The structure and function of membranes Flashcards
What does compartmentalisation mean
The formation of separate membrane-bound areas in a cell
Why is compartmentalisation necessary
It allows for the different and specific environments for the chemical reactions to exist even if they are not compatible with one another
What is the name for the cell surface membrane?
The plasma membrane
What is the main function of the plasma membrane?
It separates the cell from its external environment
What are membranes formed from?
Phospholipid bilayer
Describe and draw how the phospholipids create a bilayer (and thus the cell wall)
The many phospholipids aramge themselves in a way in which the hydrophilic phosphate heads are both on the inner and outer surface of the membrane, sandwiching the hydrophobic, fatty acid tails in the middle
What type of environment do cells normally live in?
An aqueous environment
What evidence in 1950s arose which supported the theory of the lipid bilayer?
The invention of the electron microscope showed the cell membrane as two black lines.
During 1972 what did the two scientists Singer and Nicolson propose?
The fluid-mosaic model
Why was it called the fluid-mosaic model?
Because the phospholipids are free to move within the layer relative to each other and because the proteins within the layer vary in shape,size and position.
Where are intrinsic proteins located on the membrane?
Through both layers of the membrane
Draw a diagram of an intrinsic protein
e
What is anther name for an intrinsic protein?
An integral protein
How do intrinsic proteins keep themselves in place?
Hydrophobic R-groups on their external surfaces of the protein interact with the hydrophobic core of the membrane, keeping them in place
What are the three different types of intrinsic proteins?
Channel, carrier proteins, glycoporoteins
What are channel and carrier proteins both evolved with?
Transport across the membrane
How do channel proteins allow the movement of polar molecules and ions into the cell?
They provide a hydrophilic channel that allows passive movement of polar molecules and ions down a concentration gradient through the membrane
What type of molecule does channel proteins allow through?
polar molecules and ions
What is the function of the carrier protein?
It plays a role in both passive and active transport into cells.
What is the structure of glycoporoteins?
They are proteins with attached carbohydrate chains
What do glycoproteins play a role in?
cell adhesion and as receptors for chemical signals
What is meant by cell signaling?
When the chemicals bind to the receptor on a cell membrane which causes either a direct response or sets of a cascade of events inside of the cell.
What is the structure of a glycolipid?
They are lipids with attached carbohydrate chains
What are other names for glycolipids?
Cell markers or antigens
What is the function of glycolipids?
They can be recognised by the cells of the immune system as self or non-self
What are extrinsic proteins?
They are proteins which are only present on one side of the bilayer
Draw a diagram of ab extrinsic protein
d
What is another name for an extrinsic protein?
Peripheral proteins
How are extrinsic proteins kept in place?
They have hydrophilic R-groups on their outer surfaces which interact with the polar heads of the phospholipids or intrinsic proteins.
What is the structure of cholesterol?
They are a lipid with a hydrophilic end and a hydrophobic end.
What is the function of cholesterol?
It regulates the fluidity of membranes
How does cholesterol add stability to the membrane without making it too rigid?
The cholesterol molecules are positioned between two phospholipids with the hydrophilic end interacting with the heads and the hydrophobic ends interacting with the tails, pulling them together
What do the cholesterol molecules act to prevent?
The membranes from becoming too solidly stopping the phospholipid molecules from grouping too closely and crystallising
