Chapter 14: The Plasma Membrane

phagosome

large vesicle that surrounds a particle to bring it into the cell

phagolysosome

phagosome fused with a lysosome

phagocytosis use in amoebas

capture food particles (like bacteria)

phagocytosis use in multicellular animals

defense against invading microorganisms

eliminate aged or damaged cells

macropinocytosis

uptake of extracellular fluids in large vesicles

clathrin-mediated endocytosis

mechanism for selective uptake of specific macromolecules

clathrin-coated pits

surface receptors in specialized regions that bud from the plasma membrane to form clathrin-coated vesicles

dynamin

helps clathrin-coated pits form clathrin-coated vesicles that fuse with early endosomes

low-density lipoprotein (LDL)

transports cholesterol through the bloodstream

uptake of LDL requires:

binding to specific receptors in clathrin-coated pits

FH patients’ cell response to LDL

no binding to LDL due to mutation in LDL receptors

fate of early endosomes

recycled to the plasma membrane, or

mature to late endosomes and lysosomes for degradation

type of pump in early endosomes

membrane H⁺ pump

function of membrane H⁺ pump

maintains acidic internal pH (6.0 - 6.2)

result of acidic pH in early endosomes

ligand dissociation from their receptors

phospholipids in the outer leaflet

phosphatidylcholine, sphingomyelin

phospholipids in the inner leaflet

phosphatidylethanolamine, phosphatidylserine

location of glycolipids

only in the outer leaflet

portion of glycolipids exposed on the cell surface

carbohydrate proteins

cholesterol abundance in plasma membrane

same molar amounts as phospholipids

molecules that are free to diffuse laterally within the membrane

lipids and proteins

clustered in lipid rafts (small patches)

sphingomyelin and glycolipids

two classes of membrane proteins

peripheral and integral

peripheral membrane protein

associated with membranes through ionic bonds (or other protein-protein interactions)

materials that can disrupt the bonds on peripheral membrane proteins

salts, extreme pH (polar reagents)

integral membrane protein

inserted into the lipid bilayer, hard to remove

detergent

amphipathic molecules with hydrophobic and hydrophilic groups that can solubilize integral membrane proteins

transmembrane proteins

integral proteins that span the lipid bilayer with exposed portions on both sides

structure of the transmembrane protein portion inside of the membrane

α-helices of hydrophobic amino acids

example of a transmembrane protein that only crosses the membrane once

glycophorin

example of a transmembrane protein that crosses the membrane multiple times

Band 3

protein structure where GPI anchors are added

the C terminus

function of GPI anchors

anchors proteins to the plasma membrane through covalent bonds

glycocalyx

carbohydrate coat that protects the cell from chemical/mechanical stress and invasion

apical domain in epithelial membranes (small intestine)

covered by microvilli that increase surface area for absorption

basolateral domain in epithelial membranes (small intestine)

mediates transfer of absorbed nutrients to the blood

tight junctions

separate the apical and basolateral domains in epithelial cells

lipid rafts

transient structures that concentrate proteins for cell-to-cell interaction

caveolae

small lipid rafts that start as invaginations of the plasma membrane to bring small molecules into the cell

endocytosis

the cell produces a layer of membrane to engulf particles into the cell

molecules that are able to passively diffuse across the phospholipid bilayer

gases (O₂ and CO₂), hydrophobic molecules, small polar (but uncharged) molecules

molecules that require facilitated diffusion across the phospholipid bilayer

polar and charged molecules (carbs, amino acids, ions, nucleosides)

facilitated diffusion

direction of movement determined by concentration gradients, mediated by proteins

function of carrier proteins

allow facilitated diffusion of sugars, amino acids, and nucleosides

carrier protein mechanism

binds molecules on one side of the membrane, goes through a conformational change, releases the molecule on the other side

function of channel proteins

allows free diffusion of appropriate molecules by forming open pores in the membrane

aquaporin

channel protein for rapid water diffusion, impermeable to charged ions

ion channels

allows extremely rapid ion transport, usually with gates

ligand-gated channels

open in response to binding of neurotransmitters (or other signaling molecules)

voltage-gated channels

open in response to changes in electrical potential across the plasma membrane

ion pumps

use energy from ATP hydrolysis to actively transport ions across the plasma membrane in order to maintain concentration gradients

concentration gradient of K⁺

higher inside the cell

concentration gradient of Na⁺

higher outside the cell

concentration gradient of Cl^-

higher outside the cell

concentration gradient of Ca²⁺

higher outside the cell