biochem - 8 - membranes

what are the primary functions of the cell membrane?

• separate the interior and exterior of the cell

• facilitate cell-cell interactions

• exclusion of toxic molecules and ions

• accumulation of cell nutrients; energy transduction and signal transduction

• cell locomotion; cell division (flexible)

what types of lipids may be found in a cell membrane?

• glycerophospholipids

• sphingolipids

• terpenes

• cholesterol

what type of lipid is not found in a cell membrane?

triacylglycerol

what type of lipid forms the majority of the cell membrane?

glycerophospoholipid

what function does cholesterol serve in cell membranes?

increases strength and flexibility of cell membrane

which types of membrane structures form spontaneously?

• monolayers

  • micelles

• bilayers

  • vesicles

  • liposomes

what types of molecules produce monolayers?

amphipathic lipid molecules (when interacting with water)

what types of molecules produce bilayers?

lipids, such as membrane lipids (glycerophospholipids)

categorize each as a monolayer or bilayer:

• micelle

• vesicle

• liposome

• micelle: monolayer

• vesicle: bilayer

• liposome: bilayer

what is a mcelle?

• spherical lipid aggregates which have long hydrophobic chains in the center and the charged carboxyl groups on the outside

what is a vesicle?

naturally occuring; spherical bilayer structures that can consist of multiple bilayers

what is a liposome?

made in a laboratory; artificially prepared vesicles used in laboratory experiements

draw a micelle - inside-out and normal

draw a monolayer and bilayer - formed on water

draw a unilamellar vesicle (or liposome)

• bilayer structure

draw a multimellar vesicle

• bilayer structure

describe the fluid mosaic model of membrane structure

• considers that the lipids bilayer is a fluid supporting matrix for membrane proteins

• biological membranes are dynamic structures, and both liquids and proteins are capable of movement within the bilayer

what are the two classes of membrane proteins?

• integral membrane protein (intrinsic)

  • extended into or through the bilayer

• peripheral membrane proteins (extrinsic)

  • external to the lipid bilayer

in membranes, list the types of

• lipids,

• proteins, and

• carbohydrates

that may be found

• lipids

  • glycerophospholipids

  • cholesterol, other lipids

• proteins

  • integral

    • α-helical proteins

    • β-barrel proteins

• carbohydrates

  • glycoproteins

  • glycolipids

describe the structure of integral proteins

• largely contained within the lipid bilayer, or

• attached to the membrane by only a small hydrophobic segment

describe the structure of peripheral proteins

• loosely associated with the outside of the membrane; bind to the membrane through non-covalent interactions 9hydrophobic, ionic, hydrogen-bonding) with integral proteins

describe the structure of lipid-anchored proteins

• membrane proteins (integral or peripheral) that are covalently linked to lipid molecules in the membrane

  • includes proteins bound to fatty acids such as myristric acid and palmitic acid

what type of structure is the protein bacteriorhodopsin?

α-helical integral membrane protein

what type of structure is the protein OmpX of E. coli?

β-barrel integral membrane protein

what type of structure is the protein glycophorin A?

• integral membrane protein

  • attached to the membrane by only a small hydrophobic segment

• the carbohydrates are antigenic determinants for the MN blood group system

• (ABO blood group system is due to carbohydrates attached to membrane proteins or membrane sphingolipids - the carbohydrates are the antigenic determinants)