Membranes/membrane Transport

Front 1

How are most integral proteins positioned in the cell membrane?

Back 1

Most are transmembrane proteins, with hydrophilic and hydrophobic regions reaching out into the appropriate surroundings.

Front 2

What is an average protein to lipid ratio?

Back 2

Anywhere from 1-3 proteins per lipid. A good general ratio is 2 to 1.

Front 3

What are the key features of the fluid mosaic model?

Back 3

1.) Lipid bilayer with hydrophilic and hydrophobic tails
2.) Fluid nature, with lipids that diffuse laterally across membrane plasma
3.) Proteins form mosaic pattern
4.) Some proteins anchored to the cytoskeleton.

Front 4

What are the key functions of membranes?

Back 4

1.) define boundaries of the cell and compartmentalize
2.) serve as loci of specific functions
3.) possess transport proteins that regulate movement of substances
4.) contain receptors for external signals
5.) provide mechanisms for cell to cell communication.

Front 5

What does "amphipathic" mean?

Back 5

Possessing both hydrophilic and hydrophobic regions.
i.e. phospholipids!

Front 6

What are the differences between integral, peripheral, and lipid-anchored proteins?

Back 6

integral: embedded within bilayer, held in place by affinity of hydrophobic segments to the interior of the bilayer.
peripheral: more hydrophilic and located on membrane surface, linked noncovalently to polar head groups on lipids or to other hydrophilic protein regions.
lipid-anchored: hydrophilic as well, but covalently linked to lipid molecules embedded within the bilayer.

Front 7

What are the types of membrane lipids?

Back 7

Phospholipids: most abundant. includes phosphoglycerides and sphingolipids.
Glycolipids: a lipid + a carbohydrate group. includes cerebrosides and gangliosides.
sterols: eukaryotic cells only. includes cholesterol and phytosterols.

Front 8

What is transverse diffusion, and what kind of proteins catalyze this?

Back 8

Transverse diffustion is the "flip-flop" of lipids in the lipid bilayer, and can be catalyzed by appropriately named "flippases."

Front 9

What is fluorescence recovery after photobleaching, and what is its purpose?

Back 9

Cell surface molecules are labeled with fluorescent dye, then a laser beam bleaches an area of the cell surface. More fluorescent labeled molecules then diffuse into the bleached area. This shows the lateral diffusion of molecules in the lipid bilayer.

Front 10

What is homeoviscous adaptation?

Back 10

The ability of a poikilotherm to alter the lipid composition of its membranes in order to regulate membrane fluidity.

Front 11

How are proteins arranged on the membrane of a cell?

Back 11

Asymmetrically. Membrane proteins can be located anywhere on the surface of a cell.

Front 12

What is the difference between simple diffusion, facilitated diffusion, and active transport?

Back 12

simple diffusion: unaided movement of a solute down its concentration gradient
facilitated diffusion: protein aided movement of a solute down its concentration gradient
active transport: protein aided movement of a solute AGAINST its concentration gradient

Front 13

define symport and antiport.

Back 13

symport: coupled transport in which both substances move the same direction
antiport: coupled trasport in which substances move in opposite directions.

Front 14

What are the six steps of the Na+/K+ pump?

Back 14

1.) 3 Na are taken from inside
2.) ATP phosphorylates alpha subunits
3.) A conformational change following phosphorylation expels 3 Na to outside
4.) Two K+ accepted from outside
5.) Dephosphorylation triggers conformational change
6.) 2 K+ expelled to inside; pump returns to initial state.

Front 15

What are the initial and "half-through" states of the alpha subunits in the Na+/K+ pump?

Back 15

Initial: "E1 conformation." pump open to the inside.
Half-through: "E2 conformation." pump open to the outside.

Front 16

What is faraday's constant?

Back 16

23,062 cal/mol V

Front 17

What is R?

Back 17

1.987

Front 18

How do you convert Celsius to Kelvin?

Back 18

add +273