phospholipids of cell membranes

help me :((

what does phospholipids consist of

• non-polar tails

  • saturated fatty acids (hydrocarbons)

  • unsaturated fatty acids (hydrocarbons)

• polar head group

  • due to phosphate group present that gives it the polarity

what is amphipathic

a molecule that has both hydrophobic and hydrophilic parts

why can phospholipids self-assemble into bilayers

• amphipathic nature

  • polar head likes water

  • non-polar tail does not

• held together by non-covalent interactions

• thermodynamically favourable

what are the movements that the phospholipids can or cannot do

can:

• lateral movement (10⁶/sec)

• spinning on axis

cannot:

• flipping between leaflets

what is the relationship between the fluidity of the plasma membrane and temperature, assuming no cholesterol

• direct relationship

• as temperature increases, fluidity increases

what are the factors that affect fluidity of the membrane

• degree of unsaturation on fatty acid tails

• length of fatty acids

• temperature

• presence of sterol

how does the degree of unsaturation of fatty acids affect fluidity of the membrane

• saturated lipids only:

  • more solid, tightly packed

• mixed saturated and unsaturated:

  • less solid, less packed

how does the length of fatty acids affect the fluidity of the membrane

• longer fatty acid tails:

  • more solid / less fluid

• shorter fatty acid tails:

  • less solid / more fluid

how does temperature affect the fluidity of the membrane

• direct relationship

  • when temperature increases, fluidity increases

how does the presence of sterol affect the fluidity of the membrane against temperature

• without cholesterol:

  • direct relationship betw fluidity and temperature

• with cholesterol:

  • it buffers fluidity

what molecules can freely cross the bilayer and why?

• oxygen, carbon dioxide, nitrogen, steroids, hormones

  • small, non-polar molecules

what molecules can partially cross the bilayer and why?

• H2O, ethanol, glycerol

  • small, uncharged, but polar molecules

what molecules can barely cross the bilayer and why?

• glucose, nucleosides, some amino acids

  • uncharged, but larger and polar molecules

what chemicals cannot even cross the bilayer and why?

• ions

  • charged

how do larger/polar molecules enter the plasma membrane

via proteins

• the plasma membrane is a mosaic

  • comprises of a lipid bilayer with embedded and associated proteins

are proteins polar or non-polar

both:

• depending on the sequence, regions of proteins can be either polar/non-polar/charged

how does the alpha helix allow membrane insertion to be stable

• alpha helix hides the polar backbone and allows for occupancy in the membrane

• aquaporin has a cluster of alpha helices that form a pore

what is the beta barrel protein

a series of beta sheets arranged in a cyclic fashion

• hydrogen bonding between adjacent peptide backbones hides the polarity → allows it to be in the membrane

what do beta barrel proteins do

allow for membrane insertion to be easier