BCH 4033- ch.12 lipids and biological membranes

exam 3 content

what are fatty acids?

hydrocarbon chains of various lengths and degrees of unsaturation that terminate with a carboxylic acid group

how many carbons do fatty acid chains in membranes contain?

14-24 carbons

saturated or unsaturated

how is the fluidity of fatty acids enhanced?

short chain length and unsaturation lower the melting temperature

what are the major types of membrane lipids?

phospholipids, glycolipids, cholesterol

what is a phospholipid?

a constituent of membranes that has 3 components

• a backbone (glycerol or spingosine)

• 2 fatty acid chains

• phosphorlyated alcohol

what is a glycolipid?

a sugar-containing lipid derived from sphingosine

sugar moiety is attached at the alcohol on sphingosine

what is cholesterol?

a sterol that’s a constituent of eukaryotic membranes and lipoproteins

a precursor of steroids hormones and modulates membrane fluidity

what are phosphoglycerides?

a type of phospholipid with 3 components

• a glycerol backbone

• 2 fatty acid chains

• a phosphorylated alcohol

what are the major phosphoglycerides?

phosphatidylcholine

phosphatidylserine

phosphatidylethanolamine

what is sphingomyelin and how does it differ?

a type of phospholipid

has a sphingosine backbone instead of glycerol

what do membrane lipids form?

extensively bimolecular sheets in aq. solutions (spontaneously)

what is the driving force for membrane formation?

the hydrophobic interactions among the fatty acid talks of membrane lipids

hydrophilic heads interact with aq. medium

what are lipid bilayers?

cooperative structures held together by many weak bonds

what do lipid bilayers act as and why?

a solvent for membrane proteins

because they’re highly impermeable to ions and most polar molecules but are still fluid

how do cell types get their diversity?

by the biological membranes that vary in their protein content

what is the function of integral membrane proteins and how are they released?

to interact extensively with hydrocarbon chains of membrane lipids

released only by agents that compete for the nonpolar interactions

what are peripheral membrane proteins and how are they released?

proteins bound to membranes by electrostatic and H-bond interactions with the heads of lipids

released by adding salt or changing the pH

what is the structure of a membrane-spanning protein?

usually regular and with alpha helix (most common) or beta strands

• alpha helices predicted from the AA sequence using a hydropathy plot

what is a hydropathy plot?

an analysis of AA sequences used to locate potential membrane-spanning alpha helices by IDing highly hydrophobic areas across a defined sequence window

what are membranes?

dynamic structures in which proteins and lipids diffuse rapidly in the plane of the membrane

is the rotation of lipids from one face of the membrane to another slow or fast?

slow. very slow

how is membrane asymmetry preserved?

because proteins don’t rotate across bilayers

what does the degree of membrane fluidity depend on?

the chain lengths of its lipids and the extent to which their constituent fatty acids are unsaturated

more unsaturated = more fluid

what does cholesterol regulate in animals?

membrane fluidity

what is the fluid mosaic model?

a model that describes the overall organization of biological membranes as 2D solutions of oriented lipids and globular proteins

what are the 2 types of membranes bacteria exhibit?

1. a single membrane surrounded by a cell wall

2. a double membrane → the inner membrane serves as a permeability barrier

how are compartments within a eukaryotic cell created?

by an extensive array of internal membranes

compartments used for distinct biochemical functions

are the budding and fusion of membranes controlled or uncontrolled?

controlled. highly controlled

what does receptor-mediated endocytosis enable?

the formation of intracellular vesicles when ligands bind to their corresponding receptor proteins in the plasma membrane

what is the fusion of a vesicle to a membrane?

the reverse process of receptor-mediated endocytosis

key step in releasing the signaling molecules outside the cell