1.3 Membrane structure Flashcards
(40 cards)
Diagram of a phospholipid membrane
Who proposed the fluid mosaic model?
Singer and Nicolson
When was the fluid mosaic model proposed?
1972
According to the fluid mosaic model, biological membranes consist of ___
Phospholipid bilayers with proteins embedded in the bilayer, making the membrane look like a mosaic.
What is a phospholipid?
A lipid where one of the fatty acids has been replaced by a phosphate group.
What is a bilayer?
A bilayer (‘bi’ meaning two) is a structure consisting of two layers.
What is a phospholipid bilayer?
A structure consisting of two layers of phospholipids that are arranged according to their properties.
What parts of the phospholipid bilayer are hydrophilic and hydrophobic?
The phosphate heads are hydrophilic (that is, ‘water-loving’) because of their charge, while fatty acids, which are non-polar, are hydrophobic (‘afraid of water’).
Diagram of the structure of a phospholipid (This figure includes the molecular structure of a phospholipid and a shorthand drawing of a phospholipid with the hydrophobic and hydrophilic areas shown.)
What is an amphipathic molecule?
A molecule that has both a hydrophilic and a hydrophobic part.
How do the amphipathic properties of phospholipids explain the formation of the lipid bilayer?
The hydrophilic phosphate heads face the watery environment (cell cytoplasm and extracellular fluid), while the hydrophobic fatty acid chains are sandwiched in between, completely isolated from the water.
Diagram of a simple phospholipid bilayer
What are membrane proteins?
-These are a group of proteins with diverse structures associated with the cell membrane.
-Though they all carry out different functions, they all support the plasma membrane in carrying out its distinctive function.
How can all membrane proteins be categorized?
Either as integral or peripheral proteins depending on their position in the membrane.
Integral proteins
-They are amphipathic (they have hydrophobic and hydrophilic properties) and are embedded in the plasma membrane.
-In most cases, they pass completely through the membrane.
Peripheral proteins
They are polar (hydrophilic) and are attached to the outside of the plasma membrane.
Examples of functions of membrane proteins
1) Channels
2) Carriers
3) Recognition
4) Receptors
5) Enzymes
Channel proteins
Some proteins have a pore/channel that allows the passive transport (no energy required) of substances between the inside and outside of the cell.
Carrier proteins
-These proteins bind to substances on one side of the membrane and then change shape to transport them to the other side.
-Carrier proteins that use energy to change shape are termed protein pumps.
Recognition protein
Certain proteins help the cell in differentiating between self and non-self cells (important in triggering an immune response).
Receptor proteins
These proteins usually span the whole membrane to relay information from the inside or outside of the cell.
Enzymes
These are proteins that enhance the rate of reactions that happen at the membrane level.
Diagram showing the structure and function of membrane proteins
Examples of other parts of the cell membrane other than membrane proteins
-Glycolipids
-Cholesterol