5.1 Structure of Cell Membranes Flashcards
Not only do membranes physically separate cells from their external environment, they also:
define spaces within many cells that allow them to carry out their diverse functions
what are the main component of cell membranes?
lipids because they have properties that allow them to form a barrier in an aqueous environment
also has proteins and carbohydrates embedded or associated
what is the major type of lipid found in cell membranes?
phospholipids (made up of a glycerol backbone attached to a phosphate-hydrophilic group and two fatty acids-hydrophobic)
amphipathic
having both hydrophilic and hydrophobic regions
how do amphipathic molecules arrange themselves in aqueous environment? (in water)
they arrange themselves so hydrophilic side faces outwards to interact with water and non polar groups face away from water
polar molecules like water tend to….
exclude nonpolar molecules or nonpolar groups of molecules (useful for healing cell membranes)
what is the shape of the structure determined by?
the bulkiness of the head group relative to the hydrophobic tails
micelle
a spherical structure in which lipids with bulky heads and a single hydrophobic tail are packed
bilayer (formed by lipids with less bulky head gouts and two hydrophobic tails)
a two-layered structure of the cell membrane with hydrophilic “heads” pointing outward toward the aqueous environment and hydrophobic “tails” oriented inward, away from water
the bilayer structure forms spontaneously and without the action of an enzyme as long as:
the concentration of free phospholipids is high enough and the pH of the solution is similar to that of a cell
the pH of the environment is important for cell membranes/phospholipids because :
it ensure that the head groups are in their ionized (charged) form and thus hydrophilic
liposome
an enclosed spherical bilayer structure spontaneously formed by phospholipids in environments with neutral pH, like water
lipids freely associate with one another because of:
extensive van der Waals forces between their fatty acid tails (very weak forces, can easily be broken and re-formed)
fluid
describes lipids that are able to move in the plane of the cell membrane
the degree of membrane fluidity depends on:
which types of lipid make up the membrane
in a single layer of the lipid bilayer, the strength of van der Waals interactions between the lipids’ tails depends on:
the length of the fatty acid tails and the presence of double bonds between neighbouring carbon atoms
the longer the fatty acid tails, the more surface is available for van der Waals interactions resulting in:
tighter packing and reduced mobility
saturated fatty acid tails have no double bonds which has what result on mobility?
reduced mobility because of tighter packing
unsaturated fatty acid tails have double bonds and kinks resulting in:
enhanced lipid mobility due to reduced tightness of packing
cholesterol
an amphipathic lipid that is a major component of animal cell membranes
the amphipathic structure of cholesterol allows it to:
pack tightly with phospholipids: hydrophilic hydroxyl group interacts with polar head of phospholipids, ring structure participates in van der Waals interactions with the fatty acid chains
cholesterol increases or decreases membrane fluidity depending on:
temperature
at temperatures typically found in a cell, cholesterol:
decreases membrane fluidity because of interactions between rings of cholesterol and phospholipid fatty acid tail (van der Waals forces)
at low temperatures, cholesterol:
increases membrane fluidity because it prevents phospholipids from packing tightly with other phospholipids
