L2 - Membrane Proteins

Type I protein

one transmembrane segment, amino terminus outside and carboxyl terminus inside

Type II protein

one transmembrane segment, amino terminus inside, carboxyl terminus outside

Type III protein

several transmembrane segments, terminus locations will vary

Hydropathy Index expresses free energy change associated with

the movement of an amino acid side chain from a hydrophobic environment to water - ranges from highly exergonic to highly endergonic

In the hydropathy index, Delta G < 0 is

hydrophilic

In the hydropathy index, Delta G > 0 is

hydrophobic

Overall hydropathy estimated by summing the

free energies of transfer for the residues in the sequence

Hydropathy plots

average hydropathy index plotted against residue number

Hydropathy index y axis

average hydropathy for a window

Hydropathy window

segment of given length

Hydropathy residue number x axis

the residue in the middle of the window

Hydropathy plots can help us determine the Type I and II proteins but not

Type III

___ and ___ side chains serve as membrane interface anchors

Tyr and Trp

Positive inside rule

positively charged Lys and Arg residues in the extramembrane loop of membrane proteins occur more commonly on the cytoplasmic face (inside of cell)

GPI-anchored protein

exclusively on the outer face and are clustered in certain region

Microdomain (rafts) are clusters of cholesterol and sphingolipids that make the bilayer

slightly thicker and more ordered than neighboring, phospholipid-rich regions. Can be up to 50% of the cell surface. Thickness allows other proteins to embed in the membrane to perform a variety of functions.

Transport proteins reduce the energy of activation for diffusion by

forming noncovalent interactions with the dehydrated solute and providing a hydrophilic transmembrane pathway

Ion channel is a

single gate that is unsaturateable.

Transporter (pump) have alternating gates that can never ____________________  and can pump against gradient. Is saturateable. Concentration at which the rate of transport will plateau.

can never open at the same time