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Ch. 7: Transport Across the Cell Membrane. Selectively permeable: property of biological membranes which allows some substances to pass more easily than.

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Presentation on theme: "Ch. 7: Transport Across the Cell Membrane. Selectively permeable: property of biological membranes which allows some substances to pass more easily than."— Presentation transcript:

1 Ch. 7: Transport Across the Cell Membrane

2 Selectively permeable: property of biological membranes which allows some substances to pass more easily than others Protein: too big to pass through Selectively Permeable Membrane Water molecule: can pass through pore Enlargement of Membrane

3 Transport proteins: membrane proteins that transport specific molecules or ions across biological membranes: –may provide hydrophilic tunnel through membrane –may bind to a substance and physically move it across the membrane –are specific for the substance they move

4 GLUCOSE Binding TransportRecovery Dissociation

5 Movement across the cell membrane can be: 1.Passive cell does not have to expend energy 2.Active energy-requiring process during which a transport protein pumps a molecule across a membrane, against its conc. gradient; is energetically “uphill”

6 Passive Transport: DIFFUSION net movement of a substance down a concentration gradient –results from KE of molecules –results from random molecular movement –continues until equilibrium is reached (molecules continue to move but there is no net directional movement)

7 Passive Transport: OSMOSIS diffusion of water across a selectively permeable membrane; water moves down its concentration gradient –continues until equil. is reached –at equil. water molecules move in both directions at same rate



10 –relationship between solute concentration and movement of water can be described as: HYPERTONIC: a solution w/a greater solute concentration than that inside a cell HYPOTONIC: a solution w/a lower solute concentration compared to that inside a cell ISOTONIC: a solution w/an equal solute concentration compared to that inside a cell

11 Osmotic Environment

12 Osmotic potential: A measure of the potential of water to move between regions of differing concentrations across a water- permeable membrane potentialwaterconcentrationsmembrane –osmotic potential of pure water = 0 –more solute = negative osmotic potential HI  LO EX: Ψ= -0.40 (sol’n) Ψ= -0.23 (cell) Water out

13 Glass tube Sugar solution Osmotic pressure

14 In cells with cell walls: in a hypertonic environment, PLASMOLYSIS occurs; cells shrivel and usually die in a hypotonic environment, water moves into cell, causing it to swell; cell becomes more TURGID.

15 Passive Transport: FACILITATED DIFFUSION diffusion of solutes across a membrane, with the help of transport proteins; passive transport because it is movement down a concentration gradient

16 ACTIVE TRANSPORT: protein pumps use energy from ATP

17 Examples of Active Transport protein “pumps”: 1.Sodium-Potassium Pump: –actively pumps Na+ ions out / K+ ions in –in every pump cycle, 3 Na+ leave and 2 K+ enter cell –Na+ and K+ are moved against their gradients (both concentration and electric potential!)


19 Membrane Potential: voltage across membrane; cell’s inside is negatively charged w/respect to outside –favors diffusion of cations into cell and anions out of cell Electrochemical Gradient: diffusion gradient resulting from the combined effects of membrane potential and conc. gradient


21 **The Na+-K+ pump maintains the membrane potential…HOW?**

22 2.Proton Pump: pumps protons (H+ ions) out of the cell, creating a proton gradient (protons are more concentrated outside the membrane than inside); –protons then diffuse back into cell –the force of the proton pushing back through the membrane is used to power the production of ATP



25 AND… 3.Cotransport / Coupled Channels: process where a single ATP-powered pump actively transports one solute and indirectly drives the transport of other solutes against their conc. gradients. –Example: plants use a proton pump coupled with sucrose-H+ transport to load sucrose into specialized cells


27 ACTIVE TRANSPORT: EXOCYTOSIS & ENDOCYTOSIS transport of large molecules (e.g. proteins and polysaccharides) across cell membrane

28 ExocytosisEndocytosis * exporting macromolecules by fusion of vesicles w/the plasma membrane * vesicle buds from ER or Golgi and migrates to plasma membrane * used by secretory cells to export products (e.g. insulin in pancreas) * importing macromolecules by forming vesicles derived from plasma membrane * vesicle forms in localized region of plasma membrane * used by cells to incorporate extracellular substances



31 Three types of Endocytosis: 1) Phagocytosis: solid particles (“cell eating”) 2) Pinocytosis: fluid droplets (“cell drinking”) 3) Receptor-Mediated Endocytosis: importing of specific macromolecules by inward budding of vesicles formed from COATED PITS

32 Phagocytosis

33 Pinocytosis

34 Receptor-Mediated Endocytosis

35 The cell in this beaker is _______ to the solution. A.Hypotonic B.Hypertonic C.Isotonic

36 What type of transport does this illustrate? A.Diffusion B.Facilitated diffusion C.Active transport D.Osmosis

37 Which of the following diagrams does NOT represent an electrochemical gradient? AB C

38 What process does this diagram represent? A.Proton pump B.Exocytosis C.Endocytosis D.Cotransport

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