Biological membranes

Biological membranes 

membrane function

plasma membrane- partially permable, site of cell signalling

within cells- barrier between organelle and cytoplasm, form vesicles for transport, site of chemical reactions

membrane structure

fluid mosaic model- phosoplipids form bilayer (described as fluid), some have crabohydrates attched (glycolipids), protein molecules scattered throughout, some have carbohydrate attched (glycoproteins), also cotains cholesterol. 

  phosolipids- form a barrier to water-soluble substances. have hydrophilic head and hydrophobic tail. heads face outwards, center is hydrophobic- fat-soluble substances dissolve through 

  cholesterol- gives stability- fits inbetween phosolipids and bind, forcing them to pack closer together so membrane fluid. also acts as further barrier

  proteins- can form channels (channel proteins) that allow small charged particles through. others (carrier proteins) transport larger molecules and charged particles by active transport and facilitated diffusion. they also act as receptors in cell signalling- when a molecule binds a chemical reaction inside is triggered.

  glycolipids/proteins- stabilise membrane by forming hydrogen bonds with surrounding water. also act as receptors for messenger molecules in cell signalling. also are antigens 

factors affecting permability 

solvents- some solvents (like ethanol) dissolve the lipids. ethanol increases permability more than methanol.

temperature- below 0 degrees- proteins denature ( incresae permability) + ice crystals may form and pierce membrane. between 0-45- partially permable as temp increases permablilty increases as…