Download Cell Membrane

Cell Membrane
Cell Membrane?
Location?
 Surrounding the cell
Function?
1. Protection and support for the
cell
2. Regulation of what enters and
exits the cell
WHY?
-Essential in order to maintain
*homeostasis within the cell
*maintaining normal internal
conditions
Composition of Cell Membrane
 Phospholipid Bilayer
1.
Phospholipid:


Hydrophilic Head; “water-loving”
Hydrophobic Tail; “water-fearing”
2. Bilayer

Two-layers (of phospholipids)
Composition of Cell Membrane
 Proteins embedded
throughout phospholipid
bilayer
 Integral Proteins: Span the
width of the cell membrane
 Peripheral Proteins:
Located on one side of the
cell membrane (or on the
‘periphery’)
 A variety of different types
of proteins within the cell
membrane, each with
different functions
Composition
 Cholesterol: another lipid that
maintains the structural stability of
the cell membrane
 Carbohydrates: allow for cell-tocell recognition; a “fingerprint” for
each cell
 Allows for the immune system
to recognize ‘foreign’ cells and
attack them
 Attached to proteins or
phospholipids on outside layer
of cell membrane
Fluid Mosaic Model
 Break it down:
 FLUID: The cell membrane is constantly moving
due to the lipid “tails” on its interior; they
“wiggle”
 This means that the cell membrane is pliable
 The cell membrane has the consistency of olive oil
at body temp.
 MOSAIC: Proteins of different types, randomly
positioned throughout the membrane create a
“mosaic” appearance
The cell membrane is a constantly moving
assemblage of parts.
Cell Membrane Function
 Transport of molecules from one side of the membrane to the
other in order to maintain homeostasis within the cell.
 Selectively Permeable: Only certain substances can move
across the membrane while others cannot.
 Small, non-charged molecules (H20, CO2, O2, etc.) can freely cross
the cell membrane.
 This is referred to as Passive Transport: molecules are ‘freely’ or
‘passively’ traveling through the cell membrane
 This occurs through one of two ways: Diffusion or facilitated diffusion
Passive Transport: Diffusion
 No Energy is required
 Diffusion: the movement of
molecules from a higher
concentration to a lower
concentration until equilibrium
is reached
 Concentration: the amount of
solute in the solvent
 Solute: dissolved substance
(in the solvent)
 solvent: the liquid containing
the dissolved substance
 Equilibrium: occurs when the
solute concentration is the
same throughout the system;
equal on both sides of the
membrane
Passive Transport: Facilitated Diffusion
 A form of Passive Transport (so no energy required)
 Facilitated Diffusion: Larger molecules (that are
unable to passively cross the cell membrane) are
“carried” through via a channel protein.
 Specific protein channels carry specific types of
molecules
 For example: glucose is transported across the cell
membrane via facilitated diffusion