what are the membrane functions?
1)compartmilization = each compartment can hvae its own distinct regulation and activities like intracellular digestion and photosynthesis can be isolated
2)scaffold for biochemical reactions= reactants can be embedded in membranes increasing their likelihood of interactions and reactants can be effectively ordered for faster interactions
3)selectively permeable barrier
4)transport of material in and out
5)responding to external stimuli= receptors allow external stimuli to trigger internal reactions such as dividing moving or dying
6)intracellular interactions= membranes allow for communications between cells such as contact ,adhesion and exchange of materials
7)energy transduction =machinery for photosynthesis and cellular resp are embedded in the membranes
what are the key membrane properties ?
1) fluid
2) asymmetric (two sides of membrane are different)
3)specific = to the funtion of the cell/organelle
4)self assembly= held together mainly by non cov interactions
5)semi-permeable=allows controls of contetn
6) mosaic= mixture of lipids and proteins
what is the relation between membrane fluidity and the membrane function?
include what helps membrane fluidity
the fluidity of the membrane is critical to its function, the membrane cant be too fluid or rigids
1) cholestrol content
2)temp
3)levels of unsat fatty acids
4)length of hydrocarbon chains
what is cholestrols function in fluidity ?
cholestrol acts as a fluidity buffer , prevents extremes in fluidity and helps the membrane not to get too rigid and not get too fluid
how does cholestrol prevent the membrane from freezing and melting ?
prevents freezing= it prevents the hydrocarbon tails from packing too closely and crystalizing
prevents melting= it limits the rapid movements/rotations of the phospholipid tails
what happens when its harder to get the membrane to freeze?
this results in lower transition temperature
it includes lots of unsaturated fatty acids and fatty acids with short hydrocarbon chains (less VDW interactions)
when does phase transition occur?
it occurs when a lipid bilayer converts between a fluid state to a rigid crystalline gel
when the membrane is easy to freeze what does it result in ? what does it include?
this results in high transition temperature
it includes lots of sat fatty acids and fatty acids with long chains (more vdw interactions)
What is membrane specificity ?
different membranes in cells and different cell types will have different lipid compositions
what happens to phospholipids when their in water?
they can spontaneously aggregate to form bilayers due to its ampipathic nature
when hydrophobic portions of molecules cluster ,water molecules move freely which does what?
increasing entropy
what does the phospholipid shape determine?
depending on the shape of the phospholipid it can either form a micelle or a bilayer
what are micelle shape?
individual fatty acids are wedged shaped and they form micelles , hiding all the hydrocarbon chains on the inside
what shape will phospholipids form ?
phospholipids are cylinderical there for it forms a flat bilayer which folds on to itself to sheild all edges from water(liposome), the liposome has a hydrophillic interior
What does membrane asymmetry mean? |
he two sides (leaflets) of the bilayer have different lipid compositions and functions.
Why is asymmetry important for cell function?
Certain lipids are required on specific sides for proper signaling; misplacement can trigger apoptosis.
Describe the lipid distribution in a red blood cell membrane.
Glycolipids are on the outer layer; inner layer contains more negatively charged glycerophospholipids like phosphatidylethanolamine and phosphatidylserine.
What is the glycocalyx?
A layer of sugars on the outer surface formed by glycolipids and glycoproteins; all sugars face outward.
How do lipids move within membranes?
Lipids move rapidly within a single leaflet (lateral movement, rotation), but rarely flip between leaflets spontaneously.
What enzymes help phospholipids move between layers?
Phospholipid translocators, also called flippases, catalyze flip-flop of phospholipids to maintain asymmetry.
What are lipid rafts?
Microdomains in the membrane where certain lipids and proteins cluster together; they are thicker, stiffer, and more ordered
What components are enriched in lipid rafts?
Cholesterol, sphingolipids, GPI-anchored proteins, and saturated fatty acids with long tails
What is the function of lipid rafts?
They cluster proteins of similar functions (e.g., in signaling pathways) to enhance communication efficiency.
