4.1 Cell-surface Membrane Structure Flashcards
How is the cell membrane partially permeable?
- membranes control which substances enter and leave
- let some molecules through but not others
What are the 3 ways substances can move across a cell-surface membrane?
- diffusion
- osmosis
- active transport
Why is the structure of a cell membrane ‘fluid mosaic’?
- bilayer made of constantly moving phospholipids =
fluid - different components in a membrane = mosaic
What are the 4 types of molecules in a cell-surface membrane?
- phospholipids
- cholesterol
- proteins
- carbohydrates (attached to proteins or lipids)
What is the role of channel and carrier proteins in the bilayer
- allow large molecules and ions to pass through the membrane
What is the role of receptor proteins in the membrane?
- allows the cell to detect chemicals released from other cells
- the chemicals signal to the cell to respond in some way
What are glycoproteins?
- proteins with a polysaccharide chain
What are glycolipids?
- lipids with a polysaccharide chain
Describe the role of phospholipids in the membrane
- automatically arrange themselves in the bilayer with hydrophilic heads facing out to the water on either side of membrane
- centre of bilayer is hydrophobic so membrane doesn’t allow water-soluble substances (ions) to enter
Describe the role of cholesterol in the membrane
- type of lipid that is present in all cell membranes except bacteria
- bind to the hydrophobic tails of phospholipids making membrane less rigid and more fluid
- helps maintain the shape of cells especially those that aren’t supported by other cells
How does temperature below 0° affect membrane permeability?
- phospholipids don’t have much energy so they can’t move
- channel and carrier proteins deform and increase permeability
- ice crystal may form and burst membranes
How does temperature between 0° and 45° affect membrane permeability?
- phospholipids can move around and aren’t packed as tightly together = partially permeable membrane
- increase temp = increase energy of molecules = increase permeability
How does temperature above 45° affect membrane permeability?
- phospholipid bilayer starts to melt and membrane becomes more permeable
- water inside the cell expands = increase pressure
- channel and carrier proteins deform so they can’t control what enters the permeability of the membrane