low intracellular Ca. b.) high Intracellular Ca. c.) Low intracellular K. d.) high Intracellular K. Ans- a Difficulty Index- Pre Lecture- 27 % Post Lecture- 92%

64 Q-19. Transcytosis incudes- a. Endocytosis and phagocytosis.
b. Endocytosis and pincocytosis. c. Endocytosis and exocytosis. d. Endocytosis only. Ans- C Difficulty Index- Pre Lecture- 29 % Post Lecture- 78%

65 Q-20. Transcytosis occurs at a). Epethelial Cells. b). Endocrine Cells
Q-20. Transcytosis occurs at a). Epethelial Cells. b). Endocrine Cells. c). Nerve cells. d). None of the above. Ans-a Difficulty Index= Pre Lecture % Post Lecture-74 %

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