6 plasma membrane structure and function

do all cells and organelles have the same or different membrane structures?

the same

why are the membranes described as a fluid mosaic model?

due to the mixture and movement of the phospholipids, glycoproteins, and glycolipids it’s made of

what do the molecules arranged within the phospholipid bilayer create?

the partially permeable membrane, that is the cell surface membrane

what are the components of the membrane?

• phospholipid bilayer

• cholesterol

• proteins

why do phospholipids align as a bilayer?

due to the hydrophilic heads being attracted to the water and the hydrophobic tails being repelled by water

what does the the head of a phospholipid contain?

a phosphate group (a negative charge) and a glycerol molecule which makes it attracted to water

what does the tail of a phospholipid contain?

the tails are fatty acid chains and they do not have a charge so they repel water but attract other lipids. one chain is saturated, the other is unsaturated

what else is present in some membranes?

cholesterol

what does cholesterol do in membranes?

restrict lateral (sideways) movement of other molecules in the membrane. which makes the membrane less fluid at high temperatures and prevents water and dissolved ions from leaking out of the cell

why can cholesterol be important?

if membranes became too fluid while hot, the phospholipid would become too large and water and dissolved ions would leak out which would cause dehydration or cells to burst

what types of proteins are embedded across the cell surface membrane?

either peripheral or integral

what does peripheral mean?

don’t extend completely across the membrane

what does integral mean?

span across from one side of the bilayer to another

what do peripheral proteins do?

provide mechanical support, or they are connected to proteins or lipids to make glycoproteins and glycolipids. the function of these is cell recognition as receptors

what do integral proteins do?

protein carriers or channel proteins involved in the transport of molecules across the membrane

what do protein channels do?

form tubes that fill with water to enable water soluble ions to diffuse

what do carrier proteins do?

bind with other carrier proteins and larger molecules such as glucose or amino acids and change shape to transport them to the other side of the membrane

what molecules can pass through the partially permeable plasma membrane through simple diffusion across the phospholipid bilayer?

• lipid soluble substances (e.g. hormones)

• very small molecules (CO2, H2O, O2)

what molecules cannot pass through the partially permeable plasma membrane through simple diffusion across the phospholipid bilayer?

• water soluble substances (polar substances) such as sodium ions and large molecules (glucose)