Transport proteins are

integral membrane proteins

Uniport moves

1 solute downward

Symport moves

2 solutes downward

Antiport moves 2 solutes

in opposite directions (one goes up and other goes down)

What are the four modes of membrane transport?

1. Passive diffusion (-ΔG) (favored)

2. Facilitated diffusion (-ΔG) (favored)

3. Active transport (+ΔG) (opposed)

4. Secondary active transport (+ΔG) (opposed)

Passive diffusion doesn't require proteins and means the transportation of species

moving down its concentration gradient from high to low concentrations

Passive diffusion of uncharged species move across the membrane depending on

the concentration on the two sides

Passive diffusion of a charged species also depends on the concentration and

the charge of the particle

allow transport of charged molecules such as protons across the bilayer down its concentration

Hydrophobic ionophores

The proteins "facilitate" transport, increasing the rate of transport

facilitated diffusion

Two important distinguishing features of facilitated diffusion

1. solute flows only in the favored direction

2. Transport displays saturation kinetics: there is an upper limit to how solutes can influence the rate of transport

Facilitated diffusion displays saturation

Single channels can be formed from

dimers, trimers, tetramers, or pentamers of protein subunits

Multimeric assemblies in which each subunit

has its own pore as known

Potassium channels combine

high selectivity with high conduction rates

Active transport is used to transport

against the thermodynamic potential of solutes

Active transport directly uses

ATP (hydrolysis)

Another way to refer to the sodium-potassium pump

Na,K-ATPase

Na,K-ATP maintains intracellular Na+ ____ and K+______ and it is crucial for organs ____ and_____

low, high

brain, neural tissue

Drives Na+ out and K+ in

ATP hydrolysis

how much ATP is used?

How many K+ goes from high to low?

How many Na+ goes from low to high concentration?

- 1 ATP

- 2 K+

- 3 Na+

Inhibit by binding to outside part of the transporter

cardiac glycosides(ouabain)

Secondary active transport is not directly driven by

ATP

In secondary active transport, the gradient of H+, Na+ and other cations and anions previously established by ATPase

can be used for secondary active transport against their concentration gradient

Many of these are symports with the ion and the transported

amino acids or sugar moving in the same direction

AcrB is an example of

secondary transport system

AcrB is a major multi-drug resistance transporter in

E.coli

As protons flow spontaneously inward through AcrB in the E.coli inner membrane,

drug molecules are driven outward

Both lipids and proteins of the membrane exhibit

lateral and transverse asymmetry

Proteins can associate and cluster in the plane of the membrane -They are not uniformly distributed

Lateral asymmetry of proteins

Lipids can cluster in the plane of the membrane-they are not uniformly distributed

lateral asymmetry of lipds

Mark Bretscher shows that N-terminus of glycophorin is extracellular whereas C-terminus is intracellular

Transverse asymmetry of proteins

In most cell membranes, including those of intracellular organelles, the composition of the outer monolayer is quite different from that of the inner monolayer

transverse asymmetry of lipids

Dynamic means

motion

Lipids and proteins undergo lots of movements in the membrane and these motions

support a variety of cell functions

Move PS from the outer leaflet to the inner leaflet

ATP dependent flipase (flip in)

Moves lipids including cholesterol, PC, and sphingomyelin from the inner leaflet to the outer leaflet of the membrane

ATP dependent flopase (flop out)

Randomize lipids across the membrane and thereby degrade membrane lipid asymmetry

Scramblases ( Ca^2+ activated but ATP dependent)

At low tempertures , bilayer lipids are highly ordered, forming a gel, with acyl chains extended,nearly

perpendicular to the membrane plane

S_o, solid ordered state

the lipid chains are tightly packed and undergo relatively little motion

Characteristics of S_o, solid ordered state,

1. lipid chains are in their fully extended conformation

2. surface area per liquid is minimal

3. bilayer thickness is maximal

At higher temperatures, acyl chains undergo much more motion and acyl chain C-C bonds result in bending of the acyl chains

L_d, liquid- disordered state

Characteristics of L_d, liquid- disordered state

1. surface area per lipid increases

2. lipid chains are more likely to be bent at any one time

3. bilayer thickness decrease by 10-15%

Transition from gel phase to liquid crystalline is a true

phase transition

The temperature at which this occurs is the transition temperature

Melting temp. T_m

If T_m is increasing,

the chain length would increase

-lipids can influence curvature

- integral membrane proteins with conical shapes can induce curvature

- scaffolding proteins can influence membrane shape in many ways

Membrane remodeling and curvature

What type of bending is this?

lipid composition

What type of bending is this?

membrane proteins

What type of bending is this?

amphipathic helix insertion

What type of bending is this?

scaffolding

What type of bending is this?

cytoskeleton

Membranes fusion requires proteins that _____opposite membranes and ____ them together

pierce, pull