Define plasma membrane
A semi-permeable protective layer that surrounds the cell.
Hydrophilic
When a molecule is attracted to water
Hydrophobic
When a molecule is repelled by water.
Why are phospholipids so unusual? And what is this called?
Part of the phospholipid molecule is hydrophilic, and part of it is hydrophobic. This is called Amphipathic.
What make up phospholipid molecules?
Phosphate which is polar and hydrophobic; glycerol, and fatty acid tails which is non-polar and hydrophobic.
How do hydrophobic and hydrophilic properties of the phospholipid bilayer allow a membrane to maintain its structure?
The head is hydrophilic, which means being attracted to water, while the tails are hydrophobic, meaning they repel water.
When put into water, an emergent property is that the phospholipids will self-organize, and that phospholipid molecules can flow past
What structures make up a plasma membrane, or the Phospholipid Bilayer?
Phospholipid bilayer, integral and peripheral proteins, glycoproteins, and cholesterol.
What is the Davson-Danielli model of the cell membrane?
It's a protein-lipid sandwich which means that the proteins are outside the bilayer. A lipid barrier composed of phospholipids which have hydrophobic tails on the inside and hydrophilic heads on the outside. Proteins coat the outer surface, but do not per
Why was the Davson-Danielli model proposed, and what did it help explain?
Because of evidence from electron microscopy, it helped explain that despite being very thin membranes, they are an effective barrier to the movement of certain substances.
Describe the evidence from electron microscopy that supported the Davson-Danielli model.
In high magnification electron micrographs, membranes appeared as two dark parallel lines with a lighter colored region in between. Proteins appear dark in electron micrographs and phospholipids appear light, which possible could indicate protein layers o
Why does the picture on the right undermine the Davson-Danielli model of the cell membrane?
The Davson-Danielli model only involves proteins that coats the surface of the membrane. This model however has trans-membrane proteins present. The fracture occurs along lines of weakness, including the centre of the membranes.
Who do insights gained from biochemical techniques that allow proteins to be extracted from membranes undermine the Davson-Danielli model?
The Davson-Danielli model only involves proteins that coats the surface of the membrane. Improvements in biochemical techniques allows the membrane proteins of varied size and shape. These proteins would be unable to form continuous layers on periphery on
Fluorescent antibody tagging used red or green fluorescents markers attached to antibodies which would bind to membrane proteins on the surface of the cell membrane. What did experiments with the markers find out and what conclusions could be drawn from t
Within 40 minutes, the red and green markers were mixed throughout the membrane of the fused cell. This showed that membrane proteins are free to move within the membrane rather than being fixed in a peripheral layer.
What is the Singer-Nicholson fluid mosaic model of the cell membrane, which is the current model we use today.
Phospholipid molecules form a bilayer where phospholipids are fluid and move laterally. Peripheral proteins are bound to either the inner or outer surface of the membrane. Integral proteins permeate the surface of the membrane. The membrane is a fluid mos
List the six main functions of the membrane proteins.
Transport, protein channels(facilitated) and protein pumps(active).
Receptors, peptide based hormones( insulin, glucagon, etc.)
Anchorage, cytoskeleton attachments and extra cellular matrix
Cell Recognition, MHC proteins and antigens
Intercellular Joining
What are the functions of glycoproteins found in the plasma membrane?
Glycoproteins are proteins with an oligosaccharide chain attached. (Oligo=few, and saccharide=sugar). They are important for cell recognition by the immune system and as hormone receptors.
What group does Cholesterol belong to? How much does cholesterol take up of the cell?
Steroids, and 20 percent
Where in the plasma membrane can cholesterol be found?
In between the phospholipids
What proteins cause the cholesterol to be doing in between the phospholipids?
The hydroxyl group make the head polar and hydrophilic, so it's attracted to the head of the phospholipid. The non polar tail is attracted to the phospholipid.
What do the hydrophobic hydrocarbon tails behave as, and what do the hydrophilic heads act like?
Liquid, solid
Why is it important to regulate the degree of fluidity?
It needs to be fluid enough that the cell can move. It needs to be fluid enough that the required substances can move across the membrane. If too fluid, however, the membrane could not effectively restrict the movement of substances across itself.
The presence of cholesterol in the membrane restricts the movement of phospholipids and other molecules. How does this affect the physical properties of the membrane?
It reduces membrane fluidity.
The presence of cholesterol disrupts the regular packing of the hydrocarbon tails of phospholipid molecules. What impact does this have on the physical properties of the membrane?
If increases the flexibility as it prevents the tails from crystallizing and hence behaving like a solid.
What chemical properties of the membrane are affected by cholesterol.
Reduces the permeability to hydrophilic and water soluble molecules and ions such as sodium and hydrogen. This also prevents the tails from crystallizing, or freezing.
Cholesterol also encourages the membrane to take on a concave shape. What structures and processes does this aid?
The permeability of the membrane, also the flexibility and attachment.