Transport Across the Plasma Membrane: Diffusion, Osmosis, and Active Transport

Transport Across the Plasma Membrane

Transport Across the Plasma Membrane Passive transport Active transport ATP Diffusion Facilitated diffusion Diffusion, Osmosis, Facilitated Transport, Active Transport, Exocytosis, EndocytosisCell Permeability Permeability refers to whether or not a membrane will allow molecules across.

• Permeable - the membrane allows a substance to cross through.
• Impermeable - the membrane does NOT allow a substance across.

Cell membranes are Differentially (Selectively) Permeable in that they will allow some substances to cross, whereas other substances will not be allowed through.

Diffusion

Movement of Solute Particles

2Diffusion 3Diffusion . The movement of solute particles from an area of higher solute concentration to an area of lower solute concentration.

• Molecules diffuse "down" or "with" their concentration gradients.
• Diffusion stops once a dynamic equilibrium is reached.

4· Diffusion is a passive process (no energy is required). Examples:

• Small lipid-soluble molecules
• oxygen and carbon dioxide gases
• water

5The molecules spread out until they are evenly distributed

61 Lump of sugar 2 3 Sugar molecule A lump of sugar is dropped into a beaker of water. Sugar molecules begin to break off from the lump. More and more sugar molecules move away and randomly bounce around. 4 Eventually, all of the sugar molecules become evenly distributed throughout the water.

7WHAT IS DIFFUSION?

Factors Affecting Diffusion Rate

Size and Shape of Solute Molecules

8Factors that affect the RATE of Diffusion

91. Size and Shape of the solute molecules Smaller molecules diffuse quicker!

Solubility of Solute Molecules

102. Solubility of the solute molecules in the solvent . This means how easily the solute (ex. sugar) will dissolve into the solvent (ex. water). · When a substance readily dissolves in the environment (either inside or outside of the cell), it will diffuse faster. · greater solubility = faster diffusion Solute Solvent Solution

Temperature and Diffusion

113. Temperature hotter temperature = faster diffusion 500 PYRE

Permeability of Cell Membrane

124. Permeability of the cell membrane to the solute molecules . The more permeable the cell membrane the faster the rate of diffusion.

Concentration Gradient

135. Concentration Gradient between two regions . The greater the concentration gradient = the faster the diffusion of solute molecules down the gradient · A greater concentration gradient means that the solute concentration on either side of the membrane is very different (high on one side and low on the other side)

14Concentration Gradient . The difference in concentration of molecules across a space Think of concentration gradient like a hill: The steeper the hill, the faster you move down it on your skateboard! Low High Concentration Concentration

Osmosis

Water Movement

15Osmosis

16· Osmosis is the diffusion of WATER. · Water moves from a higher "water concentration" toward a lower "water concentration". · A higher "water" concentration means a lower concentration of dissolved solutes. . Therefore, water moves TOWARD the area with the higher "solute" concentration!

17Concentrated sugar solution (Water less concentrated) O 0 O O O O O O O 0 O o O O O O Selectively permeable membrane Dilute sugar solution (Water more concentrated) O O O O Sugar molecules O Movement of water

Osmotic Pressure

18 OOsmotic Pressure is the force that causes water to move into an area. The higher the solute concentration of an area, the higher the osmotic pressure that is exerted, and the greater the tendency for water to move into that area by osmosis. The membrane allows water molecules to diffuse through Water molecules The solute cannot pass through the membrane Water molecules are attracted to the solute Osmosis across a cell membrane

Tonicity of Solutions

Isotonic Solutions

19Tonicity of Solutions

20Isotonic Solutions · have the SAME solute concentration. · A cell placed in an isotonic solution will gain and lose the same amount of water, so there will be NO NET change. Solution is Isotonic . 10% Salt Water goes in both directions 10 % Salt . Water Molecules Isotonic Amount of water transported into the cell equal to the amount of water transported out from the cell O H2O 2 H2O O Solute concentration inside the cell is Equal to the solution outside the cell Flaccid

Hypertonic Solution

21Hypertonic Solution · Has a GREATER solute concentration. · A cell placed in a hypertonic solution will LOSE water to the more concentrated solution. . The shrunken cell is said to be crenated in an animal cell and plasmolyzed in a plant cell. Solution is Hypertonic 20% Salt Water moves out of the cell 10 % Salt . Water Molecules Hypertonic Water is transported out from the cell Solute concentration inside the cell is LOWER Plasmolyzed

Hypotonic Solutions

22Hypotonic Solutions · Have a LOWER solute concentration. · A cell placed in a hypotonic solution will GAIN water because the cell has a higher solute concentration and exerts a greater osmotic pressure than the solution. . The cell will swell, plant cells become turgid, and animal cells may burst (lysis). Solution is Hypotonic 10 % Salt Water moves into the cell 20% Salt Water Molecules Hypotonic Vacuole Water is transported into the cell HO H,O 2 O Solute concentration inside the cell is HIGHER Turgid

Tonicity Comparison

23Remember Tonicity words are comparison words and can't be used alone. - If the cell is hypertonic, then the solution that surrounds the cell must be hypotonic. - If the cell is hypotonic, then the solution that surrounds the cell must be hypertonic. and so on ...

24https://llunadeneu.wordpress.com/2017/10/03/water-and-mineral-salts/ Isotonic solution (normal) Hypotonic solution (dilute) Hypertonic solution (concentrated) O C 0 O O C O O O O Solute C C O O o 0 A Normal red blood cell B Swollen red blood cell C Shrunken (crenated) red blood cell - Direction of osmotic water movement

25 WaterSemipermeable MeMbraNe Osmosis With the Amoeba Sisters

26ATT N

Facilitated & Active Transport

Facilitated Transport Overview

27Facilitated & Active Transport

28Facilitated Transport · Also called facilitated diffusion or passive transport. · Requires specific channel proteins to assist with the passage of molecules across the cell membrane. · Molecules move from high to low concentration, as in diffusion.

Facilitated Diffusion Process

29NO ENERGY is required since the molecules move with the concentration gradient. Facilitated Diffusion Outside of cell x Xx Inside of cell . Once the solute molecule has passed through, the carrier protein may assist more solute molecules through the cell membrane. · These carrier proteins are reversible

Examples of Facilitated Diffusion

30Examples: .Glucose ·Amino acids These molecules are not lipid soluble so can't pass through the cell membrane without a carrier protein.

31Facilitated diffusion Outside cell Outside cell Low concentration of solute High concentration of solute Inside cell Inside cell

Active Transport Overview

32Active Transport · Requires specific carrier proteins to move ions or molecules through the cell membrane. · Used to accumulate solute either on the inside or outside of the cell. · Molecules move against the concentration gradient.

Energy for Active Transport

33· ENERGY is required to move molecules from regions of low to high concentrations. · The energy helps the carrier protein to "change" its shape. · Energy is provided by molecules of ATP (Adenosine Triphosphate). · Cells involved in a lot of active transport have many mitochondria (which produce ATP). . lodine, Na+ ions and K+ ions all move by active transport + EXTRACELLULAR FLUID high + ATP H* concentration Proton pump H+ concentration H+ - + H+ - + H+ CYTOPLASM pH is higher [H+] is lower + pH is low [H+] is higher @1999 Addison Wesley Longman, Inc. H+ lowPassive transport Active transport Diffusion Facilitated diffusion ATP

35Diffusion Passive transport Facilitated diffusion - ATP Active transport

Sodium-Potassium Pump Mechanism

36Sodium-Potassium Pump 1 Na+ Na P Na+ P P ATP The sodium-potassium pump binds three sodium ions and a molecule of ATP. 2 K K Na Na Na P P P A ADP The splitting of ATP provides energy to change the shape of the channel. The sodium ions are driven through the channel. 3 Na Na Na K K P P P A ADP The sodium ions are released to the outside of the membrane, and the new shape of the channel allows two potassium ions to bind. 4 P K A K Release of the phosphate allows the channel to revert to its original form, releasing the potassium ions on the inside of the membrane.

Endocytosis & Exocytosis

Exocytosis Process

37Endocytosis & Exocytosis

3839Plasma membrane Extracellular fluid Cytoplasm Material for secretion Secretory vesicle (from Golgi apparatus) Molecules are expelled out of the cell when a vesicle fuses with the cell membrane. The vesicle "breaks open" and releases the molecules to the outside of the cell. EXOCYTOSIS The vesicle becomes part of the cell membrane when it fuses, so exocytosis is part of normal cell membrane growth.

Exocytosis Examples

40Exocytosis · Hormones, neurotransmitters and digestive enzymes are secreted from a cell in this way. . The Golgi apparatus often produces these secretory vesicles that carry the molecules to the cell membrane.

Endocytosis Process

41Endocytosis . Endocytosis is the intake of large particles or small molecules into a cell by an infolding of the cell membrane. . After the cell membrane "wraps" around the particle, it fuses and pinches off a vesicle (or vacuole), which contains the particle inside.

42ENDOCYTOSIS OUTSIDE THE CELL 2 Cell membrane 1 3 CYTOPLASM A Lysosome then fuses with the vesicle and digests the vesicles' contents, which then allows the molecules to enter the cell cytoplasm. Vesicle

Types of Endocytosis

43Types of Endocytosis Phagocytosis · Taking in large particles or small cells. · Occurs in certain white blood cells in humans. · Common in unicellular organisms like amoebas. · Used by Immune cells in people. Pinocytosis · Taking in of extracellular fluids and the small particles within the fluid. . These solutes have already been dissolved in the fluid. · non-specific process. . Occurs continuously in all cells.

Receptor-mediated Endocytosis

44Receptor-mediated Endocytosis Receptor-mediated endocytosis Coat protein Receptor Coated vesicle 1 Coated pit ·Specific molecule

45Certain molecules, like hormones, vitamins and lipoproteins, enter a cell by pinocytosis which involves specific receptors on the cell membrane. The receptors for the molecule are found at certain locations on the cell membrane of the cell called coated pits. This location is called a coated pit because the inner surface of the cell membrane has a special coating of proteins, so the vesicle that is formed is called a coated vesicle. Once the molecule is taken into the vesicle, the coating is removed so that a lysosome may fuse with the vesicle. Used during the transfer of many molecules between the maternal circulation and the fetal blood.