LIPID MEMBRANES AND TRANSPORT Flashcards
Describe the kind of membrane that all cells have. What makes it so unique and important for the cell? What additional membrane does the eukaryotic cell have that prokaryotic does not have?
All cells have plasma membrane
It is a barrier that prevents intracellular molecules from leaking cell and blocks harmful molecules form entering cell.
Eukaryotic cells have internal membranes that limit intracellular mem compartments and organelles.
what other functions besides barriers do cell membranes do? What specific structures are included?
sense changes in environment, control the passage of solutes across membrane, allow cells to move and acquire certain shapes.
They have membrane proteins and a bilayer.
describe the bilayer structure that all membranes have? What structures are present? what is the unique characteristic?
double layer made of lipids, specifically phospholipids. bilayer has mosaic structure, with membrane proteins embedded in in it. They have amphiphilic nature (both hydrophilic and hydrophobic).
Describe the structure of phospholipids? How do phospholipids differ?
phospholipids have hydrophilic head that have phosphate groups, hydrophobic tail that have fatty acids. They differ by their size of hydrophobic tails and chemical structure of POLAR HEAD specific groups (form ester bond with phosphate)
What are fatty acids? Provide examples of fatty acids?
simple lipids that have hydrophobic carboxylic acid head and long hydrophobic, aliphatic radical (R) tails.
Ex: fats, oils, cholesterol, steroid
Describe the structure of triacylglycerol. What are some examples? What makes them different from phospholipids?
Triacylglycerol- 3 fatty acids attached glycerol atom by ester linkages. examples include FATS (animal flat, plant oils).
makes them different- they are completely HYDROPHOBIC(lack of groups, so no H-bonds). Phospholipids are amphiphilic.
Distinguish between the energy use of carbohydrates vs. triacylglycerol in the cell. where are triacyclglycerols stored?
energy from carbohydrates (glycogen, starch) are stored for immediate use. While triacyclglycerols are for long- term storage of energy.
stored in adipocytes (as free intracellular droplets)
What are the most abundant lipids in the cell membrane? What defines the class of lipids?
phospholipids. polar head.
How do the four major membrane phospholipids differ? What structural feature define phospholipids?
They differ in size of hydrophobic tails, shape and charge.
Polar heads defines phospholipid
Ex: phosphatidyl- choline, serine, ethanolamine
What is another major component of membrane and has similar amphiphilic nature like phospholipids?
Cholesterol (form of sterol)
What feature distinguishes lipids from carbs (polysaccharide) and nucleic acids?
lipids are chemically diverse and characterized by their ability to be extracted into organic solvents, when cells are homogenized.
list all functions of lipids.
lipids serve as membrane building blocks, store energy, and SIGNALING (membrane receptors, endocrine), TRANSPORT .
What lipid structure is responsible for transporting water insoluble molecules in blood? list examples of insoluble molecules.
serum albumin
examples include: fatty acids, triacylglycerols, steroid hormones
Describe the other types of membrane lipids (besides phospholipids) that are amphiphilic. What are their chemical structures?
polyisoprenoids (made form isoprene units)
steroids- multiple ring structure, polar head that has OH group, 1 hydrocarbon tail(also made of isoprene units)
Glycolipids (2 long hydrophobic tails, polar region of OH and sugar (galactose)
Describe the behavior of phospholipids when in water.
polar heads are exposed to water, while hydrophobic, nonpolar tails minimize interaction with water and hide inside, by forming micelles
What are two ways of hiding polar tails? what are the two different structures?
in water, spontaneously form micelle or lipid bilayers (allowing tails to hide inside structure) and facing polar heads out to aqueous environment.
Why do lipid bilayers spontaneously close? what happens if bilayer had open edges or was in a planar form?
spontaneously close to form sealed compartments and prevent hydrophobic tails from being exposed to aqueous environment. if the bilayers have open edges, hydrophobic interior will be exposed to outside, water environment and be unstable
What are liposomes? what is the function?
closed bilayer compartments (sphere shape) that are artificially made by mixing pure lipids in water.
Used for drug delivery
What three chemical forces keep phospholipids together in the right orientation and stabilize plasma membrane in water? Describe how each force does this.
Hydrophobic interactions-major force that keeps lipids together, form bilayer
VDW- strengthen interactions between tails when tails are close to each other
hydrophilic- position polar heads outward in each layer
What defines the elasticity of plasma membrane? describes the different types of examples of this feature?
mobility of phospholipids
ex of movement: flexion (side to side), rotation, flip flop of leaflet (rarely occurs unless assisted by enzymes)
How can carboxyl groups of fatty acids be connected to other organic molecules?
Carboxy group can form esters or amides
What role do triacyclglycerols play in the cell?
major energy deposits the cell, structural component of cell, store energy.
How do fatty acids vary in phospholipids?
vary by length and saturation (max number of hydrogens). Some fatty acids are unsaturated (have double bonds)
provide an example of each type of lipid
Phospholipid- ex: phosphatidyl-choline, sphingomyelin
Steroid- ex: cholesterol, testosterone
Glycolipid- ex: galactocerebroside
Polyisoprenoid- (made from isoprene units)
ex: Dolichol phosphate that carries activated sugars in membrane associated synthesis of glycoproteins.
Which two enzymes help overcome and support bilayer leaflet’s asymmetric composition? List specific function of each.
Flippases and Scramblases.
Flippase- support and maintain asymmetric lipid in Golgi. They catalyze transfer of SPECIFIC phospholipids from exterior space, flip and move them into cytosolic monolayer.
Scramblases- newly synthesized phospholipids added to cytosolic half of bilayer (ER) . enzyme catalyzes transfer of random lipids from one monolayer to another, allowing for symmetric growth, even distribution.
How are newly synthesized lipid membranes and lipids delivered through plasma membrane and organelles?
lipids are synthesized in the smooth ER, passes golgi complex, and delivered to PM through TRANSPORT VESICLES
What adds to the asymmetry of cell membrane bilayers?
Functional phospholipid modification
Differentiate between saturated and unsaturated fatty acids? what feature makes them different. Provide examples of each.
saturated-fatty acids with no double bonds
ex: stearic acid, palmitic acid
unsaturated- fatty acids with 1 or more double bonds ex: oleic acid, maleic acid and fumaric acid (trans db)
What does the presence of double bond indicate in fatty acid chain
Indicates fatty acid is unsaturated, double bond creates a kink in the chain, does not allow free rotation about that specific C-C bond.
what differentiates oleic acid from stearic acid? how are they similar?
Oleic acid has double bond (unsaturated); similarities- both have 18 carbon long fatty acid chain.
What 3 factors fluidity of plasma membrane depend on? Describe the relationship between temperature and fluidity.
composition of PM and temperature and length of fatty acid.
The HIGHER the TEMPERATURE, the HIGHER the FLUIDITY
what happens to fluidity, with saturated fatty acids? Why does this occur?
when saturated fatty acids increases, the fluidity decreases. occurs because van der Waals interaction increases between lipids (strong attraction to keep tails together)
How does the Length of fatty acids affect membrane fluidity?
The longer the fatty acid, the less fluid a fatty it is. (due to more VDW interactions formed, making it stiff)
How do fatty acid residues vary in length? Which fatty acids are extremely long? How many carbon atoms?
They vary from 14 to 20 carbon atoms long. phospholipids are very long like SPHINGOMYELIN with 24 carbon atoms.
Do fats with unsaturated triacylglycerols have a Higher or Lower melting point?
Lower melting point (due to db)
Distinguish between the two types of triacyclglycerols in terms of saturation.
Plant oils have unsaturated fatty acids. Animal fats have large portion of saturated fatty acid residues.
How can cell membranes maintain fluidity at low temperatures? What occurs if the temperature is too high?
INCREASE UNSATURATED FAs. Membranes rich in unsaturated hydrocarbon tails remain fluid at lower temps.
temp too high, you will add extra fluidity and make membrane too loose and porous (not good).
Hence maintain fluidity without losing integrity in broad rang of temps.
What other major component of cell membrane is important and determines fluidity of membranes?
Cholesterol! They help create a constant rate of fluidity under broad range of temperatures. function as FLUIDITIY BUFFER
Elaborate on Cholesterol’s fluidity buffer role in cell membranes. How does it maintain it with high temps? Lower temps? what percentage of cholesterol composes membrane lipids?
cholesterol keeps fatty acid fluidity in intermediate range, regardless of temperature shifts. In high temps, it keeps membrane more solid.
lower temps- keeps membrane more liquid.
30%
Describe the interaction of cholesterol in the lipid bilayer.
Cholesterol forms nonpolar and polar interactions with membrane lipids. polar group (OH) of cholesterol are in contact with polar head of phospholipids. short nonpolar tail of cholesterol interact with hydrophobic tail of phospholipids
Describe the structure of cholesterol and how it helps maintain fluidity. Compare it to phospholipids.
Cholesterol has rigid, flat steroid ring structure that does not change conformation during temperatures shifts, which helps to maintain fluidity.
However, phospholipids can be densely packed (less fluid) or too loose based on temp
distinguish the effect of cholesterol at low temps vs its effect at high temps.in terms of mechanism
Low temps- steroid rings help break down compactness of lipids (create more space), allowing more liquidity, fluidity.
High temps- inserts vertically to preserve fluidity, keep lipids together and prevent them from spreading.
What would happen to phospholipid molecules without cholesterol?
The phospholipid membranes would change their physical properties in narrow range of temps, greatly affecting cellular functions (make them fluid and disordered)
Cholesterol- helps keep membranes fluid (elastic) and non-porous.
