BIOL266 MIDTERM2 Flashcards
State 3 functions of the plasma membrane
1- Import and export of molecules.
2- receiving information.
3- capacity of movement and expansion.
nutrients pass _______ the plasma membrane and waste products pass _______ the plasma membrane.
inward and outward.
The plasma membrane serves and prevents
- barrier that separates in the interior of the cell from the surrounding medium.
- prevents contents of the cell from escaping and mixing with the surrounding medium.
Some proteins in the plasma membrane act as
sensors in the plasma membrane to enable cell to respond to changes in its environment.
How does the plasma membrane expand?
when the cell grows or changes shape, the plasma membrane enlarges its area by adding new membrane while deforming without tearing.
The membranes that surround the organelles of cells
separate one aqueous phase (cytosol) from another (interior of organelle).
Internal membranes serve as
selective barriers.
membrane-bound organelles (internal membranes) maintain
the characteristic differences in composition between these organelles.
Name some membrane-bound organelles
- endoplasmic reticulum.
- peroxisomes.
- nucleus.
- lysosome.
- Golgi.
- transport vesicles.
- mitochondria.
General structure of cell membranes
lipids and proteins.
The lipid component of a cell membrane consists of
millions of lipid molecules arranged in two closely opposed sheets, forming a bilayer.
Properties of a single lipid molecule
1- hydrophilic head.
2- one or two hydrophobic hydrocarbon tails.
Define amphipathic molecule
molecules with both hydrophilic and hydrophobic properties.
Name five types of lipids
1- fatty acids. 2- phospholipids. 3-glycerol phospholipids. 4- non-glycerol phospholipids. 5- cholesterol.
A fatty acid consists of
a long hydrocarbon chain with a negatively charged carboxyl group.
Types of fatty acids
- in saturated fatty acids all of the carbon atoms are bonded to a maximum number of hydrogen atoms.
- unsaturated fatty acids contain one or more double bonds between carbon atoms, resulting in one covalent bond with hydrogen.
The most abundant lipid are
phospholipids.
Phospholipids consist of
two fatty acids linked to a polar head group.
In glycerol phospholipids
- the two fatty acids are bound to carbon atoms in glycerol.
- the third carbon atom is bound to a phosphate group, which is attached to another small polar molecule (radical).
Types of small polar molecules (aminos) found in glycerol phospholipids
choline, serine, inositol, ethanol amine.
The most common glycerol phospholipid in most cell membranes is
phosphatidylcholine.
The net charge of small polar molecules found in phospholipids
- choline and ethanol amine are neutral.
- serine and inositol are negatively charged.
What typer of lipid is sphingomyelin?
non-glycerol phospholipid.
Define the structure of non-glycerol phospholipids
- contain two hydrocarbon chains linked to a polar head group formed from serine rather than glycerol.
- the third carbon atom of serine is bound to a phosphate group which in turn is attached to choline.
Define the structure of glycolipids
-consist of two hydrocarbon chains linked to a polar head group formed from serine, which is attached to a polar carbohydrate molecule.
Type of carbohydrate molecule in glycolipids
glucose or galactose.
Define the structure of cholesterol
-consists of four hydrocarbon rings, one hydrophobic tail and a hydroxyl hydrophilic head.
electrostatic bonds are between
charged atoms with polar polar groups and polar molecules (water).
Why are hydrophobic molecules insoluble in water
because of their uncharged and non polar atoms, thus cannot form bonds with polar water.
What happens when hydrophobic molecules are immersed in water
- a cage-like structure of water molecules forms around the tails, this requires energy.
- to minimize energy cost if tails cluster together.
Name two conflicting forces in amphipathic molecules
1- the heads attract water.
2- the tails shun water and aggregate together.
How are the conflicting forces in amphipathic molecules resolved
this is resolved by the formation of a phospholipid bilayer- most energetically favoured state.
Name two types of synthetic lipid bilayers
1- liposomes, closed spherical vesicles.
2- flat bilayers, phospholipids applied to a small hole separating two aqueous compartment.
Three types of phospholipid mobility in lipid bilayers
1- lateral diffusion: lipid molecules within a monolayer exchange places.
2- rotation: lipid molecules within a monolayer rotate around their axis.
3- “flip-flop”: lipid molecules rarely flip from one monolayer to the other.
membrane fluidity depends on
a- length of hydrocarbon tails.
b- level of saturation of tails with respect to hydrogen.
c- presence of sterol cholesterol.
In what do length of hydrocarbon tails affect membrane fluidity
- shorter chain increase fluidity because the distance between tails are larger (less packing).
- length of chain is inversely proportional to membrane fluidity.
In what way do levels of saturation affect membrane fluidity
- unsaturated= more fluid, increase distance between neighbouring molecules.
- saturated= less fluid.
In what way do cholesterol affect membrane fluidity
- the rigid hydrocarbon rings of cholesterol interact and partially immobilize the regions of fatty acid chains, therefor stiffening the bilayer and decreasing fluidity.
Lipid bilayer is symmetric (T/F)
False, it is assymetric.
The lipid composition of two leaflets of the lipid bilayers in many membranes
are different.
Lipids present in the extracellular leaflet + explain assymetry
- glycolipids and sphingomyelin.
- the asymmetry is generated by both glycolipids and sphingomyelin are produced by enzymes exposed to the Golgi lumen and are not substrates for flippases.
Phosphatidylcholine is mostly present in which leaflet
extracellular leaflet.
Glycerol phospholipids mostly present in the cytosolic leaflet + explain asymmetry.
- phosphatidylethanolamine and phosphatidylserine.
- asymmetry generated by flippases, moving these glycerol phospholipids from the extracellular leaflet t the cytosolic leaflet.
Lipid distribute equally in each bilayer leaflet
- cholesterol, spontaneously shuttles (flip-flops) between the leaflets.
- does not require flippases.
Specific flippases recognize different substrates (T/F)
True.
