lec 2 membrane transport/potential

whats a plasma membrane

the membrane surrounding a whole cell

cellular membranes are the fluid mosaics of ____ and ___

lipids and proteins

whats the most abundant lipid in the plasma membrane, and are these hydrophobic or hydrophillic

phospholipids - amphipathic (hydrophobic and hydrophillic regions)

what are the two classes of phospholipids in animal cells?

phosphoglycerides

sphingolipids

phospho - glyceride

sphingo - lipid

compare phosphoglycerides and sphingolipids (two classes of animal cells)

phosphoglycerides: MOST ABUNDANT CLASS OF PHOSPHOLIPIDS in memb

-in its synthesis, phosphate group links to polar head group

-glycerol is backbone

-TWO fatty acid chain with ESTER BOND

sphingolipids: chemically diff but SIMILAR 3D SHAPE as phosphoglycerides

-sphingosine is backbone (no glycerol)

-ONE fatty acid chain bound to sphingosine with AMIDE BOND

-enriched in membranes of brain and nervous tissue

what is sphingosine

backbone of sphingolipids

-18 carbon amino ALCOHOL with unsaturated hydrocarbon chain

what are the 4 types of phosphoglycerides?

phosphatidyle - thano - lamine phosphatidylethanolamine

phosphatidyl - choline

phosphatidyl - serine

phosphatidyl - inositol

3 main types of sphingolipids? what is each bound to or their structure

1. Ceramides - SIMPLEST TYPE (1 fatty acid chain attached to sphingosine with AMIDE bond)

-BASE STRUCTURE FOR OTHER 2 TYPES:

2. Sphingomyelin (ceramide bound with phosphocholine or phospho-ethano-lamine

3. Glycosphingolipids (ceramide with 1 or more SUGAR residues)

2 common types of glycosphingolipids?

cerebrosides (1 sugar, glucose or galactose)

gangliosides (at least 3 sugars, but one must be sialic acid)

can phospholipids move in the plasma membrane? explain

yes most lipids and some proteins can move in the bilayer LATERALLY or ROTATE

-rarely do they flip-flop across membrane

what happens to texture/state of membranes as temperature INCREASE

membranes move from solid gel state to more FLUID STATE

are membranes with shorter or longer fatty acid chains more fluid? why

shorter fatty acid chains MORE FLUID because less surface area for stabilizing van der Waals or hydrophobic interactions between fatty acid chains of neighbouring phospholipid molecules

SO for shorter chains, more space for phospholipids to move around. for long ones, chains held tgt stronger w interactions so phospholipids cant move as much

whats a saturated vs unsaturated fatty acid

saturated: think saturated with as many H’s as possible (NO C=C carbon double bonds) usually straight tail b/c no double bonds

unsaturated: has atleast one C=C and has bend in tail

are membranes rich in saturated or unsaturated fatty acid more fluid

memranes with UNSATURATED fatty aacids are more fluid (kinks/bends in unsaturated fatty acids PREVENT tight packing between phospholipids)

what are three things that can make membranes more fluid?

high temperature, rich in unsaturated fatty acids, and shorter fatty acid chains

cholestrol acts as a ______ against temperature extremes in animal cells. and what this mean?

FLUIDITY BUFFER

-cholesterol (a steroid) has diff effects on MEMBRANE FLUIDITY at diff temperatures

cholesterol acts as a fluidity buffer against temperature extremes. how does it do that? explain for warm vs cool temperatures

WARM: cholesterol restrains phospholipid movement (decreases membrane fluidity)

COOL: cholesterol prevents tight packing between phospholipids (increases membrane fluidity)

does an increase in CHOLESTEROL increase or decrease membrane permeability (how easily substances can pass thru a membrane) and WHY?

increased choleserol DECREASES membrane permeability (harder for things to get through) BECAUSE cholesterol has a RIGID steroid ring that inserts between hydrocarbon chains of phospholipids which limits movement

what are lipid rafts? 3 functions?

membranes have regions called LIPID RAFTS (enriched in cholesterol, sphinogomyelin, gangliosides, and phosphoglycerides with saturated fatty acid chains) all are tightly packed, REDUCING FLUIDITY in lipid raft

functions:

1. lipid rafts are ORGANIZING CENTERS for assembly of signaling molecules

2. lipid rafts RECRUIT ACTIN CYTOSKELETON which further stabilizes lipid raft

3. lipid rafts FACILITATE formation of TRANSPORT VESICLES

what does lipid rafts molecular composition cause? 2 things

1. slightly THICKENS lipid bilayer

2. this recruits proteins with long transmembrane domains

describe fluidity in lipid rafts and fluidity in the membrane surrounding rafts

in lipid rafts: tightly packed components=less fluidity

memrane surrounding rafts: mostly has phosphoglycerides with UNsaturated fatty acid chains which INCREASE fluidity which ALLOW RAFTS TO MOVE ALONG MEMBRANE TO COMBINE W OTHER RAFTS to become larger rafts

describe a MEMBRANE

a COLLAGE of DIFF PROTEINS embedded in FLUID MATRIX of lipid BILAYER

what determines most of the membranes specific functions

proteins

6 major functions of transmembrane proteins?

1. Transport

2. Enzymatic activity

3. Signal transduction (converting signal)

4. Cell-Cell Recognition

5. Intercellular joining

6. Attachment to the cytoskeleton and extracellular matrix

are carbohydrates on inner or outer leaflet? why?

outer leaflet for CELL-to-CELL recognition

define membrane asymmetry

the UNEQUAL distribution of molecules (lipids, carbs, peripheral proteins) between both monolayers of plasma membrane (outer vs inner monolayer)

basically inner and outer leaflets dont contain same phospholipids.

wahts an example of smt with memrane asymmetry

lipid rafts

whats one reason its essential for cells to generate/maintain membrane asymmetry? explain what is found on each leaflet (or monolayer) and how it creates this asymmetry

-to create surface potential difference across membrane (difference in ELECTRIC CHARGE between the 2 sides)

-outer leaflet: PC (phosphatidylcholine), sphingomyelin, glycolipids

-inner leaflet: PS (phosphatidylserine), PE (phosphatifylethanolamine), PI (phosphatidylinositol)

-although most phospholipids neutral at physiological pH, PS and PI have net NEGATIVE CHARGE-both in inner leaflet, these 2 lipids create SIGNIFICANT difference in charge between both leaflets of lipid bilayer (because more negative charge on inside of membrane)

whats a subgroup of glycolipids?

glycosphingolipids

how can certain phosphoglycerides (say which ones) help anchor a protein to a membrane? what kinds of proteins usually? and bonus what are the two other neutral phosphoglycerides and what leaf of membrane are they found in

PS and PI (phosphoglycerides with negative charge on inner leaf) can INTERACT with positive charged AMINO ACID RESIDUES of (usually peripheral membrane?) proteins so that the proteins keep anchored to the membrane

-bonus: neutral: PC and PE. PC on outer, PE on inner

what are 3 important reasons why its essential for cell to generate/maintain membrane asymmetry

1. SURFACE POTENTIAL

2. CURVATURE

3. PERSERVE CELL VIABILITY

explain how membrane curvature occurs. what are examples of cylinder lipids and conical shaped lipids

-create curvature in membrane

-happens when cylindrical shaped phospholipids CREATE BILAYER while conical shaped phospholipids INSERT in leaflets which PROMOTES FORMATION OF MEMBRANE CURVATURE

cylindrical phospholipids: PC, PS, PI, sphingomyelin

conical phospholipids: PE

why is membrane asymetry important for preservation of cell viability?

PS in normally on inner leaflet

-during APOPTOSIS, PS on outer leaflet makes cell target for engulfment by macrophages (wbc white blood cells)

plasma membranes are selectively permeable, which regulates cell traffic. what this mean for hydrophobic and hydrophillic molecules? which category does gas and ions fit into.

Hydrophobic molecules (include gases) can DISSOLVE in lipid bilayer and PASS THRU MEMB RAPIDLY

Hydrophillic molecules (include ions) cross memb by PATHWAYS with specific TRANSPORT PROTEINS

what kind of gradient is established due to ions moving in and out of cell

ELECTRICAL gradient (difference of charges across plasma membrane)

-interior of cells is electrically NEGATIVE with respect to extracellular fluid

are there more K+ and Na+ concentrations in cell (cytoplasm) or extracellular fluid? how do their concentration and electrical gradients push them like in or out? and what is this combined gradients of concentration and electrical charge that affects an ion called: _______ gradient

more K+ in cell

more Na+ in extracellular fluid

Na+ more simple: conc drive Na+ into cell, electrical also drive Na+ toward negatively charged interior (into cell)

K+ more complex: conc driv K+ out of cell (its originally inside) BUT electrical drive K+ INTO CELL to negatively charged interior

electrochemical gradient

what kind of transport is diffusion

passive (because requires no energy from cell to make it happen)

is simple diffusion ideal for hydrophobic or hydrophillic molecules? are there exceptions? does it involve transport proteins?

simple diffusion ideal for hydrophobic molecules (no transport proteins needed)

-exception: small UNcharged POLAR (hydrophillic) molecules like urea, water, ethanol can cross memb by simple diffusion

describe facilitated diffusion and what its ideal for. what are 3 main types of proteins that carry out facilitated diffusion?

-transport proteins SPEED passive movement of molecules across memb

-ideal for POLAR molecules and CHARGED IONS

-3 main proteins: porins, permeases, ion channels

describe porins and 2 examples

-LARGE, non-selective, barrel-shaped transport proteins

-move HYDROPHILLIC molecs across membrane based on SIZE not charge

-form large-diameter pores (bigger than ion channels) and ARE NOT GATED (no on/off switch, permanently open)

-examples:

-Aquaporins (transport 3 billion water molec per sec)

-Aquaglyceroproteins (transport NON-water molec like glycerol)

describe how permease carries specific molecules accross membrane and whats one thing they can do that porins and ion channels cant?

permease BINDS to the molelcule and undergoes CONFORMATIONAL CHANGES

-unlike porins and ion channels, permeases can BECOME SATURATED when all binding sites are occupied by molecs (to maximize transport rate)

describe ion channels

-form smaller pores and only SPECIFIC ions can pass based on SIZE AND CHARGE

-GATED

-channels are specific to one or two ions, but usually one

list the 5 types of ion channels and when they open (in response to what cellular conditions)?

1. Ligand-gated channels - open/close when specific regulatory (EXTRACELLULAR) molec bind (molec bind from outside)

2. Voltage-gated channels - open/close in response to diff membrane potentials (charge)

3. Mechanogated channels - regulated thru interactions w/ subcellular proteins that make up cytoskeleton (mechanogated channels open/close due to sensing changes in cytoskeleton, which are caused by changes in cell shape (like swelling)) (ex. channel might feel pressure)

4. Signal-gated channels - open/close in response to specific INTRACELLULAR molec (molec bind from inside)

5. Leak channel (NOT GATED LIKE THE OTHER 4) - means NO TRIGGER required to open/close. it has an intrinsic rate of switching between open and closed gates.

whats the difference between ligand and signal gated channel

ligand gated: open/close in response to EXTRACELLULAR molec

signal gated: open/close in response to INTRACELLULAR molec

how can substances diffuse AGAINST their conc or electrochem gradient (low to high conc)?

by ACTIVE TRANSPORT (requires energy in form of ATP)

2 main forms of active transport? what are they distuinguished by?

1. Primary active transport - uses ATP (permease carrier protein use EXERGONIC reaction (ATP hydrolysis) to provide energy to transport molec)

2. Secondary active transport - uses electrochemica energy, doesnt use ATP directly (permease carrier protein MOVE one molec down its electrochem gradient to help move another molec against its conc gradient

-basically use energy from electrochemical gradient of ONE MOLEC to DRIVE TRANSPORT OF ANOTHER

what are the 4 primary active transporters that use ATP hydrolysis? examples of each?

1. P-type ATPases pump specific ions

2. V-type and F-typer ATPases (structurally related - both pump H+ ions)

3. ABC (ATP-binding cassette transporters pump LARGE ORGANIC molecs like drugs and cellular metabolites

P-type examples: Na+/K+ ATPases and Ca2+ ATPases

ABC transporter examples: multi-drug resistance proteins like P-gylcoproteins

F-type: mitochondrial ATP synthase (make ATP using H+ gradient, but can also work in reverse to create H+ gradient using energy from ATP hydrolysis)

V-type: Vacuolar ATPase (or proton pump in memb of lysosomes)

what kind of carrier is used in primary active transport? and in primary active transport are many or just one ion transported at a time

one at a time by carrier called uniporter

define uniporter, antiporter (or exchanger), and symporter (or co-transporter)

uniporter: carrier in primary active transport

antiporter: carrier for secondary active transport (when moving 2 diff ions or molecs in opposite directions)

symporter: carrier for secondary active transport (when moving 2 diff ions or molecs in same directions)

define osmosis

PASSIVE transport of water across selectively permeable membrane that seperates 2 solutions differing in osmolarity (water move from lower total solute conc to higher total solute conc (meaning move from high H2O to low H2O conc)

define osmolarity

number of particles in solution (measure of solute conc in osmoles of solute per L of solution)

-considers TOTAL solutes so both permeable (penetrating) and impermeable (non-penetrating)

whats iso hypo hyper osmotic? does osmosis net movement go from hyprt yo hypo or hypo to hyper

iso-osmotic: solutions equal in osmolarity (no net osmosis)

hypo-osmotic: osmolarity of solution LOWER than other aolution

hyper-osmotic: osmolarity of solution GREATER than other solution

osmosis net movement from hypo-osmotic to hyper-osmotic (water go to side with more solute (hyper) so the water balances it out)

define tonicity including isotonic hypotonic hypertonic and what happens to cell shape change

tonicity - what happens to cell when placed in solution (how it affects cell volume), only considers conc of impermeable solutes (penetrating solutes reach equilibrium and not affect tonicity)

isotonic - solution w same conc of NP solutes as that found in cells

hypertonic - solution with HIGHER conc of NP solutes than in cells (cell shrinks)

hypotonic - solution with LOWER conc of NP solutes than in cells (cell swells)