1.3 Membrane Structure Flashcards
Hydrophilic
A molecule that is attracted to water
Hydrophobic
non-polar molecules that repel water
Amphipathic
contains both hydrophobic and hydrophilic parts
what did Gorter and Grendel discover(1925)
they extracted phospholipids from the plasma membrane of red blood cells and calculated the area that they covered when arranged in a single monolayer was twice as large as the area of the plasma membrane.
-this lead them to conclude that the phospholipids were arranged in a bilayer.
What did Davson and Danielli(1935) propose?
They though that the plasma membranes were sandwiched between two layers of protein
Why were there doubts of the validity of Davson and Danielli’s discovery?
- the amount and type of membrane proteins vary greatly between different cells
- Membrane proteins are largely hydrophobic and therefore should not be found where the model positioned them
- Fluorescent tagging of proteins showed that they are free to move with the membrane
How was their(DD) theory discredited?
It was discovered that the light layer in the electron micrograph that they originally thought was the phospholipid bilayer was just the phospholipid tails and the dark layers which were thought to be the layers of protein were actually the phospholipid heads.
What did Singer and Nicholson propose in 1972 and what did this suggest?
the fluid mosaic model which suggested that the proteins were located within and not outside the bilayer
Why is it called the fluid mosaic model?
- The proteins and the phospholipid molecules are free to move within the membrane.
- The proteins are scattered throughout the bilayer like tiles in a mosaic.
Two types of membrane proteins?
- integral membrane proteins
- peripheral proteins
Functions of Membrane proteins
Junctions-serve to connect and join cells together
Enzymes-Fixing to membranes localises metabolic pathways
Transport-responsible for facilitated diffusion
Recognition-markers for cellular identification
Anchorage-attachment points for cytoskeleton and extra-cellular matrix
Transduction- function as receptors for peptide hormones
Glycoprotein
any proteins which have carbohydrates attached to the polypeptide chain
Glycolipid
lipids with a carbohydrate attached by a glycosidic bond.
Functions of Glycoproteins and Glycolipids
They form hydrogen bonds with the water molecules surrounding the cell and thus help to stabilize membrane structure.
What is cholesterol and where is it located?
A type of lipid and a component of animal cell membranes
- Most of the cholesterol molecule is hydrophobic so it is attracted to the tails in the centre of the membrane.
- But one end of the molecules contains(-OH) and is hydrophilic. Therefore cholesterol molecules is positioned between phospholipids in membranes.
