L9. Membrane structure & function Flashcards
how does the plasma membrane act?
- as a selective barrier
- as a means of information relay
plasma membrane - selective barrier
- separates cell form its surroundings
- enables cells to differ from its environment
plasma membrane - information relay
- receiving information using receptor proteins
- import and export of small molecules using transport proteins
- capacity for movement and expansion
explain membrane composition
- all membranes are composed of lipids and proteins
- the lipids are arranged in two closely apposed sheets forming a lipid bilayer
- this bilayer serves as a permeability barrier to most water-soluble molecules
membrane composition - lipids
- each lipid has a hydrophilic head and a hydrophobic tail
- thus are known as amphipathic
membrane composition - phospholipids
lipids that have a phosphate-containing hydrophilic head linked to a pair of hydrophobic tails
phospholipids - hydrophobicity and hydrophilicity
- the hydrophobic tails are insoluble in water bc they are uncharged and nonpolar
- the hydrophilic heads dissolve readily in water bc they are charged and polar
explain the spontaneous closing of the bilayer
because of the phospholipids hydrophobic and hydrophilic properties it is energetically favorable for the molecules to create the bilayer
spontaneous closing of phospholipid bilayer - what are liposomes
they are pure phospholipids that forms closed spherical vesicles when added to water
what does the fluidity of the phospholipid bilayer depend on
- hydrocarbon tail lengths
- saturation
fluidity of phospholipid bilayer - hydrocarbon tail length
- longer tails interact more and makes the membrane less fluid
- shorter tails interact less and makes the membrane more fluid
fluidity of phospholipid bilayer - saturation
- unsaturated tail = has kinks (double bonds present) = more fluid
- saturated tail = has no kinks (no double bonds present) = less fluid
phospholipid fluidity - bacteria and yeast
- they are able to modify the conditions with temperature
- higher temp = longer tails and fewer double bonds = less fluid
what do scramblases do
they are enzymes that randomly transfer phospholipid molecules from one monolayer to the next
scramblases - where are they located and when are they used
- located in ER membrane
- used when phospholipid synthesis adds new phospholipids to the cytolytic side of the bilayer