Cell Transport

Cell Membrane Review One of the primary functions of the cell membrane is to allow the passage of materials into and out of the cell. Many materials pass through the membrane without any assistance. Other materials, however, require proteins to either passively facilitate their transport or actively pump them against their concentration gradient (going from low to high concentration).

Cell Membrane Review

Diffusion Diffusion is the movement of molecules from regions of high concentration to low. ▫Molecules move with their concentration gradient. Molecules will randomly move with the conc gradient until equilibrium is reached. ▫Once equilibrium is reached, molecules continue to move; there’s just no net movement in one direction or another. Robert Brown conducted the first studies in random particle motion – Brownian motion. ▫From his studies, we first began to understand diffusion and its role in molecular motion. Brownian motion Is diffusion a form of active or passive transport? Diffusion (4:57)

Osmosis Osmosis is the diffusion of H 2 O across a selectively permeable membrane (like the cell membrane) Because osmosis is a form of diffusion, does the H 2 O move with or against the conc gradient? Is osmosis active or passive? Osmosis continues until equilibrium is reached.

Iso-, Hypo-, and Hypertonic Solutions Isotonic: The conc of H 2 O inside the cell is equal to the conc outside the cell ▫Equilibrium has been reached. ▫Most cells are in isotonic solutions, like blood, so they neither shrink nor swell ▫Osmotic pressure is equal on both sides of the membrane

Iso-, Hypo-, and Hypertonic Solutions Hypotonic: The conc of H 2 O inside the cell is less than the conc outside the cell ▫H 2 O moves into the cell causing the cell to swell ▫If the conc difference is great enough, the cell will cytolyze (burst). ▫Osmotic pressure is greater outside the cell ▫Plant and bacterial cells are often in fresh water (hypotonic solution), but they do not cytolyze. Why not?

Iso-, Hypo-, and Hypertonic Solutions Hypertonic: The conc of H 2 O inside the cell is greater than the conc outside the cell ▫H 2 O moves out of the cell causing the cell to shrink ▫If the conc difference is great enough, the cell will plasmolyze. ▫Osmotic pressure is greater inside the cell Blood Cells in Solutions (:58)

Iso-, Hypo-, and Hypertonic Solutions Osmosis and Tonicity (9:27)

Facilitated Diffusion Facilitated diffusion is a form of passive transport that uses a protein (facilitator) to move materials through the cell membrane. Even though a protein is needed, it’s still a form of diffusion, which means materials move from high to low conc. Why do some molecules need a facilitator protein? The proteins are highly specific, so therefore only one compound/molecule can pass through only one particular protein. ▫It’s kinda like enzymes and their substrates. Facilitated Diffusion (1:18)

Active Transport Active transport is a form of transport that moves materials against the conc gradient (from low to high conc) In order to move against the gradient, energy is required. Energy molecule required? Protein “pumps” are used to move small or large, charged or neutral particles through the membrane. Two types of active transport: endocytosis and exocytosis

Endocytosis Endocytosis is the process of taking in materials via infoldings of the cell membrane ▫Two types: phagocytosis and pinocytosis ▫Phagocytosis is taking in solid particles, while pinocytosis is taking in liquids ▫In both processes, the cytoplasm extends and takes in either solids or liquids

Phagocytosis

Pinocytosis Vesicle formation (1:52)

Exocytosis Exocytosis is the process by which cells expel substances. A vesicle or vacuole from within the cell fuses with the membrane and then expels its material into the extracellular fluid.

Exocytosis Transport Summary 1 (6:13) Transport Summary 2 (3:19)