1.3 Membrane structure Flashcards
What is the difference between a triglyceride versus phospholipid?
Phospholipid: One fatty acid is replaced with a phosphate head
What is an Ester bond? What is it between?
It is condensation between 0H group on the glycerol molecule and on OH group on phosphoric acid
What can be different between a phospholipids two tails?
One is a saturated fatty acid and the other is unsaturated
Are individual phospholipids bonded to one another?
Individual phospholipids are not bonded to one another. It’s the hydrophobic and hydrophilic attractions that keep them together.
What do phospholipids form when submerged in water?
Phospholipids form micelles when submerged in water.
What does it look like when phospholipids are at an air-water interface?
An air-water interface, tail stick out of the water
Why do phospholipids form a bilayer in plasma membrane?
Due to the amphipathic properties (hydrophobic and hydrophilic) of the phospholipid, the tails repel water and will be attracted to other hydrophobic tails. This is the same for the hydrophilic phosphate heads. Since the tails will distance itself from water, it will position itself between the two phosphate heads. The heads on either side of the tails were for me bilayer.
Explain why the model for membrane structure is known as the fluid mosaic model?
- It is fluid because the phospholipids and proteins are free to move around within the bilayer
- It is Mosaic because proteins are distributed throughout the phospholipid in a mosaic pattern (different shapes and sizes)
- It’s a model because it is a agreed structure based on experimental and chemical evidence
Why must plasma membranes be flexible? (2)
- To allow membranes to change shape e.g. for exocytosis and endocytosis
- Allows movement of organelles within cells e.g. vesicles fused with the Golgi apparatus
Why can phospholipid molecules in a bilayer only move within the plane of the bilayer?
Phosphate heads cannot pass through the hydrophobic tails in the center of the bilayer and vice versa
What did Davson and Dannielli propose of the membrane?
They proposed the ‘lipo-protein sandwich’ model that said there were layers of protein adjacent to the phospholipid bilayers, on both sides of the membrane.
What did Daveson and Dannielli mistake the micrograph for?
It was actually the plasma membranes of TWO adjacent cells
What proved the Davson-Danielli model wrong (3)?
- Freeze-fracturing electron micrographs -> found globular structures scattered through the centre of membranes
- Structure of membrane proteins -> Extracted the proteins and found they varied in size and globular shape
- Flourescent antibody tagging -> fluorescent markers were attached to antibodies that bind to membrane proteins. Showed that membrane proteins are free to move within the membrane rather than fixed in a peripheral layer
What did the freeze-etched electron micrograph tell us about the Davson-Danielli model?
- Daniel Branton used freeze fracturing to split cell membranes between the two lipid layers, revealing a 3D view of the surface texture. It suggests that the proteins are on the inside, not outside.
How did Davson-Danielli’s model suggest for proteins?
- Structure of membrane proteins. Proteins were extracted from the membranes. Analysis shows the variation in shape and size of proteins – they were not uniform. Some of hydrophobic region suggesting they were embedded it within the bilayer.
