5.1 : Structure and Function of Membranes Flashcards
Define compartmentalisation
The formation of speedster membrane - bound areas in a cell
Describe the structure of membranes
Formed from a phospholipid bilayer.
The hydrophilic phosphate heads of the phospholipids form both the inner and outer surface of a membrane.
This leaves the fatty acids tails to create a hydrophobic core inside the membrane.
Why are phospholipids suited to their purpose?
Cells normally exist in aqueous environments.
They are suited as membranes because the outer surfaces of the hydrophilic phosphate heads can interact with water.
What are the roles of membranes ?
Partially permeable barriers between the cells and its environment, between organelles and the cytoplasm and within organelles.
Site of chemical reactions
Sites of cell communication ( cell signalling )
What is the fluid - mosaic model ?
A model where the phospholipids are free to move within the layer relative to each other ( fluid ) , giving the membrane flexibility , and because the proteins embedded in the bilayer vary in shape, size and position ( mosaic ).
Describe the function of intrinsic proteins
Embedded through both layers of a membrane.
Channel proteins : provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient.
Carrier proteins : role in passive transport ( down a concentration gradient ) and active transport ( against a concentration gradient ) into cells. This often involves the shape of the protein changing.
What are glycoproteins? Function ?
They are intrinsic proteins.
Embedded in the membrane with attached carbohydrate chains of varying lengths and shapes.
Play a role in cell adhesion and as receptors for chemical signals.
When the chemical binds to the receptor, it elicits a response from the cell. This may cause a direct response or set of a cascade of events in the cell. This is cell communication / cell signalling.
Give examples of cell communication / cell signalling
Receptors for neurotransmitters such as acetylcholine at nerve cell synapses. The binding of the neurotransmitters triggers or prevents an impulse in the next neurone.
Receptors for peptide hormones, including insulin and glucagon, which affect the uptake and storage of glucose by cell.
Describe the structure and function of glycolipids
Lipids with attached carbohydrate chains.
These molecules are called antigens as they can be recognised by the cells of the immune system as self or non self.
Describe extrinsic proteins
Present in one side of the bilayer and some move between layers.
Normally have hydrophilic R - groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic proteins.
Describe the structure and function of cholesterol
Lipid with hydrophilic and hydrophobic ends.
Regulates fluidity of cells.
Positioned between phospholipids in a membrane bilayer, and because of its own polarity , it pulls them together. This way it’s adds stability without making it too rigid.
It prevents the membranes becoming too solid by stopping the phospholipids molecules grouping too closely and crystallising .
