Forces Acting Across Membranes Flashcards
How does water move between interstitial fluid and intracellular fluid?
Auqaporin channels
List some important things to know about cell membrane
- It is selective barrier (mostly impermeable to ions, freely permeable to CO2 & O2)
- Permeability changes
- Flexible, can stretch due to fatty acids. (Limited capacity to stretch, can burst)
- Proteins embedded (and associated with carbohydrates)
- Is a phospholipid bilayer
- Dynamic (constantly remodelling)
- Good insulators against movement of electrical charge.
Describe the structure of cell membrane
Phospholipid bilayer.
Phospholipids have a phosphate head hydrophilic and fatty acid tails hydrophobic.
Some glycolipids on the extracellular side - phosphate head of phospholipid replaced with glucose group
What is embedded in the cell membrane?
Proteins- can be either side of membrane. Integral proteins span the whole membrane.
Membrane carbohydrates- carbohydrate molecules attached to either proteins embedded in the membrane or phospholipids. Known as glycoproteins and glycolipids. These play an important role in cell to cell communication including self and a non-self recognition by immune system.
List 5 types of membrane proteins
Receptor (integral)
Transport (integral)
Enzyme
Communication
Structural
What are receptor proteins?
Integral proteins that span the cell membrane.
Allow communication of extracellular signal to the intracellular space create cellular response.
Ligand binds to receptor protein, the ligand-protein complex triggers intracellular response.
Give an example of a membrane protein receptor in action
When insulin binds to its receptor it generates a signal that tells the cell to insert glucose transporters into the membrane
What are transporter proteins?
Channels and transporters. They allow movement of ions or molecules across the membrane.
Channels create a continuous pore from the ECF to the ICF and they carry ions/small molecules e.g water.
Transporters are only ever open at one side of the membrane at a time and they carry larger molecules e.g glucose.
Channels can be open (water) or gated (ions). Gated channels are usually closed and open in response to a signal.
Where are glucose transporters present?
All cells (insulin independent) except in muscle and adipose tissue.
Muscle and adipose tissue have insulin receptors and they need insulin for the uptake of glucose. When insulin binds to its receptor it tells the cell to insert glucose transporters into the membrane. 
What are membrane enzymes?
Enzymes that catalyse reaction on the cell membrane. The enzymatic part of the protein may be on the internal side or the external side of the membrane.
What are structural proteins?
They anchor the cell membrane to the intracellular skeleton, extracellular matrix (collagen) and/or other cells.
What is the function membrane communication proteins?
Help with communication between cells or within cells.
What are glycoproteins?
Communication membrane proteins.
Membrane proteins with a carbohydrate group attached. They tell the immune system if the cell is one of our own or a foreign cell.
What are G proteins?
Involved with communicating extracellular messages.
They are peripheral proteins that relay a signal across the membrane from an integral receptor protein to an integral effector protein. Resulting in an intracellular response.
Do all membranes have the same protein content?
No, they differ.
E.g myelin (a specialised type of membrane that insulates nerve cells) has a very low proportion of protein (18%). Lipids are a major component as it is a good insulator.
Mitochondria inner membrane has a protein content of 75%
