Chapter 5.1

Cell Membrane

  • Bio Membranes separate interior cell from external environment

  • Different sides of membranes have different properties

  • ↑ determined by chem properties of lipids, proteins & carbs

  • consider polarity & H²O interactions

  • Constituents vary based on needed functions

  • 8nm thick - 2x length of reg. phospholipid

  • Can be artificially made- small holes inside randomly seal

  • Differ based on: (L) compos., FA chain length, # of DB, kinds of polar groups

Lipids (L)

  • phospholipid nonpolar sides interact with proteins to form insoluble barrier

  • Proteins inside phospholipid bilayer 

  • (P) & (L) interact

  • Move freely

  • interact noncovalently

  • Capability to interact & keep bilayer help fuse viscle format., phagocytosis etc.

  • many kinds

  • FA make Phos. somewhat fluid like olive oil

  • above makes mol. move side to side

  • Can travel from end to end in ~1 sec

  • Most common FA- 16-18 C & 0-2 DB

  • Unsat. makes less dense & more fluid packing

  • 25% of lipids in animal membrane is steroid cholesterol

  • Cholestrol- regulate memb. fluidity & other steriods funct.

Ex. Horomones

OH int with polar phos. head & nonpolar ring in FA chain of memb.

Proteins (P)

  • noncov. in phos. bilayer

  • held by nonpolar domains

  • (P) & (L) int.

  • Uneven distribution

  • In phos. bilayer 

  • Can:

        move things through membrane

        In cell recod. & adhesion

        Get chem sig. from ext envir.

Usually 1 protein per 25 phos.

  • above Varies on mem. funct.

  • AA arrangement in mem. decides if (p) is in lipid tails & pos.

Peripheral Mem. (P)

  • no exp. nonpolar groups & not inside bilayer, have polar/charged reg. that int with exp. parts of integral mem. (P) or (L) heads

Some move freely - Ex. Cell Fusion ~ cont. membrane forms around, & protein distributed evenly

Some Contained- “fenced” - Ex. comp. of cytoskeleton attached to mem. (P). in cytoplasm. Cytoplasm restrict attached (P) movement

Carbs (C)

  • Attached to lipids or proteins

  • Usually on ext. of mem.

  • Interact w/ ext envir

  • Can recod. specific mol

        Ex. Mol. on adjacent cell surf. 

Can be linear or branched

Help cell comm. & adhesion

Adhere cuz sim. (C) int.——edge of two cells (outer surf., between (C) &(P). or 2 (P))

Fluidity (F)

  • deter. fluidity by using strong UV to make “hole”—how quick hole fills back up deter (F)

  • Affected by:

        Liquid comp. - chol. & sat. FA (x less fluid), short chains (x more fluid)

some anesthetic nonpolar so when in cell memb. (x less fluid) reduce nerve activity

        Temp. - cold (x less fluid), cuz move slower

Some org. change lipid comp. long to short FA when cold - makes plants, bacteria and sleep animals in winter

Cell Fusion - cont. membrane forms around, & protein distributed evenly