Chapter 1.3 Membrane Structure Flashcards
What does the word amphipathic mean?
A substance that has both, hydrophobic and hydrophilic properties, is called amphipathic
What structure does the membrane of a cell have?
It is a phospholipid bilayer
Which different properties called that the two different parts of the phospholipid bilayer have?
- the phosphate head is hydrophilic
- the hydrocarbon tails are hydrophobic
What does hydrophilic mean?
attracted to water
What does hydrophobic mean?
not attracted to water
How are the two different parts of the Phospholipid bilayer called?
- phospate head
- hydrocarbon tails (lipids)
Is phosphate attracted to water?
Yes, Phosphate is hydrophilic
Are lipids attracted to water?
No, lipids are hydrophobic
How does the arrangement of Phospholipid Bilayers happen?
When phospholipids are mixed with water the phosphate heads are attracted to the water, but the hydrocarbon tails are attracted to each other=phospholipids on the outside&hydrocarbon tails facing inwards, towards each other
Who did find out about the membranes phospholipid bilayer-structure?
Gorter and Grendel
When did Gorter and Grendel find out about the phospholipid bilayer-structure of the cell’s membrane?
First experiments were made in 1924
The lipid bilayer model was published in 1927
How did Gorter and Grendel find out about the double membrane of cells?
-count the red blood cells in a blood sample
-calculated the membrane surface of all blood cells
-getting the blood cells to burst (adding distilled water)
-putting the bursted blood cells in a centrifuge
-putting the isolated membrane lipids on water (they will form a monolayer)
-calculating the area that the lipids need
(Look up: www.u-helmich.de/bio/cytologie/04/Membranen05.html)
What did Gorter and Grendel find out when they made their experiments?
They found out that the area of the phospholipids is twice as large as the area of a cells membrane
Therefore they concluded that the membrane must consist of a phospolipid bilayer
What was wrong about Gorter’s and Grendel’s lipid bilayer model?
-did not explain where protein are located in a cell membrane
Who tried to optimize Gorter and Grendel’s model?
Davson and Danielli
What did Davson and Danielli propose?
They proposed that the phospholipid bilayer was sandwiched by proteins.
Why did Davson and Danielli propose the sandwich model?
- It would explain how membranes, despite being very thin, are a effective in moving some substances
- The high magnification electron micrographs of membranes showed two dark lines with a lighter band in between=trilaminar structure (proteins appear dark, phospholipids light)
What were problems with the Davson-Danielli model?
- freeze etched electron micrographs
- structure of membrane proteins
- fluorescent antibody tagging
What are freeze etched electron micrographs and how did they not fit with the Davson-Danielli model?
Freeze fracturing was used to split open the membrane and revealed irregular rough surfaces within the membrane
These rough surfaces were interpreted as being transmembrane proteins, demonstrating that proteins were not solely localised to the outside of the membrane structure
Why did the structure of membrane proteins not fit the Davson-Danielli model?
Improvements in technology allowed proteins to be extracted from membranes. They were found to be very varied in size and globular in shape
What is fluorescent antibody tagging and why did it not fit the Davson-Danielli model ?
- Membrane proteins from two different cells were tagged with red and green fluorescent markers respectively
- When the two cells were fused, the markers became mixed throughout the membrane of the fused cell
- This demonstrated that the membrane proteins could move and did not form a static layer
Fluorescent antibody tagging of membrane proteins showed they were mobile and not fixed in place
Which model replaced the Davson-Danielli model?
The fluid mosaic model/ Sanger-Nicolson model
What does the fluid mosaic model look like?
- proteins occupy a variety of positions in the membrane
- proteins are likened to the tiles in a mosaic
- proteins are able to move
When did Sanger and Nicolson propose the fluid mosaic model?
1966
