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3.3 Cell Membrane
KEY CONCEPT The cell membrane is a barrier that
separates a cell from the external environment.
3.3 Cell Membrane
The cell membrane has two major functions.
– forms a boundary between outside and inside of the
cell.
cell membrane
inside cell
outside cell
3.3 Cell Membrane
The cell membrane has two major functions.
– forms a boundary between inside and outside of the
cell
– controls passage of materials
cell membrane
inside cell
outside cell
3.3 Cell Membrane
Phospholipid – is a molecule composed of three parts:
Head – forms hydrogen bonds with water.
• A charged phophate group---polar
• Glycerol-----polar
Tail
• Two fatty acids---nonpolar
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane is made of a phospholipid bilayer.
cell membrane
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane is made of a phospholipid bilayer.
• There are other molecules embedded in the membrane.
cell membrane
carbohydrate
chain
cholesterol
protein
protein channel
protein
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane is made of a phospholipid bilayer.
• There are other molecules embedded in the membrane.
• The fluid mosaic model describes the membrane.
cell membrane
carbohydrate
chain
cholesterol
protein
protein channel
protein
3.3 Cell Membrane
The Fluid Mosaic Model
•
The fluid mosaic model describes the describes the arrangement of
molecules that make up the cell membrane.
– Gives flexibility
– Imbedded with many proteins and protein channels to assist in
molecules leaving and entering the cell.
– Cholesterol provides support
cell membrane
carbohydrate
chain
cholesterol
protein
protein channel
protein
3.3 Cell Membrane
•
The cell membrane is selectively permeable.
Some molecules can cross the membrane
while others cannot.
3.3 Cell Membrane
•
The cell membrane is selectively permeable.
Some molecules can cross the membrane
while others cannot.
3.3 Cell Membrane
Chemical signals are transmitted across the cell
membrane.
• Receptor- a protein that detects a signal molecule and
performs an action in response.
•
•
•
It recognizes and binds to only certain molecules
(enzyme)
Receptors bind with ligands and change shape.
There are two types of
receptors.
– Intracellular receptor
- Membrane receptor
3.3 Cell Membrane
Chemical signals are transmitted across the cell
membrane.
- Intracellular receptor – Located inside the cell.
Bound by molecules that can
cross the membrane.
3.3 Cell Membrane
Chemical signals are transmitted across the cell
membrane.
• Receptors bind with ligands and change shape.
• Membrane receptor – bind to molecules that cannot enter
the cell. When bound the receptor transmits the signal
inside the cell by changing shape.
3.4
and Osmosis
3.3Diffusion
Cell Membrane
KEY CONCEPT Materials move across membranes
because of concentration differences.
3.4
and Osmosis
3.3Diffusion
Cell Membrane
• Passive transport - is the movement of molecules
across the cell membrane that does not require energy
input from a cell.
• There are two types of
passive transport.
• diffusion
• osmosis
3.4
and Osmosis
3.3Diffusion
Cell Membrane
• Molecules diffuse down a concentration gradient- which is
the difference in the concentration of a substance from one
location to another.
• Diffusion – is the movement of molecules in a fluid or gas
from a region of higher concentration to a region of lower
concentration.
• Osmosis – is the movement of
water across a semi-permeable
membrane from an area of higher
water concentration to an area of
lower water concentration.
3.4
and Osmosis
3.3Diffusion
Cell Membrane
Diffusion and osmosis are types of passive
transport.
• Osmosis is the diffusion of water molecules across a
semipermeable membrane.
3.4
and Osmosis
3.3Diffusion
Cell Membrane
Diffusion and osmosis are types of passive transport.
• There are three types of solutions.
• isotonic
•
hypertonic
•
hypotonic
3.4
and Osmosis
3.3Diffusion
Cell Membrane
Some molecules can only diffuse through transport
proteins.
• Some molecules cannot easily diffuse across the cell
membrane.
• Facilitated diffusion is
diffusion through transport
proteins.
3.3 Cell Membrane
3.5 Active Transport, Endocytosis, and
Exocytosis
KEY CONCEPT Cells use energy to transport materials
that cannot diffuse across a membrane.
3.3 Cell Membrane
3.5 Active Transport, Endocytosis, and
Exocytosis
Active transport requires energy input from a cell
and enables a cell to move a substance against its
concentration gradient.
• Passive transport requires no energy from the cell.
• Active transport is
powered by chemical
energy (ATP).
• Active transport occurs
through transport protein
pumps.
• Cells use active transport
to maintain homeostasis.
3.3 Cell Membrane
3.5 Active Transport, Endocytosis, and
Exocytosis
A cell can import and export large materials or large
amounts of material in vesicles during the
processes of endocytosis and exocytosis.
• Cells use energy to transport material in vesicles.
• Endocytosis is the process of
taking material into the cell.
• Phagocytosis is a type of
endocytosis.
3.3 Cell Membrane
3.5 Active Transport, Endocytosis, and
Exocytosis
A cell can import and export large materials or large
amounts of material in vesicles during the
processes of endocytosis and exocytosis.
• Cells use energy to transport material in vesicles.
• Exocytosis is the process of
expelling material from the
cell.