BIOLOGY
CELL MEMBRANES
ROLES
○ Boundary barrier separates aqueous mediums with different chemicals
○ Control passage of molecules in and out of the cell
○ Compartmentalisation: formation of separate membrane-bound areas in a
cell
○ Site for chemical reactions where enzymes attach to membranes
○ Site of generation of ATP in inner membrane of mitochondria and
chloroplasts
○ Cell signalling: has chemical receptors
○ Cell recognition: of self and non-self cells
○ Cell adhesion: cells stick together to form tissues
FLUID MOSAIC MODEL
Fabric of membrane : phospholipid bilayer with proteins floating randomly in it, forming a
mosaic pattern.
Phospholipids are free to move around, giving membrane its flexibility
Proteins are embedded in the membrane that are free to move around, vary in shape, size
and position (in the same way the tiles of a mosaic), so are randomly scattered or
distributed throughout the membrane.
1
, Model: agreed structure based upon experimental evidence that supports this idea.
COMPONENTS
Phospholipids: bilayer separates aqueous environments where cells normally exist
- Hydrophilic heads (phosphate groups) interact with water
- Hydrophobic tails repel water, so point inwards, away from water
Cholesterol: hydrophilic head and hydrophobic end
-positioned between phospholipids in a bilayer: hydrophilic end interacts with heads;
hydrophobic end interacts with tails, pulling them together - adding stability to membrane
without making them too rigid, reducing the mobility of phospholipids.
- prevent the membrane becoming too solid by stopping the phospholipid molecules from
grouping too closely and crystallizing.
● Regulates fluidity of membrane
Glycoproteins: have attached carbohydrate chains
● Cell adhesion
● Cell signalling : act as receptors for hormones and neurotransmitters, which when
binding to receptor, elicits direct response from cell or cascade of events.
2
CELL MEMBRANES
ROLES
○ Boundary barrier separates aqueous mediums with different chemicals
○ Control passage of molecules in and out of the cell
○ Compartmentalisation: formation of separate membrane-bound areas in a
cell
○ Site for chemical reactions where enzymes attach to membranes
○ Site of generation of ATP in inner membrane of mitochondria and
chloroplasts
○ Cell signalling: has chemical receptors
○ Cell recognition: of self and non-self cells
○ Cell adhesion: cells stick together to form tissues
FLUID MOSAIC MODEL
Fabric of membrane : phospholipid bilayer with proteins floating randomly in it, forming a
mosaic pattern.
Phospholipids are free to move around, giving membrane its flexibility
Proteins are embedded in the membrane that are free to move around, vary in shape, size
and position (in the same way the tiles of a mosaic), so are randomly scattered or
distributed throughout the membrane.
1
, Model: agreed structure based upon experimental evidence that supports this idea.
COMPONENTS
Phospholipids: bilayer separates aqueous environments where cells normally exist
- Hydrophilic heads (phosphate groups) interact with water
- Hydrophobic tails repel water, so point inwards, away from water
Cholesterol: hydrophilic head and hydrophobic end
-positioned between phospholipids in a bilayer: hydrophilic end interacts with heads;
hydrophobic end interacts with tails, pulling them together - adding stability to membrane
without making them too rigid, reducing the mobility of phospholipids.
- prevent the membrane becoming too solid by stopping the phospholipid molecules from
grouping too closely and crystallizing.
● Regulates fluidity of membrane
Glycoproteins: have attached carbohydrate chains
● Cell adhesion
● Cell signalling : act as receptors for hormones and neurotransmitters, which when
binding to receptor, elicits direct response from cell or cascade of events.
2
