Transcript The cell

The cell
Chapter 3
Cell membrane composition
• Cell membrane is the boundary between a cell
and the outside environment and controls the
passage of materials into and out of the cell
• Made of a double layer of phospholipids along
with a variety of other materials.
• A phospholipid is made of a charged phosphate
group, a glycerol, and two fatty acid chains
• Phosphate and glycerol make up the head
• The fatty acids make up the tail
• The head contains a charge and is therefore a
“polar” portion
• This allows the head to form hydrogen bonds
with water
• The tails are “nonpolar” and can’t form hydrogen
• Some of the other molecules attached to the
membrane are: Cholesterol, Proteins, and
• The cholesterol helps to strengthen the membrane
• Proteins help to allow material to pass through
the membrane, while others are components of
the cytoskeleton
• Carbohydrates serve as ID tags for the cell and
help with cellular communication.
Fluid Mosaic model
• Model that was developed by scientist to help
describe the cell membrane.
• The fluid aspects helps to describe that the
membrane is flexible and not rigid
• The mosaic aspects helps to describe how the
membrane is made of many different things
Selective permeability
• The cell membrane also shows selective
permeability which allows certain things to pass
through the membrane while keeping others out
• This property allows the cell to maintain
• Material can pass the membrane in a few ways.
Some of these require energy while others do not.
• This depends on the size, polarity, and
concentration of the material in the cell.
Chemical signals transmitted
across the membrane
• In order to receive signals the cell must have
• These receptors bind with a certain molecule at a
certain time to insure the correct action.
• The molecule a receptor binds to is called a
• Once they bind the receptor will change shape
and this is important because it effects how the
receptor will react with other molecules.
2 major receptors
• Intracellular and Membrane
• Intracellular- will be inside the cell. Many
hormones fit into this category. These can only
react in certain cells and will cause a certain
reaction to occur
• Membrane- Will be located on the outside of the
cell. Will bind and then send a signal to the inside
of the cell. The entire receptor changes shape
when this occurs. Starts a chain of events inside
the cell
3.4 Diffusion and Osmosis
• Diffusion and Osmosis are both examples of
passive transport.
• Passive transport is when there is no ATP needed
in order for a process to take place.
• Diffusion is the movement of molecules in a fluid
or gas from an area of higher concentration to an
area of lower concentration.
• As this happens the molecules will move down
the concentration gradient .
• In cells, diffusion plays an important role in
molecules passing across the cell membrane.
• The end result of diffusion is for the particles to
end up in a state of equilibrium.
• Is very similar to diffusion except it is dealing
exclusively with water.
• In this case the higher the number of dissolved
particles in a solution will effect the
concentration of water.
• 3 states of osmosis: ISOTONIC, HYPERTONIC,
• Isotonic- same concentration in the cell and in the
• Hypertonic- solution has a higher concentration
of dissolved particles than cell. Water will flow
out of the cell and cause the cell to shrink.
• Hypotonic- solution has a lower concentration
than in the cell. Water will move into the cell and
cause the cell to swell.
Transport proteins
• The use of proteins in order to bring material into
the cell is called Facilitated Diffusion.
• This is still a form of passive transport even
though proteins are being used.
• Most protein channels only allow certain
molecules to pass through such as ions.
Active transport, Endocytosis,
and Exocytosis
• Some times we must move material across the
membrane even if it goes against the
concentration gradient.
• When this occurs we must use pumps to bring the
material across the membrane.
• In this process energy must be used and this is
• All transport proteins will span the membrane.
• Most will change shape when they bond to a
target molecule.
• Can bind to one type of molecule or many
• Can move in one direction or in multiple
• Must use ATP as energy
• Ex: Sodium Potassium pump, Proton pump
• Process of bringing material into the cell by
engulfing them in the membrane.
• Steps of endocytosis:
• Cell membrane makes a pocket around the
• Pocket breaks off inside the cell and forms a
• Vesicle attaches with Lysosome in order to break
the material down for use.
• Phagocytosis is the process of the cell engulfing
large particles.
• The term literally means “cell eating”
• This process is used by the white blood cells in
the immune system to fight off infection and
• Opposite of Endocytosis
• Steps of endocytosis:
• Vesicle will form around the material in the cell
• Fuse with the cell membrane
• Material is removed from the cell
Used by nerve cells in order to have muscles move.
Impulses travel as chemical signals that are then
transported by vesicles from one nerve cell to