cell membrane structure Flashcards
membranes control what passes through them, explain how…
- cell surface membranes surround cells and separate the inside of the cells from the environment
- partially permeable membranes let some substances through but not others
- substances can move across the cell surface membrane by diffusion, osmosis, and active transport
- the membranes around organelles act as a barrier between the organelle and the cytoplasm (also partially permeable)
Cell membranes have a fluid mosaic structure, explain how…
- phospholipid molecules form a continuous double layer
- bilayer is fluid because phospholipids are constantly moving
- cholesterol molecules are present in the bilayer
- proteins scattered in the mosaic which allow large molecules and ions to pass through a membrane
- receptor proteins allow cell surface membrane to detect chemicals released from other cells and respond
- some proteins can move sideways
-some proteins have a polysaccharide chain attached called glycoproteins - some lipids also have a polysaccharide chain attached called glycolipids
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what do channel proteins in the phospholipid bilayer do
allow large molecules to pass through the membrane
what do receptor proteins do
they are on the cell surface membrane and allow the cell to detect chemicals released from other cells so that they can respond accordingly
what are lipids with a polysaccharide chain attached called
glycolipids
what are proteins with polysaccharide chains attached
glycoproteins
draw the phospholipid bilayer
google/ textbook page 38
role of heads and tails in phospholipid molecules
- head is hydrophillic and attracts water
- tail is hydrophobic and repels water
- molecules automatically arrange themselves into a bilayer
- heads face outwards and so the centre of the bilayer is hydrophobic so the membrane doesnt allow water soluble substanceslike ions through it- acts as a barrier to these dissolved substances
how does cholesterol give the membrane structure
- cholesterol is a type of lipid
-cholesterol molecules fit between the phospholipids. They bind to the hydrophobic tails of the phospholipidss causing them to pack more closely together
-this restricts the movement of the phospholipids making the membranes more rigid - cholesterol helps maintain the shape of animal cells which dont have cell walls
draw cholesterol between phospholipids
textbook page 38
how can the permeability of the cell membrane be investigated in the lab
1- cut beetroot into five equally sized pieces
2- place each beetroot in a test tube with 5cm of water
3- place all test tubes in water baths at different set temperatures for the same amount of time
4- remove beetroot leaving coloured liquid and use a colorometer to measure the absorbance of light
5- the higher the absorbance the more pigment has been released and so the higher the permeability of the membrane
explain what the membrane is like at low temperatures- not very permeable
(0 degrees)
- phospholipids dont have much energy so cant move very much- packed closely together so the membrane is rigid
- channel proteins and carrier proteins in the membrane deform increasing the permeability of the membrane
- ice crystals may form i=and pierce the membrane making it highly permeable when it thaws
explain what membrane is like between 0-45 degrees
- phospholipids can move around and arent so tightly packed together
- membrane is partially permeable
phospholipids move more as temp increases which increases permeability of the membrane
explain what the membrane is like above 45 degrees
phospholipid bilayer starts to melt and the membrane becomes permeable
- water inside the cell expands putting pressure on membrane
- channel and carrier proteins deform which means they cant control what enters and exits the cell- more permeable
