Fluid Mosaic
Model of the Cell Membrane
Between the
inner cell and the conditions of the outer cell stands the cells plasma
membrane. It is flexible and not incredibly strong. The lipid molecules of the
cell membrane naturally assemble in a
double membrane because their tails repel water and their heads attract it.
Proteins occur within the lipid molecules. The proteins receive signals from
the outside world and they transport nutrients and waste. The molecules located
within the cells are constantly moving and changing positions. A semi-permeable barrier around the cell protects the cell because it allows what comes in and what leaves. The barrier acts similar to a border patrol.
Three things
that make up the cell membrane-
1. Lipids
2. Proteins
3. Carbohydrates
Parts to the
Cell Membrane
·
Phospholipid
Bilayer: Two phospholipid layers
o
Phospholipid
bilayer (structure)
o
Carbohydrates (cell
identification)
o
Proteins (transport
channel)
·
Hydrophilic
“Head”: Water liking, attracted to
water.
o
Made up of
phosphate
·
Hydrophobic “Tail”: Repels
water
o
Made up of
lipids
·
Passive Transport-
is the movement of substances across the cell membrane.
o
What the cell
loves
o
Moves back and
forth
o
Substances can
cross the cell membrane without any input of energy by the cell.
·
Diffusion- is
the movement of molecules from an area of higher concentration to area of lower
concentration.
o
Moves until it
gets to the equilibrium
·
Concentration Gradient- Is
the difference in the concentration of molecules across a space.
o
Also moves until it gets to the equilibrium
·
Equilibrium-
Is when the concentration of the molecules of a substance is the same Osmosis-
is the process by which water molecules diffuse across a cell membrane from
high concentration to low concentration.
o
Diffusion
stops at the equilibrium
How does diffusion work throughout our cell membrane?
When there is high concentration on the outside of our
cell over time it will start to diffuse across Highà
Low concentration in the inside of our cell. It will continue to do this until
it is balanced. If it becomes too concentrated in the inside of our cell it
will diffuse towards the outside of our cell.
·
Three types of
Passive Transport
o
Diffusion-
high concentrated area à low concentrated area
o
Osmosis-
diffusion, but only deals with water
§
It’s the high
concentration of water, not sugar, etc.
§
Occurs within
our own blood cells
·
Isotonic
mediums- perfect balanced (healthy blood cell)
·
Hypertonic
mediums- more pure on the inside (unhealthy; causes cell to be damaged)
·
Hypotonic mediums- more pure water on the outside
(unhealthy)
o
Facilitative
Diffusion- larger molecules use carrier proteins to help them pass through the
cell membrane
·
Active
Transport
o
Requires
Energy
o
Types of
active transport
§
Endocytosis-
entering the cell
·
Phagocytosis-
when cells take in large particles (cell eating)
·
Pinocytosis-
when cells take in fluid (cell drinking)
§
Exocytosis-
exiting the cell
§
Sodium/potassium
pump- pump used to move sodium and potassium ions from low areas of
concentration to high concentration
·
Want to
actively pump the concentration from the inside to the outside for the sodium
ions
·
For the
potassium ions we want to have a high concentration on the inside
·
It takes the
sodium ions from the inside and loads three of them up into the enzyme. There
will be a designated spot for the ions.
·
It takes ATP
and drops off one of its phosphates which will allows the enzyme to close.
·
Then the
enzyme opens up to the outside and allows the ions to move freely. Which
creates a high concentration of sodium on the outside.
·
Then a similar
routine occurs with the potassium however only two load up at a time.
Basic Structure of a Cell Membrane
