Plasma Membranes Flashcards
What is compartmentalisation?
Formation of separate membrane-bound areas.
What are the advantages of compartmentalisation?
Allows:
- metabolic reactions to be separated
- different environmental conditions in different parts of the cell
- chemical concentration gradients to be made
- protection of cellular components e.g. nucleus
What is the main property of membranes?
They are fluid
What is fluidity?
Flexible, able to break and fuse easily.
What are the environmental roles of a cell surface membrane?
Provides a fixed set of conditions inside the cell cytosol
What are the transport roles of the cell surface membrane?
Controls transport of of substances in and out of cell
What is cell to cell signalling in the plasma membrane?
Have proteins (glycoproteins and lipoproteins) on the plasma membrane to interact with other cells
What is the detection of changes in the environment in the cell surface membrane?
Signal transduction- proteins can act as receptors for hormones e.g. insulin receptors on liver cells.
What is pseudopodia in cell surface membrane?
Some plasma membrane may form temporary protrusions for movement or food e.g amoeba.
What is anchorage in the cell surface membrane?
Anchorage for the cytoskeleton on which membrane proteins are involved.
What is cell to cell joining in plasma membranes?
Similar cells join together for example in tissue formation.
What does the plasma membrane NOT do?
- Does NOT provide support for the cell shape
- The cytoskeleton does this in animals and the cell wall in plants
What are membranes mainly composed of?
Phospholipids
What is the structure of a phospholipid?
- A polar head, which is hydrophilic, composed of a glycerol and a phosphate molecule.
- Two non-polar tails, which are hydrophobic, composed of fatty acid (hydrocarbon) chains.
- Because they contain both hydrophilic and hydrophobic regions, phospholipids are referred to as amphipathic.
What does amphipathic mean?
“Both hating”
In phospholipids, there is a water hating and a fat hating region.
How are phospholipids arranged?
- Phospholipids arrange spontaneously (self-assemble) into a bilayer
- Hydrophobic tails face inwards, shielded from surrounding polar liquids
- Hydrophilic head associate with cytosolic (inside cell) and extra cellular (outside cell) fluids.
- Tails NEVER overlap!
What enzyme can move phospholipids from one mono layer to another?
Flipase
Who devised the Fluid Mosaic Model?
Singer and Nicholson in 1972
How does the fluid mosaic model describe the structure of plasma membranes?
- Phospholipid bilayer containing hydrophilic heads facing outwards and hydrophobic fatty acid tails facing inwards.
- With, proteins randomly arranged between phospholipids.
What can proteins do in the lipid bilayer?
- They are able to move freely through the lipid bilayer
- The ease at which they do this is dependent on the number of phospholipid with unsaturated fatty acids in the phospholipids.
How are phospholipids held together?
By hydrophobic interactions
What allows for membrane fluidity?
Phospholipids.
How do phospholipids determine fluidity?
Phospholipids with short or UNSATURATED fatty acids are MORE fluid.
What does fluidity allow for?
Breaking and remaking of the membranes. For example for exocytosis and endocytosis.