Structure of the cell membrane Flashcards
(16 cards)
What is the plasma membrane?
The plasma membrane is the membrane found in all cells that forms the boundary between the cell cytoplasm and the environment
What is the plasma membrane described as?
The plasma membrane is described as the fluid - mosaic model
What are the key components of the plasma membrane? (5)
- Phospholipids
- Cholesterol
- Proteins (integral/peripheral proteins and protein channel/carrier proteins)
- Glycoproteins
- Glycolipid
What are the functions of the phospholipid in the membrane?
Phospholipids:
1. Allow lipid soluble substances to enter/ leave the cell
- Prevent water soluble substances entering the cell.
- Ensure membrane stays flexible and self sealing
How does cholesterol restrict te lateral movement of other molecules in the membrane?
Cholesterol pulls together the fatty acid tails of the phospholipid molecules, limiting their movement and that of other molecules but without making the membrane as a whole too rigid. Therefore the more cholesterol within a membrane, the less fluidity, the more rigid the membrane is
How is cholesterol useful in the membrane because of its function, especially at higher tempertaures?
At higher temperatures phospholipids gain kinetic energy and move more, increase the membranes fluidity and creating gaps
Cholesterol molecules counteract this by making the membrane more rigid, preventing the gaps from getting wider
This is done so water and dissolved ions do not leak in or out the structure, and in the long term cells do not burst or become dehydrated
What is the function of cholesterol molecules?
Restrict the movement of other molecules making up the membrane, keeping it fluid and stabilising it
What are integral proteins?
What are peripheral proteins?
Integral proteins are proteins which are embedded within the cell membrane
Peripheral proteins are protein that do not penetrate the lipid bilaterally
What are protein channels?
Example of water soluble ion in Group 1 x
Protein channels are water filled tubes that enable water soluble ions to diffuse.
example water soluble ion: sodium
What are carrier proteins?
Proteins which bind with larger molecules (e.g. glucose and amino acids). Then they change their own shape to transport these molecules across the membrane
What are glycoproteins?
Glycoproteins are carbohydrate chains that are attached to many peripheral proteins on the outer surface of the cell membrane
What is the function of glycoproteins?
- Acts as cell surface receptor, more specifically for homrones and neurotransmitters
- Helps cells attach to one another and allow cells to recognise one another
What are glycolipids?
Glycolipids are types of lipids that have a carbohydrate molecule attached to the lipid portion for the molecule
How are glycolipids located within a cell? What do glycolipids do in this position?
The carbohydrate portion extends from the phospholipid bilayer into the watery environment outside the cell where it acts as a cell surface receptor for specific chemicals
What is the function of glycolipids?
- Act as a recognition site
- Help maintain stability of the membrane
- Helps cells attach to one another, to form tissues
The cell surface membrane is partially permeable, meaning most molecules do not freely diffuse across it. Why is this the case though? {4pts}
- Molecules that are not soluble in lipids cannot pass through the phospholipid layer
- Molecules can be too large to pass through the channels in the membrane
- Some molecules have the same charge as the protein channels and when attempting to pass through are repelled
- Some molecules are electrically charged and therefore have difficulty passing through the non - polar hydrophobic tails
