Membrane Structure & Function

cell membranes allow the cell to maintain

homeostasis

2 qualities that maintain homeostasis(cell membrane)

* **Semi-permeability** → only some materials can freely cross over


* **Selectivity** → Cell controls the passage of what can’t freely cross over

phospholipid bilayer

* semi permeable
* hydrocarbon chains are hydrophobic
* low permeability to large and charge subtances
* phosphate head is hydrophilic
* ampithetic

membrane proteins

* within the membrane
* transport large and charge substances
* lipid bilayer is selective
* transport materials as needed

simple diffusion

* moves from high to low → in order to reach equilibrium

Examples:

* Oxygen
* Carbon Dioxide

rate of diffusion is influenced by

* Temperature or Kinetic Energy
* Molecular size
* Gradient Steepness

Integral Proteins

* penetrates the phospholipid bilayer, permanently attached
* transmembrane proteins

Example:

* protein pumps
* carrier channels
* glycoproteins

glycoprotein

protein on outside + attached carb

peripheral protein

anchored to only one side of the membrane

integral protein

permanently embedded within a membrane

peripheral proteins

__***temporarily***__ on one side of the membrane, can attach to integral proteins

example:

* receptor complexes in cell signaling

Nonpolar (hydrophobic) amino acids will associate

with the lipid bilayer

Polar (hydrophilic) amino acids with

face the aqueous solution

Inner surface of a protein will be lined with

polar amino acids to facilitate transport of polar/charged molecules

Junctions,

Serve to connect and join two cells together

Enzymes,

Fixing to membranes localises metabolic pathways

Transport,

Responsible for facilitated diffusion and active transport

Recognition,

May function as markers for cellular identification

Anchorag,

Attachment points for cytoskeleton and extracellular matrix

Transduction,

Function as receptors for peptide hormones