Biological Membranes Flashcards
what are the functions of plasma membranes?
- to control the movement of substances in and out of the cell
- selective permeability: keeps all of the components in the cell isolating organelles from the rest of the cytoplasm, allowing cellular processes processes to occur separately - a site for biochemical reactions
what is the structure of plasma membranes?
double membrane
phospholipid bilayer with embedded proteins
it has a hydrophilic phosphate head, a glycerol molecule and two hydrohpobic fatty acid tails.
how do phospholipids act in water?
they can form 2 structures: a micelle or a bilayer.
the hydrophilic phosphate heads face and interact with the water and the hydrophobic tails cluster together and point inwards, away from the water
micelle- forms a circle
bilayer- forms two layers
what are intrinsic proteins?
embedded within both layers of the membrane. they have amino acids with hydrophobic R-groups on their surface and they interact with the hydrophobic core of the membrane, keeping them in place
what are the two types of intrinsic proteins?
channel and carrier (both involved in transport across the membrane)
what are channel proteins?
they provide a hydrophilic channel that allows diffusion of polar molecules and ions down a concentration gradient through membranes
what are carrier proteins?
have a role in passive transport (diffusion) and active transport into cells. Often involves the shape of the protein changing.
what are glycoproteins?
intrinsic proteins that are embedded in the plasma membrane with attached carbohydrates (sugar)
what is the role of glycoproteins?
- adhesion (when cells join together to form tight junctions in certain tissues
- receptors for chemical signals (when the chemical binds to the receptor, a response is triggered in the cell which can cause a direct response or set off a cascade of events in the cell- this is called cell signalling)
what are glycolipids?
lipids with attached carbohydrate chains (sugar). these molecules are called antigens and can be recognised by the cells of the immune system as self (of the organism) or non-self (of cells belonging to another organism)
what are extrinsic proteins?
only present in one side of the bilayer. they have hydrophobic R-groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic proteins. they can be present in either layer and some move between layers
What is cholesterol in the context of cell membranes?
Cholesterol is a lipid molecule found within the phospholipid bilayer of animal cell membranes.
Where in the cell membrane is cholesterol located?
Cholesterol is positioned between phospholipid molecules in the bilayer, with its hydrophilic hydroxyl group near the phospholipid heads and its hydrophobic tail within the fatty acid tails.
What are the main roles of cholesterol in the membrane?
Stability: Prevents the membrane from becoming too fluid at high temperatures.
Flexibility: Stops the membrane from becoming too rigid at low temperatures.
Barrier: Reduces permeability to small, water-soluble molecules and ions.
How does cholesterol affect membrane fluidity?
It interacts with phospholipid tails to make the membrane less fluid at high temperatures and prevents tight packing of phospholipids, maintaining fluidity at low temperatures.
