5.1 Structure and function of membranes Flashcards
What is the function of the membrane?
- Selectively permeable barrier between cell + external environment, organelles + cytoplasm
- Site of chemical reactions
- Sites of cell signalling
What are membranes formed from?
Phospholipid bilayer
Describe the structure of the phospholipid bilayer.
Hydrophilic phosphate heads form inner + outer surface of membrane.
Fatty acid tails form a hydrophobic core inside the membrane
What are the 2 types of proteins in plasma membranes?
Intrinsic and extrinsic
Where are intrinsic proteins?
Embedded through both layers of the membrane
What is the structure of intrinsic proteins?
They have amino acids with hydrophobic R-groups on their external surfaces.
What do the hydrophobic amino acids with hydrophobic R groups on the external surface of intrinsic proteins do?
Interact with the hydrophobic core of the membrane, which keeps them in place.
What are the 2 types of intrinsic proteins?
Channel proteins
Carrier proteins
What is the function of channel proteins?
Provide hydrophilic channel - allows passive movement of polar molecules + ions down a conc. gradient through membranes.
What are channel proteins held in position by?
Interactions between hydrophobic core of membrane + hydrophobic R-groups on the outside of proteins.
What is the function of carrier proteins?
Enable passive transport down a concentration gradient + active transport against a concentration gradient. This often involves the protein’s shape changing.
What type of protein are glycoproteins?
Intrinsic
Where can glycoproteins be found?
Embedded in the plasma membrane
What is the structure of glycoproteins?
Carb. chains attached to their surface
What is the function of glycoproteins?
Cell adhesion (when cells join to form tight junctions in certain tissues). Receptors for chemical signals.
What are glycolipids?
Lipids w/ attached carb. chains
Why are glycolipids referred to as ‘Cell markers’ or ‘Antigens’?
They can be recognised by the immune system as self (of orgasm) or non-self (belonging to other organisms)
Where are extrinsic proteins?
Either side of bilayer.
Can move between layers.
Describe the structure of intrinsic proteins.
Hydrophilic R-groups on outer surfaces + interact w/ polar heads of phospholipids / intrinsic proteins.
What is cholesterol?
A lipid with a hydrophilic end and hydrophobic end, like a phospholipid
What is the function of cholesterol?
Regulate membrane fluidity
Where can cholesterol molecules be found? How does this relate to its function?
Between phospholipids in the membrane bilayer.
The hydrophilic end interacts w/ hydrophilic heads.
The hydrophobic end interacts w/ hydrophobic tails, pulling them together.
Due to this, cholesterol adds stability to membranes without making them too rigid.
How do cholesterol molecules prevent membranes from becoming too solid?
By stopping phospholipids grouping too closely and cystallising
