Membranes and membrane transport Flashcards
role of the plasma membrane
effective barrier between aqueous solutions
- holds useful substances inside of the cell and prevents potentially harmful substances from entering
the plasma membrane maintains…
homeostasis by controlling transport in and out of the cell
diffusion
net movement of particles from a region of their higher to a region of their lower concentration - passive because it is a result of random movement of particles
concentration gradient
the existence of the difference in concentrations of a specific particle of two different areas separated by a plasma membrane
passive vs active transport
passive is the consequence of random movement of particles - energy needs to be invested for active transport
the speed at which diffusion occurs depends on…
the difference between concentrations (how steep the concentration gradient is)
even when C of two areas are equalized…
particles move back and forth (but net movement will be zero)
simple diffusion
diffusion of small, moleculated (?), hydrophobic (non-polar) substances across a “bare” phospholipid layer - example: O2, CO2, ethanol, water (to some extent)
facilitated diffusion
diffusion of big, charged, hydrophilic (polar) substances across the membrane through protein channels - example: glucose, amino acids, proteins, starch, sodium ions, water (to some extent)
- direction of movement cannot be controlled (down the gradient)
osmosis
facilitated diffusion of water molecules across a semi-permeable membrane (water attracted to solutes)
aquaporin
protein channel transporting water molecules - only water can pass through due to specific diameter size and chemical properties of its wall
types of globular proteins embedded in the plasma membrane
1) integral - embedded (amphipathic)
a) transmembrane
i) protein channel (some can open and close their pores)
2) peripheral (surface) - attached (hydrophilic)
active transport
through protein pumps
- particles enter the pump
- E from ATP used to change the conformation of the pump so that the particles can exit on the other side
- pump spontaneously goes back to original conformation
direction of movement controlled
glycoproteins vs glycolipids
- polypeptides with carbohydrates attached
- lipids (1-2 f.a.) with carbohydrates attached
roles of glycoproteins and glycolipids
1|cell adhesion - form carbohydrate-rich layer on the outer cell face called glycocalyx
- glycocalyx of adjacent cells can fuse
2|cell recognition - differences in the types of glycoproteins and glycolipids - development of organs - immune system distinguishing between self and non-self cells (destroying pathogens)
