2.1.5 B) Fluid Mosaic Model of Membrane Structure + Roles of its Components Flashcards
Components in fluid mosaic model of membrane structure:
- phospholipids
- cholesterol
- glycolipids
- proteins
- glycoproteins
What is the main component of membranes?
phospholipids
Diagram of phospholipid structure:
What are phospholipids?
a type of lipid made from two fatty acid chain ‘tails’ attached to a phosphate group ‘head’
What is the shape that phospholipids form due to?
the shape of the structures that phospholipids form is due to their polar nature, and the way they interact with water
How are the phosphate group and fatty acid chains in the phospholipid different?
- the phosphate group head is polar and hydrophilic (‘water-loving’)
- while the fatty acid chains of the tail are non-polar and hydrophobic (‘water-hating’)
Role of membrane bound receptors:
sites where hormones and drugs can bind
What does ‘fluid’ refer to in the fluid mosaic model?
- phospholipids are constantly moving and free to move around - not bonded together (hydrophobic section holds them together)
- molecules are in constant motion and molecules can move freely through the lipid bilayer
What does the ease with which phospholipids can move around depend on?
the ease with which they do this is dependent on the number of phospholipids with unsaturated fatty acids in the phospholipids
What does ‘mosaic’ refer to in the fluid mosaic model?
mosaic the way the membrane looks if viewed from above due to protein molecules scattered throughout
Diagram of fluid mosaic model:
What is the shape that phospholipids form due to?
the shape of the structures that phospholipids form is due to their polar nature, and the way they interact with water
What structure do phospholipids form when exposed to water?
- micelle or a bilayer - in each structure the hydrophilic heads face the water and the hydrophobic tails point inwards away from the water
- Phospholipids may also form a layer on the surface of the water with heads in the water and tails sticking up out of the water - monolayer
Why is the head of a phospholipid attracted to water?
- When phospholipids are surrounded by water, H+ ions dissociate from the phosphate group
- This makes the phosphate group negatively charged
- This negative charged means it is attracted to water, whereas the fatty acid tails are repelled by water as they are non-polar
What structure do phospholipids form in the cell membrane and why?
- Inside and outside of a cell membrane is aqueous solution
- the head is hydrophilic (attracts water) and the tail is hydrophobic (repels water)
- the phospholipids form a bilayer (molecules automatically arrange to form a bilayer) with two rows of phospholipids, heads pointing outwards towards the water on either side of the membrane and tails pointing inwards
How do phospholipids move around in the cell membrane and what does this provide the cell?
- Phospholipids move around in bilayer, but tail never moves into water etc.
- This provides stability to the membrane
Role of phospholipids in cell membrane:
- forms phospholipid bilayer which is the fundamental basis of the membrane in which all other components are embedded
- form a barrier to dissolved (water-soluble) substances
- the centre of the bilayer is hydrophobic so the membrane doesn’t allow water-soluble substances (like ions and polar molecules (molecules that carry a charge)) to diffuse through it
- fat-soluble substances (e.g. fat soluble vitamins) dissolve in the bilayer and pass directly through the membrane
What is cholesterol?
a type of lipid that’s present in all cell membranes (except bacterial cell membranes)
Where is cholesterol found in the cell membrane?
cholesterol molecules fit between the phospholipids
Role of cholesterol in cell membrane:
- helps to maintain the fluidity of the cell membrane therefore giving it stability
- at higher temps they bind to the hydrophobic tails of the phospholipids causing them to pack more closely together - prevents the membrane from becoming too fluid and makes the membrane more rigid
- at lower temps cholesterol prevents phospholipids from packing too close together prevents the membrane from becoming too rigid/stiff and increases fluidity
- cholesterol also has hydrophobic regions so it’s able to create a further barrier to polar substances moving though the membrane
Where are glycolipids found?
attached to phospholipids
What are glycolipids?
lipids with carbohydrates attached
Role of glycoplipids in the cell membrane:
- stabilise the membrane by forming bonds with surrounding water molecules
- act as receptors for messenger molecules in cell signalling and are sites where drugs, hormones and antibodies bind
- antigens - cell surface molecules involved in self-recognition and the immune response
- helps cells attach to each other
- acts as recognition sites for specific chemicals
Role of proteins in the cell membrane:
control what enters and leaves the cell
What are the different proteins found in the cell membrane?
- channel protein (intrinsic protein)
- carrier protein (intrinsic protein)
- extrinsic protein
What type of protein are channel proteins?
intrinsic/transmembrane proteins - span the whole width of the membrane
Role of channel proteins in cell membrane:
- form hydrophilic channels through which allows passive movement of polar hydrophilic substances (e.g. polar molecules) down concentration gradient
- these channels can be opened or closed
- so allow small charge particles through the membrane
What type of protein are carrier proteins?
intrinsic/transmembrane proteins - span the whole width of the membrane
Role of carrier proteins in cell membrane:
- act as transporters than can transport substances (larger molecules and charged particles) across the membrane against concentration gradients by active transport (with use of energy from ATP) and facilitated diffusion
- involves the protein changing shape
Extrinsic proteins:
proteins that are confined to the inner or outer surface of the membrane - occur on the membrane or are partly embedded in it
Role of extrinsic proteins in cell membrane:
- act as receptors for molecules (e.g. hormones) in cells signalling → when a molecule binds to the protein a chemical reaction is triggered inside the cell
- act as enzymes
What are glycoproteins?
proteins with attached carbohydrate chains
Role of glycoproteins in the cell membrane:
- stabilise the membrane by forming bonds with surrounding water molecules
- act as receptors for messenger molecules in cell signalling and are sites where drugs, hormones and antibodies bind
- antigens - cell surface molecules involved in self-recognition and the immune response
