Module 2 - Plasma Membranes

What can the structure of cell membranes be described as?

fluid-mosaic model - fluid - phospholipids form bilayer in which phospholipids molecules are constantly moving 
mosaic - proteins of differents sizes + shapes embedded in phospholipid layer

What are the key components of cell membranes?

phospholipid bilayer - made of phospholipids with hydrophilic heads + hydrophobic tails
cholesterol - add stability
proteins - can be extrinsic or intrinsic
glycoproteins + glycolipids - carbohydrates attached to proteins or lipids

What is the phospholipid bilayer?

each phospholipids molecule made of hydrophilic head + 2 hydrophobic tails - causes the phospholipids to arrange themselves into bilayer so heads facing outwards towards water + tails facing inwards away from water - creates hydrophobic centre in bilayer so water-soluble substances cannot pass through - however lipid-soluble substances can dissolve in bilayer + pass directly through membrane - small non-polar substances can pass through

What is the function of cholesterol?

provides stability - consists of hydrophilic + hydrophobic region - hydrophobic region binds to phospholipids fatty acid tails causing them to pack more closely together - reduces fluidity as restricts movement of molecules

What is the function of intrinsic protein?

embedded through both sides of phospholipid bilayer - these proteins include channel + carrier proteins which transport large molecules and ions across membrane 

What is the function of extrinsic proteins?

including peripheral present on only one side of phospholipid bilayer - these proteins provide support to membrane or may be involved in cell signalling

What is the function of glycoproteins?

cell adhesion - attachment of cells to one another
cell recognition - allows cells to recognise one another
cell signalling - communication between cells

What is the function of glycolipids?

same as glycoproteins functions

What are the roles of cell membranes?

cell-surface membranes - surround cells to act as barries between the cell and its environment,controlling which substance enters and leaves the cell
membrane around organelles - surround organelles to act as a barrier between organelle + cytoplasm,dividing the cell into different compartments (compartmentalisation)
both are partially permeable meaning they let some molecules pass through but not others

How does temperature affect cell membranes?

at low temperatures (below 0) - phospholipids do not have much kinetic energy + are packed closely together to form a rigid cell membrane decreasing the permeability of membrane
at medium temperatures (0-40) - as temperature increases phospholipids have more kinetic energy so move faster + aren’t packed closelt together increasing permeability of membrane
at high temperatures (above 40) - phospholipid bilayer breaks down channel + carrier proteins denature,meaning cannot control what enters or leaves the cell as gaps appear in membrane this increases permeability of membrane

How are solvents linked to cell membranes?

solvents are liquids that have the ability to dissolve substances - when cells placed in solvents such as ethanol phospholipids dissolve causing membrane to make it more permeable - increasing concentration of solvent will further increase permeability of cell membrane - organic solvents dissolve lipids damaging cell membrane 

How do fatty acids affect permeability at low temperature?

determined by proportion of saturated to unsaturated fatty acids - saturated fatty acids are compressed at low temperatures but kinks in unsaturated fatty acids counteract this by pushing against neighbouring phospholipids - membrane with higher proportion of unsaturated acids will be more permeable than one with a higher proportion of saturated fatty acids at same temperatures