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CELL MEMBRANE
How the cell membrane helps to
maintain homeostasis
HOMEOSTASIS
Definition:
The maintenance of a stable environment.
• In cells this happens by monitoring what goes
in and out of the cell.
Cell Membrane
Cell Membrane
PROTEINS IN THE MEMBRANE
Proteins - are involved in the passage of molecules through the membrane.
A. Channel proteins - a protein that allows a particular molecule or ion to
freely cross the membrane as it enters or leaves the cell.
B. Carrier proteins (Transport)- a protein that selectively interacts with a
specific molecule or ion so that it can cross the cell membrane to enter or
exit the cell.
C. Receptor proteins - A protein that has a specific shape so that specific
molecules can bind to them. The binding of a molecule, such as a
hormone, can influence the metabolism of the cell.
D. Enzyme proteins - An enzyme that catalyzes a specific reaction.
E. Cell-recognition proteins (Cell surface marker) - Glycoprotein's that
identify the cell. They make up the cellular fingerprint by which cells can
recognize each other.
How Cells Maintain Homeostasis
Passive Transport
1) Movement of any substance
across a membrane without
the use of chemical energy
(ATP).
2) Movement of molecules will
go with the concentration
gradient
(High to Low)
3) Kinetic Energy
Active Transport
1) Movement of any substance
across the membrane using
chemical energy – ATP
2)
Movement of the molecule
will go across/against the
concentration gradient
(opposite-low to high)
PASSIVE DIFFUSION
FOUR TYPES
• Diffusion
• Osmosis
• Facilitated Diffusion
• Diffusion with Ion Channels
DEFINITION OF DIFFUSION
The process that molecules or ions spread from
an area of high concentration to an area of
low concentration
Examples: Air freshener, food coloring in water, sugar cube dissolving
Diffusion
What causes Diffusion?
The KINETIC ENERGY of the molecules
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Diffusion is driven by the molecules’ kinetic energy.
Kinetic Energy – the energy of motion.
Molecules are in constant motion because they have
kinetic energy, they will move in a random motion.
If they are concentrated in a small area they will keep
rebounding until they spread out
Which way will the molecules move?
Particles will move down(go with) the
CONCENTRATION GRADIENT
Definition: Difference in concentration of
molecules across a distance
What do the particles want to
reach?
EQUILIBRIUM
Definition:
When all the molecules are spread out equally
in a given area
Note: This can be reached in the absence of
other influences
Diffusion across the Cell
Membrane
Cell Membrane is Semi-permeable- It will let some
molecules through
• Diffusion of a molecule across a membrane depends on
the size of the molecule and the solubility (polar,
nonpolar)
• Small molecules like water are small enough to get
through the pores in the membrane and will pass
through by Osmosis
Molecules that can diffuse through the
membrane by Simple Diffusion
Yes!
Oxygen (nonpolar)
Carbon Dioxide (nonpolar)
Water (Osmosis, small
enough)
No!
Large Particles
Starch
Ions (Charged Particles)
Glucose(Hydrophilic)
OSMOSIS
The process by which WATER molecules diffuse
through a cell membrane from an area of
high concentration to an area of lesser
concentration
Direction of OSMOSIS
Depends on relative concentration of solute
molecules on both sides of the cell membrane
• Water will either enter the cell or exit the cell
CHEMISTRY REVIEWWhat is a solution?
• Solute - Item that is dissolved
Ex: Sugar
• Solvent - Item that does the dissolving
Ex: Water
• In a cell, Water is the solvent and Organic and
Inorganic molecules are the solutes.
Give examples of solutes in the cell?
Direction of water if cell is placed
in a Hypotonic Solution
Hypotonic Solution –When the concentration of
solute molecules outside the cell is lower than
the concentration of the solute molecules
inside the cytosol of the cell.
• The outside solution is said to be hypotonic
compared to the cytosol inside the cell
Direction of Water:
Condition:
Into the cell
Cytolysis
Direction of the water if a cell is placed in a
Hypertonic Solution
Hypertonic Solution- When the concentration of
solute molecules outside the cell is Higher
than the concentration of the solute
molecules inside the cytosol of the cell.
• The outside solution is said to be hypertonic
compared to the cytosol inside of the cell
Direction of Water:
Condition:
Out of the cell
Plasmolysis
REMEMBER
Water moves from the hypotonic solution to
the hypertonic solution
VOCAB WORDS
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Osmotic Pressure – The ability of osmosis to generate
enough pressure to increase a volume of water
Turgor Pressure - Water pressure within a cell
Plasmolysis- When water leaves the cell and turgor
pressure is lost and the cell shrinks
Cytolysis – When the cell takes in so much water it
bursts caused by an increase in turgor pressure
Contractile Vacuoles – Organelles that remove water
QUESTIONS?
• What type of solutions would a cell have to be
in for cytolysis to occur? Plasmolysis to occur?
• If you were to place celery into a glass of
water, would you have cytolysis, plasmolysis
or neither?
Plant vs. Animal Cell
FACILITATED DIFFUSION
• Used when molecules are too large to pass
through membrane or are not soluble in the
membrane
• These molecules moves with the
concentration gradient
• Do not use cellular energy-Passive Transport
Carrier Proteins (Transport)
Carrier Proteins transport solute molecules
through the membrane without expending
energy.
Transport molecules that can’t get through the
membrane by simple diffusion
Are specific to one Molecule ! Like a Key.
FOUR STEPS
1. Molecule will bind with a carrier protein on
the surface of the cell membrane
2. The carrier protein will change shape
shielding the molecule from the interior of
the cell membrane
3. The Molecule is released on the other side of
the membrane
4. The carrier protein then returns to its
original shape WATCH!
FACILITATED DIFFUSION
Glucose
Glucose is an excellent example of facilitated diffusion. Cells
depend on Glucose to create energy for the cell
Glucose is to large of a molecule to pass through the cell
membrane and it is not soluble in the lipid bilayer
When glucose is low in concentration on the inside it will
enter the cell by facilitated diffusion, same if
concentration is high on the inside of the cell
Ion Channels (Gated/Non Gated)
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Proteins in the membrane form an Ion channel across
the lipid membrane.
Ions that cannot diffuse through the membrane can
move through these channels
Move molecules from high concentration to low w/o
use of energy (Passive Transport)
Moves ions such as sodium, potassium, calcium and
chloride.
They are specific to one ion. ION CHANNELS
Gated Channels Vs. Non Gated
Gated Channels:
Open according to external stimuli such as
stretching of the cell membrane, electrical
signals, and chemicals.
Non Gated Channels: Always Open
ION CHANNELS
ACTIVE TRANSPORT
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Moves solutes against the concentration
gradient (from low to high)
Particles are moved from areas of LOW
concentration to areas of HIGH
concentration
Uses energy in the form of ATP
May use a Carrier Protein - Cell Membrane
“Pump”
PASSIVE VS ACTIVE TRANSPORT
EXAMPLES:
Examples of substances that are transported this
way: Sugar, amino acids, Sodium, Potassium,
Calcium, and Hydrogen ion
TYPES:
1. Endocytosis
2. Exocytosis
3. Cell Membrane “Pumps”
MOVEMENT IN VESICLES
ENDOCYTOSIS AND EXOCYTOSIS
Large Macromolecules can’t get through the
membrane with the use of pumps so they
need an alternate method
These methods require the cell to expend
energy
ENDOCYTOSIS
The process by which cells engulf substances
that are too large to enter the cell by passing
through the membrane (using ATP)
Items Engulfed:
External Fluids, Macromolecules, Large Particle
and Cells
Process
1.The particle is enclosed by a portion of the
cell, called a Vesicle
2.This vesicle then pinches off from the cell
membrane and enters the cytoplasm
3.The contents of the vesicle fuse with a
Lysosome and are digested by lysosomal
enzymes or it can fuse with another
membrane-bound organelle WATCH
TWO TYPES OF ENDOCYTOSIS
BASED ON MATERIAL TAKEN IN:
Examples: Food Particles, waste materials, proteins
• 1. Pinocytosis – the movements of solutes or fluids into
the cell
• 2. Phagocytosis – the movement of large food particles
or whole microorganisms into the cell
Example:
1. White blood cells engulf and digest bacteria and virusesPHAGOCYTES
2. Unicellular organisms also feed by endocytosis
EXOCYTOSIS (TO EXIT)
• The passage of large molecules outside the cell
• Process is the same as endocytosis but moves the
molecules out of the cell (uses ATP) WATCH
Example:
• The Golgi Bodies put the proteins in vesicles to be
transported out of the cell.
• Cells also use this to remove waste from the cell
PHAGOCYTOSIS
PINOCYTOSIS
Sodium-Potassium Pump