Transport Chapter 7.3+ Cellular Biology

What you need to know! The role of passive transport, active transport, and bulk transport in the movement of water and nutrients in cells. How water will move if a cell is placed in an isotonic, hypertonic, or hypotonic solution. How electrochemical gradients are formed.

Types of Transport Movement of substances may be active or passive. Passive transport: diffusion of substances down a concentration gradient (high  low) Active Transport works against concentration gradients and requires energy (ATP)

Diffusion The natural movement of molecules down a concentration gradient (high concentration toward low concentration) Results in equilibrium (even distribution) Reason: random movement of all molecules driven by kinetic energy (thermal motion)

Passive Transport Diffusion of particles in and out of a cell The cell does not invest any energy Membranes are selectively permeable and help regulate the diffusion of particles Permeable for very small, uncharged, hydrophobic molecules and gases Impermeable for ions and large molecules Facilitated diffusion: proteins embedded in the membrane allow for the diffusion of certain impermeable molecules Osmosis is the diffusion of water across a selectively permeable membrane

Passive Transport

Facilitated Diffusion Diffusion aided by proteins Channel proteins – always open Ion channels Gated channels Carrier proteins – opens and closes

Channel Protein (Aquaporin)

Osmosis Two Factors to consider: 1.Solute concentration (salt, sugar, other substances…) 2.Water concentration: High solute concentration means low water concentration Low solute concentration means high water concentration Distilled water is solute free (100% water) Water will always flow down hill: high to low water concentration (aka high to low water potential)

Osmoregulation Water balance in living systems Cells w/out walls: Tonicity Isotonic: environment and cell have the same concentration of solute Hypertonic: environment has higher solute concentration Hypotonic: environment has lower solute concentration Cells w/ Walls: Turgor pressure Turgid: firm cell supported by full central vacuole and cell wall Flaccid: limp cell supported only by a cell wall Plasmolysis: extreme dehydration causes a separation of the cell membrane and plasma from the cell wall Special Adaptations: contractile vacuole

Osmoregulation

Plasmolysis

Active Transport Movement of solutes against a concentration gradient Requires the expenditure of ATP Transport (carrier) proteins move solutes across the membrane Electrogenic pumps are common active transporters that create electrochemical gradients to store energy for later use Animals: Sodium-potassium pump exchanges 3 Na + for 2 K + at the cost of 1 ATP Plants, fungi, and bacteria: proton pump moves H+ at the cost of ATP

Sodium-Potassium Pump

Cotransport Pump a molecule up it’s concentration gradient to store energy Allow the molecule to diffuse back down it’s concentration gradient Energy released Use the energy released to actively transport another molecule up it’s concentration gradient

Bulk Transport Uses membrane bound vesicles to move large amounts of substances across the cell membrane 1.Exocytosis: fusing of vesicle with membrane, releasing contents outside of cells Example: secretion of hormones, enzymes, neurotransmitters 2.Endocytosis: pinching in of membrane around molecules leading to internalization Example: phagocytosis (eat), pinocytosis (drink), receptor mediated endocytosis (intake of specific molecules)

Endocytosis and Exocytosis

Receptor Mediated Endocytosis

WBC (Macrophage) Phagocytosis