Membrane Transport and Potential

what is the most abundant lipid

phospholipids

what does amphipathic mean

hydrophobic and hydrophillic

what are the two classes of phospholipids

phosphoglycerides and sphingolipids

phosphoglyceride structure

phosphate group links to polar head group

sphingolipid structure

sphingosine as the backbone rather than glycerol, one fatty acid chain and amide bond

types of sphingolipids

ceramides, sphingomyelin, glycosphingolipids

ceramides

form the base structure for the other two types of sphingolipids, one fatty acid chain is attached to sphingosine with amide bond

sphinomyelin

ceramide bound with phosphocholine or phosphoethanolamine

glycosphingolipids

ceramides with one or more sugar residues

what are the two types of glycosphingolipids

cerebrosides, gangliosides

what does it mean for the membrane to be fluid

phospholipids drift laterally or rotate

what are factors that affect fluidity

high temperatures, short fatty acid chains, unsaturated fatty acids

why are shorter fatty acid chains better than long

less surface area to allow for stabilizing van der waals or hydrophobic interactions

why are unsaturated fatty acids better than saturated

kinks/bends due to C=C prevent packing

how does cholesterol affect fluidity

warm temperatures restrain movement of phospholipids, cool temperatures prevent tight packing

how does cholesterol affect membrane permeability?

increase in cholsterol decreases permeability

what are lipid rafts composed of

enriched in cholesterol, sphingomyelin, gangliosides and phosphoglycerides with saturated fatty acid chains

how does the composition of lipid rafts affect the membrane

the components are packed tightly to reduce fluidity and the composition causes thickening of the bilayer to recruit proteins with long transmembrane domains

what are the functions of lipid rafts

organizing centers for the assembly of signalling molecules, recruiting actin cytoskeleton, facilitating the formation of transport vesicles

what are the functions of membrane proteins

transport, enzymatic activity, signal transduction, cell-to-cell recognition, intercellular joining, attachment to cytoskeleton and extracellular matix

where are carbohydrates located

outer leaflet for cell to cell recognition

what are carbohydrates (glucose and galactose) bound to

lipids or proteins

what is a subgroup of glycolipids

glycosphingolipids

what are the three reasons as to why asymmetry is important

surface potential difference

creates curvature in membrane

preservation of cell viability

how does surface potential difference work

outer leaflet- PC, sphingomyelin, glycolipids
inner leaflet- PS, PE, PI
PS and PI have net negative charges and interact with positive charged amino acid residues so the proteins remain anchoredI

PC, PS, PE, PI (what do they stand for)

phosphatidylcholine, phosphatidylcerine, phosphatidylethanolamine, phosphatidylinositol

how does curvature in the membrane work

insertion of cone-shaped phospholipids (PE) promote curvature
cylindrical shape (PC, PS, PI, sphingolipids) create the bilayer

how does the preservation of cell viability work

the extracellular expression of PS targets the cell for engulfment by macrophages (cell apoptosis)

what does selective permeability mean and how is it regulated

not everything can pass through, regulated by the hydrophobic interior and hydrophilic exterior

how is the concentration and electrical gradient established

movement of ions in and out

what is the charge of the interior of the cell

negative

how do the Na+ gradients work in living cells

concentration gradient and electrical gradient drive Na+ into the cell

how do the K+ gradients work

electrical gradient drives it into the cell, concentration gradient drives it out

electrochemical gradients

combined gradients

what direction does the concentration gradient move if you are going from high to low

down

passive transport

no energy is needed from the cell

examples of passive transport

simple and facilitated diffusion

how does facilitated diffusion work

transport proteins move molecules

what are the 3 main proteins of facilitated diffusion

porins, permease, carriers, ion channels

porins

large, non selective, barrel shaped transport proteins that move molecules based on size

permease carriers

facilitate transport of specific molecules across membrane by having molecules bind to induce a conformational change

when do permease carriers become saturated

when all binding sites are occupied

ion channels

form small pores that only specific ions can pass through based on size and charge

what are the five types of ion channels

ligand-gated (regulatory molecules)

voltage gated (membrane potentials)

mechanogated (subcellular proteins in cytoskeleton)

signal-gated (intracellular molecules)

leak channel (not gated, intrinsic rate of switching)

active transport

requires energy (ATP) to move substances, substances diffuse against concentration gradient

what are the types of active transport

primary and secondary active transport

primary active transport

involves permease carrier proteins and uses an exergonic reaction to provide energy to transport a molecule

example of primary active transport

Na+ - K+ pump moves Na+ using atp to establish a sodium concentration gradient

secondary active transport

permease carrier proteins that move one molecule down its electrochemical gradient to help another move against its concentration gradient

what is a key difference between primary and secondary active transport

primary uses atp, secondary uses electrochemical energy

example of secondary active transport

sodium moves along Na+-K+ pump concentration gradient to drive the transport of glucose against its concentration gradient