Starter What happens to particles when you heat them up Explain the term “fluid mosaic” with reference to the cell membrane

Learning objectives Recall the structure of a cell membrane Identify components of the cell membrane Explain the term “fluid mosaic” Describe the functions of the components of the cell membrane Explain the effect of temperature in cell membrane fluidity

Phospholipid bilayer Phospholipid has a hydrophilic and a hydrophobic section Phosphate head turns towards water causing them to line up as a bilayer This makes up the majority of the membrane structure The individual phospholipids occasionally cross from one layer to the other. Hydrophilic can pass through the hydrophobic section On an electron microscope seen as 2 dark lines with a light section in between

Phospholipid bilayer properties Forms a barrier to large molecules e.g glucose, steroids. Allows small and polar molecules through Water can pass through as it is small and polar Some solutes can pass through so we say it is partially permeable

Why have anything else? Substances that cannot pass through the phospholipid bilayer may be needed by the cell Cells need to respond to external factors e.g. hormones Cells need to be recognised as belonging Cells need to bind together at times

Glycoproteins The carbohydrate chain can communicate to the immune system that the cell belongs Can be hormone receptor sites, hormone binds and triggers a reaction in the cell Can bind drugs and therefore affect cell metabolism (reactions) Can bind cells together

Glycolipids The carbohydrate chain can communicate to the immune system that the cell belongs Can be hormone receptor sites, hormone binds and triggers a reaction in the cell Can bind drugs and therefore affect cell metabolism (reactions)

Cholesterol This is a steroid molecule which fits between the fatty acid tails It can help to block substances such as water molecules and ions passing so easily through the bilayer

Proteins = transport Two types carrier and channel act slightly differently and are involved in different transport processes

Task From the information given so far complete this table There may be more than one component to a section Function of membrane Component part How it does it Transport Cell binding Barrier Receptor Cell recognition Cell signalling Stability

Function of membraneComponent partHow it does it TransportproteinsCarrying or forming channels Cell bindingglycoproteinCarbohydrate chains can bind to eachother BarrierphospholipidHydrophobic section will not allow large or highly charged substances to pass ReceptorGlycolipid,glycoprot ein and proteins The substance binds to them which triggers a reaction in the cell Cell recognitionGlycolipids and glycoproteins Carbohydrate chain is recognised by the immune system as belonging Cell signallingGlycolipids and glycoproteins Carbohydrate chain is recognised by the immune system as belonging StabilitycholesterolMakes the phopholipid bilayer a bit more rigid

Applying common sense 1.Page 26 SAQ 1 – also give me a reason why 2.Explain why a warm cell will allow more water to pass through the phospholipid bilayer than a cold cell

How organisms cope with temperature Unsaturated fatty acids increase the fluidity of membranes as they stop the phospholipids from fastening closely together You have looked at the effect of temperature on fluidity on the membrane Will an organism adapted to cold or hot conditions have more unsaturated fatty acids in their phospholipids, WHY?

How organisms cope with temperature In hot conditions the problem is too much fluidity for the membrane so the organism has less unsaturated fatty acids to try to increase stability In cold conditions the problem is not enough fluidity so the organism increases the proportion of unsaturated fatty acids to increase fluidity