AP Biology Membrane Transport | Winston-Salem Forsyth County Schools

University:
Winston-Salem Forsyth County Schools
Course:
AP Biology
Academic year:

2023
Views:

481

Pages:

2
Author:

Efrain Villa

Membrane Transport Cell Membrane/Cell Wall ● Made up of a phospholipid bilayer, proteins, steroids, glycoproteins, & glycolipids (glyco = carbohydrate chain) ● Selectively permeable ○ Small, nonpolar molecules can easily pass through (including N2, O2, & CO2) ○ Hydrophilic substances (large polar molecules & ions) need embedded channels (positively charged) or transport proteins ○ Polar uncharged molecules (H2O can pass through the membrane in small amounts ● Separates the internal environment of the cell from the external environment ● The cell wall of plants/prokaryotes/fungi is composed of complex carbohydrates (cellulose for plants or chitin for fungi) ● Phospholipids have a hydrophilic phosphate head & a hydrophobic tail (fatty acid chain tail) ● Embedded proteins can be hydrophilic (with charged polar side groups) or hydrophobic (with nonpolar side groups) Transport ● Passive transport (No energy/ATP): ○ Molecules moving from high to low concentration down the concentration gradient (plays a primary role in the import of materials & the export of waste) ○ Facilitated Diffusion ■ Aquaporins (No energy required): Helps a few water molecules pass through the membrane from a high to low concentration ■ Charged ions (Na+ & K+) require channel proteins (positively charged) to pass through the membranes from a high to low concentration ● Na+ Channels & K+ Channels/ Sodium-Potassium Pump: 1. Sodium enters the cell through the Sodium channel 2. The cell’s charge becomes positive & the Potassium channel opens i. Occurs with neurons 3. Potassium exits the cell 4. The sodium potassium pump prevents this process and maintains the membrane potential by pumping the K+ back in & the Na+ out (this part of the process requires energy, and is therefore active transport) ● Active transport (Needs energy/ATP): ○ Molecules moving from low to high concentration; against the gradient ○ Membrane proteins ○ Endocytosis (Needs energy): ■ Moves large molecules into/out of the cell. Macromolecules enter through vesicles from the plasma membrane & are then digested through lysosomes ■ Phagocytosis (food): Eating large molecules ■ Pinocytosis (water): Drinking small molecules ■ Receptor Mediated: Molecules need to bind to the receptors in order for a vesicle to be formed ○ Exocytosis ■ Used to export protein produced in the ER through vesicle that will fuse with the membrane ● Membranes may become polarized by the movement of ions across the membrane