BMB test 1: 1.5

How do peripheral membrane proteins affect biological membranes?

PMPS are essentially "water-soluble" proteins that mpart structural and functional versatility upon bio moelcules

What do amphiphilic molecules do in water?

amphiphilic molecules such as detergents and phospholipids associate (but do not solubilize/dissolve) into micelles/bicelles as to form a homogenous solution

What is a function of nano discs?

artificial membranes for research in that they represent a more native system for the stabilization/folding of membrane proteins than liposomes, micelles, and micelles

How are lipids distributed on each face o the lipid bilayer face?

asymmetrically distributed

Why are lipid tails within the core of the bilayer under constant motion?

free rotation about the C-C bond

How is the liquid crystal phase of the lipid bilayer characterized?

gel-like solid with an ordered array (T < Tm)

What are the characteristics of integral proteins when in water?

highly hydrophobic and insoluble (predicate out)

what drives the formation of such artificial membrane systems?

hydrophobic effect

What allows amphiphilic substance to form micelles/bicelles?

hydrophobic effect, amphiphilic substance shield their hydrophobic groups while exposing their hydrophilic groups to water

What type of molecules associate into micelles?

in aqueous solution, single-tailed detergents (amphiphilic) such has sodium dodecyl sulfate (SDS) and fatty acids associate into micelles (monolayers)

What are the two classes of membrane proteins?

integral and peripheral depending on the nature of their interactions whittle lipid bilayer

What roles do alpha helical transmembrane proteins hold?

play roles in signal transition (cell surface receptors) and energy generation (protein pumps)

How are glycoproteins/proteoglycans formed?

proteins decorated with oligosaccharides

What are apolipoproteins?

proteins involved in lipid metabolism

What are membrane scaffold proteins (MSPs)?

proteins involved in lipid metabolism that harbors amphipathic character (apolipoproteins)

How do hydrophobic nutrients and drugs absorb into tissues?

readily dissolve into lipid bilayer of lipososme

What are all the living organisms enclosed by?

semi-permeable barrier/cell membrane called lipid bilayer

What is a characteristic of peripheral membrane proteins?

water-soluble

What is a liposome?

3D spherical structures fully enclosed by a single bilayer with a central aqueous cavity

What are alpha helical transmembrane proteins?

?can either traverse through the bilayer once (monotopic) or multiple times (polytopic) to form a helical bundle

How is the liquid solution phase of the lipid bilayer characterized?

viscous liquid with high mobility (T > Tm)

Why is transverse diffusion rare?

Exchange of lipids across the bilayer leaflets (transverse diffusion) is rare due to thermodynamic constraints

What do integral membrane proteins contain?

a transmembrane structure consisting of alpha helices and beta barrels with a hydrophobic surface

Why are biological membranes highly dynamic and fluid?

ability of lipids to rapidly exchange with each other within the plane of the same bilayer leaflet (lateral diffusion)

What do peripheral membrane proteins do?

adhere to the surface of either the inner or outer leaflet of the bilayer via association with lipid head groups or non-transmembrane regions of integral membrane proteins

What are two types of secondary structure that occur in transmembrane proteins?

alpha helices and beta pleaded sheet

What is an example of PMPs giving structural support to proteins?

attachment of spectrin, actin, and ankyrin to the inner leaflet of bio membranes not only serves as the "membrane skeleton" (cell shape) but also framework for signal networks from nucleus to cell surface

How is the motion of the lipid bilayer described and why?

because of the mobility of lipids primarily within the same plane of the bilayer, the motion is often described as 2D fluid

What characterizes amphiphilic nature?

both hydrophilic and hydrophobic characters, possessing both polar (charged) and apolar regions

What are some of the functions of liposomes?

can serve as articifical membranes for research and vehicles for delivery of hydrophilic nutrients and drugs that do not readily dissolve through cell membranes

What may the central cavity of detergent micelles be filled with?

central cavity may be filled with water depending on the concentration of detergents molecules

What is the transition temperature dependent on?

chain length (x) and degree of saturation (m) of fatty acids of membrane lipids

What helps maintain the fluidity of the lipid bilayer at ambient temperature?

cholesterol

How is cholesterol affected when T > Tm?

cholesterol (due to its highly rigid fused ring system) decreases bilayer fluidity by interfering wit the motions of lipid tails

How is cholesterol affected the T < Tm?

cholesterol increases bilayer fluidity by disrupting close packing lipid tails

What factors influence the fluidity of a bilayer?

cholesterol, chain length, and degree of saturation

What are nano discs comprised of?

comprised of a central phospholipid bilayer wherein the outer ordinary/perimeter of apolar tails is shielded by amphipathic proteins called "membrane scaffold proteins" in a double-belt fashion

What causes phospholipid micelles to form liposomes

disruption by physical treatments such has sanitation

What molecules aggregate into to bicelles? Why?

double tailed amphiphilic molecules form micelles because unfavorable steric clashes between double-tailed lids require them to pack into a disc-like bilayer (hydrophobic effect)

What is the fluid mosaic model?

dynamic arrangement and interactions of membrane lipids and proteins

What are beta barrel transmembrane proteins?

essentially comprised of a large multi-stranded beta sheet that twists and coils to form a closed hollow channel, which allows passive diffusion of nutrients, salts, and water

What drives the formation of micelles?

it is thermodynamically more favorable for non-polar detergent tails to exclude water and engage in van der Waals contacts with the neighboring tails in addition to being entropically favorable (TdeltaS > 0)

Why can cholesterol act as a fluidity buffer?

its ability to fit between phospholipids allows it to either broaden or abolish the phase transition in lipid bilayers in vitro in response to changes in temperature

What kind of movement do integral membrane proteins participate in?

lateral diffusion along plane of bilayer

Why does the lipid bilayer undergo a dramatic phase transition in vitro?

lipid bilayer transitioned from being highly viscous fluid (liquid solution) to a gel-like solid (liquid crystal) as the temperature is lowered to and below a certain threshold value, transition temperature

What are cell membranes composed of?

lipid bilayers

How do liposomes deliver hydrophilic nutrients and drugs?

liposomes fuse with biological membranes and empty their contents inside the cell

What conditions provide a higher transition temperature?

longer chain length and/or higher the degree of saturation, the higher the Tm

What are the four distinct type of artificial/synthetic membrane system that ordered aggregates of amphiphiles form?

micelles (monolayers), micelles (bilayer), liposomes (bilayer), and nano discs (bilayer)

What is the movement like for polar heads in the lipid bilayer?

motion of the head groups is relatively restricted due to steric clashes or unfavorable polarity

How do nano discs and lipid bicelles differ?

nano discs represent relatively homogenous structures and lipid bicelles are highly heterogeneous (poorly defined 3D architecture)

Is cholesterol polar or non-polar?

non-polar (allows it to interact with fatty acid chains)

Protein components of bio molecules are ______________ distributed on both sides

not evenly

What is an example of proteins not being evenly distributed on bio molecules?

oligosaccharides of glycoproteins are almost exclusively attached to their extracellular regions (where they play a central role in mediating cell-cell interactions)

What is an example of lipid distribution on each face of the lipid bilayer?

sphingomyelin and phosphatidyl choline are predominately located in the extracellular leaflet of erythrocytes, whereas phosphatidylethanolamine and phosphaitdylserine are on the cytoplamsic side

Why do lipids not engage in transverse diffusion as quickly as lateral diffusion?

such flip-flop requires the outer polar head to rotate and become momentarily immersed in the apolar environment of lipid tails at the core of the bilaye

What is the composition of a lipid bilayer?

tails of lipids align up against each other while the heads point either toward exterior or interior of cell in manner akin to a liposome architecture

What is the fluidity of the lipid bilayer dependent on?

temperature and lipid composition

What is the hydrophobic effect?

the ability to exclude water from their apolar tails

How are integral membrane proteins similar to amphiphiles?

the protein regions (transmembrane segments) immersed within the bilayer are predominately composed of non-polar amino acid residues, while the intervening regions (loops) reusing on the extracellular and cytoplasmic faces are dominated by polar and charged residues

Why do glycerophospolipids and sphingolipids, but not fatty acids, form bilayers?

the tail geometry and the relative size difference between the hydrophobic and hydrophilic regions prevent fatty acids form forming bilayers. Phospholipids have two fatty acid chains that favor disc like formation where as fatty acids have one fatty acid chain that favors sphere formation.

What is the transition temperature (Tm)?

the temperature t which the bilayer "melts"

Why do apolar tails exclude water?

thermodynamic grounds

Why are lipids asymmetrically distributed in bilayers?

to attune specific cell types for their specific need sand physiological functions

What do integral proteins do?

traverse through the lipid bilayer once (montopic) or multiple time (polytopic)

What do transmembrane segments traversing lipid bilayers usually adopt?

two major folds or topologies, alpha-helical or beta-barrel

How do peripheral membrane proteins adherer to the surface of the bilayer leaflets?

via association with lipid head groups or non-transmembrane regions of IMPs

How do polar heads interact with water?

via hydrogen bonds