Lipids and Cell Membrane

major forms of lipids

triglyceride - long term energy storage

phospholipid - arranged into lipid bilayer

steroid - impacts membrane fluidity

fatty acid saturation and length affect physical properties

unsaturated fats - have at least one double bond, creating kinks or bends in the linear chain, prevents the fatty acid chain from packing as tightly, resulting in a liquid form at room temp

saturated fats - have single bonds, allowing them to pack their chains together tightly and be solid at room temp

longer fatty acid chains have more atoms and intermolecular forces involved, therefore higher temperature is required to melt the chain

chemical composition of plasma membrane

• phospholipid bilayer

• membrane proteins

• cholesterol

new and old model of membranes

fluid mosaic model - proteins and phospholipids form complex, dynamic mosaic

sandwich model - phospholipid bilayer between membrane proteins

membrane proteins

integral - amphipathic proteins that span across membrane

• amphipathic - have a hydrophilic and hydrophobic region

• transmembrane domain - stretch of 20 hydrophobic amino acids
  

peripheral - proteins that dont cross membrane

membrane protein functions

anchoring - connect cytoskeleton to extracellular matrix (ECM)

defense - detect foreign substances

cell identity - unique proteins mark cells as “self”

cell communication - relay signal through transduction pathway

transport - molecules across membrane

factors that affect fluidity and permeability

saturation of fatty acid

• unsaturated - more fluid/ permeable

• saturated - less fluid/ permeable

length of fatty acid

• longer - less permeable

cholesterol

• decreases permeability as it is tucked between the fatty acid tails and blocks the passageway

passive transport

no energy required

• simple diffusion (down concentration gradient)

• facilitated diffusion (down concentration gradient through transport protein)

  channels - like a bridge

  carriers - like a ferry

passive transport

• osmosis - water move from high to low concentration

hypertonic - water move out of cell

hypotonic - water move into cell

isotonic - same concentration

active transport

requires energy (against concentration gradient)

• (primary) ATP powered pump - Hydrolysis of ATP powers integral membrane proteins for transport

  • (secondary) cotransport - uses energy from electrochemical gradient to move substance down concentration gradient

    uniporter - one substance one direction

    symporter - two substance same direction

    antiporter - two substances opposite direction

Bulk transport

active transport that requires energy

endocytosis - move molecules in cell

• phagocytosis - cell eating

• pinocytosis - cell drinking

• receptor mediated - take specific molecules that bind to receptor, forming coated vesicle

exocytosis - move molecules out of cell