Chapter 7 - Membrane Structure and Function Flashcards
what are state ingredients of membranes?
lipids and proteins - carbohydrates also important
lipids are the most abundant in the plasma membrane
what does amphipathic mean? what demonstrates this characteristic?
phospholipids form membranes - they are an amphipathic molecules meaning it has both a hydrophilic region and hydrophobic region
membrane proteins are also amphipathic - embed themselves in phospholipid bilayer
which part of the phospholipid faces water? inside?
hydrophobic tail faces inwards while hydrophilic heads face water
what is the fluid mosaic model?
the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids
where are lipids made?
where are membrane phospholipids made and the the assembly of the membrane take place?
smooth ER
membrane phospholipids and assembly of membrane + protein occurs in rough ER and golgi apparatus
phospholipid movement in the plasma membrane?
Most drift laterally (weak hydrophobic interaction)
Rarely does a lipid flip b/c it requires energy like ATP
proteins don’t usually move b/c larger but some can
which experiment showed that the plasma membrane isn’t static?
took two cells and labeled them with different colors and after an hour the proteins become equally distributed – this experiment shows that membrane isn’t static
phospholipid phase in relation to temperature
As temperature cools, membranes go from fluid to solid state b/c phospholipids pack together
what allows a membrane to stay fluid at lower temperatures?
membrane remains fluid to a lower temperature if it’s rich in phospholipids with unsaturated hydrocarbon tails - kinks in the tail b/c of double bond means they can’t pack closely together
different environments have different temperatures so you need a balance of sat/unsat to maintain fluidity
effects of cholesterol on the membrane
it’s a fluidity buffer
at high temperatures (body temp): cholesterol makes the membrane less fluid by restraining the phospholipid movement - gives structure to cell membrane
but at lower temperatures cholesterol also hinders the close packing of phospholipids and lowers the temperature required for the membrane to solidify
what determines most of the function of the plasma membrane?
the proteins
what are the two types membrane proteins?
1) integral proteins
2) peripheral proteins
what is an integral protein?
Integral protein is able to penetrate the hydrophobic interior of the lipid bilayer
the majority of integral proteins of transmembrane proteins - some only extend partway into the hydrophobic interior
what are trans-membrane proteins?
a type of integral proteins that span the membrane: a portion is inside and the other part is sticking outside
the hydrophobic regions of an integral protein consist of one or more stretches of non polar amino acids usually coiled into alpha helices
the hydrophilic regions are exposed to the aqueous solutions on either side of the membrane (extracellular and cytoplasmic side) - some proteins also have hydrophilic channels that allow passage through the membrane of hydrophilic substances
what are peripheral proteins?
peripheral proteins are not embedded in the lipid bilayer at all - they are appendages loosely bound to the surface of the membrane (often to exposed parts of integral proteins) or phospholipid head
how do membrane proteins attach?
on cytoplasmic side, some membrane proteins are held in place by attachment to the cytoskeleton
on extracellular side, they are attached to fibers of the ECM
what are the 6 major functions of membrane proteins?
1) Transport: if they’re too large or hydrophilic, proteins
help these molecules get across w/ channels
2) Enzyme activity: enzymes are embedded in the membrane which is useful because spatially you can keep chemical reactions close together
3) Signal transduction: may have a binding site with a specific shape that fits the shape of the chemical messenger (receptor) or the external messenger(signaling molecule) may cause protein shape to change to allow message to be relayed to the inside of the call
4) Cell-cell recognition: glycoproteins serve as ID tags
5) Intercellular joining: tight or gap junctions can form
6) Cytoskeleton and ECM attachment
how do cells recognize other cells?
cell recognize other cells by binding to molecules, that often contain carbohydrates, on the extracellular surface of the plasma membrane
membrane carbohydrates
usually short, branched, chains of fewer than 15 sugar units
some are covalently bonded to lipids forming glycolipids
most are covalently bonded to proteins which are glycoproteins
membrane sidedness and synthesis
o Distinct inside and outside faces
o The asymmetrical distribution of proteins, lipids, and associated carbohydrates is determined when the membrane is built by the ER and golgi
what are the components that make a cell’s membrane selectively permeable?
1) hydrophobic interior: polar molecules and ions can’t pass
2) specific transport proteins
what are transport proteins? what do they do?
transmembrane proteins that help hydrophilic substances pass through the lipid bilayer
channel proteins are a type of transport protein that have hydrophilic channels for certain molecules or atomic ions to use as a tunnel through the membrane