Topic 1.3: Membrane Structure Flashcards
Components of a phospholipid
a) Polar head
b) Non-polar tails
Component of polar head
a) Glycerol
b) Phosphate group
Component of non-polar tails
Two chains of fatty acids
Amphipathic
Containing both hydrophilic and hydrophobic regions
Arrangement of phospholipis
Bilayer
a) Hydrophobic tails face inwards
b) Hydrophilic head face outwards
Properties of the phospholipid bilayer
a) Held together by weak hydrophobic interactions between the tails.
b) Individual phospholipids can move within the bilayer (fluidity and flexibility)
c) Amphipatic properties restrict passage of certain substances.
Components in animal cell membranes
a) Cholesterol
b) Proteins
c) Phospholipids
Functions of cholesterol
a) Reduces fluidity by immobilising the outer membrane surface
b) Reduces permeability to some molecules
c) Prevents crystallization by separating phospholipid tails
Integral proteins
a) Permanently attached to the membrane
b) Typically transmembrane
Peripheral proteins
a) Temporarily attached
b) Associate with one surface of the membrane
Functions of Membrane Proteins
a) Transport
b) Receptors
c) Anchorage
d) Cell recognition
e) Intercellular joinings
f) Enzymatic activity
Transport
a) Protein channels
b) Protein pumps
Receptors
Peptide-based hormones
Anchorage
Cytoskeleton attachments
Cell Recognition
MHC proteins and antigens
Intercellular joinings
Tight junctions
Enzymatic activity
Metabolic pathways
Drawing of the fluid-mosaic model
a) Phospholipid bilayer
b) Glycoprotein
c) Carrier protein
d) Channel protein
e) Cholesterol
Davson-Danielli model
a) Two layers of protein adjacent to the phospholipid bilayer
b) EMG showing two dark lines with a lighter band.
Problems with Davson-Danielli model
a) Constant lipid-protein ratio and a uniform thickness
b) Permeability of certain substances such as H2O
c) Temperatures at which membranes solidified did not correlate with those expected.
Falsification of Davson-Danielli model
a) Membrane proteins were discovered to be insoluble in H2O. Not able to form a uniform and continuous layer.
b) Fluorescent antibody tagging of membrane proteins showed they were mobile and not fixed
c) Freeze fracturing was used to split open the membrane and revealed irregular roguht surfaces within the membrane.
Singer-Nicolson model
Proteins were embedded within the lipid bilayer rather than existing as separate layers
