Cell Membrane Structure Flashcards
Are cell-surface membranes permeable?
They’re partially permeable - they let some molecules through but not others
How can substances move across cell-surface membranes
By diffusion, osmosis or active transport
What do the membranes around organelles do?
The membrane around organelles divide the cell into different compartments - they act as a barrier between the organelle and the cytoplasm. They are also partially permeable and control what substance enter and leave the organelle
Cell membranes have a what structure?
Fluid mosaic structure
When was the fluid mosaic model suggested?
In 1972, the fluid mosaic model was suggested to describe the arrangement of molecules in the membrane
Where are the phospholipids in the cell membrane?
Phospholipid molecules form a continuous, double layer (bilayer). The bilayer is ‘fluid’ because the phospholipids are constantly moving
Give two molecules found within the phospholipid bilayer
- Cholesterol molecules
2. Proteins
How are proteins found in the bilayer?
Proteins are found scattered through the bilayer. These include channel proteins and carrier proteins, which allow large molecules or ions to pass through the membrane. receptor proteins on the cell-surface membrane allow the cell to detect chemicals released from other cells. The chemicals signal to the cell to respond in some way
How do proteins move to the bilayer?
Some proteins are able to move sideways through the bilayer, while others are fixed in position
What do some proteins in the bilayer have attached?
Some proteins have a polysaccharide attached - these are called glycoproteins
Phospholipids form a barrier to what?
Phospholipids form a barrier to dissolved substances
How to phospholipids form a barrier to dissolved substances?
Phospholipids have a hydrophilic head (attracts water) and a hydrophobic tail (repels water). The molecules arrange themselves into a bilayer - the heads face out towards the water on either side of the membrane. The centre of the bilayer is hydrophobic so the membrane doesn’t allow water-soluble substances to pass through it
What does cholesterol give the membrane?
Cholesterol gives the membrane stability
How does cholesterol give the membrane stability?
Cholesterol is a type of lipid. It is present in all cell membranes (except bacterial cell membranes). Cholesterol molecules fit between the phospholipids. They bind to the hydrophobic tails, causing them to pack together more closely. This restricts the movement of the phospholipids, making the membrane more rigid
