Lec 1 Transport Across membranes

phosphatidylserine is a xxx, involved with….

• a type of membrane phospholipid

• involved in apoptosis

what are phosphotidylinositols, what are they involved w

• a type of membrane phospholipid

• involved w signaling

what are CD Markers , how are they used?

=cluster differentiation markers, used to identify cell types + functions

- are proteins, glycoproteins, or glycolipids that are specific to a cell.

They can be single molecules or groups of molecules.

- Used for diagnosis and cell testing: flow cytometry and/orfluorescence microscopy

what do Cadherins, integrins and selectin share in common?

all CAMs

what are cadherins?

= involved in surface adhesion forming

homodimers. Mediate cell to cell interaction. Bind to the same type of CAM (Homophilic).

– Important for development of nervous system and during gastrulation.

what are integrins?

integrins = surface adhesion proteins that bind to

different types of CAMs (heterophilic). Form

heterodimer proteins composed of two unlike subunits, α and β. Mediate cell-to-extracellular interactions.

– Important for cell functions: apoptosis,

differentiation, transcription, etc.

what are selectins?

= have extracellular domains that bind specific

polysaccharides on the surface of an adjacent cell. Act as monomers. Bind to different types of CAMs. - heterophillic

– essential for immune system (leukocyte migration).

what is FRAP

fluorescence recovery after photobleaching, show how the lipids will eventually shuffle around

what does flippase do?

catalyze translocation of the amino-

phospholipids (phosphatidylethanolamine - PE) and phosphatidylserine (PS) from the extracellular to the cytoplasmic leaflet

– consume ~1 ATP per molecule of phospholipid

translocated

what does floppase do?

move plasma membrane phospholipids from

the cytoplasmic leaflet to the extracellular leaflet

– are ATP-dependent

what does scrambles do? what does it require

moves lipids in either direction FAVOURING equilibrium, no ATP required, but DO require Ca+2 ion from inside cell

what are micro domains/ rafts? what is function and what re they made of

• make the bilayer slightly

thicker and more ordered (less fluid) than

neighboring, phospholipid-rich regions

• clusters of cholesterol

  and sphingolipids

what are caveolae?

aka little caves

Involved in variety of cellular

functions:

• membrane trafficking within

cells and the transduction of external signals into

cellular responses

• allow for extra elasticity, if cells needs to expand surface area ex. osmotic pressure

what are caveolin

= integral proteins that binds to inner membrane (usually associated w rafts of cholesterol)

*think caveolIN IN the caves

• form dimers and force bilayer to curve INWARDS

what does fusion of 2 membranes require?

❖ Recognition each other (signal)

❖ Hemifusion (Close apposition and

local disruption of bilayer

❖ Fusion (fusion proteins)

*curvature ability of membranes is also important

what are SNAREs? what are 2 main types

SNAREs (snap receptors) = family of proteins

1. v-SNAREs = SNAREs in the cytoplasmic face of the intracellular vesicle. (v = vesicle)

2. t-SNAREs = SNAREs in the target membrane with which the vesicle fuses. (t =target)

what are fusion proteins and 2 important ones

Fusion porteins= mediate specific

fusion of two membranes by bringing

about specific recognition and a

transient local distortion of the bilayer

structure

1. SNAP25= regulatory protein induced by Ca+

2. NSF (N-ethylmaleimide-sensitive

fusion factor) proteins that

disassemble SNARE complex post-fusion

how do polar vs non-polar and ions compounds cross membrane?

-nonpolar uncharged small compounds can

dissolve in the lipid bilayer and cross a membrane

unassisted

VS

-polar compounds and ions require a specific membrane protein carrier

what are 3 classes of transport systems?

1. UNIPORT → only 1 substrate

2. SYMPORT (co transport)

3. ANTIPORT (co transport)

what is simple diffusion? what is relevancy of electrochemical gradient?

= movement of a solute from the region of higher conc. to the region of lower conc , unassisted by a protein transporter, until equal concentration.

• electrochemical gradient—>determines direction a charged solute moves across a membrane (bc it will go from high to low in the case)

what is membrane potential Vm?

• difference of charge separated by permeable membrane

produces a force that:

opposes ion movements that increase Vm

drives movements that reduce Vm

what is facilitated diffusion? what are 3 key transporters?

= simply facilitate movement down a

concentration gradient, increasing the transport rate

GLUCOSE TRANSPORTERS:

1. GLUT1: in erythrocytes+blood/brain B+placenta+most tissues, important for basic glucose uptake and blood brain barrier

2. GLUT4: in mucle+heart+fat, important for mediating glucose intake in cell by insulin action, insulin is inc—> GLUT4 activity will be inc

3. see pic, Anion exchanger for CO2 transport from blood to around body to eventually leave in lungs

what is active transport and 2 types?

= movement of solute AGAINST it’s conc. gradient, results in amount above eq. point

1. primary active transport; the energy released by ATP hydrolysis DIRECTLY drives solute S1 movement against an electrochemical gradient

a gradient of an ion (often

Na+) has been established by primary active T ransport. → Movement of S1 down its electrochemical gradient (from high to low) now provides the energy to drive cotransport of a

second solute, S2, against its electrochemical gradient

what is SERCA PUMP? what are 3 domains ?

• brings Ca+ from cytosol to sER

• uniport

• has three domains:

A-actuator

P-phosphorylation domain

n-nucleotide binding domain

info on sodium potassium pump, what is ratio? what is membrane potential

• 3 Na+ OUT to 2K+ IN

• ranges from -50 to -70 mv

what are F-type ATPases, what’s an example?

= energy coupling factors, can hydrolyze and synthesize ATP

what are ATP-binding cassets?

= ABC transporters, family of ATP-driven transporters that pump substrates across a membrane against a concentration gradient

• have 2 TMDs (transmembrane domains)

• have 2 NBDs (nucleotide binding domains—> the cassettes)