Review Passive transport: the movement of any substance across a cell membrane without the use of cell energy Types of Passive Transport Diffusion Osmosis Facilitated Diffusion Gated Channels Based on the principals of polarity Polar substances cannot freely cross the membrane Non-polar substances can

Facilitated Diffusion Definition: a process in which substances move down their concentration gradient across the cell membrane with the assistance of carrier proteins Basic Process Molecule to be transported comes in contact with correct transport protein Transport protein changes shape Molecule is released into cell

Carrier Proteins Ion Channel: protein which forms a pore (hole), that spans the width of the membrane Allows specific ions to diffuse across the membrane May be open all the time or gated Transport Protein: protein with a channel that allows larger molecules to diffuse through the membrane

Gated Channels Specialized form of a transport/carrier protein Has a gate that must be opened before a molecule can diffuse into or out of a cell The Gate must be unlocked prior to a molecule moving through the membrane Open/Closed based on the extracellular environment

Active Transport Definition: the movement of any substance across a cell membrane with the use of energy from ATP Typically, move substances UP their concentration gradient Examples Sodium-Potassium Pump Endocytosis Exocytosis

Sodium-Potassium Pump Sodium ions (Na + ) usually more concentrated outside of cell, Potassium ions (K + ) more concentrated inside of cell 3 Na + pumped out, 2 K + pumped in Uses carrier proteins (aka membrane pumps) Typically used in cells To maintain polarization

Sodium Potassium Pump Steps 3 Sodium (NA+) inside the cell bind to the pump, and ATP is changed to ADP (energy consumption) Pump changes shape 2 Potassium (K) from outside the cell take the place of the sodium Pump returns to the original shape and potassium is released inside of the cell

Proton Pumps an active transport mechanism that consumes ATP (energy) to force Hydrogen ions against the concentration gradient

Movement by Vesicles Vesicles are the sacs of the cell that are used to move large molecules around the cell and in/out of the cell Transports molecules that are too large to be moved across membranes by other means Two types of movement across cell membrane Endocytosis Exocytosis

Endocytosis Movement of substance into a cell Membrane forms a pouch and pinches off to form vesicle May fuse with lysosomes or other organelles

Exocytosis Movement of a substance out of a cell Vesicles in cells fuse with cell membrane and release contents ex. Releasing proteins

EndocytosisExocytosis

Passive vs. Active Transport Which one uses energy? What are the different types of passive transport? What are the different types of active transport?

Internal Transport Endomembrane System Includes the ER, Golgi, lysosomes, vacuoles, and cell membrane Creation of vesicles that are eventually used to transport cellular products to the cell membrane or Creation of vesicles that bring needed materials from outside the cell to the specific structure that needs them Process behind endo and exocytosis

Internal Transport Endoplasmic reticulum Network of membranes that form tubes Attached to the nuclear membrane Two types that are attached to each other Smooth ER: cytoplasmic surfaces lack ribosomes Creates lipids Breaks down carbohydrates brought to the ER by endocytosis Rough ER: ribosomes cover the cytoplasmic surface Creates secretory proteins that will exit the cell through exocytosis

Internal Transport Golgi Apparatus Flattened membranous sacs Center of manufacturing, warehousing, sorting, and shipping Prepares proteins for secretion from the cell Vesicles carry proteins made by the ER to the Golgi, the Golgi then modifies as needed

Cell Size Why are cells small? Metabolism sets limits on the size range of cells Surface area to volume ratio prevents cells from becoming to big It takes too long to move material from one side to the other in a larger cell