Structure of the cell membrane Flashcards
All membranes around and within all cells have the same structure, including cell organelles. What is this structure known as?
The plasma membrane also known as the cell surface membrane
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
Why is the plasma membrane described as the fluid - mosaic model?
Described as fluid: because the individual phospholipid molecules can move relative to one another, giving the membrane a flexible structure that constantly changes shape
Described as mosaic: because the proteins that are embedded in the bilayer vary in shape, size and pattern the same way the stones/tiles of a mosaic
The phospholipid bilayer is a partially permeable membrane. How is this partially permeable membrane formed?
All these molecules are arranged within the phospholipid bilayer to create a partially permeable membrane, that is the cell surface membrane
What are the key components of the plasma membrane?
- Phospholipids
- Cholesterol
- Proteins (integral/peripheral proteins and protein channel/carrier proteins)
- Glycoproteins
- Glycolipid
How is the phospholipid bilayer formed?
The phospholipids align as a bilayer due to the hydrophilic heads being attracted to water and the hydrophobic tail being repelled by water
What does the “bilayer” refer to?
The bilayer refers to the two layers of phospholipids arranged to form the phospholipid bilayer
What is the positioning of the hydrophobic tail in the phospholipid bilayer?
The hydrophobic tails point facing the centre of the cell surface membrane
What is the positioning of the hydrophilic head in the phospholipid bilayer?
The hydrophilic heads point outside of the cell surface membrane
What are the functions of the phospholipid in the membrane?
The phospholipids allow lipid soluble substances to enter and leave the cell. They prevent water soluble substances entering and leaving the cell. Lastly making sure the membrane stays flexible and self sealing
Where are cholesterol molecules located, involving the phospholipid bilayer?
Cholesterol molecules are located within the phospholipid bilayer of the cell surface membrane
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
What is the function of cholesterol molecules?
Cholesterol molecules strengthen the membrane. They restrict the lateral movement of other molecules in the membrane
How is cholesterol useful in the membrane because of its function?
Cholesterol makes the membrane less fluid at higher temperatures. This prevents the possibility of the gaps between the phospholipid bilayer becoming too big, due to increased temperature, causing water and dissolved ions to leak in or out the cell. In the long run, potentially causing dehydration or cells bursting