the fluid mosaic model Flashcards
What is the membrane structure composed of?
Lipids, proteins and carbohydrates
What type of lipid is the structure made of?
Phospholipids
What is a phospholipid?
A type of lipid (a glycerol molecule) with a phosphate group attached to it and two fatty acid tails
What is the fluid Mosaic model?
A form of the cell surface membrane, composed of two layers of fatty acids and phosphate groups assembled into opposing sheets
What do the phospholipid molecules form?
A flexible, thin, continuous double layer (bilayer)
Why is this arrangement fluid?
The phospholipids are constantly moving
What is the structure of the phospholipid molecule?
They have a hydrophilic head and a hydrophobic tail
What is the structure of the head of a phospholipid molecule?
The head contains a phosphate group and because its hydrophilic it attracts water and is polar
What is the structure of the tail of a phospholipid molecule? And what do the tails form?
The tail is made of two fatty acids and because its hydrophobic it will repel water and is non-polar. The tails form fatty acid chains
Which way do the hydrophilic heads face in the bilayer?
The hydrophilic heads face out towards the water on either side of the membrane
Which way do the hydrophobic tails face in the bilayer
The hydrophobic tales are on the inside making the centre of the bilayer hydrophobic
Why don’t membranes allow water soluble substances through it?
Because the centre of the bilayer is hydrophobic meaning that water-soluble substances like ions will be repelled
Why does the fluid music structure reference mosaics?
Because protein molecules are scattered through the bilayer like tiles in a mosaic
Are the proteins scattered throughout the bilayer stationary?
No, because phospholipid bilayer is fluid the proteins can move around within it. They can slide around the membrane very quickly and collide with each other, but can never flip from one side to the other
What are the 6 types of protein?
Integral proteins, peripheral proteins, transport proteins, receptor proteins, recognition proteins and structural proteins
What do integral/ channel proteins do?
What do they form?
They span from one side of the phospholipid bilayer to the other
They form protein tunnels that allow specific molecules to pass through the cell membrane, often acting as cell receptors
What do peripheral proteins do?
These sit on one of the surfaces and form a temporary bond with the cell membrane allowing them to detach and reattach at specific times with specific signals and
What do peripheral proteins allow the cell to do?
Coordinate and communicate using a network of proteins and reactions
What do integral proteins allow the cell to do?
Channelling and transporting molecules across the membrane
What are recognition proteins ?
Often glycoproteins embedded in the cell membrane which allow cells to communicate with others
What is an example of recognition protein?
The A and B antigens on red blood cell membrane
What do the transport proteins do?
Where does the transport take place?
Allow the transport of most small molecules across the membrane
It takes place through it integral proteins which provide hydrophilic channels for the passage of ions and polar molecules?
What examples of transport do transport protein allow?
Facilitated diffusion and active transport
What are receptor proteins?
Proteins that are on the outside surface of the cell membranes and have a specific binding site where hormones or other chemicals combined to form a hormone receptor complex
What does the hormone receptor complex trigger?
It triggers other events in the cell membrane or inside the cell
What are structural proteins?
What are they attached to?
Structural proteins are on the inside surface of the cell membrane and are attached to the cytoskeleton
What do the structural proteins do?
They are involved in maintaining the cell shape or in changing the cells shape for motility.
Can structural proteins be on the outside surface of the cell membrane?
Yes, they can be used on the outside surface in cell adhesion which is sticking cells together temporarily or permanently
What is a glycoprotein?
A type of protein that has a polysaccharide (carbohydrate) chain attached to it
What is a glycolipid?
A type of lipid that has a polysaccharide (carbohydrate) chain attached to it
What do the fatty acid chains do?
They link together to stabilise and strengthen the membrane
What is cholesterol?
What is their structure?
A type of lipid that is present in the membrane. It fits in between the phospholipids, forming bonds between them. This makes the cell membranes more rigid and can regulate its fluidity
They have hydrophilic head some hydrophobic tails
Where are the carbohydrates found in the cell membrane?
What do they form?
On the outer surface of all eukaryotic cells attached to the membrane proteins or sometimes to the phospholipids
On the surface, they form glycolipids
What is the outer layer of the structure called?
The extrinsic layer
What is the inner layer of the structure called?
The intrinsic layer
How does the saturation of the tales influence on the fluidity?
The more unsaturated they are, the more fluid the membrane because spent tales fits together more loosely
What do glycolipids do?
they keep the membrane stable by forming hydrogen bonds with the water molecules outside the cell
what types of molecules can pass directly through the cell membrane?
small
uncharged
oxygen
carbon dioxide
how does the ability to recognise the cell by the membrane help the immune system? (2 things)
white blood cells wont attack them if they are identified as out own cells
they can be identified as foreign bodies
how does the bilayer help the cell?
creates a barrier between the external and internal environment and maintains them
what will too much cholesterol in the membrane do?
Too much cholesterol will make the membrane too rigid/less fluid and make exchange less efficient.
what will too little cholesterol in the membrane do?
Too little cholesterol will mean that the membrane is too fluid and breaks up/doesn’t provide necessary
structure
why does the bilayer form?
lipids cause water so arrange into a cage like structure, so forming a bilayer will reduce this effect
at high temps, how does cholesterol affect membrane fluidity?
decreases it
at low temps, how does cholesterol affect membrane fluidity?
increases it
