Plasma Membrane Flashcards
What is the function of the cell membrane?
- let substances in and out of the cell
- compartmentalise cell contents and organelles
- communication
What is meant by partially permeable?
- only allows some molecules through
Why is the membrane described as a fluid mosaic model?
- fluid: individual phospholipid and protein molecules move around within their layer
- mosaic: pattern produced by scattered protein molecules which vary in shape, size and position when surface membrane is viewed from above
- model: agreed structure is based on chemical and experimental evidence so classed as a model
Where are phospholipid bi-layers found?
- cell surface/plasma membrane
- organelles
- vesicles
What is compartmentalism?
- formation of separate membrane-bound areas in a cell
Why is compartmentalism vital to a cell?
- contains reactions in separate parts of the cell
- allows specific conditions required for said reactions, such as chemical gradients to be maintained
- protects vital cell components
What is the function of a phospholipid?
- forms partially permeable bilayer due to hydrophobic fatty acid tails and hydrophilic heads
- form membrane bound compartments
- acts as a barrier
- allows movement of small, soluble, lipids only
- regulates fluidity
How are membranes formed?
- from a phospholipid bilayer
- hydrophilic phosphate heads of the phospholipid form both the inner and outer surface of a membrane
- they sandwich the fatty acid tails of the phospholipids to form a hydrophobic core inside the membrane
What is cholesterol’s function?
- helps regulate fluidity of membrane
- prevents phospholipids forming too closely and becoming solid
- adds stability to membranes without them becoming too rigid
What is the structure of cholesterol?
- lipid with hydrophobic and hydrophilic end
- hydrophilic ends interact with hydrophilic phosphate heads
- hydrophobic end interacts with hydrophobic fatty acid tails
- positioned between phospholipids
What are glycolipids?
- lipid attached to carbohydrate (sugar) chain of varying length
What are the roles of glycolipids?
- cell markers/antigens on cell surfaces: white blood cells recognise the shape of glycolipid as “self” so don’t start an immune response
What are glycoproteins?
- protein attached to carbohydrate (sugar) chain of varying length
- intrinsic protein
- embedded in cell surface membrane
What are the roles of glycoproteins?
- cell adhesion
- receptors involved in chemical signalling:
e. g. neurotransmitters binding to receptors on the postsynaptic neuron triggering a response
e. g. hormone receptors such as those for insulin and glucagon which are present on the cells and liver - some drugs act by binding to a receptor to block or even trigger its activity
What are intrinsic proteins?
- embedded within the membrane
- are transmembrane proteins
- stay in place due to hydrophobic R-groups on their external surfaces which interact with hydrophobic core of bilayer
What are channel proteins?
- intrinsic/integral proteins
- have hydrophilic channel allowing passive moment of molecules that are not small/and or lipid soluble
What are carrier proteins?
- intrinsic/integral proteins
- allows molecules that aren’t small and/or lipid soluble to move
- can either be towards or against concentration gradient (active/passive)
- often change shape during transport
What are extrinsic proteins?
- present on one side of membrane but can move between layers
- stay in place due to hydrophilic R-groups on the external surfaces which interact with the polar heads of the phospholipids
- site of chemical reactions e.g. enzymes
- can also interact with intrinsic proteins to act as receptors
What’s the difference between intrinsic end extrinsic proteins?
Intrinsic: - embedded in both sides of bilayer - e.g. channel or carrier protein Extrinsic: - embedded in one side of bilayer - e.g. enzyme
Alcohol, caffeine, and nicotine are all lipid-soluble molecules, having an almost instant and widespread effect on the body. Why?
- lipid soluble molecules can pass through membrane
- by simple diffusion
- so diffuse quickly through whole body
Membranes, particularly those present in mitochondria, are often highly folded. What are the advantages of the folding?
- process occur across membranes
- process is enzyme controlled
- folding gives increased surface area
- so more enzymes increased rate of reaction
- therefore increase rate of ATP production
